91. Which of the following mixtures is most likely to show a negative deviation from Raoult’s law?
a) Water and ethanol
b) Acetone and benzene
c) Chloroform and acetone
d) Carbon disulfide and acetone
Answer: c) Chloroform and acetone
Explanation:
Chloroform and acetone form strong hydrogen bonds between their molecules, which are stronger than the interactions in the pure components. This leads to a negative deviation from Raoult’s law, where the vapor pressure is lower than expected.
92. For which of the following compounds will the van’t Hoff factor (ii) be greater than 1?
a) Glucose
b) Sucrose
c) NaCl
d) Urea
Answer: c) NaCl
Explanation:
NaCl is an electrolyte and dissociates into Na⁺ and Cl⁻ ions in solution, which results in a van’t Hoff factor greater than 1. Glucose, sucrose, and urea are non-electrolytes and do not dissociate in solution, so their i is 1.
93. The elevation in boiling point of a solution is directly proportional to:
a) The vapor pressure of the solution
b) The molality of the solution
c) The molecular weight of the solute
d) The volume of the solvent
Answer: b) The molality of the solution
Explanation:
The elevation in boiling point (ΔTb) is directly proportional to the molality (m) of the solution according to the equation ΔTb=i×Kb×m, where Kb is the ebullioscopic constant and i is the van’t Hoff factor.
94. Which of the following solutions will have the lowest freezing point?
a) 0.1 M NaCl
b) 0.1 M urea
c) 0.1 M K₂SO₄
d) 0.1 M glucose
Answer: c) 0.1 M K₂SO₄
Explanation:
K₂SO₄ dissociates into 3 ions (2 K⁺ and 1 SO₄²⁻), producing more particles in solution than NaCl (2 ions) and urea and glucose (which do not dissociate). The larger the number of particles, the greater the freezing point depression.
95. Which of the following colligative properties is most useful for determining the molar mass of polymers?
a) Boiling point elevation
b) Freezing point depression
c) Osmotic pressure
d) Vapor pressure lowering
Answer: c) Osmotic pressure
Explanation:
Osmotic pressure is the most sensitive colligative property for determining the molar mass of large molecules like polymers. Small concentrations of these molecules can cause significant osmotic pressure changes.
96. Which of the following compounds would have the highest van’t Hoff factor (ii) in an aqueous solution?
a) NaCl
b) CaCl₂
c) Glucose
d) KNO₃
Answer: b) CaCl₂
Explanation:
CaCl₂ dissociates into 3 ions (1 Ca²⁺ and 2 Cl⁻), whereas NaCl and KNO₃ dissociate into 2 ions each. Glucose does not dissociate. Therefore, CaCl₂ has the highest van’t Hoff factor.
97. Raoult’s law is not obeyed by solutions that exhibit:
a) Ideal behavior
b) Negative deviations
c) Positive deviations
d) Both b and c
Answer: d) Both b and c
Explanation:
Raoult’s law is valid for ideal solutions. Non-ideal solutions that exhibit positive or negative deviations from Raoult’s law do not obey it due to the differing strength of solute-solvent interactions compared to the pure components.
98. Which of the following colligative properties does not depend on temperature?
a) Boiling point elevation
b) Osmotic pressure
c) Freezing point depression
d) Relative lowering of vapor pressure
Answer: d) Relative lowering of vapor pressure
Explanation:
Relative lowering of vapor pressure depends only on the mole fraction of the solute and is independent of temperature. Boiling point elevation, freezing point depression, and osmotic pressure are temperature-dependent.
99. What happens to the boiling point of a solvent when a non-volatile solute is added?
a) It increases
b) It decreases
c) It remains the same
d) It becomes equal to the freezing point
Answer: a) It increases
Explanation:
The addition of a non-volatile solute to a solvent increases the boiling point of the solution, a phenomenon known as boiling point elevation. This occurs because the presence of solute particles lowers the vapor pressure of the solution.
100. Which of the following explains the colligative property of freezing point depression?
a) Lowering of vapor pressure
b) Increase in solute-solvent interactions
c) Increase in boiling point
d) None of the above
Answer: a) Lowering of vapor pressure
Explanation:
Freezing point depression occurs because the addition of a solute lowers the vapor pressure of the solution, making it harder for the solvent to freeze. The temperature must be lowered further to reach the freezing point.
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