11. The van’t Hoff factor (i) for NaCl in water is:
A. 1
B. 2
C. 3
D. 0
Answer: B. 2
Explanation:
NaCl dissociates into Na⁺ and Cl⁻ ions in water. Since it dissociates into two particles, the van’t Hoff factor (i) for NaCl is 2.
12. Raoult’s law is followed by:
A. All solutions
B. Solutions showing positive deviation
C. Solutions showing negative deviation
D. Ideal solutions
Answer: D. Ideal solutions
Explanation:
Raoult’s law is strictly followed by ideal solutions where the interactions between all components are uniform. Non-ideal solutions exhibit deviations from Raoult’s law.
13. Which of the following compounds will show the highest boiling point elevation when dissolved in water?
A. Glucose
B. NaCl
C. K₂SO₄
D. Urea
Answer: C. K₂SO₄
Explanation:
K₂SO₄ dissociates into 3 ions (2 K⁺ and 1 SO₄²⁻), so it will produce the most solute particles in solution, leading to the highest elevation in boiling point, as boiling point elevation is proportional to the number of particles.
14. The lowering of vapor pressure is a colligative property because it:
A. Depends on the nature of the solute
B. Depends on the mass of the solute
C. Depends on the number of solute particles
D. Is independent of the solvent
Answer: C. Depends on the number of solute particles
Explanation:
Lowering of vapor pressure is a colligative property because it depends on the number of solute particles in the solution, not the nature of the solute.
15. Which of the following solutions will have the lowest freezing point?
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 particles (Ba²⁺ and 2 Cl⁻), leading to a higher effect on freezing point depression. The more particles present, the greater the freezing point depression.
16. Which of the following statements is correct about an ideal solution?
A. It shows a positive deviation from Raoult’s law
B. It shows a negative deviation from Raoult’s law
C. The enthalpy change of mixing is zero
D. The enthalpy of mixing is positive
Answer: C. The enthalpy change of mixing is zero
Explanation:
In an ideal solution, the enthalpy change of mixing is zero, meaning no heat is absorbed or evolved when the solute and solvent mix.
17. The osmotic pressure of a solution is directly proportional to:
A. The volume of the solvent
B. The number of solute particles
C. The temperature
D. Both B and C
Answer: D. Both B and C
Explanation:
Osmotic pressure is directly proportional to the number of solute particles in the solution and the temperature of the system. The relationship is given by Van’t Hoff’s equation for osmotic pressure.
18. Raoult’s law predicts that the partial vapor pressure of each volatile component in a solution is proportional to:
A. Its molality
B. Its mole fraction
C. Its molecular mass
D. The temperature
Answer: B. Its mole fraction
Explanation:
According to Raoult’s law, the partial vapor pressure of each component in an ideal solution is directly proportional to its mole fraction in the solution.
19. Which property does not change with the number of particles in a solution?
A. Boiling point elevation
B. Freezing point depression
C. Osmotic pressure
D. Density
Answer: D. Density
Explanation:
Density is not a colligative property, so it does not depend solely on the number of particles in the solution. Colligative properties like boiling point elevation, freezing point depression, and osmotic pressure are dependent on the number of solute particles.
20. The elevation in boiling point of a solution is directly proportional to the:
A. Molarity of the solution
B. Molality of the solution
C. Number of moles of solute
D. Mole fraction of solvent
Answer: B. Molality of the solution
Explanation:
The elevation in boiling point is directly proportional to the molality of the solution. The relation is given by:
ΔTb=Kb⋅m
Where mm is the molality and Kb is the ebullioscopic constant.
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