Board papers questions chapter 1- solutions

1. Van’t Hoff factor values for KCl and K2SO4 respectively are :
2. Assertion (A) : Chloroform and acetone mixture shows
negative deviation from Raoult’s law.
Reason (R) : In chloroform and acetone mixture, A – A or B –
B type intermolecular interactions are weaker than A – B type
interactions.
3. State Henry’s law and write its two applications.
4. An antifreeze solution is prepared by dissolving 31 g of
ethylene glycol (Molar mass = 62 g mol–1) in 600 g of water.
Calculate the freezing point of the solution. (Kf for water =
1·86 K kg mol–1)
5. Calculate elevation of the boiling point of the solution when
4g of MgSO4 (molar mass = 120 g/mol) was dissolved in 100
g of water, assuming MgSO4 undergoes complete ionisation.
(Kb for water = 0.52 K kg mol–1)
6. CBQ:
The causefordeviationfromRaoult’
slawinthecolligativepropertiesofnon-ideal solutions lie in the
nature of interactions at the molecular level. These properties
show deviations from Raoult’s law due to difference in
interactions between solute – solvent, solute – solute and
solvent – solvent. Some liquids on mixing, form azeotropes
which are binary mixtures having the same composition in
liquid and vapour phase and boil at a constant temperature. In
such cases, it is not possible to separate the components by
fractional distillation. There are two types of azeotropes
 called minimum boiling azeotrope and maximum boiling
azeotrope.
Based on the above passage, answer the following
questions :
(a) Pure ethanol cannot be prepared by fractional distillation
of ethanol – water mixture. Comment.
(b) Why does a mixture of chloroform and acetone show
deviation from ideal behaviour ?
(c) (i) The vapour pressure of pure benzene at a certain
temperature is 1.25 atm. When 1.2 g of non-volatile,
non-electrolyte solute is added to 60 g of benzene (M = 78 g
mol–1), the vapour pressure of the solution becomes 1.237
atm. Calculate the molar mass of the non-volatile solute.
OR
The boiling point of benzene is 353.23 K. When 1.80 g of a
non-volatile solute was dissolved in 90 g of benzene, the
boiling point is raised to 354.11 K. Calculate the molar mass
of the solute. Kb for benzene is 2.53 K kg mol–1.
7. Calculate elevation of the boiling point of solution when 2 g of
MgSO4 (molar mass = 120 g/mol) was dissolved in 100 g of
water, assuming MgSO4 undergoes complete dissociation.
[Kb for water = 0.52 K kg mol–1]
8. (i)At the same temperature, CO2 gas is more soluble in water
than O2 gas. Which one of them will have higher value of KH
and why ? (ii) How does the size of blood cells change when
placed in an aqueous solution containing more than 0·9%
(mass/volume) sodium chloride ?
 (iii) 1 molal aqueous solution of an electrolyte A2B3 is 60%
ionized. Calculate the boiling point of the solution. (Given : Kb
for H2O = 0·52 K kg mol 1)
9. (i) The vapour pressures of A and B at 25ºC are 75 mm Hg
and 25 mm Hg, respectively. If A and B are mixed such that
the mole fraction of A in the mixture is 0·4, then calculate the
mole fraction of B in vapour phase.

(ii) Define colligative property. Which colligative property is

preferred for the molar mass determination of macromolecules ?

(iii) Why are equimolar solutions of sodium chloride and

glucose not isotonic ?

10. An azeotropic solution of two liquids has boiling point

lower than either of them when it :
(A) is saturated (B) shows positive deviation from Raoult’s
law

(C) shows negative deviation from Raoult’s law

(D) shows no deviation from Raoult’s law

11. The relative lowering of vapour pressure of an aqueous solution

containing non-volatile solute is 0·0225. The mole fraction of the
non-volatile solute is :

(A) 0·80 (B) 0·725 (C) 0·15 (D) 0·0225

12. A 6% solution of glucose (molar mass = 180 g mol 1 2 group

in ) is isotonic with 2 5% solution of an unknown organic
substance. Calculate the molecular weight of the unknown organic
substance.
13. The vapour pressure of a solvent at 283 K is 100 mm Hg.
Calculate the vapour pressure of a dilute solution containing 1
mole of a strong electrolyte AB in 50 moles of the solvent at 283 K
(assuming complete dissociation of solute AB).

14. A 4% solution of urea (molar mass = 60 g mol 1) is isotonic

with 52% solution of an unknown organic substance. Calculate the
molecular weight of the unknown organic substance.

15. On mixing 10 mL of acetone with 50 mL of chloroform, the total

volume of the solution will be :

(A) < 60 mL (B) > 60 mL (C) = 60 mL (D) = 100 mL

16. A 1% solution of ‘X’ is isotonic with 6% solution of sucrose (

molar mass is 342g/mol). The molar mass of solute ’X’ is

(A) 34·2 g mol -1 (B) 57 g mol -1 (C) 114 g mol -1 (D) 3·42 g mol -1

17. Assertion (A) : Addition of ethylene glycol to water lowers its

freezing point. Reason (R) : Ethylene glycol is insoluble in water due
to lack of its ability to form hydrogen bonds with water molecules.

18. (a) Define molal depression constant. How is it related to

enthalpy of fusion ?

OR

(b) What type of deviation is shown by ethanol and acetone

mixture ? Give reason. What type of azeotropic mixture is formed
by that deviation ?

19. A solution is prepared by dissolving 5 g of a non-volatile solute

in 200 g of water. It has a vapour pressure of 31·84 mm Hg at 300
K. Calculate the molar mass of the solute. (Vapour pressure of
pure water at 300 K = 32 mm Hg)

20. Assertion (A) : Hmix and Vmix are zero for non-ideal
solutions. Reason (R) : Solute-solvent interactions are not same as
pure solute-solute and pure solvent-solvent interactions in
non-ideal solutions.

21. Assertion (A) : ΔmixH and ΔmixV are zero for an ideal solution.

Reason (R) : the solution which obeys Raoult’s law over the entire
range of concentration is called an ideal solution

22. (i) define reverse osmosis (ii) why are aquatic species more
comfortable in cold water in comparison to warm water?

(iii) A solution containing 2 g of glucose (M = 180g/mol) on 100g

of water is prepared at 303K . if the vapour pressure of pure water
at 303K is 32.8mm mercury what would be the vapour pressure of
the solution?

23. predict whether Van’t Hoff factor will be less or greater than
one when ethanoic acid is dissolved in benzene

Define ideal solution

Calculate the mass of CaCl2( molar mass = 111g/mol) to be

dissolved in 500 g of water to lower its freezing point by 2K ,
assuming that CaCl2 undergoes complete dissociation (Kf for
water = 1.86K Kg / mol)

24. Isotonic solution have same

(a) density (b) refractive index (c) osmotic pressure (d)
volume

25. Van’t Hoff factor for Na2SO4. 10 H2O assuming complete

ionization is (a) 1 (b)3 (c) 13 (d) 2

26. Ishan’s automobile radiator is filled with 1.0Kg of water, how

many grams of ethylene glycol (molar mass = 62g/mol) must Ishan
add to get the freezing point of the solution lowered to -2.80C . Kf
for water is 1.86K Kg/mol

What type of deviation from Raoult’s law is shown by ethanol and

acetone mixture. Give reason.

27. boiling point of water at 750mm Hg pressure is 99.680 C. how

much sucrose to be added (molar mass 342g/mol) to 500g water
such that it boils at 1000 C? ( Kb of water is 0.52K Kg/mol)

(b) State Henry’s law and write one application of it.