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 concentration of methanol in terms of molarity?

• A. 0.134 M
• B. 0.178 M
• C. 0.156 M
• D. 0.200 M

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, this is 20.2 mL × 0.782 g/mL.
2. Determine the number of moles of methanol. Use the formula: moles = mass / molar mass. The molar mass of methanol (CH3OH) is approximately 32.04 g/mol.
3. Calculate the total volume of the solution in liters. The final volume of the solution is given as 118 mL, which needs to be converted to liters by dividing by 1000.
4. Determine the molarity of the methanol solution. Molarity (M) is defined as the number of moles of solute (methanol) divided by the volume of the solution in liters.
5. Compare the calculated molarity with the given options to identify the correct answer.