61. Which of the following mixtures shows positive deviation from Raoult’s law?
a) Acetone and chloroform
b) Ethanol and water
c) Carbon disulfide and acetone
d) Benzene and toluene
Answer: c) Carbon disulfide and acetone
Explanation:
Positive deviation from Raoult’s law occurs when the interactions between the solute and solvent molecules are weaker than those in the pure components, resulting in higher vapor pressure than expected. Carbon disulfide and acetone show this behavior.
63. What is the van’t Hoff factor (ii) for Na₂SO₄ in aqueous solution?
a) 2
b) 3
c) 1
d) 4
Answer: b) 3
Explanation:
Sodium sulfate (Na₂SO₄) dissociates into 2 Na⁺ ions and 1 SO₄²⁻ ion in aqueous solution, giving a total of 3 ions. Therefore, the van’t Hoff factor (ii) for Na₂SO₄ is 3.
64. The colligative property of freezing point depression is most pronounced for which of the following?
a) 1 M glucose
b) 1 M NaCl
c) 1 M BaCl₂
d) 1 M K₃PO₄
Answer: d) 1 M K₃PO₄
Explanation:
The freezing point depression is more significant when there are more particles in solution. K₃PO₄ dissociates into 4 ions (3 K⁺ and 1 PO₄³⁻), making its effect on freezing point depression greater than the other solutes.
65. Which of the following statements is true for a solution of a non-volatile solute in a volatile solvent?
a) The vapor pressure of the solution is equal to that of the solvent
b) The freezing point of the solution is higher than that of the pure solvent
c) The boiling point of the solution is lower than that of the pure solvent
d) The vapor pressure of the solution is lower than that of the pure solvent
Answer: d) The vapor pressure of the solution is lower than that of the pure solvent
Explanation:
Adding a non-volatile solute to a volatile solvent lowers the vapor pressure of the solution. The solute particles reduce the number of solvent molecules escaping into the vapor phase, resulting in a lower vapor pressure.
66. What will be the boiling point elevation of a solution of 1 molal NaCl in water? (Assume complete dissociation, i=2, Kb=0.52°C⋅kg/mol)
a) 0.52°C
b) 1.04°C
c) 0.26°C
d) 2.08°C
Answer: b) 1.04°C
Explanation:
The boiling point elevation is calculated using ΔTb=i×Kb×m
67. Which of the following represents the relationship between vapor pressure lowering and mole fraction of solute?
a) ΔP=PA0×xB
b) ΔP=PA0×xA
c) ΔP=PB0×xA
d) ΔP=PB0×xB
Answer: a) ΔP=PA0×xB
Explanation:
Raoult’s law for vapor pressure lowering states that the lowering in vapor pressure (ΔP) is proportional to the vapor pressure of the pure solvent (PA0) and the mole fraction of the solute (xB).
68. In an ideal solution, the enthalpy of mixing is:
a) Positive
b) Negative
c) Zero
d) Infinite
Answer: c) Zero
Explanation:
In an ideal solution, the enthalpy of mixing is zero because the interactions between the solute and solvent molecules are similar to those in the pure components, resulting in no heat being absorbed or released during mixing.
69. Which of the following solutions shows negative deviation from Raoult’s law?
a) Acetone and carbon tetrachloride
b) Ethanol and benzene
c) Acetone and chloroform
d) Water and urea
Answer: c) Acetone and chloroform
Explanation:
Negative deviation occurs when the interactions between solute and solvent are stronger than those in the pure components. Acetone and chloroform exhibit hydrogen bonding, leading to stronger interactions and negative deviation from Raoult’s law.
70. The relative lowering of vapor pressure for a solution is directly proportional to:
a) The temperature of the solution
b) The mole fraction of the solute
c) The molality of the solute
d) The vapor pressure of the solute
Answer: b) The mole fraction of the solute
Explanation:
According to Raoult’s law, the relative lowering of vapor pressure is directly proportional to the mole fraction of the solute in the solution. This relationship is key to understanding how solutes affect the vapor pressure of solvents.
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