1
XII CHEMISTRY ACTUAL TEST UNIT 1-10 WITH
QUESTIONS AND ANSWERS
UNIT 1 : SOLUTIONS
1. Which are the different modes of expressing concentration of a solution?
(I) Mole fraction :- Mole fraction is the ratio of number of moles of one component to
the total number of moles of the solution. Mole fraction is temperature independent.
(II) Molarity :- Molarity is defined as the number of moles of solute in one litre of the
solution. Molarity is temperature dependent.
(III) Molality :- Molality is defined as the number of moles of solute in one kilogram of the
solvent. Molality is temperature independent.
2. State Henry’s law and give its applications.
At constant temperature , solubility of a gas in a liquid is directly proportional to the pressure of the gas.
𝒎 ∝𝑷
Applications: In Soda water , In scuba diving apparatus , Anoxia
3. State Raoult’s law
The partial vapour pressure of each component is directly proportional to its mole fraction in solution.
𝑷𝑨 ∝ 𝑿𝑨 , OR 𝑷𝑨 = 𝑷𝟎𝑨𝑿𝑨
𝑷𝑩 ∝ 𝑿𝑩 , OR 𝑷𝑩 = 𝑷𝟎𝑩𝑿𝑩
PA = Partial pressure of solvent in solution
, PB = Partial pressure of solute in
solution
𝑷𝑨𝟎 = Partial pressure of solvent in pure state ,
𝑷𝑩𝟎 = Partial pressure of solute in pure
state XA = Mole fraction of solvent ,
XB = Mole fraction of solute
,2
4. What are ideal solutions?
𝟎
Solutions which obey Raoult’s law. 𝑷𝑨 = 𝑷𝑨𝑿𝑨 , 𝑷𝑩 = 𝑷𝟎𝑩𝑿𝑩
∆V mixing = 0 , ∆H mixing = 0
A-B interaction = A-A interaction or B-B interaction
Examples : (i) n-hexane + n-heptane , (ii) Benzene + Toluene
5. What are non ideal solutions?
Solutions which do not obey Raoult’s law
∆V mixing ≠ 0 ∆H mixing≠ 0
A-B interaction ≠ A-A interaction or B-B
interaction Non ideal solutions are two types.
(i) Non ideal solutions having positive deviation
(ii) Non ideal solutions having negative deviation
6. Explain Non ideal solutions having positive deviation
𝑷𝑨 > 𝑷𝟎𝑿𝑨 , 𝑷𝑩 > 𝑷𝟎 𝑿𝑩
𝑨 𝑩
∆V mixing> 0 , ∆H mixing> 0
A-B interaction is lesser
Examples: Alcohol + Acetone , Acetone + Carbon
di sulphide
7. Ethanol-acetone mixture → Positive deviation from Raoult’s law.
8. Explain Non ideal solutions having negative deviation
𝑷𝑨 < 𝑷𝟎𝑿𝑨 , 𝑷𝑩 < 𝑷𝟎 𝑿𝑩
𝑨 𝑩
∆V mixing <0 , ∆H mixing< 0
A-B interaction is greater
Examples: Chloroform +
Acetone ,
Water + Nitric acid
,3
9. Chloroform and acetone mixture → Negative deviation from Raoult’s law.
, 4
10. What are azeotropes or azeotropic mixture? Explain
each. Liquid mixtures which boil at constant
temperature.
These are two types . (1) Maximum boiling azeotropes and ( 2) Minimum boiling azeotropes
Maximum boiling azeotropes Minimum boiling azeotropes
These are formed by non ideal solutions These are formed by non ideal solutions showing
showing negative deviation. positive deviation.
e.g. HNO3 (68 %) and water (32%) mixture e.g. Ethanol(95.6 %) and water (4.4%) mixture
11. What are colligative properties?
Properties of dilute solutions depend only on the number of solute particles irrespective of their nature.
12. Which are four colligative properties?
(a) Relative lowering of vapour pressure
(b) Elevation of boiling point
(c) Depression of freezing point
(d) Osmotic pressure
13. Relative lowering of vapour pressure:-
𝑷𝟎 − 𝑷𝑨
𝑨 = 𝑿𝑩
𝑷𝟎𝑨
𝑷𝟎 –𝑷𝑨
𝑨 = Relative lowering of vapour pressure . XB = Mole fraction of solute
𝑷𝟎𝑨
This shows that the relative lowering of vapour pressure of a solution containing a non-volatile
solute is equal to the mole fraction of the solute in the solution.
14. By using relative lowering of vapour pressure, derive the expression to calculate molecular mass of solute.
𝑷𝟎𝑨− 𝑷𝑨 𝑾𝑩 𝑴𝑨
=
𝑷𝟎
𝑨 𝑴𝑩 𝑾𝑨
𝑾𝑩𝑴𝑨𝑷𝟎𝑨
𝑩
𝑾𝑨(𝑷𝟎𝑨–𝑷𝑨)
15. With the help of graph explain elevation in boiling point.
When a non volatile solute is added to pure solvent, boiling point of the solution is increased. The
increase in boiling point is called elevation of boiling point.
∆Tb = Tb – Tb0
∆Tb = elevation in boiling
point, Tb = boiling point of
solution ,
Tb0 = boiling point of pure solvent.
XII CHEMISTRY ACTUAL TEST UNIT 1-10 WITH
QUESTIONS AND ANSWERS
UNIT 1 : SOLUTIONS
1. Which are the different modes of expressing concentration of a solution?
(I) Mole fraction :- Mole fraction is the ratio of number of moles of one component to
the total number of moles of the solution. Mole fraction is temperature independent.
(II) Molarity :- Molarity is defined as the number of moles of solute in one litre of the
solution. Molarity is temperature dependent.
(III) Molality :- Molality is defined as the number of moles of solute in one kilogram of the
solvent. Molality is temperature independent.
2. State Henry’s law and give its applications.
At constant temperature , solubility of a gas in a liquid is directly proportional to the pressure of the gas.
𝒎 ∝𝑷
Applications: In Soda water , In scuba diving apparatus , Anoxia
3. State Raoult’s law
The partial vapour pressure of each component is directly proportional to its mole fraction in solution.
𝑷𝑨 ∝ 𝑿𝑨 , OR 𝑷𝑨 = 𝑷𝟎𝑨𝑿𝑨
𝑷𝑩 ∝ 𝑿𝑩 , OR 𝑷𝑩 = 𝑷𝟎𝑩𝑿𝑩
PA = Partial pressure of solvent in solution
, PB = Partial pressure of solute in
solution
𝑷𝑨𝟎 = Partial pressure of solvent in pure state ,
𝑷𝑩𝟎 = Partial pressure of solute in pure
state XA = Mole fraction of solvent ,
XB = Mole fraction of solute
,2
4. What are ideal solutions?
𝟎
Solutions which obey Raoult’s law. 𝑷𝑨 = 𝑷𝑨𝑿𝑨 , 𝑷𝑩 = 𝑷𝟎𝑩𝑿𝑩
∆V mixing = 0 , ∆H mixing = 0
A-B interaction = A-A interaction or B-B interaction
Examples : (i) n-hexane + n-heptane , (ii) Benzene + Toluene
5. What are non ideal solutions?
Solutions which do not obey Raoult’s law
∆V mixing ≠ 0 ∆H mixing≠ 0
A-B interaction ≠ A-A interaction or B-B
interaction Non ideal solutions are two types.
(i) Non ideal solutions having positive deviation
(ii) Non ideal solutions having negative deviation
6. Explain Non ideal solutions having positive deviation
𝑷𝑨 > 𝑷𝟎𝑿𝑨 , 𝑷𝑩 > 𝑷𝟎 𝑿𝑩
𝑨 𝑩
∆V mixing> 0 , ∆H mixing> 0
A-B interaction is lesser
Examples: Alcohol + Acetone , Acetone + Carbon
di sulphide
7. Ethanol-acetone mixture → Positive deviation from Raoult’s law.
8. Explain Non ideal solutions having negative deviation
𝑷𝑨 < 𝑷𝟎𝑿𝑨 , 𝑷𝑩 < 𝑷𝟎 𝑿𝑩
𝑨 𝑩
∆V mixing <0 , ∆H mixing< 0
A-B interaction is greater
Examples: Chloroform +
Acetone ,
Water + Nitric acid
,3
9. Chloroform and acetone mixture → Negative deviation from Raoult’s law.
, 4
10. What are azeotropes or azeotropic mixture? Explain
each. Liquid mixtures which boil at constant
temperature.
These are two types . (1) Maximum boiling azeotropes and ( 2) Minimum boiling azeotropes
Maximum boiling azeotropes Minimum boiling azeotropes
These are formed by non ideal solutions These are formed by non ideal solutions showing
showing negative deviation. positive deviation.
e.g. HNO3 (68 %) and water (32%) mixture e.g. Ethanol(95.6 %) and water (4.4%) mixture
11. What are colligative properties?
Properties of dilute solutions depend only on the number of solute particles irrespective of their nature.
12. Which are four colligative properties?
(a) Relative lowering of vapour pressure
(b) Elevation of boiling point
(c) Depression of freezing point
(d) Osmotic pressure
13. Relative lowering of vapour pressure:-
𝑷𝟎 − 𝑷𝑨
𝑨 = 𝑿𝑩
𝑷𝟎𝑨
𝑷𝟎 –𝑷𝑨
𝑨 = Relative lowering of vapour pressure . XB = Mole fraction of solute
𝑷𝟎𝑨
This shows that the relative lowering of vapour pressure of a solution containing a non-volatile
solute is equal to the mole fraction of the solute in the solution.
14. By using relative lowering of vapour pressure, derive the expression to calculate molecular mass of solute.
𝑷𝟎𝑨− 𝑷𝑨 𝑾𝑩 𝑴𝑨
=
𝑷𝟎
𝑨 𝑴𝑩 𝑾𝑨
𝑾𝑩𝑴𝑨𝑷𝟎𝑨
𝑩
𝑾𝑨(𝑷𝟎𝑨–𝑷𝑨)
15. With the help of graph explain elevation in boiling point.
When a non volatile solute is added to pure solvent, boiling point of the solution is increased. The
increase in boiling point is called elevation of boiling point.
∆Tb = Tb – Tb0
∆Tb = elevation in boiling
point, Tb = boiling point of
solution ,
Tb0 = boiling point of pure solvent.
