Chemistry | Aster Classes

Balbharati solutions, for, Chemistry, 12th, Standard, HSC, Maharashtra, State, Board, chapter 2, Solutions,

Exercise | Q 1.01 | Page 44

Choose the most correct option.

The vapour pressure of a solution containing 2 moles of a solute in 2 moles of water (vapour pressure of pure water = 24 mm Hg) is ______.

24 mm Hg

32 mm Hg

48 mm Hg

12 mm Hg

Solution

12 mm Hg

The colligative property of a solution is _______

vapour pressure

boiling point

osmotic pressure

freezing point

Solution

osmotic pressure.

In calculating osmotic pressure the concentration of solute is expressed in _______.

molarity

molality

mole fraction

mass percent

Solution

molarity

Ebullioscopic constant is the boiling point elevation when the concentration of a solution is _______.

1 m

1 M

1 mass %

1-mole fraction of solute.

Solution

1m

Cryoscopic constant depends on _______.

nature of solvent

nature of solute

nature of solution

number of solvent molecules

Solution

number of solvent molecules.

Identify the CORRECT statement.

Vapour pressure of solution is higher than that of pure solvent.

Boiling point of solvent is lower than that of solution.

Osmotic pressure of solution is lower than that of solvent.

Osmosis is a colligative property.

Solution

Boiling point of solvent is lower than that of solution.

A living cell contains a solution which is isotonic with 0.3 M sugar solution. What osmotic pressure develops when the cell is placed in 0.1 M KCl solution at body temperature?

5.08 atm

2.54 atm

4.92 atm

2.46 atm

solution

2.54 atm.

The osmotic pressure of blood is 7.65 atm at 310 K. An aqueous solution of glucose isotonic with blood has the percentage (by volume)________.

5.41 %

3.54 %

4.53 %

53.4 %

solution

5.41 %

Vapour pressure of a solution is _______.

directly proportional to the mole fraction of the solute

inversely proportional to the mole fraction of the solute

inversely proportional to the mole fraction of the solvent

directly proportional to the mole fraction of the solvent

solution

inversely proportional to the mole fraction of the solute.

Pressure cooker reduces cooking time for food because _______.

boiling point of water involved in cooking is increased

heat is more evenly distributed in the cooking space

the higher pressure inside the cooker crushes the food material 

cooking involves chemical changes helped by a rise temperature

solution

boiling point of water involved in cooking is increased

Henry’s law constant for a gas CH3Br is 0.159 mol dm-3 atm-1 at 25 °C. What is the solubility of CH3Br in water at 25 °C and partial pressure of 0.164 atm?

0.0159 mol L-1

0.164 mol L-1

0.026 M

0.042 M

solution

0.026 M

Which of the following statement is NOT correct for 0.1 M urea solution and 0.05 M sucrose solution?

Osmotic pressure exhibited by urea solution is higher than that exhibited by sucrose solution

Urea solution is hypertonic to sucrose solution

They are isotonic solutions

Sucrose solution is hypotonic to urea solution

solution

They are isotonic solutions.

Exercise | Q 2.01 | Page 45

Answer the following in one or two sentences.

What is osmotic pressure?

solution

The hydrostatic pressure (on the side of solution) that stops osmosis is called an osmotic pressure of the solution.

OR

The excess of pressure on the side of the solution that stops the net flow of solvent into the solution through a semipermeable membrane is called osmotic pressure.

A solution concentration is expressed in molarity and not in molality while considering osmotic pressure. Why?

solution

1. The osmotic pressure measurements are made at a specific constant temperature. Molarity remains constant at a specific temperature.

2. It is not necessary to express concentration in a temperature-independent unit like molality.

Hence, the solute concentration is expressed in molarity while calculating osmotic pressure rather than molality

Write the equation relating boiling point elevation to the concentration of the solution.

solution

The boiling point elevation is directly proportional to the molality of the solution. Thus,

Δ Tb ∝ m

∴ Δ Tb ∝ Kb m

where, m is the molality of solution. The proportionality constant Kb is called boiling point elevation constant or molal elevation constant or ebullioscopic constant.

A 0.1 m solution of K2SO4 in water has a freezing point of – 4.3 °C. What is the value of van’t Hoff factor if Kf for water is 1.86 K kg mol–1?

solution

Given: Molality of K2SO4 solution = m = 0.1 m 

Freezing point of solution = Tf = – 4.3 °C 

Kf of water = 1.86 K kg mol–1

To find: van’t Hoff factor

Formula: ΔTf = i Kf m

Calculation: 

ΔTf = 

Tf0 – Tf

= 0 °C – (- 4.3 °C) = 4.3 °C = 4.3 K

Now, using formula,

ΔTf = i Kf m

What is van’t Hoff factor?

solution

van’t Hoff factor (i) is defined as the ratio of colligative property of a solution of electrolyte divided by the colligative property of nonelectrolyte solution of the same concentration.

How is van’t Hoff factor related to degree of ionization?

Solution

The van’t Hoff factor is related to degree of ionization as follows:

i = 1 + α (n – 1)

or

α = 

i=  i — 1

     n– 1

where, α = Degree of ionization/dissociation

i = van’t Hoff factor

n = Moles of ions obtained from ionization of 1 mole of electrolyte.

Which of the following solution will have higher freezing point depression and why?

i. 0.1 m NaCl

ii. 0.05 m Al2(SO4)3

Solution

NaCl   →   Na+     +    Cl-

0.1 m       0.1 m         0.1 m 

Total particles in solution = 0.2 mol

For 0.05 m Al2(SO4)3:

Al2(SO4)3    →  2Al3+     + 3

SO42-

0.05 m             0.1 m            0.15 m

Total particles in solution = 0.25 mol

Al2(SO4)3 solution contains more number of particles than NaCl solution. Hence, Al2(SO4)3 solution has maximum ΔTf.

Therefore, the freezing point depression of 0.05 m Al2(SO4)3 solution will be higher than 0.1 m NaCl solution.

State Raoult’s law for a solution containing a nonvolatile solute.

Solution

The Raoult’s law states that, “the vapour pressure of solvent over the solution is equal to the vapour pressure of pure solvent multiplied by its mole fraction in the solution.”

What is the effect on the boiling point of water if 1 mole of methyl alcohol is added to 1 dm3 of water? Why?

Solution

i. When 1 mole of methyl alcohol is added to 1 dm3 of water, the boiling point of water decreases.

ii. Methyl alcohol is a volatile liquid. Therefore, it increases the vapour pressure of a solution at a given temperature. Hence, the solution boils at lower temperature.

Which of the four colligative properties is most often used for molecular mass determination? Why?

Solution

i. Among the four colligative properties, osmotic pressure is most often used for molecular mass determination.

ii. Osmotic pressure is much larger and therefore more precisely measurable property than other colligative properties.

Therefore, it is useful to determine molar masses of very expensive substances and of the substances that can be prepared in small quantities.

How vapour pressure lowering is related to a rise in the boiling point of solution?

Solution

i. At the boiling point of a liquid, its vapour pressure is equal to 1 atm.

ii. In order to reach boiling point, the solution and solvent must be heated to a temperature at which their respective vapour pressures attain 1 atm.

iii. At any given temperature the vapour pressure of a solution is lower than that of pure solvent. Hence, the vapour pressure of solution needs a higher temperature to reach 1 atm than that of needed for vapour pressure of solvent.

Therefore, vapour pressure lowering causes a rise in the boiling point of a solution.

What are isotonic and hypertonic solutions?

Solution

i. Isotonic solutions:

Two or more solutions having the same osmotic pressure are said to be isotonic solutions.

e.g. For example, 0.1 M urea solution and 0.1 M sucrose solution are isotonic because their osmotic pressures are equal. Such solutions have the same molar concentrations but different concentrations in g/L. If these solutions are separated by a semipermeable membrane, there is no flow of solvent in either direction.

ii. Hypertonic solution:

If two solutions have unequal osmotic pressures, the more concentrated solution with higher osmotic pressure is said to be the hypertonic solution.

e.g. For example, if osmotic pressure of sucrose solution is higher than that of urea solution, the sucrose solution is hypertonic to urea solution.

Exercise | Q 3.3 | Page 46

Answer the following.

A solvent and its solution containing a nonvolatile solute are separated by a semipermeable membrane. Does the flow of solvent occur in both directions? Comment giving a reason.

Solution

1. When a solution and pure solvent or two solutions of different concentrations are separated by a semipermeable membrane, the solvent molecules pass through the membrane.

2. The passage of solvent molecules through the semipermeable membrane takes place in both directions, since the solvent is on both sides of the membrane.

3. However, the rate of passage of solvent molecules into the solution or from a more dilute solution to more concentrated solution is found to be greater than the rate in the reverse direction.

4. This is favorable since the vapour pressure of solvent is greater than that of solution.

The osmotic pressure of CaCl2 and urea solutions of the same concentration at the same temperature are respectively 0.605 atm and 0.245 atm, calculate van’t Hoff factor for CaCl2.

Solution

Given: Osmotic pressure of CaCl2 solution = 0.605 atm

Osmotic pressure of urea solution = 0.245 atm

To find: The value of van’t Hoff factor

Formulae: π = MRT, π = iMRT

Calculation: For urea solution

π = MRT

0.245 atm = MRT       ….(i)

For CaCl2 solution

π = iMRT

0.602 atm = iMRT       ….(ii)

Explain reverse osmosis.

Solution

i. If a pressure larger than the osmotic pressure is applied to the solution side, then pure solvent from the solution passes into pure solvent side through the semipermeable membrane. This phenomenon is called reverse osmosis.

ii. For example, consider fresh water salt water separated by a semipermeable membrane. When the pressure larger than the osmotic pressure of a solution is applied to solution, pure water from salty water passes into fresh pure water through the membrane. Thus, the direction of osmosis can be reversed by applying a pressure larger than the osmotic pressure.

iii. The schematic set up for reverse osmosis is as follows:

How molar mass of a solute is determined by osmotic pressure measurement?

Solution


Chapter 10, Types of Chemical Reactions, sslc, chemistry, 10th, tamilnadu board, science, full, solution,

I. Choose the correct answer:

Question 1

H2(g) + Cl29(g) → 2HCl(g)

(a) Decomposition Reaction

(b) Combination Reaction

(c) Single Displacement Reaction

(d) Double Displacement Reaction

Answer:

(a) Decomposition Reaction

Question 2.

Photolysis is a decomposition reaction caused by ______.

(a) heat

(b) electricity

(c) light

(d) mechanical energy

Answer:.

(c) light

Hint:

2NaCl(aq) represents which of the following types of reaction?

(a) Neutralisation

(b) Combustion

(c) Precipitation

(d) Single displacement.

Answer:

(c) Precipitation

Hint: This reaction involves the precipitation of white BaSO4 by mixing of Na2SO4 (aq) and BaCl2 (aq). Hence it belongs to precipitation reaction.


Question 5.

Which of the following statements are correct about a chemical equilibrium?

(i) It is dynamic in nature

(ii) The rate of the forward and backward reactions are equal at equilibrium

(iii) Irreversible reactions do not attain chemical equilibrium

(iv) The concentration of reactants and products may be different

(a) (i), (ii) and (iii)

(b) (i), (ii) and (iv)

(c) (ii), (iii) and (iv)

(d) (i), (iii) and (iv)

Answer:

(a) (i), (ii) and (iii)


Question 6.

A single displacement reaction is represented by

X(s)H2(g)

. the following(s) could be X?

(i) Zn

(ii) Ag

(iii) Cu

(iv) Mg.

Choose the best pair.

(a) i and ii

(b) ii and iii

(c) iii and iv

(d) i and iv.

Answer:

(d) i and iv.

Hint:

Zn + 2HCl → ZnCl2 + H2

Mg + 2HCl → MgCl2 + H2.

Question 7.

Which of the following is not an “element + element → compound” type reaction?

(a) C(s) + O2(g) → CO2(g)

(b) 2K(s) + Br2(l) → 2KBr(s)

(c) 2CO(g) + O2(g) → 2CO2(g)

(d) 4Fe(s) + 3O2(g) → 2Fe2O3(s)

Answer:

(c) 2CO(g) + O2(g) → 2CO2(g)

Question 8. (www.asterclasses.com)

Which of the following represents a precipitation reaction?

(a) A(s) + B(s) → C(s) + D(s)

(b) A(s) + B(aq) → C(aq) + D(l)

(c) A(aq) + B(aq) → C(s) + D(aq)

(d) A(aq) + B(s) → C(aq) + D(l)

Answer:

(c) A(aq) + B(aq) → C(s) + D(aq)

Question 9.

The pH of a solution is 3. Its [OH–] concentration is ______.

(a) 1 × 10-3 M

(b) 3 M

(c) 1 × 10-11 M

(d) 11 M.

Answer:

(c) 1 × 10-11 M

Hint: pH = 3

It means [H+] = 10-3

[H+] [OH–] = 10-14

[10-3] [OH–] = 10-14

[OH–] = 10-11

Question 10. www.asterclasses.com

Powdered CaCO3 reacts more rapidly than flaky CaCO3 because of :

(a) large surface area

(b) high pressure

(c) high concentration

(d) high temperature

Answer:

(a) large surface area

II. Fill in the blanks:

www.asterclasses.com

1. A reaction between an acid and a base is called ………..

2. When zinc metal is placed in hydrochloric acid, ………. gas is evolved.

3. The equilibrium attained during the meiting of ice is known as ………..

4. The pH of a fruit juice is 5.6. If you add slaked lime to this juice, its pH ……….

5. The value of ionic product of water at 25 °C is ………..

6. The normal pH of human blood is …………

7. Electrolysis is type of ……….. reaction.

8. The number of products formed in a synthesis reaction is ………..

9. Chemical volcano is an example for ……….. type of reaction.

10. The ion formed by dissolution of H+ in water is called …………

Answer:

1. neutralization

2. H2

3. physical equilibrium

4. increases to ‘7’

5. 1 × 10-14 mol² dm-6

6. 7.4

7. decomposition

8. 1

9. decomposition

10. hydronium ion

III. Match the following:

Question 1.

Identify the types of reaction:

Answer:

A. (iii)

B. (i)

C. (iv)

D. (ii)

IV. True or False: (If false give the correct statement)

Silver metal can replace hydrogen gas from nitric acid.

The pH of rain water containing dissolved gases like SO3, CO2, NO2 will be less than 7.

At the equilibrium of a reversible reaction, the concentration of the reactants and the products will be equal.

Periodical removal of one of the products of a reversible reaction increases the yield.

On dipping a pH paper in a solution, it turns into yellow. Then the solution is basic.

Answer:

False – Silver cannot displace H2 from HNO3 acid, since it is placed below hydrogen in the activity series.

True

False – At equilibrium the concentration of the reactants and products do not change it remains constant, but the concentration of the reactants and the products will not be equal.

True

False – The solution is neutral if the solution is basic it will be green in colour.

V. Short answer questions:

Question 1.

When an aqueous solution of potassium chloride is added to an aqueous solution of silver nitrate, a white precipitate is formed. Give the chemical equation of this reaction.

Answer:

Question 2.

Why does the reaction rate of a reaction increase in raising the temperature?

Answer:

On increasing temperature heat is supplied to the reactant. This energy breaks more bonds and thus speed up the chemical reaction. Foods kept at room temperature spoils faster than that kept in the refrigerator.

Question 3.

Define combination reaction. Give one example for an exothermic combination reaction.

Answer:

A combination reaction is a reaction in which two or more reactants combine to form a compound.

Eg: C(s) + O2(g) → CO2(g) + heat

Question 4.

Differentiate reversible and irreversible reactions.

Answer:

VI. Answer in detail:

Question 1.

What are called thermolysis reactions?

Answer:

Thermal decomposition reactions are called ‘thermolysis’ reaction. In this type of reaction, the reactant is decomposed by applying heat. There are two types of thermolysis reactions. They are:

(i) Compound to element / element decomposition:

A compound is decomposed into two elements.

Eg:

(ii) Compound to compound / compound decomposition:

A compound is decomposed into two compounds.

Eg:

ASTER CLASSES 10th Science Guide Chapter 10 Types of Chemical Reactions 5

Question 2.

Explain the types of double displacement reactions with examples.

Answer:

There are two major classes of double displacement reactions. They are,

(i) Precipitation Reactions: When aqueous solutions of two compounds are mixed, if they react to form an insoluble compound and a soluble compound, then it is called precipitation reaction.

Pb

Question 3.

Explain the factors influencing the rate of a reaction.

Answer:

Important factors that affect rate of a reaction are:

Nature of the reactants

Concentration of the reactants

Temperature

Catalyst

Pressure

Surface area of the reactants

1. Nature of the reactants : The reaction of sodium with hydrochloric acid is faster than that with acetic acid, because Hydrochloric acid is a stronger acid than acetic acid and thus more reactive. So, the nature of the reactants influence the reaction rate.

2Na(s) + 2HCl(aq) → 2NaCl(aq) + H2(g) (fast)

2Na(s) + 2CH3COOH(aq) → 2CH3COONa(aq) + H2(g) (slow)

2. Concentration of the reactants : Changing the amount of the reactants also increases the reaction rate. More the concentration, more particles per volume exist in it and hence faster the reaction. Granulated zinc reacts faster with 2M hydrochloric acid than 1M hydrochloric acid.

3. Temperature : Most of the reactions go faster at higher temperature. Because adding heat to the reactants provides energy to break more bonds and thus speed up the reaction. Calcium carbonate reacts slowly with hydrochloric acid at room temperature. When the reaction mixture is heated the reaction rate increases.

4. Pressure : If the reactants are gases, increasing their pressure increases the reaction rate. This is because, on increasing the pressure the reacting particles come closer and collide frequently.

5. Catalyst : A catalyst is a substance which increases the reaction rate without being consumed in the reaction. In certain reactions, adding a substance as catalyst speeds up the reaction. For example, on heating potassium chlorate, it decomposes into potassium chloride and oxygen gas, but at a slower rate. If manganese dioxide is added, it increases the reaction rate.

6. Surface area of the reactants : Powdered calcium carbonate reacts more readily with hydrochloric acid than marble chips. Because, powdering of the reactants increases the surface area and more energy is available on collision of the reactant particles. Thus, the reaction rate is increased.

Question 4.

How does pH play an important role in everyday life?

Answer:

The pH of blood is almost 7.4. Any increase or decrease in this value leads to diseases

Citrus fruits require slightly alkaline soil, while rice requires acidic soil and sugarcane requires neutral soil.

If the pH of rainwater becomes less than 7, it becomes acid rain which is harmful in day-to-day life.

pH changes cause tooth decay.

During indigestion, the stomach produces too much acid and this causes pain and irritation.

Question 5.

What is chemical equilibrium? What are its characteristics?

Answer:

Chemical equilibrium is a state of a reversible chemical reaction where the,

Rate of forward reaction = Rate of backward reaction.

No change in the amount of the reactants and products takes place.

Characteristics of equilibrium:

In a chemical equilibrium, the rates of the forward and backward reactions are equal.

The observable properties such as pressure, concentration, colour, density, viscosity etc., of the system remain unchanged with time.

The chemical equilibrium is a dynamic equilibrium, because both the forward and backward reactions continue to occur even though it appears static externally.

In physical equilibrium, the volume of all the phases remain constant.

VII. HOT Questions:

Question 1.

A solid compound ‘A’ decomposes on heating into ‘B’ and a gas ‘C’ On passing the gas ‘C’ through water, it becomes acidic. Identify A, B and C.

Answer:

A – CaCO3, solid compound

‘A’ decomposes on heating into ‘B’ and a gas ‘C’.

On passing the gas CO2 through water, it becomes acidic.

A – CaCO3, Calcium carbonate

B – CaO, Calcium oxide

C – CO2, Carbondioxide gas

Question 2.

Can a nickel spatula be used to stir copper sulphate solution? Justify your answer.

Answer:

No, nickel spatula cannot be used to stir the copper sulphate solution. Actually, on the basis of activity series, nickel is more reactive than copper, so nickel will displace copper from its solution and copper will be deposited on nickel spatula.

VIII. Solve the following problems:

Question 1.

Lemon juice has a pH 2, what is the concentration of H+ ions?

Answer:

pH = – log [H+]

[H+] = antilog of [-pH]

= antilog [-2]

[H+] = 10-2 M

[OR]

PH = – log [H+]

[H+] = 10-pH

[H+] = 10-2M

Question 2.

Calculate the pH of 1.0 × 10-4 molar solution of HNO3.

Answer:

pH = – log [H+]

HNO3 → H+ + NO3–

pH = -log [1 × 10-4]

= -(-4)log10 10 = 4

pH = 4

Question 3.

What is the pH of 1.0 x 10-5 molar solution of KOH?

Answer:

KOH → K+ + OH–

pOH = -log[OH–]

= -log [1 × 10-5]

pOH = 5

pH + pOH = 14

∴ pH of KOH = 14 – 5 = 9

pH = 9

Question 4.

Laundry detergent has a pH 8.5, What is the concentration of H+ ions?

Answer:

pH = 8.5

pH = – log [H+]

[H+] = 10-pH

[H+] = 10-8.5

[H+] = 3.16 × 10-9 M

Question 5.

The hydroxide ion concentration of a solution is 1 × 10-11M. What is the pH of the solution?

Answer:

[OH–] = 1 × 10-11 M

pOH = – log[OH–]

= – log[1 × 10-11]

= -log101 – log1010-11

= -(-11) log1010 = 11

pOH = 11

pH + pOH = 14

pH = 14 – 11

pH = 3

ASTER CLASSES 10th Science Guide Chapter 10 Types of Chemical Reactions

Important Questions and Answers

I. Choose the correct answer:

Question 1.

The unit of rate of a reaction is:

(a) dm³/mol

(b) dm-3

(c) mol dm-3

(d) mol

Answer:

(c) mol dm-3

Question 2.

As the molecule is dissociated by the absorption of heat it is otherwise called as ______.

(a) Thermolysis

(b) Photolysis

(c) Electrolysis

(d) None of these.

Answer:

(a) Thermolysis

Question 3.

The chemical formula of marble is:

(a) CaCO3

(b) MgCO3

(c) Na2CO3

(d) PbCO3

Answer:

(a) CaCO3

Question 4.

As the decomposition is caused by light, this kind of reaction is called ______.

(a) Thermolysis

(b) Photolysis

(c) Electrolysis

(d) None of these.

Answer:

(b) Photolysis

Question 5.

Fluorine will displace the following halide ion from the solution:

(a) chloride

(b) bromide

(c) iodide

(d) all the above

Answer:

(d) all the above

Question 6.

The decomposition of AgBr into grey coloured silver metal is an example of ……… reaction.

(a) compound to element/element

(b) compound to compound/compound

(c) combination

(d) neutralization

Answer:

(a) compound to element/element

Question 7.

The Metathesis reaction among the following is:

(a) C3H8(g) +5O2(g) → 3CO2(g) + 4H2O + heat

(b) Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)

(c) HNO3(aq) + NH4OH(aq) → NH4NO3(aq) + H2O(l)

Answer:

(c) HNO3(aq) + NH4OH(aq) → NH4NO3(aq) + H2O(l)

Question 8.

KI and Pb(NO3)2 solutions are mixed to give a precipitate. What is the colour of the precipitate?

(a) White

(b) Brown

(c) Red

(d) Yellow.

Answer:

(d) Yellow

Question 9.

The pH of rain water is approximately:

(a) 7

(b) 8

(c) 4

(d) 14

Answer:

(a) 7

Question 10.

Most of the reactions go faster at ______.

(a) low temperature

(b) moderate temperature

(c) 0°C

(d) high temperature.

Answer:

(d) high temperature

II. Fill in the blanks.

1. A chemical equation provides information on the ……….. of the substances and the reaction condition.

2. The symbol ‘aq’ in a chemical equation represent the physical state of the substance as ……….

3. 2Na(s) + Cl2(g) → 2NaCl(s) represent the combination reaction between a ……… and ……

4. After white washing with a solution of slaked lime a thin layer of ……….. is formed.

5. Reactions in which heat is absorbed is called ……….. reactions.

6. Electrolytic refining of copper is based on ……….. reaction.

7. When 10-6 mole of a monobasic strong acid is dissolved in water, the pH of the solution is ………..

8. When pH of a solution is 2, the [H+] in mol/L is ……….

9. Combustion of coal is an example of ………. reaction.

10. [ ] represents the concentration of either the reactant or product in ……….

Answer:

1. physical state

2. aqueous solution

3. metal, non-metal

4. CaCO3

5. endothermic

6. electrolytic decomposition

7. 6

8. 1 × 10-2

9. irreversible

10. mol/Lit

III. Match the following.

Question 1.

Match the following table:

Answer:

A. (v)

B. (iii)

C. (iv)

D. (ii)

E. (i)

Question 2.

Match the following table:

ASTER CLASSES  10th Science Guide Chapter 10 Types of Chemical Reactions 10

Answer:

A. (v)

B. (iv)

C. (i)

D. (iii)

E. (ii)

Question 3.

Match the following table:

Answer:

A. (iii)

B. (v)

C. (iv)

D. (ii)

E. (i)

Question 4.

Match the following table:

Answer:

A. (iv)

B. (v)

C. (i)

D. (ii)

E. (iii)

IV. True or False: (if false give the correct statement)

Formation of calcium silicate from silica and calcium oxide is a combination reaction.

Most of the combination reactions are endothermic in nature.

Decomposition of mercuric oxide into mercury and O2 is an example of . photolysis.

Chlorine can displace fluoride ion from its aqueous solution.

Magnesium is more reactive than iron.

Answer:

True

False – Most of the combination reactions are exothermic in nature.

False – Decomposition of mercuric oxide into mercury and O2 is an example of thermolysis.

False – Chlorine is less reactive than Fluorine, so it cannot displace fluoride ion from its aqueous solution.

True

V. Short answer questions:

Question 1.

Write a note on double displacement reaction with an example.

Answer:

When two compounds react, if their ions are interchanged, then the reaction is called double displacement reaction.

Eg: NaOH(aq) + HCl(aq) → NaCl(aq) + H2O

Question 2.

Identify the wrong statements and correct them.

Sodium benzoate is used in food preservative.

Nitric acid is not used as fertilizer in agriculture.

Sulphuric acid is called the king of chemicals.

The pH of acid is greater than 7.

Acetic acid is used in aerated drinks.

Answer:

Correct statement.

Wrong statement. Nitric acid is used as a fertilizer in agriculture.

Correct statement.

Wrong statement. The pH of the acid is lesser than 7.

Wrong statement. Carbonic acid is used in aerated drinks.

Question 3.

Why a combustion reaction may be called as an exothermic oxidation?

Answer:

In a combustion reaction heat is evolved, it is an exothermic reaction. As oxygen is added, it is also an oxidation. So, combustion may be called as an exothermic oxidation.

Question 4.

Take two conical flasks. Label them as I and II. Take a small amount of copper sulphate solution in the first conical flask. Take a small amount of granulated zinc in the second conical flask. Allow the copper sulphate solution to react with the zinc.

Name the type of reaction.

Say whether the metal zinc is more reactive or less reactive.

Write a complete and balanced reaction.

Say whether this change is reversible or irreversible.

Answer:

The reaction taken place is displacement reaction.

Metal zinc is more reactive.

Balanced chemical equation.

This change is an irreversible change.

Question 5.

What is an irreversible reaction? Give an example.

Answer:

The reaction that cannot be reversed is called irreversible reaction. The irreversible reactions are unidirectional, i.e., they take place only in the forward direction. Consider the combustion of coal into carbon dioxide and water.

Samacheer Kalvi 10th Science Guide Chapter 10 Types of Chemical Reactions 13

Question 6.

Define the rate of a reaction.

Answer:

“Rate of a reaction is the change in the amount or concentration of any one of the reactants or products per unit time”.

Consider the following reaction,

A → B

The rate of this reaction is given by

Rate = –

d[A]dt

= +

d[B]dt

Where,

[A] – Concentration of A

[B] – Concentration of B

The negative sign indicates the decrease in the concentration of A with time. The positive sign indicates the increase in the concentration of B with time.

Question 7.

What is meant by combination reaction? Give an example.

Answer:

A reaction in which a single product is formed from two or more reactants is known combination reaction.

2Mg + O2 → 2MgO.

Question 8.

What is a catalyst?

Answer:

A catalyst is a substance which increases the reaction rate without being consumed in the reaction.

Question 9.

Define Displacement reaction. Give an example.

Answer:

The reaction in which a more reactive element displaces a less reactive element from its compound is called displacement reaction.

Pb+⟶+Cu↓

Lead displaces copper from copper chloride solution.

Question 10.

When a aerated soft drink bottle is kept open it will go flat. Why?

Answer:

(i) In the sealed aerated soft drink bottle, the dissolved CO2, in the form of carbonic acid and gaseous CO2 are in equilibrium.

(ii) When we open the bottle the gaseous CO2 will escape and the dissolved CO2 begins to undissolve to the gas phase to maintain the equilibrium. So when we keep the bottle open for a long time it will go flat with all the dissolved CO2 gone.

Question 11.

Can copper displace zinc or lead from their salt solutions?

Answer:

No, copper cannot displace zinc or lead from their salt solutions. Because copper is less reactive than zinc and lead.

Question 12.

What is called as acid rain?

Answer:

The pH of rain water is approximately ‘7’ but when the air is polluted with oxides of S and N, they get dissolved in the rain water and make its pH less than 7, then it is called acid rain.

Question 13.

Write the differences between combination and decomposition reaction.

Answer:

ASTER CLASSES 10th Science Guide Chapter 10 Types of Chemical Reactions 

VI. Answer in detail:

Question 1.

Two acids ‘A’ and ‘B’ were kept in beakers. Acid ‘A’ undergoes partial dissociation in water, whereas acid ‘B’ undergoes complete dissociation in water.

Of the two acids ‘A’ and ‘B’ which is weak acid and which is strong acid?

What is a weak acid?

What is a strong acid?

Give one example of each.

Answer:

Of the two acids ‘A’ and ‘B’, ‘A’ is a weak acid and ‘B’ is a strong acid.

A weak acid is the one which ionises partially when dissolved in water.

A strong acid is the one which ionises completely when dissolved in water.

Weak acid – Acetic acid(CH3COOH)

Strong acid – Sulphuric acid (H2SO4).

Question 2.

Sodium hydroxide and HCl acid react as shown in this equation

NaOH(aq)4 + HCl(aq) → NaCl(aq) + H2O

(i) Which type of chemical reaction is this?

Answer:

Neutralization reaction

(ii) The reaction is exothermic. Explain what that means?

Answer:

When heat is evolved during a chemical reaction it is called exothermic.

(iii) Differentiate exothermic and endothermic reaction.

Answer:

Exothermic :

Heat is evolved.

Temperature increases.

Endothermic :

Heat is absorbed.

Temperature decreases.

(iv) What happens to the temperature of the solution as the chemicals react?

Answer:

Temperature of the solution increases.

Question 3.

Take two conical flasks. Label them as I and II. Take a small amount of CuSO4 in the I conical flask and small amount of granulated Zinc in the II conical flask. Allow the CuSO4 solution to react with Zinc.

(i) Name the type of reaction.

Answer:

Displacement reaction.

(ii) Say whether the metal Zn is more reactive or less reactive.

Answer:

Zinc is more reactive than Copper.

(iii) Write the complete and balanced reaction.

Answer:

Zn(s)+ CuSO4(aq) → ZnSO4(aq) + Cu(s)↓

(iv) Say whether this change is reversible or irreversible

Answer:

Irreversible.

Question 4.

Suggest a reason for each observation given below.

In fireworks, powdered magnesium is used rather than magnesium ribbon.

Zinc and dilute H2SO4 react much more quickly when a few drops of copper sulphate solutions are added.

The reaction between magnesium carbonate and dilute hydrochloric acid speeds up when some concentrated HCl is added.

I. Choose the correct answer:

Question 1

H2(g) + Cl29(g) → 2HCl(g)

(a) Decomposition Reaction

(b) Combination Reaction

(c) Single Displacement Reaction

(d) Double Displacement Reaction

Answer:

(a) Decomposition Reaction

Question 2.

Photolysis is a decomposition reaction caused by ______.

(a) heat

(b) electricity

(c) light

(d) mechanical energy

Answer:.

(c) light

Hint:

2NaCl(aq)

represents which of the following types of reaction?

(a) Neutralisation

(b) Combustion

(c) Precipitation

(d) Single displacement.

Answer:

(c) Precipitation

Hint: This reaction involves the precipitation of white BaSO4 by mixing of Na2SO4 (aq) and BaCl2 (aq). Hence it belongs to precipitation reaction.

Question 5.

Which of the following statements are correct about a chemical equilibrium?

(i) It is dynamic in nature

(ii) The rate of the forward and backward reactions are equal at equilibrium

(iii) Irreversible reactions do not attain chemical equilibrium

(iv) The concentration of reactants and products may be different

(a) (i), (ii) and (iii)

(b) (i), (ii) and (iv)

(c) (ii), (iii) and (iv)

(d) (i), (iii) and (iv)

Answer:

(a) (i), (ii) and (iii)

Question 6.

A single displacement reaction is represented by

X(s)H2(g)

. the following(s) could be X?

(i) Zn

(ii) Ag

(iii) Cu

(iv) Mg.

Choose the best pair.

(a) i and ii

(b) ii and iii

(c) iii and iv

(d) i and iv.

Answer:

(d) i and iv.

Hint:

Zn + 2HCl → ZnCl2 + H2

Mg + 2HCl → MgCl2 + H2.

Question 7.

Which of the following is not an “element + element → compound” type reaction?

(a) C(s) + O2(g) → CO2(g)

(b) 2K(s) + Br2(l) → 2KBr(s)

(c) 2CO(g) + O2(g) → 2CO2(g)

(d) 4Fe(s) + 3O2(g) → 2Fe2O3(s)

Answer:

(c) 2CO(g) + O2(g) → 2CO2(g)

Question 8.

Which of the following represents a precipitation reaction?

(a) A(s) + B(s) → C(s) + D(s)

(b) A(s) + B(aq) → C(aq) + D(l)

(c) A(aq) + B(aq) → C(s) + D(aq)

(d) A(aq) + B(s) → C(aq) + D(l)

Answer:

(c) A(aq) + B(aq) → C(s) + D(aq)

Question 9.

The pH of a solution is 3. Its [OH–] concentration is ______.

(a) 1 × 10-3 M

(b) 3 M

(c) 1 × 10-11 M

(d) 11 M.

Answer:

(c) 1 × 10-11 M

Hint: pH = 3

It means [H+] = 10-3

[H+] [OH–] = 10-14

[10-3] [OH–] = 10-14

[OH–] = 10-11

Question 10.

Powdered CaCO3 reacts more rapidly than flaky CaCO3 because of :

(a) large surface area

(b) high pressure

(c) high concentration

(d) high temperature

Answer:

(a) large surface area

II. Fill in the blanks:

1. A reaction between an acid and a base is called ………..

2. When zinc metal is placed in hydrochloric acid, ………. gas is evolved.

3. The equilibrium attained during the meiting of ice is known as ………..

4. The pH of a fruit juice is 5.6. If you add slaked lime to this juice, its pH ……….

5. The value of ionic product of water at 25 °C is ………..

6. The normal pH of human blood is …………

7. Electrolysis is type of ……….. reaction.

8. The number of products formed in a synthesis reaction is ………..

9. Chemical volcano is an example for ……….. type of reaction.

10. The ion formed by dissolution of H+ in water is called …………

Answer:

1. neutralization

2. H2

3. physical equilibrium

4. increases to ‘7’

5. 1 × 10-14 mol² dm-6

6. 7.4

7. decomposition

8. 1

9. decomposition

10. hydronium ion

III. Match the following:

Question 1.

Identify the types of reaction:

Answer:

A. (iii)

B. (i)

C. (iv)

D. (ii)

IV. True or False: (If false give the correct statement)

Silver metal can replace hydrogen gas from nitric acid.

The pH of rain water containing dissolved gases like SO3, CO2, NO2 will be less than 7.

At the equilibrium of a reversible reaction, the concentration of the reactants and the products will be equal.

Periodical removal of one of the products of a reversible reaction increases the yield.

On dipping a pH paper in a solution, it turns into yellow. Then the solution is basic.

Answer:

False – Silver cannot displace H2 from HNO3 acid, since it is placed below hydrogen in the activity series.

True

False – At equilibrium the concentration of the reactants and products do not change it remains constant, but the concentration of the reactants and the products will not be equal.

True

False – The solution is neutral if the solution is basic it will be green in colour.

V. Short answer questions:

Question 1.

When an aqueous solution of potassium chloride is added to an aqueous solution of silver nitrate, a white precipitate is formed. Give the chemical equation of this reaction.

Answer:

Question 2.

Why does the reaction rate of a reaction increase in raising the temperature?

Answer:

On increasing temperature heat is supplied to the reactant. This energy breaks more bonds and thus speed up the chemical reaction. Foods kept at room temperature spoils faster than that kept in the refrigerator.

Question 3.

Define combination reaction. Give one example for an exothermic combination reaction.

Answer:

A combination reaction is a reaction in which two or more reactants combine to form a compound.

Eg: C(s) + O2(g) → CO2(g) + heat

Question 4.

Differentiate reversible and irreversible reactions.

Answer:

VI. Answer in detail:

Question 1.

What are called thermolysis reactions?

Answer:

Thermal decomposition reactions are called ‘thermolysis’ reaction. In this type of reaction, the reactant is decomposed by applying heat. There are two types of thermolysis reactions. They are:

(i) Compound to element / element decomposition:

A compound is decomposed into two elements.

Eg:

(ii) Compound to compound / compound decomposition:

A compound is decomposed into two compounds.

Eg:

ASTER CLASSES 10th Science Guide Chapter 10 Types of Chemical Reactions 5

Question 2.

Explain the types of double displacement reactions with examples.

Answer:

There are two major classes of double displacement reactions. They are,

(i) Precipitation Reactions: When aqueous solutions of two compounds are mixed, if they react to form an insoluble compound and a soluble compound, then it is called precipitation reaction.

Pb

.

Question 3.

Explain the factors influencing the rate of a reaction.

Answer:

Important factors that affect rate of a reaction are:

Nature of the reactants

Concentration of the reactants

Temperature

Catalyst

Pressure

Surface area of the reactants

1. Nature of the reactants : The reaction of sodium with hydrochloric acid is faster than that with acetic acid, because Hydrochloric acid is a stronger acid than acetic acid and thus more reactive. So, the nature of the reactants influence the reaction rate.

2Na(s) + 2HCl(aq) → 2NaCl(aq) + H2(g) (fast)

2Na(s) + 2CH3COOH(aq) → 2CH3COONa(aq) + H2(g) (slow)

2. Concentration of the reactants : Changing the amount of the reactants also increases the reaction rate. More the concentration, more particles per volume exist in it and hence faster the reaction. Granulated zinc reacts faster with 2M hydrochloric acid than 1M hydrochloric acid.

3. Temperature : Most of the reactions go faster at higher temperature. Because adding heat to the reactants provides energy to break more bonds and thus speed up the reaction. Calcium carbonate reacts slowly with hydrochloric acid at room temperature. When the reaction mixture is heated the reaction rate increases.

4. Pressure : If the reactants are gases, increasing their pressure increases the reaction rate. This is because, on increasing the pressure the reacting particles come closer and collide frequently.

5. Catalyst : A catalyst is a substance which increases the reaction rate without being consumed in the reaction. In certain reactions, adding a substance as catalyst speeds up the reaction. For example, on heating potassium chlorate, it decomposes into potassium chloride and oxygen gas, but at a slower rate. If manganese dioxide is added, it increases the reaction rate.

6. Surface area of the reactants : Powdered calcium carbonate reacts more readily with hydrochloric acid than marble chips. Because, powdering of the reactants increases the surface area and more energy is available on collision of the reactant particles. Thus, the reaction rate is increased.

Question 4.

How does pH play an important role in everyday life?

Answer:

The pH of blood is almost 7.4. Any increase or decrease in this value leads to diseases

Citrus fruits require slightly alkaline soil, while rice requires acidic soil and sugarcane requires neutral soil.

If the pH of rainwater becomes less than 7, it becomes acid rain which is harmful in day-to-day life.

pH changes cause tooth decay.

During indigestion, the stomach produces too much acid and this causes pain and irritation.

Question 5.

What is chemical equilibrium? What are its characteristics?

Answer:

Chemical equilibrium is a state of a reversible chemical reaction where the,

Rate of forward reaction = Rate of backward reaction.

No change in the amount of the reactants and products takes place.

Characteristics of equilibrium:

In a chemical equilibrium, the rates of the forward and backward reactions are equal.

The observable properties such as pressure, concentration, colour, density, viscosity etc., of the system remain unchanged with time.

The chemical equilibrium is a dynamic equilibrium, because both the forward and backward reactions continue to occur even though it appears static externally.

In physical equilibrium, the volume of all the phases remain constant.

VII. HOT Questions:

Question 1.

A solid compound ‘A’ decomposes on heating into ‘B’ and a gas ‘C’ On passing the gas ‘C’ through water, it becomes acidic. Identify A, B and C.

Answer:

A – CaCO3, solid compound

‘A’ decomposes on heating into ‘B’ and a gas ‘C’.

On passing the gas CO2 through water, it becomes acidic.

A – CaCO3, Calcium carbonate

B – CaO, Calcium oxide

C – CO2, Carbondioxide gas

Question 2.

Can a nickel spatula be used to stir copper sulphate solution? Justify your answer.

Answer:

No, nickel spatula cannot be used to stir the copper sulphate solution. Actually, on the basis of activity series, nickel is more reactive than copper, so nickel will displace copper from its solution and copper will be deposited on nickel spatula.

VIII. Solve the following problems:

Question 1.

Lemon juice has a pH 2, what is the concentration of H+ ions?

Answer:

pH = – log [H+]

[H+] = antilog of [-pH]

= antilog [-2]

[H+] = 10-2 M

[OR]

PH = – log [H+]

[H+] = 10-pH

[H+] = 10-2M

Question 2.

Calculate the pH of 1.0 × 10-4 molar solution of HNO3.

Answer:

pH = – log [H+]

HNO3 → H+ + NO3–

pH = -log [1 × 10-4]

= -(-4)log10 10 = 4

pH = 4

Question 3.

What is the pH of 1.0 x 10-5 molar solution of KOH?

Answer:

KOH → K+ + OH–

pOH = -log[OH–]

= -log [1 × 10-5]

pOH = 5

pH + pOH = 14

∴ pH of KOH = 14 – 5 = 9

pH = 9

Question 4.

Laundry detergent has a pH 8.5, What is the concentration of H+ ions?

Answer:

pH = 8.5

pH = – log [H+]

[H+] = 10-pH

[H+] = 10-8.5

[H+] = 3.16 × 10-9 M

Question 5.

The hydroxide ion concentration of a solution is 1 × 10-11M. What is the pH of the solution?

Answer:

[OH–] = 1 × 10-11 M

pOH = – log[OH–]

= – log[1 × 10-11]

= -log101 – log1010-11

= -(-11) log1010 = 11

pOH = 11

pH + pOH = 14

pH = 14 – 11

pH = 3

ASTER CLASSES 10th Science Guide Chapter 10 Types of Chemical Reactions

Important Questions and Answers

I. Choose the correct answer:

Question 1.

The unit of rate of a reaction is:

(a) dm³/mol

(b) dm-3

(c) mol dm-3

(d) mol

Answer:

(c) mol dm-3

Question 2.

As the molecule is dissociated by the absorption of heat it is otherwise called as ______.

(a) Thermolysis

(b) Photolysis

(c) Electrolysis

(d) None of these.

Answer:

(a) Thermolysis

Question 3.

The chemical formula of marble is:

(a) CaCO3

(b) MgCO3

(c) Na2CO3

(d) PbCO3

Answer:

(a) CaCO3

Question 4.

As the decomposition is caused by light, this kind of reaction is called ______.

(a) Thermolysis

(b) Photolysis

(c) Electrolysis

(d) None of these.

Answer:

(b) Photolysis

Question 5.

Fluorine will displace the following halide ion from the solution:

(a) chloride

(b) bromide

(c) iodide

(d) all the above

Answer:

(d) all the above

Question 6.

The decomposition of AgBr into grey coloured silver metal is an example of ……… reaction.

(a) compound to element/element

(b) compound to compound/compound

(c) combination

(d) neutralization

Answer:

(a) compound to element/element

Question 7.

The Metathesis reaction among the following is:

(a) C3H8(g) +5O2(g) → 3CO2(g) + 4H2O + heat

(b) Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)

(c) HNO3(aq) + NH4OH(aq) → NH4NO3(aq) + H2O(l)

Answer:

(c) HNO3(aq) + NH4OH(aq) → NH4NO3(aq) + H2O(l)

Question 8.

KI and Pb(NO3)2 solutions are mixed to give a precipitate. What is the colour of the precipitate?

(a) White

(b) Brown

(c) Red

(d) Yellow.

Answer:

(d) Yellow

Question 9.

The pH of rain water is approximately:

(a) 7

(b) 8

(c) 4

(d) 14

Answer:

(a) 7

Question 10.

Most of the reactions go faster at ______.

(a) low temperature

(b) moderate temperature

(c) 0°C

(d) high temperature.

Answer:

(d) high temperature

II. Fill in the blanks.

1. A chemical equation provides information on the ……….. of the substances and the reaction condition.

2. The symbol ‘aq’ in a chemical equation represent the physical state of the substance as ……….

3. 2Na(s) + Cl2(g) → 2NaCl(s) represent the combination reaction between a ……… and ……

4. After white washing with a solution of slaked lime a thin layer of ……….. is formed.

5. Reactions in which heat is absorbed is called ……….. reactions.

6. Electrolytic refining of copper is based on ……….. reaction.

7. When 10-6 mole of a monobasic strong acid is dissolved in water, the pH of the solution is ………..

8. When pH of a solution is 2, the [H+] in mol/L is ……….

9. Combustion of coal is an example of ………. reaction.

10. [ ] represents the concentration of either the reactant or product in ……….

Answer:

1. physical state

2. aqueous solution

3. metal, non-metal

4. CaCO3

5. endothermic

6. electrolytic decomposition

7. 6

8. 1 × 10-2

9. irreversible

10. mol/Lit

III. Match the following.

Question 1.

Match the following table:

Answer:

A. (v)

B. (iii)

C. (iv)

D. (ii)

E. (i)

Question 2.

Match the following table:

ASTER CLASSES  10th Science Guide Chapter 10 Types of Chemical Reactions 10

Answer:

A. (v)

B. (iv)

C. (i)

D. (iii)

E. (ii)

Question 3.

Match the following table:

Answer:

A. (iii)

B. (v)

C. (iv)

D. (ii)

E. (i)

Question 4.

Match the following table:

Answer:

A. (iv)

B. (v)

C. (i)

D. (ii)

E. (iii)

IV. True or False: (if false give the correct statement)

Formation of calcium silicate from silica and calcium oxide is a combination reaction.

Most of the combination reactions are endothermic in nature.

Decomposition of mercuric oxide into mercury and O2 is an example of . photolysis.

Chlorine can displace fluoride ion from its aqueous solution.

Magnesium is more reactive than iron.

Answer:

True

False – Most of the combination reactions are exothermic in nature.

False – Decomposition of mercuric oxide into mercury and O2 is an example of thermolysis.

False – Chlorine is less reactive than Fluorine, so it cannot displace fluoride ion from its aqueous solution.

True

V. Short answer questions:

Question 1.

Write a note on double displacement reaction with an example.

Answer:

When two compounds react, if their ions are interchanged, then the reaction is called double displacement reaction.

Eg: NaOH(aq) + HCl(aq) → NaCl(aq) + H2O

Question 2.

Identify the wrong statements and correct them.

Sodium benzoate is used in food preservative.

Nitric acid is not used as fertilizer in agriculture.

Sulphuric acid is called the king of chemicals.

The pH of acid is greater than 7.

Acetic acid is used in aerated drinks.

Answer:

Correct statement.

Wrong statement. Nitric acid is used as a fertilizer in agriculture.

Correct statement.

Wrong statement. The pH of the acid is lesser than 7.

Wrong statement. Carbonic acid is used in aerated drinks.

Question 3.

Why a combustion reaction may be called as an exothermic oxidation?

Answer:

In a combustion reaction heat is evolved, it is an exothermic reaction. As oxygen is added, it is also an oxidation. So, combustion may be called as an exothermic oxidation.

Question 4.

Take two conical flasks. Label them as I and II. Take a small amount of copper sulphate solution in the first conical flask. Take a small amount of granulated zinc in the second conical flask. Allow the copper sulphate solution to react with the zinc.

Name the type of reaction.

Say whether the metal zinc is more reactive or less reactive.

Write a complete and balanced reaction.

Say whether this change is reversible or irreversible.

Answer:

The reaction taken place is displacement reaction.

Metal zinc is more reactive.

Balanced chemical equation.

This change is an irreversible change.

Question 5.

What is an irreversible reaction? Give an example.

Answer:

The reaction that cannot be reversed is called irreversible reaction. The irreversible reactions are unidirectional, i.e., they take place only in the forward direction. Consider the combustion of coal into carbon dioxide and water.

Samacheer Kalvi 10th Science Guide Chapter 10 Types of Chemical Reactions 13

Question 6.

Define the rate of a reaction.

Answer:

“Rate of a reaction is the change in the amount or concentration of any one of the reactants or products per unit time”.

Consider the following reaction,

A → B

The rate of this reaction is given by

Rate = –

d[A]dt

= +

d[B]dt

Where,

[A] – Concentration of A

[B] – Concentration of B

The negative sign indicates the decrease in the concentration of A with time. The positive sign indicates the increase in the concentration of B with time.

Question 7.

What is meant by combination reaction? Give an example.

Answer:

A reaction in which a single product is formed from two or more reactants is known combination reaction.

2Mg + O2 → 2MgO.

Question 8.

What is a catalyst?

Answer:

A catalyst is a substance which increases the reaction rate without being consumed in the reaction.

Question 9.

Define Displacement reaction. Give an example.

Answer:

The reaction in which a more reactive element displaces a less reactive element from its compound is called displacement reaction.

Pb+⟶+Cu↓

Lead displaces copper from copper chloride solution.

Question 10.

When a aerated soft drink bottle is kept open it will go flat. Why?

Answer:

(i) In the sealed aerated soft drink bottle, the dissolved CO2, in the form of carbonic acid and gaseous CO2 are in equilibrium.

(ii) When we open the bottle the gaseous CO2 will escape and the dissolved CO2 begins to undissolve to the gas phase to maintain the equilibrium. So when we keep the bottle open for a long time it will go flat with all the dissolved CO2 gone.

Question 11.

Can copper displace zinc or lead from their salt solutions?

Answer:

No, copper cannot displace zinc or lead from their salt solutions. Because copper is less reactive than zinc and lead.

Question 12.

What is called as acid rain?

Answer:

The pH of rain water is approximately ‘7’ but when the air is polluted with oxides of S and N, they get dissolved in the rain water and make its pH less than 7, then it is called acid rain.

Question 13.

Write the differences between combination and decomposition reaction.

Answer:

ASTER CLASSES 10th Science Guide Chapter 10 Types of Chemical Reactions 

VI. Answer in detail:

Question 1.

Two acids ‘A’ and ‘B’ were kept in beakers. Acid ‘A’ undergoes partial dissociation in water, whereas acid ‘B’ undergoes complete dissociation in water.

Of the two acids ‘A’ and ‘B’ which is weak acid and which is strong acid?

What is a weak acid?

What is a strong acid?

Give one example of each.

Answer:

Of the two acids ‘A’ and ‘B’, ‘A’ is a weak acid and ‘B’ is a strong acid.

A weak acid is the one which ionises partially when dissolved in water.

A strong acid is the one which ionises completely when dissolved in water.

Weak acid – Acetic acid(CH3COOH)

Strong acid – Sulphuric acid (H2SO4).

Question 2.

Sodium hydroxide and HCl acid react as shown in this equation

NaOH(aq)4 + HCl(aq) → NaCl(aq) + H2O

(i) Which type of chemical reaction is this?

Answer:

Neutralization reaction

(ii) The reaction is exothermic. Explain what that means?

Answer:

When heat is evolved during a chemical reaction it is called exothermic.

(iii) Differentiate exothermic and endothermic reaction.

Answer:

Exothermic :

Heat is evolved.

Temperature increases.

Endothermic :

Heat is absorbed.

Temperature decreases.

(iv) What happens to the temperature of the solution as the chemicals react?

Answer:

Temperature of the solution increases.


Question 3.

Take two conical flasks. Label them as I and II. Take a small amount of CuSO4 in the I conical flask and small amount of granulated Zinc in the II conical flask. Allow the CuSO4 solution to react with Zinc.

(i) Name the type of reaction.

Answer:

Displacement reaction.

(ii) Say whether the metal Zn is more reactive or less reactive.

Answer:

Zinc is more reactive than Copper.

(iii) Write the complete and balanced reaction.

Answer:

Zn(s)+ CuSO4(aq) → ZnSO4(aq) + Cu(s)↓

(iv) Say whether this change is reversible or irreversible

Answer:

Irreversible.


Question 4.

Suggest a reason for each observation given below.

In fireworks, powdered magnesium is used rather than magnesium ribbon.

Zinc and dilute H2SO4 react much more quickly when a few drops of copper sulphate solutions are added.

The reaction between magnesium carbonate and dilute hydrochloric acid speeds up when some concentrated HCl is added.

Answer:

In fireworks, powdered magnesium is used because it has more surface area than magnesium ribbon. Because of more surface area, powdered magnesium reacts faster than magnesium ribbon.

Zinc and dilute H2SO4 react much more quickly when a few drops of copper sulphate solution is added. Copper sulphate acts as a catalyst which increases the rate of the reaction.

When the concentration of the reactants increases, the rate of the reaction also increases. So the reaction between magnesium carbonate and dilute hydrochloric acid speeds up by the addition of some concentrated HCl.

Answers:

In fireworks, powdered magnesium is used because it has more surface area than magnesium ribbon. Because of more surface area, powdered magnesium reacts faster than magnesium ribbon.

Zinc and dilute H2SO4 react much more quickly when a few drops of copper sulphate solution is added. Copper sulphate acts as a catalyst which increases the rate of the reaction.

When the concentration of the reactants increases, the rate of the reaction also increases. So the reaction between magnesium carbonate and dilute hydrochloric acid speeds up by the addition of some concentrated HCl.


Chapter 9, Atoms and Molecules, sslc, chemistry, 10th, tamilnadu board, science, full, solution,

Questions and Answers

I. Choose the best answer:

Question 1.

A solution is a mixture.

(a) homogeneous

(b) heterogeneous

(c) homogeneous and heterogeneous

(d) non-homogeneous

Answer:

(a) homogeneous

Question 2.

The number of components in a binary solution is ______.

(a) 2

(b) 3

(c) 4

(d) 5.

Answer:

(a) 2

Question 3.

Which of the following is the universal solvent?

(a) Acetone

(b) Benzene

(c) Water

(d) Alcohol

Answer:

(c) Water

Question 4.

A solution in which no more solute can be dissolved in a definite amount of solvent at a given temperature is called ______.

(a) Saturated solution

(b) Un saturated solution

(c) Supersaturated solution

(d) Dilute solution.

Answer:

(a) Saturated solution

Question 5.

Identify the non-aqueous solution.

(a) sodium chloride in water

(b) glucose in water

(c) copper sulphate in water

(d) sulphur in carbon-di-sulphide

Answer:

(d) sulphur in carbon-di-sulphide

Question 6.

When pressure is increased at a constant temperature the solubility of gases in liquid ______.

(a) No change

(b) increases

(c) decreases

(d) no reaction.

Answer:

(b) increases

Question 7.

Solubility of NaCl in 100 ml water is 36 g. If 25 g of salt is dissolved in 100 ml of water how much more salt is required for saturation:

(a) 12 g

(b) 11 g

(c) 16 g

(d) 20 g

Answer:

(b) 11 g

Question 8.

A 25% alcohol solution means ______.

(a) 25 ml of alcohol in. 100 ml of water

(b) 25 ml of alcohol in 25 ml of water

(c) 25 ml of alcohol in 75 ml of water

(d) 75 ml of alcohol in 25 ml of water.

Answer:

(c) 25 ml of alcohol in 75 ml of water

Question 9.

Deliquescence is due to:

(a) Strong affinity to water

(b) Less affinity to water

(c) Strong hatred to water

(d) Inertness to water

Answer:

(a) Strong affinity to water

Question 10.

Which of the following is hygroscopic in nature?

(a) ferric chloride

(b) copper sulphate pentahydrate

(c) silica gel

(d) none of the above.

Answer:

(c) silica gel

II. Fill in the blanks:

The component present in lesser amount, in a solution is called ……..

Example for liquid in solid type solution is ……….

Solubility is the amount of solute dissolved in ……… g of solvent.

Polar compounds are soluble in ……… solvents.

Volume percentage decreases with increases in temperature because ………

Answer:

III. Match the following:

Answer:

A. (iii)

B. (i)

C. (iv)

D. (ii)

ASTER CLASSES  10th Science Guide Chapter 9 Solutions

IV. True or False: (If false give the correct statement):

Solutions which contain three components are called binary solution.

In a solution the component which is present in lesser amount is called solvent.

Sodium chloride dissolved in water forms a non-aqueous solution.

The molecular formula of green vitriol is MgSO4. 7H2O

When Silica gel is kept open, it absorbs moisture from the air, because it is hygroscopic in nature.

Answer:

False – Solutions which contain two components are called binary solution.

False – In a solution the component which is present in lesser amount is called solute.

False – Sodium chloride dissolved in water forms an aqueous solution.

False – The molecular formula of green vitriol is FeSO4. 7H2O

True

V. Short Answer Questions:

Question 1.

Define the term: Solution

Answer:

A solution is a homogeneous mixture of two or more substances.

Question 2.

What is mean by the binary solution?

Answer:

A solution must at least be consisting of two components. Such solutions which are made of one solute and one solvent are called binary solutions.

E.g., On adding CuSO4 crystals to water.

Question 3.

Give an example each

gas in liquid;

solid in liquid;

solid in solid;

gas in gas.

Answer:

Gas in liquid – CO2 in water

Solid in liquid – NaCl in water

Solid in solid – Alloys

Gas in gas – He – O2 gas

Question 4.

What is the aqueous and non-aqueous solution? Give an example.

Answer:

Aqueous solution: The solution in which water act as a solvent is called aqueous solution. In general, ionic compounds are soluble in water and form aqueous solutions more readily than covalent compounds. E.g. Common salt in water.

Non – Aqueous solution: The solution in which any liquid, other than water act as a solvent is called non-aqueous solution. Alcohols, benzene, ethers, etc., are used as non – aqueous solvents. E.g. Sulphur dissolved in carbon disulphide.

Question 5.

Define Volume percentage.

Answer:

Volume percentage is defined as the percentage by volume of solute (in ml) present in the given volume of solution.

Question 6.

The aquatic animals live more in a cold region. Why?

Answer:

Aquatic animals live more in cold regions because the solubility of oxygen is more in cold water (at low temperature). Therefore, aquatic animals are more comfortable in cold water.

Question 7.

Define Hydrated salt.

Answer:

Ionic substances which crystallise out from their saturated aqueous solution with a definite number of molecules of water are called hydrated salts.

Question 8.

A hot saturated solution of copper sulphate forms crystals as it cools. Why?

Answer:

The capability of a solution to maintain a certain concentration of solute is temperature-dependent. When a saturated solution of copper sulphate at above room temperature is allowed to cool, the solution becomes supersaturated and in the absence of stirring or the return of the previous solution temperature, the solute starts to precipitate out. i.e., crystal formation occurs.

Question 9.

Classify the following substances into deliquescent, hygroscopic. Cone. Sulphuric acid, Copper sulphate penta hydrate, Silica gel, Calcium chloride and Gypsum salt.

Answer:

VI. Long answer questions:

Question 1.

Write notes on?

saturated solution

unsaturated solution

Answer:

Saturated solution: A solution in which no more solute can be dissolved in a definite amount of the solvent at a given temperature is called saturated solution, e.g. 36 g of sodium chloride in 100 g of water at 25°C forms a saturated solution.

Unsaturated solution: Unsaturated solution is one that contains less solute than that of the saturated solution at a given temperature, e.g. 10 g or 20 g or 30 g of Sodium chloride in 100 g of water at 25°C forms an unsaturated solution.

Question 2.

Write notes on various factors affecting solubility.

Answer:

There are three main factors which affects the solubility of a solute. They are

Nature of the solute and solvent

Temperature

Pressure

1. Nature of the solute and solvent : The nature of the solute and solvent plays an important role in solubility. Even though water is Universal solvent, all substances do not dissolve in water. Dissolution occurs when similarities exist between the solvent and the solute.

Ionic compounds are soluble in polar solvent like water and covalent compounds are soluble in non-polar solvents like ether, benzene, alcohol etc.

2. Effect of Temperature :

Solubility of solid in liquid : Generally solubility of a solid solute in a liquid increases with increase in temperature.

In Endothermic process : Solubility increases with increase in temperature.

In Exothermic process : Solubility decreases with increase in temperature.

Solubility of Gases in liquid : Solubility of gases in liquid decreases with increase in temperature.

3. Effect of Pressure : Effect of pressure is observed only in the case of solubility of a gas in a liquid. When the pressure is increased, the solubility of a gas in liquid increases.

Question 3.

(a) What happens when MgSO4.7H2O is heated? Write the appropriate equation

(b) Define solubility.

Answer:

(a) When Epsom salt MgSO4.7H2O crystals are gently heated, it loses seven water molecules and becomes anhydrous MgSO4.

Samacheer Kalvi 10th Science Guide Chapter 9 Solutions 4

(b) Solubility is defined as the amount of solute in grams that can be dissolved in 100 g of the solvent to form its saturated solution at a given temperature and pressure.

Question 4.

In what way hygroscopic substances differ from deliquescent substances.

Answer:

Question 5.

A solution is prepared by dissolving 45 g of sugar in 180 g of water. Calculate the mass percentage of solute.

Answer:

Mass of the solute (sugar) = 45 g

Mass of the solvent (Water) = 180 g

Formula:

Mass percentage of solute (sugar)

The mass percentage of solute = 20%

Question 6.

3.5 litres of ethanol is present in 15 litres of aqueous solution of ethanol. Calculate volume percent of ethanol solution.

Answer:

Volume of ethanol = 3.5 lit = 3500 ml

Volume of water = 15 lit = 15000 ml

Formula:

The volume percentage of ethanol solution = 18.92

VII. HOT Questions

Question 1.

Vinu dissolves 50 g of sugar in 250 ml of hot water, Sarath dissolves 50 g of same sugar in 250 ml of cold water. Who will get a faster dissolution of sugar? and Why?

Answer:

Vinu will get a faster dissolution of sugar. Because generally solubility of a solid solute in a liquid solvent increases with increase in temperature. Therefore Vinu dissolves 50 g of sugar in 250 ml of hot water than Sarath dissolves 50 g of sugar in 250 ml of cold water.

Question 2.

‘A’ is a blue coloured crystalline salt. On heating it loses blue colour and to give ‘B’ When water is added, ‘B’ gives back to ‘A’. Identify A and B, write the equation.

Answer:

Since ‘A’ is a blue coloured crystalline salt, it is CuSO4. 5H2O (Blue vitriol). On heating it loses all five water molecules and becomes colourless anhydrous CuSO4.

When water is added ‘B’ gives back A.

Question 3.

Will the cool drinks give more fizz at top of the hills or at the foot? Explain.

Answer:

At hilltops, the temperature will become less and pressure also decreases. Because temperature and pressure are directly proportional to each other. At low-pressure carbonate, cool drinks will give less fizz and give more fizz at the foot.

ASTER CLASSES 10th Science Solutions Additional Important Questions and Answers

I. Choose the correct answer:

Question 1.

The dissolution of sugar and salt in water results in a solution.

(a) Binary

(b) Ternary

(c) Quaternary

(d) Saturated

Answer:

(b) Ternary

Question 2.

In a solution, the component which is present in a lesser amount is called ______.

(a) solvent

(b) dissolution

(c) solute

(d) mole.

Answer:

(c) solute

Question 3.

The supersaturated solution of NaCl in 100 g of water at 25°C contains:

(a) 40 g of NaCl

(b) 10 g of NaCl

(c) 20 g of NaCl

(d) 30 g of NaCl

Answer:

(a) 40 g of NaCl

ASTER CLASSES10th Science Guide Chapter 9 Solutions

Question 4.

How many component(s) present in binary solution?

(a) 1

(b) 2

(c) 3

(d) 4.

Answer:

(b) 2

Question 5.

Formalin is an aqueous solution of:

(a) formic acid

(b) ammonia

(c) formaldehyde

(d) carbon tetrachloride

Answer:

(c) formaldehyde

Question 6.

The effect of pressure on the solubility of a gas in liquids is given by:

(a) Boyle’s Law

(b) Charle’s Law

(c) Henry’s Law

(d) Avogadro’s Law

Answer:

(c) Henry’s Law

Question 7.

Which one of the following is an example of an aqueous solution?

(a) Sugar in water

(b) Sulphur in carbon disulphide

(c) Iodine dissolved in carbon tetrachloride

(d) Benzoic acid in ethers.

Answer:

(a) Sugar in water

Question 8.

The type of solution when CO2 is dissolved in water:

(a) solid/liquid

(b) liquid in liquid

(c) gas in liquid

(d) liquid in solid

Answer:

(c) gas in liquid

Question 9.

Tin amalgam is an example of ……… solution.

(a) solid in solid

(b) liquid in solid

(c) solid in liquid

(d) liquid in liquid

Answer:

(b) liquid in solid

Question 10.

In which case solubility decreases with increase in temperature?

(a) Endothermic process

(b) Exothermic process

(c) Both (a) and (b)

(d) None of these.

Answer:

(b) Exothermic process

Question 11.

Fat is soluble in:

(a) water

(b) alcohol

(c) CCl4

(d) ether

Answer:

(d) ether

Question 12.

The deliquescent substance among the following is:

(a) con.H2SO4

(b) P2O5

(c) CaCl2

(d) SiO2

Answer:

(c) CaCl2

ASTER CLASSES 10th Science Guide Chapter 9 Solutions

Question 13.

Mass percentage is expressed as ______.

(a) v/v

(b) w/w

(c) v/w

(d) w/v.

Answer:

(b) w/w

Question 14.

Hygroscopic substances are used as ……… agents.

(a) foaming

(b) drying

(c) oxidising

(d) reducing

Answer:

(b) drying

Question 15.

The molecular formula of Epsom salt is ______.

(a) CuSO4.5H2O

(b) FeSO4.7H2O

(c) MgSO4.7H2O

(d) ZnSO4.7H2O.

Answer:

(c) MgSO4.7H2O

II. Fill in the blanks:

1. A true solution is a ……… mixture of solute and solvent.

2. Soil cannot store more nitrogen than it can hold because soil is said to be in a state of ………

3. In the dissolution of NaOH in water, the solubility …….. with increase in temperature.

4. Aquatic animals are more comfortable in cold water because as the temperature is less the solubility of dissolved oxygen ………

5. Hydrated salts contain ……… of crystallization.

6. He-O2 mixture is a binary solution of …….. in ………. solution.

7. The solvent used for dissolving Sulphur is ……….

8. The solubility of NaOH at 25°C is ……….

9. According to Henry’s Law, the solubility of a gas in liquid is ………. proportional to the pressure of the gas over the solution at definite temperature.

10. Anhydrous Calcium chloride is a ………. substance.

11. ……… substances absorb enough water from the atmosphere and get completely dissolved.

12. When 90g of sodium bromide is dissolved in 100 g of water at 25°C it forms a ………. solution.

13. ………. is an example of a binary solution with liquid in Gas.

14. Air and sea water are important ……… solution.

15. A quaternary solution contains ……….. components.

16. The primary factor which determines the characteristic of a solution is ………..

Answer:

1. Homogeneous

2. saturation

3. decreases

4. increases

5. water

6. Gas, Gas

7. CS2 (or) Carbon disulphide

8. 80 g

9. directly

10. Hygroscopic

11. deliquescent

12. Unsaturated

13. Cloud

14. Homogeneous

15. four

16. Physical state

III. Match the following

Question 1.

Match the column I with column II.

ASTER CLASSES 10th Science Guide Chapter 9 Solutions 10

Answer:

A. (iv)

B. (iii)

C. (v)

D. (ii)

E. (i)

Question 2.

Match the column I with column II.

Answer:

A. (iii)

B. (iv)

C. (v)

D. (ii)

E. (i)

Question 3.

Match the column I with column II.

Answer:

A. (v)

B. (iii)

C. (ii)

D. (i)

E. (iv)

Question 4.

Match the column I with column II.

Answer:

A. (iii)

B. (iv)

C. (v)

D. (i)

E. (ii)

Question 5.

Match the column I with column II.

ASTER CLASSES 10th Science Guide Chapter 9 Solutions 

Answer:

A. (iv)

B. (iii)

C. (i)

D. (v)

E. (ii)

IV. True or False: (If false give the correct statement)

1. In an aqueous solution of copper sulphate, the solvent is copper sulphate.

2. A solution containing sugar and salt in water is a binary solution.

3. An example of a solid solution is alloy.

4. The difference between concentrated and dilute solution can be observed by means of colour (or) density.

5. A saturated solution contains 91 g of Glucose in 100 g of water at 25°C.

6. Fat is dissolved in the aqueous solvent ether.

7. The solubility of a gas in a liquid is inversely proportional to the pressure of the gas at a definite temperature.

8. Mass percentage of a solution is expressed as .

9. The white vitriol is represented by the formula ZnSO4 . 7H2O.

10. Ferric chloride is a Hygroscopic substance.

Answer:

1. False – In an aqueous solution of copper sulphate, the solvent is water.

2. False – A solution containing sugar and salt in water is a ternary solution.

3. True

4. True

5. True

6. False – Fat is dissolved in the non-aqueous solvent ether.

7. False – The solubility of a gas in a liquid is directly proportional to the pressure of the gas at a definite temperature.

8. True

9. True

10. False – Ferric chloride is a deliquescent substance.

V. Short answer questions:

Question 1.

(i) Which gas is dissolved in soft drinks?

(ii) What will you do to increase the solubility of this gas?

Answer:

(i) Carbon-di-oxide (CO2) is dissolved in soft drinks.

(ii) An increase in pressure will increase the solubility of CO2 gas.

Question 2.

Identify the type of binary solution given below.

Answer:

Alloys

Amalgam

Ethyl alcohol in water

Aerated drinks

Answer:

Solid in solid

liquid in solid

liquid in liquid

Gas in liquid

Question 3.

Explain why Nitrogen in soil is called a saturated solution in nature?

Answer:

Nitrogen in soil is an example of a saturated solution in nature. Soil cannot store more Nitrogen than it can hold.

Question 4.

Define Mass percentage.

Answer:

Mass percentage of a solution is defined as the percentage by mass of the solute present in the solution.

Question 5.

Define the term Molarity (M).

Answer:

Question 6.

Define the term Molality (m).

Answer:

Question 7.

Define the supersaturated solution.

Answer:

A supersaturated solution is one that contains more solute than the saturated solution at a given temperature.

E.g. 40 g of sodium chloride in 100 g of water at 25°C.

Question 8.

Justify the following statements with an explanation.

(i) Solubility of NH4Cl increases with increase in temperature.

Answer:

Solubility of NH4Cl increases with increase in temperature because it is an endothermic process.

(ii) Solubility of NaOH decreases with increase in temperature.

Answer:

Solubility of NaOH decreases with increase in temperature because it is an exothermic process.

Question 9.

Calculate the molarity of a solution containing 4 g of NaOH in 500 ml of water.

Answer:

Mass of NaOH = 4 g

Volume of solution = 500 ml

= 0.1 × 2

= 0.2 M

Question 10.

Calculate the molality of a solution containing 3 g of urea (molecular mass = 60) in 750 g of water.

Answer:

Mass of urea (solute) = 3 g

Mass of water (solvent) = 750 g

Formula:

Question 11.

Define dissolution.

Answer:

The process of uniform distribution of solute into solvent is called dissolution.

VI. Long answer questions:

Question 1.

Answer the blanks given in the table.

Answer:

Question 2.

Write a note on the type of solution based on the type of solvent.

Answer:

(i) Aqueous solution : The solution in which water acts as a solvent is called aqueous solution. In general, ionic compounds are soluble in water and form aqueous solutions more readily than covalent compounds.

Eg: Common salt in water, Sugar in water, Copper sulphate in water etc..

(ii) Non-Aqueous solution : The solution in which any liquid, otter than water, acts as a solvent is called non-aqueous solution. Solvent other than water is referred to as non-aqueous solvent. Generally, alcohols, benzene, ethers, carbon disulphide, acetone, etc., are used as non- aqueous solvents.

Eg: Sulphur dissolved in carbon disulphide, Iodine dissolved in carbon tetrachloride.

Question 3.

Justify the following statements with an explanation.

The solubility of calcium oxide decreases with increase in temperature,

What happens to the solubility in the exothermic process with regard to temperature?

In the endothermic process, solubility increases with increase in temperature.

At a given temperature, an increase in pressure increases the solubility of the gas

Answer:

In an exothermic process, the solubility decreases. When calcium oxide dissolves in water, an exothermic reaction takes place, and so the solubility of calcium oxide decreases

In an exothermic process, the solubility decreases with the increase in temperature, as there is already an evolution of heat and it is observed.

In an endothermic process, the solubility increases. The solubility of KNO3 in water is an endothermic reaction and so solubility increases with the increase of temperature.

At a given temperature, an increase in pressure increases the solubility of gas according to Henry’s law. e.g. (CO2 in soft drinks)

VII. Hot Questions.

Question 1.

50 ml tincture of benzoin, antiseptic solution contains 10 ml of benzoin. Calculate the volume of percentage of benzoin.

Answer:

Volume of the solute, Benzoin = 10 ml

Volume of the solution, tincture of benzoin = 50 ml

= 20% (v/v)

Question 2.

Neomycin, the antibiotic cream contains 300 mg of neomycin sulphate the active ingredient in 30 g of ointment base. Calculate the mass percentage of neomycin.

Answer:

Mass of neomycin sulphate(solute) = 300 mg

Mass of the ointment (solution) = 30 g

Formula:

VIII. Numerical problems:

Question 1.

Calculate the molality of the solution containing 18 g of Glucose (Molecular mass 180) in 2 kg of water.

Answer:

Mass of Glucose = 18 g

Molecular mass of Glucose = 180

= 0. 05 m

Question 2.

Calculate the molarity of a solution containing 5.85 g of sodium chloride in 500 ml of the water. (Molecular mass = 58.5)

Answer:

Mass of the solute = 5.85 g

Volume of the solution = 500

No. of moles of NaCl =

5.8558.5

= 0.1

=

× 1000 = 0.2 M


Chapter 7, Atoms and Molecules, sslc, chemistry, 10th, tamilnadu board, science, full, solution,

Science ssc chemistry

I. Choose the best answer:

Question 1.

Which of the following has the smallest mass?

(a) 6.023 × 1023 atoms of He

(b) 1 atom of He

(c) 2 g of He

(d) 1-mole atoms of He

Answer:

(b) 1 atom of He

Question 2.

Which of the following is a triatomic molecule?

(a) Glucose

(b) Helium

(c) Carbon dioxide

(d) Hydrogen.

Answer:

(c) Carbon dioxide

Hint:

(a) Glucose = C6H12O6 (Polyatomic molecule)

(b) Helium = He (Monoatomic molecule)

(c) Carbon dioxide = CO2 (Triatomic molecule)

(d) Hydrogen = H2 (Diatomic molecule)

So, (c) is the correct answer.

Question 3.

The volume occupied by 4.4 g of CO2 at S.T.P:

(a) 22.4 litre

(b) 2.24 litre

(c) 0.24 litre

(d) 0.1 litre

Answer:

(b) 2.24 litre

Question 4.

Mass of 1 mole of Nitrogen atom is _____.

(a) 28 amu

(b) 14 amu

(c) 28 g

(d) 14 g.

Answer:

(b) 14 amu

Hint: Atomic mass of Nitrogen is 14.00674 grams. It is equal to 1 mole of Nitrogen atoms.

So, answer (b) is correct.

Question 5.

Which of the following represents 1 amu?

(a) Mass of a C – 12 atom

(b) Mass of a hydrogen atom

(c) 1/12 th of the mass of a C – 12 atom

(d) Mass of O – 16 atom

Answer:

(c) 1/12 th of the mass of a C – 12 atom

Question 6.

Which of the following statement is incorrect?

(a) One gram of C – 12 contains Avogadro’s number of atoms.

(b) One mole of oxygen gas contains Avogadro’s number of molecules.

(c) One mole of hydrogen gas contains Avogadro’s number of atoms.

(d) One mole of electrons stands for 6.023 × 1023 electrons.

Answer:

(a) One gram of C – 12 contains Avogadro’s number of atoms.

Hint: 12 g of Carbon contains 6.023 × 1023 atoms,

1 g of Carbon contain

6.023×12

= 5.018 × 1022 atoms and its is not Avogadro’s number of atoms.

So (a) is the incorrect statement.

Question 7.

The volume occupied by 1 mole of a diatomic gas at S.T.P is:

(a) 11.2 litre

(b) 5.6 litre

(c) 22.4 litre

(d) 44.8 litre

Answer:

(c) 22.4 litre

Question 8.

In the nucleus of 20Ca40, there are

(a) 20 protons and 40 neutrons

(b) 20 protons and 20 neutrons

(c) 20 protons and 40 electrons

(d) 40 protons and 20 electrons

Answer:

(b) 20 protons and 20 neutrons

Question 9.

The gram molecular mass of oxygen molecule is_____.

(a) 16 g

(b) 18 g

(c) 32 g

(d) 17 g.

Answer:

(c) 32 g

Hint: By definition, the gram molecular mass of oxygen molecule O2 is 32 g.

So the answer (c) is correct.

Question 10.

1 mole of any substance contains molecules.

(a) 6.023 × 1023

(b) 6.023 × 10-23

(c) 3.0115 × 1023

(d) 12.046 × 1023

Answer:

(a) 6.023 × 1023

II. Fill in the blanks:

1. Atoms of different elements having ……… mass number, but ………. atomic numbers are called isobars.

2. Atoms of different elements having same number of ………. are called isotones.

3. Atoms of one element can be transmuted into atoms of other element by ………….

4. The sum of the numbers of protons and neutrons of an atom is called its …………

5. Relative atomic mass is otherwise known as …………

6. The average atomic mass of hydrogen is ……….. amu.

7. If a molecule is made of similar kind of atoms, then it is called ……….. atomic molecule.

8. The number of atoms present in a molecule is called its ………….

9. One mole of any gas occupies ………… ml at S.T.P

10. Atomicity of phosphorous is …………

Answer:

1. same, different

2. neutrons

3. artificial transmutation

4. mass number

5. standard atomic weight

6. 1.008

7. homo

8. atomicity

9. 22, 400

10. four

III. Match the following:

 1

Answer:

A. (ii)

B. (iii)

C. (v)

D. (i)

E. (iv)

IV. True or False: (If false give the correct statement)

Two elements sometimes can form more than one compound.

Nobel gases are diatomic.

The gram atomic mass of an element has no unit.

1 mole of Gold and Silver contain same number of atoms.

Molar mass of CO2 is 42 g.

Answer:

True

False – Noble gases are Monoatomic.

False – The unit of gram atomic mass of an element is gram.

True

False – Molar mass of CO2 is 44 g.

V. Assertion and Reason:

Answer the following questions using the data given below:

Question 1.

Assertion: Atomic mass of aluminium is 27

Reason: An atom of aluminium is 27 times heavier than 1/12 th of the mass of the C-12 atom.

(a) Assertion and Reason are correct, Reason explains the Assertion.

(b) Assertion is correct, Reason is wrong.

(c) Assertion is wrong, Reason is correct.

(d) Assertion and Reason are correct, Reason doesn’t explains Assertion.

Answer:

(a) Assertion and Reason are correct, Reason explains the Assertion.

Question 2.

Assertion: The Relative Molecular Mass of Chlorine is 35.5 a.m.u.

Reason: The natural abundance of Chlorine isotopes are not equal.

(a) Assertion and Reason are correct, Reason explains the Assertion.

(b) Assertion is correct, Reason is wrong.

(c) Assertion is wrong, Reason is correct.

(d) Assertion and Reason are correct, Reason doesn’t explains Assertion.

Answer:

(c) Assertion is wrong, Reason is correct.

VI. Short answer questions:

Question 1.

Define: Relative atomic mass.

Answer:

Relative atomic mass of an element is the ratio between the average mass of its isotopes to

1

part of the mass of a carbon-12 atom. It is denoted as Ar.

[OR]

2

Question 2.

Write the different types of isotopes of oxygen and its percentage abundance.

Answer:

Oxygen has three stable isotopes. They are

3

Question 3.

Define Atomicity.

Answer:

The number of atoms present in the molecule is called its ‘Atomicity’.

Question 4.

Give any two examples for heteroatomic molecules.

Answer:

HI, HCl, CO, HBr, HF.

Question 5.

What is Molar volume of a gas?

Answer:

One mole of any gas occupies 22.4 litres.

(or)

22400 ml at S.T.R This volume is called as molar volume.

Question 6.

Find the percentage of nitrogen in ammonia.

Answer:

Molar mass of NH3 = 1(14) + 3(1) = 17 g

4

VII. Long answer questions:

Question 1.

Calculate the number of water molecule present in one drop of water which weighs 0.18 g.

Answer:

The molecular mass of water (H2O) is 18.

18 g of water molecule = 1 mole.

0. 18 g of water =

118×0.18

= 0.01 mole.

1 mole of water (Avogadro’s number) contains 6.023 × 1023 water molecules.

0. 01 mole of water contain

6.023×

= 6.023 × 1021 molecules.

Question 2.

N2 + 3 H2 → 2 NH3

(The atomic mass of nitrogen is 14, and that of hydrogen is 1)

1 mole of nitrogen (……..g) +

3 moles of hydrogen (………g) →

2 moles of ammonia (………g)

Answer:

1 mole of nitrogen (28 g) +

3 moles of hydrogen (6 g) →

2 moles of ammonia (34 g)

Question 3.

Calculate the number of moles in

(i) 27 g of Al;

(ii) 1.51 × 1023 molecules of NH4Cl.

Answer:

(i) 27 g of Al

Given mass atomic mass =

GivenMassAtomicMass

=

= 1 mole

(ii) 1.51 x 1023 molecules of NH4Cl

Number of moles

5

Question 4.

Give the salient features of “Modern atomic theory”.

Answer:

The salient features of “Modem atomic theory” are,

An atom is no longer indivisible.

Atoms of the same element may have different atomic mass.

Atoms of different elements may have the same atomic masses.

Atoms of one element can be transmuted into atoms of other elements. In other words, an atom is no longer indestructible.

Atoms may not always combine in a simple whole-number ratio.

Atom is the smallest particle that takes part in a chemical reaction.

The mass of an atom can be converted into energy [E = mc2].

Question 5.

Derive the relationship between Relative molecular mass and Vapour density.

Answer:

Relative molecular mass : The relative molecular mass of a gas or vapour is the ratio between the mass of one molecule of the gas or vapour to mass of one atom of hydrogen.

Vapour density : Vapour density is the ratio of the mass of certain volume of a gas or vapour, to the mass of an equal volume of hydrogen, measured under the same conditions of temperature and pressure.

6

According to Avogadro’s law equal volumes of all gases contain equal number of molecules.

Let the number of molecules in one volume = n, then

When cancelling ‘n’ which is common at STP, we get

8

Since hydrogen is diatomic,

9

2 × Vapour density = Relative Molecular mass of a gas

[OR]

Relative Molecular Mass = 2 × Vapour density

VIII. HOT Question:

Question 1.

Calcium carbonate is decomposed on heating in the following reaction

CaCO3 → CaO + CO2

How many moles of Calcium carbonate is involved in this reaction?

Calculate the gram molecular mass of calcium carbonate involved in this reaction.

How many moles of CO2 are there in this equation?

Answer:

CaCO3 → CaO + CO2

1 mole of CaCO3 is involved in this reaction.

Gram molecular mass of calcium carbonate

CaCO3 = (40 + 12 + 3 × 16) = 52 + 48 = 100 g

1 mole of CO2 is in this equation.


IX. Solve the following problems:

Question 1.

How many grams are there in the following?

(i) 2 moles of a hydrogen molecule, H2

(ii) 3 moles of chlorine molecule, Cl2

(iii) 5 moles of sulphur molecule, S8

(iv) 4 moles of a phosphorous molecule, P4

Solution:

(i) 2 moles of a hydrogen molecule, H2

Mass of 1 mole of hydrogen molecule = 2 g

Mass of 2 moles of hydrogen molecule = 2 × 2 = 4 g.

(ii) 3 moles of chlorine molecule, Cl2

Mass of 1 mole of chlorine molecule = 71 g

Mass of 3 moles of chlorine molecules = 71 × 3 = 213 g.

(iii) 5 moles of sulphur molecule, S8

Mass of 1 mole of sulphur molecule = 32 g

Mass of 5 moles of sulphur molecules = 32 × 5 = 160 g.

(iv) 4 moles of the phosphorous molecule, P4

Mass of 1 mole of phosphorous molecule = 30.97 g

Mass of 4 moles of phosphorous molecules = 30.97 × 4 = 123.88 g.

Question 2.

Calculate the % of each element in calcium carbonate. (Atomic mass: C – 12, O – 16, Ca – 40)

Answer:

Formula to find % of each element

10

Question 3.

Calculate the % of oxygen in Al2(SO4)3.

(Atomic mass: Al – 27, O – 16, S – 32)

Answer:

Formula:

11

Molar mass of Al2(SO4)3 = [2(Atomic mass of Al) + 3(Atomic mass of S) + 12(Atomic mass of O)]

= 2(27) + 3(32) + 12(16) = 342 g

% of Oxygen =

12(16)342

× 100 = 56.14%.

Question 4.

Calculate the % relative abundance of B – 10 and B – 11, if its average atomic mass is 10.804 amu.

Answer:

% of relative abundance can be calculated by the formula.

Average atomic mass of the element

= Atomic mass of 1st isotope × abundance of 1st isotope + Atomic mass of 2nd isotope × abundance of 2nd isotope

∴ Average atomic mass of Boron

= Atomic mass of B – 0 × abundance of B -10 + Atomic mass of B – 11 × abundance of B – 11

Let the abundance of B – 10 be ‘x’ and B – 11 be (1 – x)

So, 10.804 = 10 × x + 11 (1 – x)

10.804 = 10x + 11 – 11x

x = 11 – 10.804

x = 0.196

1 -x = 1 – 0.196 = 0.804

Therefore % abundance of B – 10 is 19.6% and B – 11 is 80.4%

[OR]

Let the % of the isotope B – 10 = x

Then the % of the isotope B – 11 = 100 – x

12

1100 – x = 1080.4

x = 19.6

% abundance of B – 10 = 19.6%

% abundance of B – 11 = 80.4%


Questions and Answers

I. Choose the correct answer.

Question 1.

The first scientific theory of an atom was proposed by:

(a) Ruther Ford

(b) Newland

(c) John Dalton

(d) Neils Bohr

Answer:

(c) John Dalton

Question 2.

Identify the pair that indicates isobars among the following _____.

(a)

1Ca40

Question 3.

Which one of the following represents 180 g of water?

(a) 5 moles of water

(b) 90 moles of water

(c) 6.023 × 1024 molecules of water

(d) 6.023 × 1022 molecules of water

Answer:

(c) 6.023 × 1024 molecules of water

Question 4.

The isotope of Carbon-12 contains _____.

(a) 6 protons and 7 electrons

(b) 6 protons and 6 neutrons

(c) 12 protons and no neutrons

(d) 12 neutrons and no protons.

Answer:

(b) 6 protons and 6 neutrons

Question 5.

Which contains the greatest number of moles of oxygen atoms?

(a) 1 mol of water

(b) 1 mole of NaOH

(c) 1 mole of Na2CO3

(d) 1 mole of CO

Answer:

(c) 1 mole of Na2CO3

Question 6.

The mass of proton or neutron is approximately _____.

(a) 1 amu

(b) 1.609 × 10-19 g

(c) 1 g

(d) 6.023 × 10-23 g.

Answer:

(a) 1 amu

Question 7.

The natural abundance of C-12 and C-13 are 98.90% and 1.10% respectively. The average atomic mass of carbon is:

(a) 12 amu

(b) 12.011 amu

(c) 14 amu

(d) 12.90 amu

Answer:

(b) 12.011 amu

Question 8.

The relative atomic mass of magnesium-based on C – 12 scale is _____.

(a) 24 g

(b) 24

(c) 24 amu

(d) 24 kg

Answer:

(b) 24

Question 9.

If 1.5 moles of oxygen combine with Al to form Al2O3, the mass of Al in g (atomic mass of Al = 27) used in the reaction is:

(a) 2.7

(b) 54

(c) 40.5

(d) 81

Answer:

(b) 54

Question 10.

The atomicity of methane is:

(a) 5

(b) 4

(c) 3

(d) 6

Answer:

(a) 5

Question 11.

Find the odd one out _____.

(a)

8

.

Answer:

(c)

O12

Question 12.

The volume occupied by 3 moles of HCl gas at STP is:

(a) 22.4 L

(b) 44.8 L

(c) 2.24 L

(d) 67.2 L

Answer:

(d) 67.2 L

Question 13.

The mass percentage of hydrogen in ethane (C2H6) is:

(a) 25%

(b) 75%

(c) 80%

(d) 20%

Answer:

(d) 20%

Question 14.

Which one of the following is a homo diatomic molecule?

(a) H2

(6) CO

(c) NO

(d) O3.

Answer:

(a) H2

Question 15.

The percentage of nitrogen in urea is about:

(a) 38.4

(b) 46.6

(c) 59.1

(d) 61.3

Answer:

(b) 46.6

Question 16.

Out of the following the largest number of atoms are contained in:

(a) 11 g of CO2

(b) 4 g of H2

(C) 5 g of NH3

(d) 8 g of SO2

Answer:

(b) 4 g of H2

Question 17.

Which of the following is an example of a homo triatomic molecule?

(a) Phosphorous

(b) Sulphur

(c) Bromine

(d) Ozone.

Answer:

(d) Ozone.

Question 18.

For the reaction A + 2B → C, 5 moles of A and 8 moles of B will produce:

(a) 5 moles of C

(b) 4 moles of C

(c) 8 moles of C

(d) 13 moles of C

Answer:

(b) 4 moles of C

Question 19.

The vapour density of a gas is 32. Its relative molecular mass will be:

(a) 32

(b) 16

(c) 64

(d) 96

Answer:

(c) 64

Question 20.

Find the odd one out _____.

(a) Silver

(b) Potassium

(c) Iron

(d) Phosphorous.

Answer:

(d) Phosphorous.

II. Fill in the blanks.

The volume occupied by 16 g of oxygen is ………..

One mole of a triatomic gas contains ………… atoms.

Equal volume of all gases under the same conditions of temperature and pressure contain equal number of …………

The mass of an atom can be converted into energy by using the formula …………

The percentage composition is useful to determine the ………… formula and ………… formula.

Answer:

11.2 L

3 × 6.023 × 1023

molecules

E = me²

empirical, molecular

III. Match the following:

Question 1.

Match the Column I with Column II.

13

Answer:

A. (ii)

B. (iii)

C. (i)

D. (v)

E. (iv)

Question 2.

Match the Column I with Column II.

14

Answer:

A. (iii)

B. (i)

C. (iv)

D. (v)

E. (ii)

Question 3.

Match the Column I with Column II.

15

Answer:

A. (iv)

B. (v)

C. (ii)

D. (iii)

E. (i)

Question 4.

Match the Column I with Column II.

16

Answer:

A. (v)

B. (iii)

C. (iv)

D. (i)

E. (ii)

IV. True or False: (If false give the correct statement)

Atoms always combine in a simple whole number ratio.

2 × RMM = VD

The average atomic mass of Beryllium is 9.012 because of the presence of isotopes.

The noble gases are diatomic.

The number of atoms present in one mole of phosphorus(P4) is 4 × 6.023 × 1023

Answer:

False -Atoms may not combine always in a simple whole number ratio.

False – 2 × VD = RMM

True

False – The noble gases are mono atomic.

True

V. Assertion and Reason:

Answer the following questions using the data given below:

Question 1.

Assertion: The standard unit for expressing mass of atom is amu.

Reason: Atomic mass unit is one-twelth of the mass of a C-12 atom

(a) Assertion and Reason are correct, Reason explains the Assertion.

(b) Assertion is correct, Reason is wrong.

(c) Assertion is wrong, Reason is correct.

(d) Assertion and Reason are correct, Reason doesn’t explains Assertion.

Answer:

(a) Assertion and Reason are correct, Reason explains the Assertion.

Question 2.

Assertion: The volume occupied by 44 g of CO2 is 22.4 L

Reason: The volume occupied by one mole of any gas is 22.4 L

(a) Assertion and Reason are correct, Reason explains the Assertion.

(b) Assertion is correct, Reason is wrong.

(c) Assertion is wrong, Reason is correct.

(d) Assertion and Reason are correct, Reason doesn’t explains Assertion.

Answer:

(a) Assertion and Reason are correct, Reason explains the Assertion.

VI. Short answer questions:

Question 1.

Define vapour density.

Answer:

Vapour density is the ratio of the mass of certain volume of a gas or vapour, to the mass of an equal volume of hydrogen measured under the same condition of temperature and pressure.

[OR]

Question 2.

What are isobars? Give an example.

Answer:

Atoms of different elements that have same atomic masses but different atomic numbers are called isobars.

e.g.,

18

.

Question 3.

Write the differences between an atom and a molecule.

Answer:

Question 4.

What is artificial transmutation?

Answer:

Atoms of one element can be transmuted into atoms of other elements. In other words, the atom is no longer indestructible. It is known as artificial transmutation.

Question 5.

Classify the following based on atomicity.

Answer:

(i) Bromine

2 – Diatomic

(ii) Argon

1 – Monoatomic

(iii) Ozone

3 – Triatomic

(iv) Sulphur

8 – Polyatomic

Question 6.

Define atomic mass unit.

Answer:

Atomic mass unit is one-twelfth of the mass of carbon – 12 atom, as an isotope of carbon which contains 6 protons and 6 neutrons. It is amu.

VII. Long answer questions:

Question 1.

Explain how Avogadro hypothesis is used to derive the value of atomicity.

Answer:

(i) The Avogadro’s law states that “equal volumes of all gases under similar conditions of temperature and pressure contain the equal number of molecules”.

(ii) Let us consider the reaction between hydrogen and chlorine to form hydrogen chloride gas.

H2 (g) + Cl2 (g) → 2HCl (g)

⇒ 1 volume + 1 volume → 2 volumes.

(iii) According to Avogadro’s law, 1 volume of any gas is occupied by “n” number of molecules,

“n” molecules + “n” molecules → “2n” molecules

If “n” = 1, then

1 molecule + 1 molecule → 2 molecules.

12

molecule +

(v)

12

molecule of hydrogen contains 1 atom.

So, 1 molecule of hydrogen contains 2 atoms.

So, hydrogen atomicity is 2. Similarly, chlorine atomicity is also 2.

So, H2 and Cl2 are diatomic molecules.

Question 2.

Write a note on the following,

(i) Isotopeos

(ii) Isobars

(iii) Relative atomic mass.

Answer:

(i) Isotopes : Atoms of same element with different mass number. Eg: 17Cl35, 17Cl37.

(ii) Isobars : Atoms of different elements with same mass number. Eg: 18Ar40, 20Ca40

(iii) Relative Atomic Mass (RAM) :

Question 3.

Sodim bicarbonate breaks down on heating as follows:

2NaHCO3 → Na2CO3 + H2O + CO2

(Atomic mass of Na = 23, H = 1, C = 12, O = 16)

(i) How many moles of NaHCO3 are there in the equation?

Answer:

2 moles.

(ii) What is the mass of CO2 produced in the equation?

Answer:

44 g

(iii) How many moles of water molecules are produced in the equation?

Answer:

1 mole.

(iv) What is the mass of NaHCO3 used in this equation?

Answer:

= 2[23 + 1 + 12 + 3(16)]

= 2[84]

= 168 g

(v) What is the volume occupied by CO2 in this equation?

Answer:

22.4 lit.

VIII. Hot Questions

Question 1.

Why do we take an atomic mass of Carbon – 12 as standard?

Answer:

Carbon – 12 is the standard while measuring the atomic masses. Because no other nuclides other than C – 12 have exactly whole-number masses in this scale. This is due to the different mass of neutrons and protons acting to change the total mass in nuclides with proton/neutron ratio other than 1 : 1 ratio of carbon – 12.

Question 2.

The cost of common salt (NaCl) is Rs 18 per kg. Calculate the cost of the salt per mole.

Answer:

Gram molar mass of NaCl = 23 + 35.5

= 58.5 g

1000 g of NaCl costs = Rs 18

∴ 58.5 g of NaCl costs =

181000

× 58.5

= Rs 1.053

The cost of one mole of NaCl = Rs 1.053

Question 3.

What will be the mass of one

12C

atom in g?

Answer:

1 mol of

12C

atoms = 6.022 × 1023 atoms = 12 g

Thus, 6.022 × 1023 atoms of

12C

have mass = 12 g

∴ 1 atom of

12C

will have mass =

× 7 × 10-3

18.82 × 1022 NH3 molecule

Question 6.

What is the mass in grams of the following?

(a) 3 moles of NaOH

(b) 6.023 × 1022 atoms of Ca

(c) 224 L of CO2

Answer:

Formula:

(a) 3 moles of NaOH

Mass of 3 moles of NaOH = 3 × mol. mass of NaOH

GMM of NaOH = 23 + 16 + 1 = 40 g

Mass of 3 moles of NaOH = 3 × 40 = 120 g

(b) 6.023 × 1022 atoms of Ca = n × atomic mass of ca

= 4 g

(c) 224 L of CO2

Mass of 224 L of CO2

= 10 × 44

= 440 g

Question 7.

How many grams are therein:

(i) 5 moles of water

(ii) 2 moles of Ammonia

(iii) 2 moles of Glucose

Solution:

(i) 5 moles of water.

Mass of 1 mole of water (H2O) = 18 g (2 + 16)

Mass of 5 moles of H2O = 18 × 5 = 90 g.

(ii) 2 moles of ammonia.

Mass of 1 mole of ammonia (NH3) = 17 g (14 + 3)

Mass of 2 moles of ammonia = 17 × 2 = 34 g.

(iii) 2 moles of glucose.

Mass of 1 mole of glucose (C6H12O6) = 180 g (72 + 12 + 96)

Mass of 2 moles of glucose = 180 × 2 = 360 g.

Question 8.

Calculate tbe molar mass of the following compounds.

(a) Urea (NH2CONH2)

(b) Ethanol(C2H5OH);

(c) Boric acid (H3BO3)

[Atomic mass of N – 14, H – 1, C – 12, B – 11, O – 16]

Answer:

(a) Urea (NH2CONH2) = 2(14) + 4(1) + 1(16) + 1(12)

= 28 + 4 + 16 + 12

= 60 g

(b) Ethanol(C2H5OH) = 2(12) + 6(1) + 1(16)

= 24 + 6 + 16 = 46 g

(c) Boric acid (H2BO3) = 3(1) + 1(11) + 3(16)

= 3 + 11 + 48

= 62 g

Question 9.

Mass of one atom of an element is 6.645 × 10-23 g. How many moles of element are there in 0.320 kg.

Answer:

Mass of one atom of an element = 6.645 × 10-23 g

∴ Mass of 1 mol of atom = 6.645 × 10-23 × 6.023 × 1023 = 40 g

Number of moles =

I. Choose the best answer:

Question 1.

Which of the following has the smallest mass?

(a) 6.023 × 1023 atoms of He

(b) 1 atom of He

(c) 2 g of He

(d) 1-mole atoms of He

Answer:

(b) 1 atom of He

Question 2.

Which of the following is a triatomic molecule?

(a) Glucose

(b) Helium

(c) Carbon dioxide

(d) Hydrogen.

Answer:

(c) Carbon dioxide

Hint:

(a) Glucose = C6H12O6 (Polyatomic molecule)

(b) Helium = He (Monoatomic molecule)

(c) Carbon dioxide = CO2 (Triatomic molecule)

(d) Hydrogen = H2 (Diatomic molecule)

So, (c) is the correct answer.

Question 3.

The volume occupied by 4.4 g of CO2 at S.T.P:

(a) 22.4 litre

(b) 2.24 litre

(c) 0.24 litre

(d) 0.1 litre

Answer:

(b) 2.24 litre

Question 4.

Mass of 1 mole of Nitrogen atom is _____.

(a) 28 amu

(b) 14 amu

(c) 28 g

(d) 14 g.

Answer:

(b) 14 amu

Hint: Atomic mass of Nitrogen is 14.00674 grams. It is equal to 1 mole of Nitrogen atoms.

So, answer (b) is correct.

Question 5.

Which of the following represents 1 amu?

(a) Mass of a C – 12 atom

(b) Mass of a hydrogen atom

(c) 1/12 th of the mass of a C – 12 atom

(d) Mass of O – 16 atom

Answer:

(c) 1/12 th of the mass of a C – 12 atom

Question 6.

Which of the following statement is incorrect?

(a) One gram of C – 12 contains Avogadro’s number of atoms.

(b) One mole of oxygen gas contains Avogadro’s number of molecules.

(c) One mole of hydrogen gas contains Avogadro’s number of atoms.

(d) One mole of electrons stands for 6.023 × 1023 electrons.

Answer:

(a) One gram of C – 12 contains Avogadro’s number of atoms.

Hint: 12 g of Carbon contains 6.023 × 1023 atoms,

1 g of Carbon contain

6.023×12

= 5.018 × 1022 atoms and its is not Avogadro’s number of atoms.

So (a) is the incorrect statement.

Question 7.

The volume occupied by 1 mole of a diatomic gas at S.T.P is:

(a) 11.2 litre

(b) 5.6 litre

(c) 22.4 litre

(d) 44.8 litre

Answer:

(c) 22.4 litre

Question 8.

In the nucleus of 20Ca40, there are

(a) 20 protons and 40 neutrons

(b) 20 protons and 20 neutrons

(c) 20 protons and 40 electrons

(d) 40 protons and 20 electrons

Answer:

(b) 20 protons and 20 neutrons

Question 9.

The gram molecular mass of oxygen molecule is_____.

(a) 16 g

(b) 18 g

(c) 32 g

(d) 17 g.

Answer:

(c) 32 g

Hint: By definition, the gram molecular mass of oxygen molecule O2 is 32 g.

So the answer (c) is correct.

Question 10.

1 mole of any substance contains molecules.

(a) 6.023 × 1023

(b) 6.023 × 10-23

(c) 3.0115 × 1023

(d) 12.046 × 1023

Answer:

(a) 6.023 × 1023

II. Fill in the blanks:

1. Atoms of different elements having ……… mass number, but ………. atomic numbers are called isobars.

2. Atoms of different elements having same number of ………. are called isotones.

3. Atoms of one element can be transmuted into atoms of other element by ………….

4. The sum of the numbers of protons and neutrons of an atom is called its …………

5. Relative atomic mass is otherwise known as …………

6. The average atomic mass of hydrogen is ……….. amu.

7. If a molecule is made of similar kind of atoms, then it is called ……….. atomic molecule.

8. The number of atoms present in a molecule is called its ………….

9. One mole of any gas occupies ………… ml at S.T.P

10. Atomicity of phosphorous is …………

Answer:

1. same, different

2. neutrons

3. artificial transmutation

4. mass number

5. standard atomic weight

6. 1.008

7. homo

8. atomicity

9. 22, 400

10. four

III. Match the following:

Answer:

A. (ii)

B. (iii)

C. (v)

D. (i)

E. (iv)

IV. True or False: (If false give the correct statement)

Two elements sometimes can form more than one compound.

Nobel gases are diatomic.

The gram atomic mass of an element has no unit.

1 mole of Gold and Silver contain same number of atoms.

Molar mass of CO2 is 42 g.

Answer:

True

False – Noble gases are Monoatomic.

False – The unit of gram atomic mass of an element is gram.

True

False – Molar mass of CO2 is 44 g.

V. Assertion and Reason:

Answer the following questions using the data given below:

Question 1.

Assertion: Atomic mass of aluminium is 27

Reason: An atom of aluminium is 27 times heavier than 1/12 th of the mass of the C-12 atom.

(a) Assertion and Reason are correct, Reason explains the Assertion.

(b) Assertion is correct, Reason is wrong.

(c) Assertion is wrong, Reason is correct.

(d) Assertion and Reason are correct, Reason doesn’t explains Assertion.

Answer:

(a) Assertion and Reason are correct, Reason explains the Assertion.

Question 2.

Assertion: The Relative Molecular Mass of Chlorine is 35.5 a.m.u.

Reason: The natural abundance of Chlorine isotopes are not equal.

(a) Assertion and Reason are correct, Reason explains the Assertion.

(b) Assertion is correct, Reason is wrong.

(c) Assertion is wrong, Reason is correct.

(d) Assertion and Reason are correct, Reason doesn’t explains Assertion.

Answer:

(c) Assertion is wrong, Reason is correct.

VI. Short answer questions:

Question 1.

Define: Relative atomic mass.

Answer:

Relative atomic mass of an element is the ratio between the average mass of its isotopes to

1

part of the mass of a carbon-12 atom. It is denoted as Ar.

[OR]

Question 2.

Write the different types of isotopes of oxygen and its percentage abundance.

Answer:

Oxygen has three stable isotopes. They are

Question 3.

Define Atomicity.

Answer:

The number of atoms present in the molecule is called its ‘Atomicity’.

Question 4.

Give any two examples for heteroatomic molecules.

Answer:

HI, HCl, CO, HBr, HF.

Question 5.

What is Molar volume of a gas?

Answer:

One mole of any gas occupies 22.4 litres.

(or)

22400 ml at S.T.R This volume is called as molar volume.

Question 6.

Find the percentage of nitrogen in ammonia.

Answer:

Molar mass of NH3 = 1(14) + 3(1) = 17 g

VII. Long answer questions:

Question 1.

Calculate the number of water molecule present in one drop of water which weighs 0.18 g.

Answer:

The molecular mass of water (H2O) is 18.

18 g of water molecule = 1 mole.

0. 18 g of water =

118×0.18

= 0.01 mole.

1 mole of water (Avogadro’s number) contains 6.023 × 1023 water molecules.

0. 01 mole of water contain

6.023×

= 6.023 × 1021 molecules.

Question 2.

N2 + 3 H2 → 2 NH3

(The atomic mass of nitrogen is 14, and that of hydrogen is 1)

1 mole of nitrogen (……..g) +

3 moles of hydrogen (………g) →

2 moles of ammonia (………g)

Answer:

1 mole of nitrogen (28 g) +

3 moles of hydrogen (6 g) →

2 moles of ammonia (34 g)

Question 3.

Calculate the number of moles in

(i) 27 g of Al;

(ii) 1.51 × 1023 molecules of NH4Cl.

Answer:

(i) 27 g of Al

Given mass atomic mass =

GivenMassAtomicMass

=

= 1 mole

(ii) 1.51 x 1023 molecules of NH4Cl

Number of moles

Question 4.

Give the salient features of “Modern atomic theory”.

Answer:

The salient features of “Modem atomic theory” are,

An atom is no longer indivisible.

Atoms of the same element may have different atomic mass.

Atoms of different elements may have the same atomic masses.

Atoms of one element can be transmuted into atoms of other elements. In other words, an atom is no longer indestructible.

Atoms may not always combine in a simple whole-number ratio.

Atom is the smallest particle that takes part in a chemical reaction.

The mass of an atom can be converted into energy [E = mc2].

Question 5.

Derive the relationship between Relative molecular mass and Vapour density.

Answer:

Relative molecular mass : The relative molecular mass of a gas or vapour is the ratio between the mass of one molecule of the gas or vapour to mass of one atom of hydrogen.

Vapour density : Vapour density is the ratio of the mass of certain volume of a gas or vapour, to the mass of an equal volume of hydrogen, measured under the same conditions of temperature and pressure.

According to Avogadro’s law equal volumes of all gases contain equal number of molecules.

Let the number of molecules in one volume = n, then

When cancelling ‘n’ which is common at STP, we get

Since hydrogen is diatomic,

2 × Vapour density = Relative Molecular mass of a gas

[OR]

Relative Molecular Mass = 2 × Vapour density

VIII. HOT Question:

Question 1.

Calcium carbonate is decomposed on heating in the following reaction

CaCO3 → CaO + CO2

How many moles of Calcium carbonate is involved in this reaction?

Calculate the gram molecular mass of calcium carbonate involved in this reaction.

How many moles of CO2 are there in this equation?

Answer:

CaCO3 → CaO + CO2

1 mole of CaCO3 is involved in this reaction.

Gram molecular mass of calcium carbonate

CaCO3 = (40 + 12 + 3 × 16) = 52 + 48 = 100 g

1 mole of CO2 is in this equation.

IX. Solve the following problems:

Question 1.

How many grams are there in the following?

(i) 2 moles of a hydrogen molecule, H2

(ii) 3 moles of chlorine molecule, Cl2

(iii) 5 moles of sulphur molecule, S8

(iv) 4 moles of a phosphorous molecule, P4

Solution:

(i) 2 moles of a hydrogen molecule, H2

Mass of 1 mole of hydrogen molecule = 2 g

Mass of 2 moles of hydrogen molecule = 2 × 2 = 4 g.

(ii) 3 moles of chlorine molecule, Cl2

Mass of 1 mole of chlorine molecule = 71 g

Mass of 3 moles of chlorine molecules = 71 × 3 = 213 g.

(iii) 5 moles of sulphur molecule, S8

Mass of 1 mole of sulphur molecule = 32 g

Mass of 5 moles of sulphur molecules = 32 × 5 = 160 g.

(iv) 4 moles of the phosphorous molecule, P4

Mass of 1 mole of phosphorous molecule = 30.97 g

Mass of 4 moles of phosphorous molecules = 30.97 × 4 = 123.88 g.

Question 2.

Calculate the % of each element in calcium carbonate. (Atomic mass: C – 12, O – 16, Ca – 40)

Answer:

Formula to find % of each element

Question 3.

Calculate the % of oxygen in Al2(SO4)3.

(Atomic mass: Al – 27, O – 16, S – 32)

Answer:

Formula:

Molar mass of Al2(SO4)3 = [2(Atomic mass of Al) + 3(Atomic mass of S) + 12(Atomic mass of O)]

= 2(27) + 3(32) + 12(16) = 342 g

% of Oxygen =

12(16)342

× 100 = 56.14%.

Question 4.

Calculate the % relative abundance of B – 10 and B – 11, if its average atomic mass is 10.804 amu.

Answer:

% of relative abundance can be calculated by the formula.

Average atomic mass of the element

= Atomic mass of 1st isotope × abundance of 1st isotope + Atomic mass of 2nd isotope × abundance of 2nd isotope

∴ Average atomic mass of Boron

= Atomic mass of B – 0 × abundance of B -10 + Atomic mass of B – 11 × abundance of B – 11

Let the abundance of B – 10 be ‘x’ and B – 11 be (1 – x)

So, 10.804 = 10 × x + 11 (1 – x)

10.804 = 10x + 11 – 11x

x = 11 – 10.804

x = 0.196

1 -x = 1 – 0.196 = 0.804

Therefore % abundance of B – 10 is 19.6% and B – 11 is 80.4%

[OR]

Let the % of the isotope B – 10 = x

Then the % of the isotope B – 11 = 100 – x

Samacheer Kalvi 10th Science Guide Chapter 7 Atoms and Molecules 12

1100 – x = 1080.4

x = 19.6

% abundance of B – 10 = 19.6%

% abundance of B – 11 = 80.4%

Important Questions and Answers

I. Choose the correct answer.

Question 1.

The first scientific theory of an atom was proposed by:

(a) Ruther Ford

(b) Newland

(c) John Dalton

(d) Neils Bohr

Answer:

(c) John Dalton

Question 2.

Identify the pair that indicates isobars among the following _____.

(a)

1Ca40

Question 3.

Which one of the following represents 180 g of water?

(a) 5 moles of water

(b) 90 moles of water

(c) 6.023 × 1024 molecules of water

(d) 6.023 × 1022 molecules of water

Answer:

(c) 6.023 × 1024 molecules of water

Question 4.

The isotope of Carbon-12 contains _____.

(a) 6 protons and 7 electrons

(b) 6 protons and 6 neutrons

(c) 12 protons and no neutrons

(d) 12 neutrons and no protons.

Answer:

(b) 6 protons and 6 neutrons

Question 5.

Which contains the greatest number of moles of oxygen atoms?

(a) 1 mol of water

(b) 1 mole of NaOH

(c) 1 mole of Na2CO3

(d) 1 mole of CO

Answer:

(c) 1 mole of Na2CO3

Question 6.

The mass of proton or neutron is approximately _____.

(a) 1 amu

(b) 1.609 × 10-19 g

(c) 1 g

(d) 6.023 × 10-23 g.

Answer:

(a) 1 amu

Question 7.

The natural abundance of C-12 and C-13 are 98.90% and 1.10% respectively. The average atomic mass of carbon is:

(a) 12 amu

(b) 12.011 amu

(c) 14 amu

(d) 12.90 amu

Answer:

(b) 12.011 amu

Question 8.

The relative atomic mass of magnesium-based on C – 12 scale is _____.

(a) 24 g

(b) 24

(c) 24 amu

(d) 24 kg

Answer:

(b) 24

Question 9.

If 1.5 moles of oxygen combine with Al to form Al2O3, the mass of Al in g (atomic mass of Al = 27) used in the reaction is:

(a) 2.7

(b) 54

(c) 40.5

(d) 81

Answer:

(b) 54

Question 10.

The atomicity of methane is:

(a) 5

(b) 4

(c) 3

(d) 6

Answer:

(a) 5

Question 11.

Find the odd one out _____.

(a)

8

.

Answer:

(c)

O12

Question 12.

The volume occupied by 3 moles of HCl gas at STP is:

(a) 22.4 L

(b) 44.8 L

(c) 2.24 L

(d) 67.2 L

Answer:

(d) 67.2 L

Question 13.

The mass percentage of hydrogen in ethane (C2H6) is:

(a) 25%

(b) 75%

(c) 80%

(d) 20%

Answer:

(d) 20%

Question 14.

Which one of the following is a homo diatomic molecule?

(a) H2

(6) CO

(c) NO

(d) O3.

Answer:

(a) H2

Question 15.

The percentage of nitrogen in urea is about:

(a) 38.4

(b) 46.6

(c) 59.1

(d) 61.3

Answer:

(b) 46.6

Question 16.

Out of the following the largest number of atoms are contained in:

(a) 11 g of CO2

(b) 4 g of H2

(C) 5 g of NH3

(d) 8 g of SO2

Answer:

(b) 4 g of H2

Question 17.

Which of the following is an example of a homo triatomic molecule?

(a) Phosphorous

(b) Sulphur

(c) Bromine

(d) Ozone.

Answer:

(d) Ozone.

Question 18.

For the reaction A + 2B → C, 5 moles of A and 8 moles of B will produce:

(a) 5 moles of C

(b) 4 moles of C

(c) 8 moles of C

(d) 13 moles of C

Answer:

(b) 4 moles of C

Question 19.

The vapour density of a gas is 32. Its relative molecular mass will be:

(a) 32

(b) 16

(c) 64

(d) 96

Answer:

(c) 64

Question 20.

Find the odd one out _____.

(a) Silver

(b) Potassium

(c) Iron

(d) Phosphorous.

Answer:

(d) Phosphorous.

II. Fill in the blanks.

The volume occupied by 16 g of oxygen is ………..

One mole of a triatomic gas contains ………… atoms.

Equal volume of all gases under the same conditions of temperature and pressure contain equal number of …………

The mass of an atom can be converted into energy by using the formula …………

The percentage composition is useful to determine the ………… formula and ………… formula.

Answer:

11.2 L

3 × 6.023 × 1023

molecules

E = me²

empirical, molecular

III. Match the following:

Question 1.

Match the Column I with Column II.

Answer:

A. (ii)

B. (iii)

C. (i)

D. (v)

E. (iv)

Question 2.

Match the Column I with Column II.

Answer:

A. (iii)

B. (i)

C. (iv)

D. (v)

E. (ii)

Question 3.

Match the Column I with Column II.

Answer:

A. (iv)

B. (v)

C. (ii)

D. (iii)

E. (i)

Question 4.

Match the Column I with Column II.

Answer:

A. (v)

B. (iii)

C. (iv)

D. (i)

E. (ii)

IV. True or False: (If false give the correct statement)

Atoms always combine in a simple whole number ratio.

2 × RMM = VD

The average atomic mass of Beryllium is 9.012 because of the presence of isotopes.

The noble gases are diatomic.

The number of atoms present in one mole of phosphorus(P4) is 4 × 6.023 × 1023

Answer:

False -Atoms may not combine always in a simple whole number ratio.

False – 2 × VD = RMM

True

False – The noble gases are mono atomic.

True

V. Assertion and Reason:

Answer the following questions using the data given below:

Question 1.

Assertion: The standard unit for expressing mass of atom is amu.

Reason: Atomic mass unit is one-twelth of the mass of a C-12 atom

(a) Assertion and Reason are correct, Reason explains the Assertion.

(b) Assertion is correct, Reason is wrong.

(c) Assertion is wrong, Reason is correct.

(d) Assertion and Reason are correct, Reason doesn’t explains Assertion.

Answer:

(a) Assertion and Reason are correct, Reason explains the Assertion.

Question 2.

Assertion: The volume occupied by 44 g of CO2 is 22.4 L

Reason: The volume occupied by one mole of any gas is 22.4 L

(a) Assertion and Reason are correct, Reason explains the Assertion.

(b) Assertion is correct, Reason is wrong.

(c) Assertion is wrong, Reason is correct.

(d) Assertion and Reason are correct, Reason doesn’t explains Assertion.

Answer:

(a) Assertion and Reason are correct, Reason explains the Assertion.

VI. Short answer questions:

Question 1.

Define vapour density.

Answer:

Vapour density is the ratio of the mass of certain volume of a gas or vapour, to the mass of an equal volume of hydrogen measured under the same condition of temperature and pressure.

[OR]

Question 2.

What are isobars? Give an example.

Answer:

Atoms of different elements that have same atomic masses but different atomic numbers are called isobars.

e.g.,

18

.

Question 3.

Write the differences between an atom and a molecule.

Answer:

Question 4.

What is artificial transmutation?

Answer:

Atoms of one element can be transmuted into atoms of other elements. In other words, the atom is no longer indestructible. It is known as artificial transmutation.

Question 5.

Classify the following based on atomicity.

Answer:

(i) Bromine

2 – Diatomic

(ii) Argon

1 – Monoatomic

(iii) Ozone

3 – Triatomic

(iv) Sulphur

8 – Polyatomic

Question 6.

Define atomic mass unit.

Answer:

Atomic mass unit is one-twelfth of the mass of carbon – 12 atom, as an isotope of carbon which contains 6 protons and 6 neutrons. It is amu.

VII. Long answer questions:

Question 1.

Explain how Avogadro hypothesis is used to derive the value of atomicity.

Answer:

(i) The Avogadro’s law states that “equal volumes of all gases under similar conditions of temperature and pressure contain the equal number of molecules”.

(ii) Let us consider the reaction between hydrogen and chlorine to form hydrogen chloride gas.

H2 (g) + Cl2 (g) → 2HCl (g)

⇒ 1 volume + 1 volume → 2 volumes.

(iii) According to Avogadro’s law, 1 volume of any gas is occupied by “n” number of molecules,

“n” molecules + “n” molecules → “2n” molecules

If “n” = 1, then

1 molecule + 1 molecule → 2 molecules.

12

molecule +

(v)

12

molecule of hydrogen contains 1 atom.

So, 1 molecule of hydrogen contains 2 atoms.

So, hydrogen atomicity is 2. Similarly, chlorine atomicity is also 2.

So, H2 and Cl2 are diatomic molecules.

Question 2.

Write a note on the following,

(i) Isotopeos

(ii) Isobars

(iii) Relative atomic mass.

Answer:

(i) Isotopes : Atoms of same element with different mass number. Eg: 17Cl35, 17Cl37.

(ii) Isobars : Atoms of different elements with same mass number. Eg: 18Ar40, 20Ca40

(iii) Relative Atomic Mass (RAM) :

Question 3.

Sodim bicarbonate breaks down on heating as follows:

2NaHCO3 → Na2CO3 + H2O + CO2

(Atomic mass of Na = 23, H = 1, C = 12, O = 16)

(i) How many moles of NaHCO3 are there in the equation?

Answer:

2 moles.

(ii) What is the mass of CO2 produced in the equation?

Answer:

44 g

(iii) How many moles of water molecules are produced in the equation?

Answer:

1 mole.

(iv) What is the mass of NaHCO3 used in this equation?

Answer:

= 2[23 + 1 + 12 + 3(16)]

= 2[84]

= 168 g

(v) What is the volume occupied by CO2 in this equation?

Answer:

22.4 lit.

VIII. Hot Questions

Question 1.

Why do we take an atomic mass of Carbon – 12 as standard?

Answer:

Carbon – 12 is the standard while measuring the atomic masses. Because no other nuclides other than C – 12 have exactly whole-number masses in this scale. This is due to the different mass of neutrons and protons acting to change the total mass in nuclides with proton/neutron ratio other than 1 : 1 ratio of carbon – 12.

Question 2.

The cost of common salt (NaCl) is Rs 18 per kg. Calculate the cost of the salt per mole.

Answer:

Gram molar mass of NaCl = 23 + 35.5

= 58.5 g

1000 g of NaCl costs = Rs 18

∴ 58.5 g of NaCl costs =

181000

× 58.5

= Rs 1.053

The cost of one mole of NaCl = Rs 1.053

Question 3.

What will be the mass of one

12C

atom in g?

Answer:

1 mol of

12C

atoms = 6.022 × 1023 atoms = 12 g

Thus, 6.022 × 1023 atoms of

12C

have mass = 12 g

∴ 1 atom of

12C

will have mass =

× 7 × 10-3

18.82 × 1022 NH3 molecule

Question 6.

What is the mass in grams of the following?

(a) 3 moles of NaOH

(b) 6.023 × 1022 atoms of Ca

(c) 224 L of CO2

Answer:

Formula:

(a) 3 moles of NaOH

Mass of 3 moles of NaOH = 3 × mol. mass of NaOH

GMM of NaOH = 23 + 16 + 1 = 40 g

Mass of 3 moles of NaOH = 3 × 40 = 120 g

(b) 6.023 × 1022 atoms of Ca = n × atomic mass of ca

= 4 g

(c) 224 L of CO2

Mass of 224 L of CO2

= 10 × 44

= 440 g

Question 7.

How many grams are therein:

(i) 5 moles of water

(ii) 2 moles of Ammonia

(iii) 2 moles of Glucose

Solution:

(i) 5 moles of water.

Mass of 1 mole of water (H2O) = 18 g (2 + 16)

Mass of 5 moles of H2O = 18 × 5 = 90 g.

(ii) 2 moles of ammonia.

Mass of 1 mole of ammonia (NH3) = 17 g (14 + 3)

Mass of 2 moles of ammonia = 17 × 2 = 34 g.

(iii) 2 moles of glucose.

Mass of 1 mole of glucose (C6H12O6) = 180 g (72 + 12 + 96)

Mass of 2 moles of glucose = 180 × 2 = 360 g.

Question 8.

Calculate tbe molar mass of the following compounds.

(a) Urea (NH2CONH2)

(b) Ethanol(C2H5OH);

(c) Boric acid (H3BO3)

[Atomic mass of N – 14, H – 1, C – 12, B – 11, O – 16]

Answer:

(a) Urea (NH2CONH2) = 2(14) + 4(1) + 1(16) + 1(12)

= 28 + 4 + 16 + 12

= 60 g

(b) Ethanol(C2H5OH) = 2(12) + 6(1) + 1(16)

= 24 + 6 + 16 = 46 g

(c) Boric acid (H2BO3) = 3(1) + 1(11) + 3(16)

= 3 + 11 + 48

= 62 g

Question 9.

Mass of one atom of an element is 6.645 × 10-23 g. How many moles of element are there in 0.320 kg.

Answer:

Mass of one atom of an element = 6.645 × 10-23 g

∴ Mass of 1 mol of atom = 6.645 × 10-23 × 6.023 × 1023 = 40 g

Number of moles =

CBSE, Syllabus, for, Class 12, 2020 – 2021, (Reduced & Revised, Chemistry,

⇒ CBSE Class 12 Chemistry Syllabus (Reduced) 2020-21 (Released on 7th July) 

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