Question

What is the molarity of a solution prepared by dissolving 10 grams of NaOH (molar mass = 40 g/mol) in 500 mL of solution?

• A. \( 0.25 \, \text{M} \)
• B. \( 0.5 \, \text{M} \)
• C. \( 1 \, \text{M} \)
• D. \( 2 \, \text{M} \)

Hint:

Molarity is calculated using the formula: \[ \text{Molarity (M)} = \frac{\text{Mass (g)}}{\text{Molar Mass (g/mol)} \times \text{Volume (L)}} \] Always convert volume to litres before substituting.

Answer 1

The Correct Option is B

Step 1: Calculate moles of NaOH. 
Given mass of NaOH = 10 g 
Molar mass of NaOH = 40 g/mol 
\[ \text{Moles of NaOH} = \frac{10}{40} = 0.25 \, \text{mol} \] 
Step 2: Convert volume to litres. 
Given volume = 500 mL = 0.5 L 
Step 3: Use molarity formula. 
\[ \text{Molarity (M)} = \frac{\text{moles of solute}}{\text{volume of solution in L}} = \frac{0.25}{0.5} = 0.5 \, \text{M} \] Correction: the correct molarity is \( 0.5 \, \text{M} \), so the correct answer is: