What is the molarity of a solution prepared by dissolving 4.2 grams of NaF (molar mass = 42 grams/mol) in 200 mL of water?

• A. 0.10 M
• B. 0.20 M
• C. 1.0 M
• D. 0.50 M

Answer: (D)

Verified step by step guidance

1. Identify the formula for molarity, which is the number of moles of solute divided by the volume of solution in liters: \(M = \frac{\text{moles of solute}}{\text{volume of solution in liters}}\).
2. Calculate the number of moles of NaF by dividing the mass of NaF by its molar mass: \(\text{moles of NaF} = \frac{4.2\ \text{g}}{42\ \text{g/mol}}\).
3. Convert the volume of the solution from milliliters to liters because molarity requires liters: \$200\ \text{mL} = 0.200\ \text{L}$.
4. Substitute the moles of NaF and the volume in liters into the molarity formula: \(M = \frac{\text{moles of NaF}}{0.200\ \text{L}}\).
5. Perform the division to find the molarity of the NaF solution.