Converting Molality to Molarity: Examples and Explanations

📚 Quick Study Guide

• ⚖️ Molality (m) is defined as moles of solute per kilogram of solvent. Formula: $m = \frac{\text{moles of solute}}{\text{kilograms of solvent}}$
• 💧 Molarity (M) is defined as moles of solute per liter of solution. Formula: $M = \frac{\text{moles of solute}}{\text{liters of solution}}$
• 🌡️ Conversion requires knowledge of the solution's density.
• ➗ The key steps are: 1) Assume a volume (e.g., 1 kg of solvent), 2) Calculate moles of solute, 3) Determine the volume of the solution using density, and 4) Calculate molarity.

Practice Quiz

1. What is the molality of a solution containing 10 grams of NaOH in 500 grams of water? (Molar mass of NaOH = 40 g/mol)
   1. 0.25 m
   2. 0.5 m
   3. 1.0 m
   4. 2.0 m
2. A solution of H2SO4 has a molality of 4.0 m. What does this mean?
   1. 4.0 moles of H2SO4 in 1 liter of solution.
   2. 4.0 moles of H2SO4 in 1 kg of solvent.
   3. 4.0 grams of H2SO4 in 1 liter of solution.
   4. 4.0 grams of H2SO4 in 1 kg of solvent.
3. To convert molality to molarity, what information is essential?
   1. The molar mass of the solute.
   2. The density of the solution.
   3. The volume of the solution.
   4. The temperature of the solution.
4. A solution has a molality of 2.0 m. If the molar mass of the solute is 50 g/mol, how many grams of solute are present in 500 g of solvent?
   1. 50 g
   2. 100 g
   3. 200 g
   4. 25 g
5. What is the molarity of a 2.0 m solution of KCl if the density of the solution is 1.08 g/mL? (Molar mass of KCl = 74.5 g/mol)
   1. 1.85 M
   2. 2.0 M
   3. 2.16 M
   4. 2.32 M
6. Which of the following is NOT a step in converting molality to molarity?
   1. Assume 1 kg of solvent.
   2. Calculate moles of solute.
   3. Measure the pH of the solution.
   4. Determine the volume of the solution using density.
7. A solution is prepared by dissolving 116.8 g of NaCl in 1000 g of water. The density of the solution is 1.08 g/mL. What is the molarity of the solution? (Molar mass of NaCl = 58.4 g/mol)
   1. 1.0 M
   2. 1.85 M
   3. 2.0 M
   4. 2.16 M