81. Which of the following is not a colligative property?
a) Boiling point elevation
b) Osmotic pressure
c) Freezing point depression
d) Surface tension
Answer: d) Surface tension
Explanation:
Surface tension is a property that depends on the nature of the liquid molecules and their interactions, not on the number of solute particles in solution. Therefore, it is not a colligative property.
82. Which of the following solutions will have the highest boiling point?
a) 1 M glucose
b) 1 M NaCl
c) 1 M K₂SO₄
d) 1 M urea
Answer: c) 1 M K₂SO₄
Explanation:
The boiling point elevation depends on the number of solute particles in the solution. K₂SO₄ dissociates into 3 ions (2 K⁺ and 1 SO₄²⁻), producing more particles than NaCl (2 ions), glucose, and urea (which do not dissociate), resulting in a higher boiling point for K₂SO₄.
83. In which of the following solutions will the van’t Hoff factor be 1?
a) NaCl
b) KNO₃
c) Glucose
d) MgCl₂
Answer: c) Glucose
Explanation:
Glucose is a non-electrolyte and does not dissociate in solution, so its van’t Hoff factor (i) is 1. The other compounds are electrolytes and dissociate into ions, leading to i>1.
84. Which of the following solutions will show the least depression in freezing point?
a) 0.1 M NaCl
b) 0.1 M glucose
c) 0.1 M BaCl₂
d) 0.1 M urea
Answer: b) 0.1 M glucose
Explanation:
Glucose is a non-electrolyte and does not dissociate, so it produces fewer particles in solution compared to the electrolytes, resulting in the least depression in freezing point.
85. Raoult’s law is valid for which type of solution?
a) Non-ideal solutions
b) Ideal solutions
c) Concentrated solutions
d) Solutions with strong intermolecular forces
Answer: b) Ideal solutions
Explanation:
Raoult’s law is valid for ideal solutions, where the intermolecular forces between the solute and solvent molecules are similar to those in the pure substances, leading to no enthalpy change on mixing.
86. Which of the following will not cause a deviation from Raoult’s law?
a) Hydrogen bonding between solute and solvent
b) Weak intermolecular forces between solute and solvent
c) Strong solute-solvent interactions
d) Identical solute and solvent molecules
Answer: d) Identical solute and solvent molecules
Explanation:
If the solute and solvent molecules are identical, the solution behaves ideally, and Raoult’s law will hold without any deviation. Deviation occurs when the interactions between solute and solvent are significantly different from those in the pure substances.
87. The van’t Hoff factor (ii) for an electrolyte is:
a) Always less than 1
b) Always equal to 1
c) Always greater than 1
d) Independent of the number of ions
Answer: c) Always greater than 1
Explanation:
For electrolytes, the van’t Hoff factor (ii) is always greater than 1 because they dissociate into more than one ion in solution. The factor reflects the total number of particles produced by dissociation.
88. Which of the following shows positive deviation from Raoult’s law?
a) Water and ethanol
b) Acetone and chloroform
c) Benzene and toluene
d) Ethanol and hexane
Answer: d) Ethanol and hexane
Explanation:
Positive deviation from Raoult’s law occurs when the solute-solvent interactions are weaker than those between the pure components. Ethanol and hexane have weak interactions, leading to higher vapor pressure and positive deviation.
89. Which of the following is an example of a non-ideal solution with negative deviation?
a) Benzene and toluene
b) Ethanol and water
c) Acetone and chloroform
d) Hexane and heptane
Answer: c) Acetone and chloroform
Explanation:
Acetone and chloroform form hydrogen bonds, which are stronger than the interactions in the pure components, leading to a negative deviation from Raoult’s law.
90. Which of the following can be used to calculate molecular weight based on freezing point depression?
a) Raoult’s law
b) van’t Hoff factor
c) Osmotic pressure
d) Cryoscopic constant
Answer: d) Cryoscopic constant
Explanation:
The cryoscopic constant (Kf) is used in the calculation of molecular weight through freezing point depression. By measuring the freezing point depression and knowing Kf, the molar mass of the solute can be determined.
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