21. Which of the following is the van’t Hoff factor for K₂SO₄ in aqueous solution?
a) 2
b) 3
c) 1
d) 4
Answer: b) 3
Explanation:
Potassium sulfate (K₂SO₄) dissociates in water into 2 potassium ions (K⁺) and 1 sulfate ion (SO₄²⁻), resulting in a total of 3 ions. Therefore, the van’t Hoff factor ii for K₂SO₄ is 3.
22. Which of the following statements about colligative properties is correct?
a) Colligative properties are dependent on the chemical identity of the solute.
b) Colligative properties are dependent on the number of solute particles in the solution.
c) Colligative properties apply only to electrolytes.
d) Colligative properties depend on the molar mass of the solute.
Answer: b) Colligative properties are dependent on the number of solute particles in the solution.
Explanation:
Colligative properties (e.g., boiling point elevation, freezing point depression) depend on the concentration and number of solute particles in the solution, not on their chemical identity.
23. A solution exhibits a boiling point higher than that of the pure solvent. This is due to:
a) Decreased vapor pressure of the solvent in the solution
b) Increased vapor pressure of the solvent in the solution
c) Increased volume of the solution
d) Increased molarity of the solvent
Answer: a) Decreased vapor pressure of the solvent in the solution
Explanation:
Boiling point elevation occurs because the vapor pressure of the solvent decreases when a non-volatile solute is added, requiring a higher temperature for the vapor pressure to equal atmospheric pressure.
24. Which of the following can be used to calculate the molar mass of an unknown solute?
a) Osmotic pressure
b) Freezing point depression
c) Boiling point elevation
d) All of the above
Answer: d) All of the above
Explanation:
Molar mass of an unknown solute can be determined using any of the colligative properties (osmotic pressure, freezing point depression, or boiling point elevation), as all these properties are related to the number of solute particles in the solution.
25. When a non-volatile solute is added to a solvent, which of the following properties decreases?
a) Boiling point
b) Freezing point
c) Osmotic pressure
d) Vapor pressure
Answer: d) Vapor pressure
Explanation:
The addition of a non-volatile solute lowers the vapor pressure of the solvent because fewer solvent molecules are available to escape into the vapor phase. As a result, the vapor pressure of the solution is lower than that of the pure solvent.
26. Which of the following represents the correct relationship between boiling point elevation and the molality of a solution?
a) ΔTb=Kf×m
b) ΔTb=Kb×m
c) ΔTb=Kb×M
d) ΔTb=Kf×M
Answer: b) ΔTb=Kb×m
Explanation:
Boiling point elevation is directly proportional to the molality of the solution (mm) and the ebullioscopic constant (Kb). The formula is ΔTb=Kb×m, where ΔTb is the boiling point elevation.
27. If the freezing point of a solution decreases by 5°C when a non-volatile solute is added, what would happen to the boiling point of the same solution?
a) It would decrease
b) It would increase
c) It would remain the same
d) It would depend on the nature of the solute
Answer: b) It would increase
Explanation:
The addition of a non-volatile solute causes a depression in the freezing point and an elevation in the boiling point. Both effects are colligative properties that depend on the number of solute particles in the solution.
28. Which of the following equations represents osmotic pressure (Π) for a dilute solution?
a) Π=iMRT
b) Π=nRT/V
c) Π=P1−P2
d) Π=iKf×m
Answer: a) Π=iMRT
Explanation:
Osmotic pressure (Π) is given by the equation Π=iMRT where i is the van’t Hoff factor, M is the molarity of the solution, R is the gas constant, and T is the absolute temperature.
29. Which of the following solutions will have the highest boiling point?
a) 1 M NaCl
b) 1 M glucose
c) 1 M BaCl₂
d) 1 M urea
Answer: c) 1 M BaCl₂
Explanation:
The boiling point elevation is higher for solutions with more solute particles. BaCl₂ dissociates into 3 ions (Ba²⁺ and 2 Cl⁻), leading to a higher number of particles in solution compared to NaCl (2 ions), glucose (no dissociation), and urea (no dissociation). Hence, 1 M BaCl₂ will have the highest boiling point.
30. Which of the following solutions will exhibit the highest freezing point depression?
a) 0.1 M KCl
b) 0.1 M glucose
c) 0.1 M CaCl₂
d) 0.1 M urea
Answer: c) 0.1 M CaCl₂
Explanation:
Freezing point depression is greater for solutions with more solute particles. CaCl₂ dissociates into 3 ions (Ca²⁺ and 2 Cl⁻), which means it produces more particles than KCl (2 ions), glucose, or urea (no dissociation). Thus, 0.1 M CaCl₂ will show the highest freezing point depression.
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