31. The freezing point of an aqueous solution is lower than that of pure water because:
A. The solute lowers the vapor pressure of the solvent
B. The solute raises the vapor pressure of the solvent
C. The solute raises the freezing point
D. The solute decreases the osmotic pressure
Answer: A. The solute lowers the vapor pressure of the solvent
Explanation:
The addition of a solute lowers the vapor pressure of the solvent, which results in a lower freezing point. This is known as freezing point depression.
32. A solution of NaCl in water freezes at a lower temperature than pure water because:
A. The vapor pressure of the solution is higher than that of pure water
B. NaCl is non-volatile
C. NaCl undergoes ionization in water
D. The boiling point of the solution is higher than that of pure water
Answer: C. NaCl undergoes ionization in water
Explanation:
NaCl dissociates into Na⁺ and Cl⁻ ions in water, increasing the number of solute particles, which causes a greater depression in the freezing point, leading to the solution freezing at a lower temperature than pure water.
33. Which of the following solutions will exhibit the highest osmotic pressure?
A. 0.1 M glucose
B. 0.1 M NaCl
C. 0.1 M BaCl₂
D. 0.1 M urea
Answer: C. 0.1 M BaCl₂
Explanation:
BaCl₂ dissociates into three ions (Ba²⁺ and 2 Cl⁻), producing more particles in solution. Since osmotic pressure is directly proportional to the number of solute particles, BaCl₂ will have the highest osmotic pressure.
34. Colligative properties of solutions are affected by:
A. Size of solute molecules
B. Shape of solute molecules
C. Number of solute particles
D. Color of the solute
Answer: C. Number of solute particles
Explanation:
Colligative properties depend only on the number of solute particles in the solution, regardless of their size, shape, or other physical characteristics.
35. In an ideal solution, the enthalpy of mixing is:
A. Positive
B. Negative
C. Zero
D. Infinite
Answer: C. Zero
Explanation:
For an ideal solution, the enthalpy of mixing is zero, meaning no heat is absorbed or released when the solute and solvent are mixed. The solution forms without any change in energy.
36. Which of the following factors does not affect the colligative properties of a solution?
A. Nature of solute
B. Number of solute particles
C. Molality of the solution
D. Van’t Hoff factor
Answer: A. Nature of solute
Explanation:
Colligative properties are not dependent on the nature of the solute but only on the number of solute particles, their concentration (molality), and the van’t Hoff factor.
37. The boiling point of a liquid increases when a solute is added because:
A. The solute increases the vapor pressure of the liquid
B. The solute decreases the vapor pressure of the liquid
C. The solute increases the density of the liquid
D. The solute decreases the density of the liquid
Answer: B. The solute decreases the vapor pressure of the liquid
Explanation:
When a solute is added, the vapor pressure of the solvent decreases. Consequently, a higher temperature is required to make the vapor pressure equal to the external pressure, thus increasing the boiling point.
38. The depression in freezing point is a colligative property because it:
A. Depends on the chemical nature of the solute
B. Depends on the number of solute particles
C. Depends on the freezing point of the solvent
D. Depends on the vapor pressure of the solute
Answer: B. Depends on the number of solute particles
Explanation:
Freezing point depression is a colligative property that depends solely on the number of solute particles present in the solution, not their chemical nature.
39. Which of the following statements is correct about vapor pressure lowering?
A. It increases with an increase in the mole fraction of the solute
B. It decreases with an increase in the mole fraction of the solute
C. It is independent of the number of solute particles
D. It depends on the molecular weight of the solute
Answer: A. It increases with an increase in the mole fraction of the solute
Explanation:
The relative lowering of vapor pressure increases with the mole fraction of the solute. More solute particles reduce the number of solvent molecules at the surface, decreasing the vapor pressure.
40. In a solution of a non-volatile solute in a volatile solvent, the vapor pressure of the solvent:
A. Increases
B. Decreases
C. Remains constant
D. Becomes zero
Answer: B. Decreases
Explanation:
In a solution, the vapor pressure of the solvent is lowered by the presence of a non-volatile solute. This occurs because the solute particles occupy some of the surface area, reducing the number of solvent molecules that can evaporate.
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