Colligative Properties of Dilute Solutions (a Relative Lowering of Vapour Pressure, Depression of Freezing Point...) NEET Questions

Physical Chemistry - Solutions

Colligative Properties of Dilute Solutions (a Relative Lowering of Vapour Pressure, Depression of Freezing Point...) MCQ Questions


7.
For a dilute solution, the formula relating relative lowering of vapour pressure to molar masses is:
A.
(p₁° − p₁)/p₁° = (w₂ × M₁)/(M₂ × w₁)
B.
(p₁° − p₁)/p₁° = (w₁ × M₂)/(M₁ × w₂)
C.
(p₁° − p₁)/p₁° = (w₁ × M₁)/(M₂ × w₂)
D.
(p₁° − p₁)/p₁° = (w₂ × M₂)/(M₁ × w₁)
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ANSWER :
A. (p₁° − p₁)/p₁° = (w₂ × M₁)/(M₂ × w₁)
8.
Vapour pressure of pure benzene is 0.850 bar. When 0.5 g of a non-volatile solid is added to 39.0 g of benzene (M = 78 g/mol), the vapour pressure becomes 0.845 bar. The molar mass of the solute is approximately:
A.
78 g mol⁻¹
B.
340 g mol⁻¹
C.
85 g mol⁻¹
D.
170 g mol⁻¹
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ANSWER :
D. 170 g mol⁻¹
9.
The relative lowering of vapour pressure depends on:
A.
The size of the solute molecules
B.
The volume of solution
C.
The mole fraction of solute only
D.
The chemical nature of the solute
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ANSWER :
C. The mole fraction of solute only
10.
If 18 g of a non-volatile solute is dissolved in 90 g of water, and the vapour pressure of pure water is 25 mm Hg, the lowering of vapour pressure (assume solute molar mass = 60 g/mol) is approximately:
A.
5.0 mm Hg
B.
1.5 mm Hg
C.
0.5 mm Hg
D.
2.5 mm Hg
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ANSWER :
B. 1.5 mm Hg
11.
The elevation of boiling point of a dilute solution is given by:
A.
ΔTb = Kb / m
B.
ΔTb = Kb × m
C.
ΔTb = Kb × M
D.
ΔTb = Kf × m
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ANSWER :
B. ΔTb = Kb × m
12.
The unit of molal boiling point elevation constant (Kb) is:
A.
K mol kg⁻¹
B.
K mol L⁻¹
C.
K kg mol⁻¹
D.
K kg L⁻¹
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ANSWER :
C. K kg mol⁻¹