Question

A solution contains 10 g of NaOH dissolved in 500 mL of water. What is the molarity of the NaOH solution?

• A. 0.25 M
• B. 0.5 M
• C. 1.0 M
• D. 2.0 M

Hint:

Remember: Molarity is calculated by dividing the moles of solute by the volume of solution in liters. Ensure units are consistent when using the formula.

Answer 1

The Correct Option is A

Step 1: Calculate the moles of NaOH The molar mass of sodium hydroxide (\( \text{NaOH} \)) is: \[ M_{\text{NaOH}} = 23 + 16 + 1 = 40 \, \text{g/mol} \] The number of moles of NaOH in 10 g is: \[ \text{Moles of NaOH} = \frac{\text{Mass of NaOH}}{\text{Molar mass of NaOH}} = \frac{10 \, \text{g}}{40 \, \text{g/mol}} = 0.25 \, \text{mol} \] Step 2: Convert the volume of solution to liters Given that the volume of the solution is 500 mL, convert it to liters: \[ \text{Volume of solution} = \frac{500 \, \text{mL}}{1000} = 0.5 \, \text{L} \] Step 3: Calculate the molarity of the NaOH solution Molarity (\( M \)) is defined as the number of moles of solute per liter of solution: \[ M = \frac{\text{Moles of NaOH}}{\text{Volume of solution in liters}} = \frac{0.25 \, \text{mol}}{0.5 \, \text{L}} = 0.5 \, \text{M} \] Answer: Therefore, the molarity of the NaOH solution is \( 0.5 \, \text{M} \). So, the correct answer is option (2).