AP Chemistry Questions on Colligative Properties: Exam Prep

📚 Quick Study Guide

• 💧 Colligative Properties: Properties of solutions that depend on the concentration of solute particles, not their identity.
• 🌡️ Vapor Pressure Lowering: The vapor pressure of a solution is lower than that of the pure solvent. $P_{solution} = X_{solvent} * P^0_{solvent}$, where $X$ is the mole fraction and $P^0$ is the vapor pressure of the pure solvent.
• ❄️ Freezing Point Depression: The freezing point of a solution is lower than that of the pure solvent. $\Delta T_f = i * K_f * m$, where $i$ is the van't Hoff factor, $K_f$ is the freezing point depression constant, and $m$ is the molality.
• 🔥 Boiling Point Elevation: The boiling point of a solution is higher than that of the pure solvent. $\Delta T_b = i * K_b * m$, where $i$ is the van't Hoff factor, $K_b$ is the boiling point elevation constant, and $m$ is the molality.
• osmotic pressure: the pressure that would have to be applied to a pure solvent to prevent it from passing into a given solution by osmosis, often used to determine the molecular weights of macromolecules. $\Pi = iMRT$, where $\Pi$ is the osmotic pressure, $i$ is the van't Hoff factor, $M$ is the molarity, $R$ is the ideal gas constant, and $T$ is the temperature in Kelvin.
• ➕ Van't Hoff Factor (i): The number of particles a solute dissociates into in solution. For example, NaCl dissociates into 2 ions ($Na^+$ and $Cl^-$), so $i = 2$.

🧪 Practice Quiz

1. Which of the following solutions will have the lowest freezing point?
   1. 0.1 m $NaCl$
   2. 0.1 m $C_6H_{12}O_6$ (glucose)
   3. 0.1 m $CaCl_2$
   4. 0.1 m $KCl$
2. What is the boiling point elevation of a solution containing 10 grams of glucose ($C_6H_{12}O_6$) in 200 grams of water? ( $K_b$ for water = 0.512 °C/m, Molar mass of glucose = 180.16 g/mol)
   1. 0.14 °C
   2. 0.29 °C
   3. 0.58 °C
   4. 1.02 °C
3. The osmotic pressure of a solution containing 1 gram of a protein in 100 mL of water is 2.5 torr at 25°C. What is the molar mass of the protein? (R = 62.36 L·torr/mol·K)
   1. 6.1 x 10³ g/mol
   2. 6.1 x 10⁴ g/mol
   3. 6.1 x 10⁵ g/mol
   4. 6.1 x 10² g/mol
4. Which of the following statements about colligative properties is FALSE?
   1. Colligative properties depend on the identity of the solute.
   2. Boiling point elevation is a colligative property.
   3. Freezing point depression is a colligative property.
   4. Osmotic pressure is a colligative property.
5. What is the van't Hoff factor for $Al_2(SO_4)_3$?
   1. 2
   2. 3
   3. 4
   4. 5
6. A solution of ethanol ($C_2H_5OH$) in water has a mole fraction of ethanol of 0.10. What is the vapor pressure of the solution at 25°C if the vapor pressure of pure water at this temperature is 23.8 torr? (Assume ideal behavior.)
   1. 2.38 torr
   2. 21.4 torr
   3. 23.8 torr
   4. 26.2 torr
7. Which of the following will have the highest osmotic pressure?
   1. 0.2 M $NaCl$
   2. 0.2 M Glucose
   3. 0.2 M $MgCl_2$
   4. 0.2 M Sucrose