71. Which of the following solutions will have the highest boiling point?
a) 0.1 M NaCl
b) 0.1 M glucose
c) 0.1 M urea
d) 0.1 M BaCl₂
Answer: d) 0.1 M BaCl₂
Explanation:
The boiling point elevation depends on the number of particles in the solution. BaCl₂ dissociates into 3 ions (Ba²⁺ and 2 Cl⁻), producing more particles than NaCl (2 ions), glucose, and urea (no dissociation), resulting in a higher boiling point for BaCl₂.
72. Which of the following factors does not affect the freezing point depression?
a) The number of solute particles
b) The identity of the solute particles
c) The molality of the solution
d) The van’t Hoff factor
Answer: b) The identity of the solute particles
Explanation:
Freezing point depression is a colligative property, meaning it depends on the number of solute particles, not their identity. Factors like molality and the van’t Hoff factor, which reflect the number of particles in the solution, do affect freezing point depression.
73. Which of the following mixtures forms an ideal solution?
a) Benzene and toluene
b) Acetone and water
c) Ethanol and water
d) Hexane and ethanol
Answer: a) Benzene and toluene
Explanation:
Ideal solutions follow Raoult’s law and have similar intermolecular forces between solute and solvent. Benzene and toluene have similar structures and interact similarly, making them form an ideal solution.
74. What is the freezing point of a 2 molal solution of NaCl in water? (Assume complete dissociation, i=2, and Kf=1.86°C⋅kg/mol)
a) -1.86°C
b) -3.72°C
c) -7.44°C
d) -5.58°C
Answer: d) -7.44°C
74. What is the freezing point of a 2 molal solution of NaCl in water?
a) -1.86°C
b) -3.72°C
c) -7.44°C
d) -5.58°C
Answer: c) -7.44°C
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75. Which of the following colligative properties is used in the determination of molar mass of macromolecules such as proteins?
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, such as proteins. Small concentrations of macromolecules can cause significant changes in osmotic pressure.
76. Which of the following will exhibit the largest freezing point depression for a 1 molal aqueous solution?
a) NaCl
b) K₂SO₄
c) Glucose
d) MgCl₂
Answer: b) K₂SO₄
Explanation:
K₂SO₄ dissociates into 3 ions (2 K⁺ and 1 SO₄²⁻), whereas NaCl dissociates into 2 ions and glucose does not dissociate at all. The freezing point depression depends on the number of particles in the solution, so K₂SO₄ will exhibit the largest depression.
77. Which of the following solutions will have the highest vapor pressure at a given temperature?
a) 0.5 M NaCl
b) 0.5 M urea
c) 0.5 M KNO₃
d) 0.5 M MgCl₂
Answer: b) 0.5 M urea
Explanation:
Urea is a non-electrolyte and does not dissociate, so it contributes fewer solute particles to the solution compared to the electrolytes (NaCl, KNO₃, and MgCl₂), which dissociate into ions. As a result, the solution of urea will have the highest vapor pressure.
78. Which of the following statements about Raoult’s law is correct?
a) It applies only to non-volatile solutes
b) It applies to all types of solutions
c) It is applicable to ideal solutions
d) It is applicable only at high pressures
Answer: c) It is applicable to ideal solutions
Explanation:
Raoult’s law is valid for ideal solutions, where the intermolecular forces between solute and solvent are similar to those in the pure substances. It is not applicable to non-ideal solutions or at high pressures where deviations may occur.
79. For a solution of a non-volatile solute in water, the vapor pressure:
a) Remains the same as pure water
b) Is higher than pure water
c) Is lower than pure water
d) Is independent of the concentration of the solute
Answer: c) Is lower than pure water
Explanation:
When a non-volatile solute is dissolved in a solvent, the vapor pressure of the solution decreases compared to the pure solvent. This occurs because fewer solvent molecules can escape into the vapor phase due to the presence of solute particles.
80. What is the expected van’t Hoff factor (ii) for BaCl₂ in an aqueous solution?
a) 2
b) 3
c) 4
d) 1
Answer: b) 3
Explanation:
BaCl₂ dissociates into 3 ions in solution: one Ba²⁺ ion and two Cl⁻ ions. Therefore, the van’t Hoff factor (i) for BaCl₂ is 3.
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