Questions on Freezing Point Depression
Multiple-Choice Questions – Freezing Point Depression
1. What is freezing point depression?
A) Increase in the freezing point of a solvent
B) Increase in the temperature of a liquid
C) Decrease in the freezing point of a solvent when a solute is added
D) Boiling of a solution at a lower temperature
E) Melting of solute particles
2. Which of the following best explains freezing point depression?
A) Solute increases the vapor pressure
B) Solute forms stronger bonds with air molecules
C) Solute particles disrupt the formation of a solid lattice
D) Solute lowers boiling point
E) Solute cools the container
3. Freezing point depression is a:
A) Physical constant
B) Chemical change
C) Colligative property
D) Non-colligative property
E) Form of phase separation
4. Which factor does not affect freezing point depression?
A) Nature of solute
B) Concentration of solute
C) Type of solvent
D) Atmospheric pressure
E) Number of solute particles
5. What happens to the freezing point when a solute is added to a pure solvent?
A) It increases
B) It remains unchanged
C) It decreases
D) It becomes zero
E) It turns into the boiling point
6. What is the formula for calculating freezing point depression?
A) ΔTₙ = Kf × m × i
B) ΔTf = Kb × m
C) ΔTf = Kp × V
D) ΔTf = i × R × T
E) ΔTₙ = m × n
7. In the formula ΔTf = Kf × m × i, the symbol Kf stands for:
A) Freezing point temperature
B) Solubility factor
C) Cryoscopic constant of the solvent
D) Volume constant
E) Ionic pressure
8. What does m represent in ΔTf = Kf × m × i?
A) Mass of solute
B) Molar mass of solvent
C) Molality of the solution
D) Mole fraction
E) Molecular number
9. The van’t Hoff factor (i) accounts for:
A) The temperature of freezing
B) The boiling point shift
C) The number of particles the solute dissociates into
D) The solubility rate
E) The vapor pressure
10. Which of the following solutes will cause the greatest freezing point depression per mole?
A) Glucose (C₆H₁₂O₆)
B) NaCl
C) K₂SO₄
D) CH₃OH
E) C₂H₅OH
11. A solution with a higher molality will:
A) Freeze at a higher temperature
B) Boil at a lower temperature
C) Freeze at a lower temperature
D) Be more volatile
E) Have constant freezing point
12. Which of the following is true about the freezing point of salt water compared to pure water?
A) It freezes at a higher temperature
B) It freezes at the same temperature
C) It freezes at a lower temperature
D) It doesn’t freeze
E) It boils more easily
13. Which of the following solvents would likely have the greatest value of Kf?
A) Water
B) Benzene
C) Acetic acid
D) Ether
E) Glycerol
14. What unit is used for the freezing point depression constant (Kf)?
A) °C/mol
B) K/mol
C) °C·kg/mol
D) mol/kg
E) g/mol
15. Why does CaCl₂ lower the freezing point more than NaCl?
A) It dissolves slower
B) It forms fewer ions
C) It is heavier
D) It produces more ions (i = 3)
E) It has a higher Kf
16. Which condition increases the freezing point depression of a solution?
A) Lower molality
B) Non-electrolyte solutes
C) Decrease in solute amount
D) Increase in solute particles
E) Use of volatile solutes
17. What is the freezing point of a 1 molal solution of a non-electrolyte in water? (Kf for water = 1.86 °C·kg/mol)
A) –1.00 °C
B) –0.93 °C
C) –1.86 °C
D) 0 °C
E) +1.86 °C
18. Why is salt often spread on icy roads in winter?
A) To melt the snow chemically
B) To raise the freezing point of water
C) To keep water frozen
D) To lower the freezing point so ice melts
E) To add weight
19. Which solution would have the lowest freezing point?
A) 1 m NaCl
B) 1 m C₆H₁₂O₆
C) 1 m CaCl₂
D) 1 m CH₃OH
E) 1 m sucrose
20. Which of the following causes freezing point depression in a solution?
A) Increase in gas pressure
B) Solute particles preventing crystal formation
C) Increase in solvent density
D) Vapor condensing
E) Boiling of solvent
Answer Key with Full Explanations
1. C – Adding a solute to a solvent causes its freezing point to drop.
2. C – Solute particles interrupt the formation of solid crystals.
3. C – It's a colligative property, depending on solute particle number.
4. D – Atmospheric pressure affects boiling, not freezing point.
5. C – The freezing point is lowered due to solute presence.
6. A – Correct equation for freezing point depression.
7. C – Kf is the cryoscopic constant unique to each solvent.
8. C – m is molality, in mol/kg of solvent.
9. C – The van’t Hoff factor (i) indicates the number of particles after dissociation.
10. C – K₂SO₄ dissociates into 3 ions (2K⁺ and SO₄²⁻), giving highest i.
11. C – More concentrated solution = greater depression in freezing point.
12. C – Salt water freezes below 0°C due to solute effect.
13. A – Water has a relatively high Kf, commonly used as standard.
14. C – Unit for Kf is °C·kg/mol.
15. D – CaCl₂ dissociates into 3 ions (i = 3), NaCl into 2 (i = 2).
16. D – More particles = greater effect on freezing point.
17. C – ΔTf = Kf × m = 1.86 × 1 = 1.86°C depression → freezing point = –1.86°C
18. D – Salt lowers the freezing point, causing ice to melt.
19. C – CaCl₂ dissociates into more particles → greatest depression.
20. B – Solute particles interfere with solidification.
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