A solution is prepared by dissolving 20.2 mL of methanol (CH3OH) in 100.0 mL of water at 25°C. The final volume of the solution is 118 mL. The densities of methanol and water at this temperature are 0.782 g/mL and 1.00 g/mL, respectively. For this solution, what is the mass percentage of methanol?

• A. 13.4%
• B. 17.1%
• C. 19.2%
• D. 15.9%

Answer: (A)

Verified step by step guidance

1. Calculate the mass of methanol using its volume and density. Use the formula: mass = volume × density. For methanol, the volume is 20.2 mL and the density is 0.782 g/mL.
2. Calculate the mass of water using its volume and density. Use the formula: mass = volume × density. For water, the volume is 100.0 mL and the density is 1.00 g/mL.
3. Determine the total mass of the solution by adding the mass of methanol and the mass of water.
4. Calculate the mass percentage of methanol in the solution using the formula: mass percentage = (mass of methanol / total mass of solution) × 100%.
5. Compare the calculated mass percentage with the given options to identify the correct answer.