AP Chemistry Questions: Freezing Point Depression and Colligative Properties

🧊 Quick Study Guide

• 💧 Colligative properties are properties of solutions that depend on the concentration of solute particles, not their identity.
• 🌡️ Freezing point depression is the decrease in the freezing point of a solvent upon the addition of a non-volatile solute.
• ➗ Formula for freezing point depression: $$\Delta T_f = i \cdot K_f \cdot m$$, where:
  • $\Delta T_f$ is the freezing point depression
  • $i$ is the van't Hoff factor (number of particles the solute dissociates into)
  • $K_f$ is the cryoscopic constant (freezing point depression constant) of the solvent
  • $m$ is the molality of the solution (moles of solute per kilogram of solvent)
• 📝 Molality (m) is calculated as: $$m = \frac{\text{moles of solute}}{\text{kilograms of solvent}}$$
• 🧊 The freezing point of a solution is: $$T_{f, \text{solution}} = T_{f, \text{solvent}} - \Delta T_f$$

🧪 Practice Quiz

1. Question 1: What is a colligative property?
   1. A property that depends on the identity of the solute.
   2. A property that depends only on the concentration of solute particles.
   3. A property that is independent of temperature.
   4. A property specific to gases.
2. Question 2: What does the van't Hoff factor represent?
   1. The molar mass of the solute.
   2. The number of particles a solute dissociates into in solution.
   3. The density of the solution.
   4. The volume of the solvent.
3. Question 3: What is the freezing point depression ($$\Delta T_f$$) if 0.5 mol of NaCl is dissolved in 1 kg of water? ( $K_f$ of water = 1.86 °C/m, i = 2)
   1. 0.93 °C
   2. 1.86 °C
   3. 0.465 °C
   4. 3.72 °C
4. Question 4: What is the molality of a solution containing 10g of glucose (MW = 180 g/mol) in 200g of water?
   1. 0.278 m
   2. 0.056 m
   3. 5.56 m
   4. 0.556 m
5. Question 5: Which of the following solutions will have the lowest freezing point?
   1. 1.0 m NaCl
   2. 1.0 m Glucose
   3. 1.0 m $CaCl_2$
   4. 1.0 m Sucrose
6. Question 6: What is the freezing point of a solution containing 0.2 mol of solute in 500g of water, if the solute does not dissociate? ($K_f$ of water = 1.86 °C/m, Normal freezing point of water = 0 °C)
   1. -0.744 °C
   2. 0.744 °C
   3. -0.372 °C
   4. 0 °C
7. Question 7: Which of the following factors does NOT affect the freezing point depression?
   1. The identity of the solute.
   2. The molality of the solution.
   3. The van't Hoff factor.
   4. The cryoscopic constant of the solvent.