61. The vapor pressure of a solvent in a solution is proportional to:
A. The molality of the solution
B. The mole fraction of the solute
C. The mole fraction of the solvent
D. The concentration of the solution
Answer: C. The mole fraction of the solvent
Explanation:
According to Raoult’s law, the vapor pressure of the solvent in a solution is proportional to the mole fraction of the solvent in the solution.
62. The colligative property most useful in determining the molecular weight of macromolecules is:
A. Boiling point elevation
B. Freezing point depression
C. Osmotic pressure
D. Vapor pressure lowering
Answer: C. Osmotic pressure
Explanation:
Osmotic pressure is highly sensitive to changes in the concentration of solute particles, making it the most useful colligative property for determining the molecular weight of large macromolecules such as polymers.
63. Which of the following does not follow Raoult’s law?
A. Ideal solutions
B. Non-ideal solutions
C. Dilute solutions
D. Electrolyte solutions
Answer: B. Non-ideal solutions
Explanation:
Non-ideal solutions show deviations (positive or negative) from Raoult’s law due to differences in interactions between solute-solvent, solute-solute, and solvent-solvent molecules.
64. Which solution will show the greatest elevation in boiling point?
A. 0.1 M glucose
B. 0.1 M NaCl
C. 0.1 M AlCl₃
D. 0.1 M urea
Answer: C. 0.1 M AlCl₃
Explanation:
AlCl₃ dissociates into four ions (Al³⁺ and 3 Cl⁻), producing the most solute particles in the solution. Since boiling point elevation depends on the number of solute particles, AlCl₃ will show the greatest elevation.
65. The decrease in vapor pressure of a solvent in a solution is due to:
A. Increase in solvent molecules
B. The presence of solute particles
C. Increase in temperature
D. Increase in solvent volume
Answer: B. The presence of solute particles
Explanation:
The addition of solute particles reduces the number of solvent molecules at the surface, lowering the vapor pressure of the solvent.
66. Which of the following colligative properties is used to calculate the molar mass of a solute by measuring the decrease in the freezing point of a solvent?
A. Boiling point elevation
B. Freezing point depression
C. Vapor pressure lowering
D. Osmotic pressure
Answer: B. Freezing point depression
Explanation:
Freezing point depression is used to determine the molar mass of a solute. The extent of freezing point lowering depends on the number of solute particles in the solution.
67. The molal elevation constant (K_b) depends on:
A. The nature of the solute
B. The nature of the solvent
C. The concentration of the solution
D. The volume of the solvent
Answer: B. The nature of the solvent
Explanation:
The molal elevation constant (K_b) is a property of the solvent and represents the boiling point elevation per molal concentration of solute.
68. In a dilute solution, which of the following is true for colligative properties?
A. They depend on the nature of solute particles
B. They depend on the number of solute particles
C. They depend on the color of the solute
D. They depend on the molecular weight of the solute
Answer: B. They depend on the number of solute particles
Explanation:
Colligative properties depend only on the number of solute particles in the solution, irrespective of their chemical or physical properties.
69. The van’t Hoff factor for an electrolyte that dissociates completely in solution is:
A. Less than 1
B. Equal to 1
C. Greater than 1
D. Equal to zero
Answer: C. Greater than 1
Explanation:
For electrolytes that dissociate into ions, the van’t Hoff factor (i) is greater than 1 because the number of solute particles increases as the solute dissociates.
70. Which of the following is true for an ideal solution?
A. The enthalpy of mixing is positive
B. The enthalpy of mixing is negative
C. The enthalpy of mixing is zero
D. The volume of mixing increases
Answer: C. The enthalpy of mixing is zero
Explanation:
For an ideal solution, the enthalpy of mixing is zero, meaning there is no heat change when the solute and solvent are mixed.
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