Unit-2–Solutions
Section A
I. Multiple Choice Questions
1.
Osmotic pressure of a solution is 0.0821 atm at a temperature of 300 K. The concentration in
moles/litre will be
(a) 0.33
(b) 0.666
(c) 0.3 × 10-2
(d) 3
2.
The boiling point of an azeotropic mixture of water and ethanol is less than that of water and ethanol.
The mixture shows
(a) no deviation from Raoult’s Law.
(b) positive deviation from Raoult’s Law.
(c) negative deviation from Raoult’s Law.
(d) that the solution is unsaturated.
3.
In comparison to a solution of 0.01 M glucose, the depression in freezing point of a 0.01 M MgCl2
solution is
(a) the same
(b) about twice
(c) about three times
(d) about six times
4.
An azeotropic mixture of two liquids boils at a temperature lower than either of them when
a) it is saturated
b) it does not deviate from Raoults law
c) it shows positive deviation from Raoult’s law d) it shows negative deviation from Raoults law
5.
A system that forms minimum boiling azeotrope is
(a) ethyl alcohol-water
(c) acetone-chloroform
(b) benzene-toluene
(d) carbon disulfide-acetone
II. Read the passage given and answer the questions given:
Scuba divers must cope with high concentrations of dissolved gases while breathing air at high pressure
underwater. Increased pressure increases the solubility of atmospheric gases in blood. When the divers come
towards surface, the pressure gradually decreases. This releases the dissolved gases and leads to the formation
of bubbles of nitrogen in the blood. This blocks capillaries and creates a medical condition known as bends,
which are painful and dangerous to life. To avoid bends, as well as the toxic effects of high concentrations of
nitrogen in the blood, the tanks used by scuba divers are filled with air diluted with helium, nitrogen, and
oxygen.
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(v)
III. Assertion-reason questions:
In the following questions, a statement of assertion followed by a statement of reason is given.
Choose the correct answer out of the following choices.
(a) Assertion and reason both are correct statements and reason is the correct explanation for assertion.
(b) Assertion and reason both are correct statements and reason is not the correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement
(d) Assertion is wrong statement but reason is correct statement
6.
Assertion: Molality of a solution in liquid state changes with temperature.
Reason: The volume of a solution changes with change in temperature.
7.
Assertion: 0.1 M HCl solution has higher osmotic pressure than 0.1 M NaCl solution.
Reason: Cl- ions being common, the small size H+ ions have greater ionic mobility than large
size Na+ ions.
8.
Assertion: Lowering of vapour pressure is directly proportional to osmotic pressure of the solution.
Reason: Osmotic pressure is a colligative property.
9. Assertion: Non ideal solutions always form azeotropes.
Reason: Boiling point of azeotrope may be higher or lower than boiling points of both components.
10. Assertion: Out of various colligative properties, osmotic pressure is used for determination of
molecular masses of polymers.
Reason: Polymer solutions do not possess a constant boiling point or freezing point.
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Section B
IV. Answer the following:
11. Raoult’s law is a special case of Henry’s law. Explain.
12. Differentiate between ideal solution and non-ideal solution.
13. Define Cryoscopic constant.
14. Define the terms ‘osmosis’ and ‘osmotic pressure’. What is the advantage of using osmotic pressure as
compared to other colligative properties for the determination of molar masses of solutes in solutions?
15. Two liquids A and B form ideal solutions. At 300 K, the vapour pressure of solution containing 1 mole
of A and 3 mole of B is 550mm Hg. At the same temperature, if one more mole of B is added to this
solution, the vapour pressure of the solution increases by 10 mm Hg. Determine the vapour pressure of
A and B in their pure states.
16. Henrys law constant for a solution of methane in benzene at 298K is 4.27 x 105 mm Hg.
Calculate the solubility of methane in benzene at 298 K under 760 mm Hg.
17. What mass of ethylene glycol (molar mass = 62.0 g mol-1) must be added to 5.50 kg of water to lower
the freezing point of water from 0 to – 10.0°0 (kf for water = 1.86 K kg mol-1).
18. Calculate the boiling point of a solution when 2 g of Na2SO4 (M = 142 g/mol) was dissolved in 50 g
of water, assuming Na2SO4 undergoes complete dissociation.
19. 2 g of benzoic acid dissolved in 25 g of benzene shows a depression in freezing point equal to
1.62 K. Molal depression constant for benzene is 4.9 K kg /mol. What is the percentage
association of the acid if it forms dimer in solution?
20. Calculate the freezing point of solution when 1.9 g of MgCl2 (M = 95 g mol-1) was dissolved in 50 g
of
water, assuming MgCl2 undergoes complete ionization. (Kf for water = 1.86 K kg mol-1)
21. A 10% solution (by mass) of sucrose in water has a freezing point of 269.15 K. Calculate the freezing
point of 10% glucose in water if the freezing point of pure water is 273.15 K.
Given: (Molar mass of sucrose = 342 g mol-1, Molar mass of glucose = 180 g mol-1)
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