Boiling Point Elevation Formula: Worked Examples for AP Chemistry

📚 Quick Study Guide

🧪 Colligative properties are properties of solutions that depend on the concentration of solute particles, not their identity. 🌡️ Boiling point elevation is the increase in the boiling point of a solvent caused by the presence of a solute. 🔢 The formula for boiling point elevation is: $$\Delta T_b = i * K_b * m$$ 🧊 Where:
• 🔍 $\Delta T_b$ is the change in boiling point.
• 💡 $i$ is the van't Hoff factor (number of particles the solute dissociates into).
• 📝 $K_b$ is the ebullioscopic constant (boiling point elevation constant) of the solvent.
• 📚 $m$ is the molality of the solution (moles of solute per kilogram of solvent).

🧪 Practice Quiz

1. What is the boiling point elevation when 10.0 g of NaCl is dissolved in 100.0 g of water? ( $K_b$ for water = 0.512 °C/m, Molar mass of NaCl = 58.44 g/mol)
1. 0.175 °C
2. 0.292 °C
3. 1.75 °C
4. 2.92 °C
2. What does the van't Hoff factor represent in the boiling point elevation formula?
1. The mass of the solute
2. The volume of the solvent
3. The number of particles the solute dissociates into
4. The boiling point of the pure solvent
3. If the boiling point elevation of a solution is 1.024 °C, and the molality is 1.0 m, what is the ebullioscopic constant ($K_b$) assuming $i = 1$?
1. 0.512 °C/m
2. 1.024 °C/m
3. 2.048 °C/m
4. 0.256 °C/m
4. Which of the following solutions will have the highest boiling point, assuming equal molalities and ideal behavior?
1. Glucose (i = 1)
2. NaCl (i = 2)
3. $CaCl_2$ (i = 3)
4. Urea (i = 1)
5. What is the molality of a solution if 20.0 g of $MgCl_2$ (Molar mass = 95.211 g/mol) is dissolved in 250.0 g of water?
1. 0.210 m
2. 0.841 m
3. 0.420 m
4. 1.68 m
6. The boiling point of a solution of 5.0 g of an unknown non-electrolyte solute in 50.0 g of water is 100.45 °C. What is the molar mass of the solute? ($K_b$ of water = 0.512 °C/m)
1. 28.4 g/mol
2. 56.8 g/mol
3. 113.6 g/mol
4. 227.2 g/mol
7. What is the new boiling point of a solution containing 34.2 g of sucrose (Molar mass = 342 g/mol) in 200 g of water? ($K_b$ for water = 0.512 °C/m)
1. 100.0512 °C
2. 100.512 °C
3. 100.256 °C
4. 100.102 °C