Boiling Point Elevation: Worked Examples and Real-World Applications

📚 Quick Study Guide

• 🌡️ Boiling point elevation is a colligative property, meaning it depends on the number of solute particles, not their identity.
• ⚗️ The formula for boiling point elevation is: $\Delta T_b = iK_bm$, where $\Delta T_b$ is the boiling point elevation, $i$ is the van't Hoff factor, $K_b$ is the ebullioscopic constant, and $m$ is the molality of the solution.
• 💧 Molality ($m$) is defined as moles of solute per kilogram of solvent.
• 🧊 The van't Hoff factor ($i$) represents the number of ions a solute dissociates into when dissolved in a solution. For example, NaCl has $i=2$ because it dissociates into Na$^+$ and Cl$^-$ ions.
• 🔥 Real-world applications include antifreeze in car radiators (ethylene glycol elevates the boiling point and depresses the freezing point) and cooking (adding salt to water increases the boiling point slightly).
• 💡 Remember to convert grams to moles and grams to kilograms when calculating molality.

🧪 Practice Quiz

1. What type of property is boiling point elevation?

   1. Intensive property
   2. Additive property
   3. Colligative property
   4. Extensive property

2. What does the van't Hoff factor represent?

   1. The molar mass of the solute
   2. The number of ions a solute dissociates into
   3. The density of the solution
   4. The volume of the solvent

3. If $K_b$ for water is 0.512 °C kg/mol, what is the boiling point elevation of a solution containing 2 moles of solute in 1 kg of water, assuming $i = 1$?

   1. 0.256 °C
   2. 0.512 °C
   3. 1.024 °C
   4. 2.048 °C

4. Which of the following is an example of boiling point elevation in everyday life?

   1. Melting ice
   2. Adding salt to a roadway in winter
   3. Using antifreeze in a car radiator
   4. Freezing water

5. What is the molality of a solution containing 4 grams of NaOH (molar mass = 40 g/mol) in 500 g of water?

   1. 0.1 m
   2. 0.2 m
   3. 0.008 m
   4. 0.02 m

6. A solution contains 10 grams of glucose (molar mass = 180 g/mol) in 200 g of water. Calculate the molality of the solution.

   1. 0.278 m
   2. 0.556 m
   3. 0.056 m
   4. 1.11 m

7. What is the boiling point elevation if 0.5 moles of NaCl are dissolved in 1 kg of water? (Assume $K_b$ = 0.512 °C kg/mol for water)

   1. 0.256 °C
   2. 0.512 °C
   3. 1.024 °C
   4. 0.768 °C