Question

What is the molarity of solution containing 3.2g of NaOH (Molar mass 40g mol\(^{-1}\)) in 250 cm\(^3\) of water?

• A. 0.512 mol dm\(^{-3}\)
• B. 0.32 mol dm\(^{-3}\)
• C. 0.032 mol dm\(^{-3}\)
• D. 0.02 mol dm\(^{-3}\)

Hint:

Always ensure to convert the volume into dm\(^3\) before calculating molarity.

Answer 1

The Correct Option is B

Step 1: Use the formula for molarity.
The formula for molarity is: \[ M = \frac{\text{moles of solute}}{\text{volume of solution in dm}^3} \] First, calculate the moles of NaOH: \[ \text{moles of NaOH} = \frac{\text{mass of NaOH}}{\text{molar mass of NaOH}} = \frac{3.2 \, \text{g}}{40 \, \text{g/mol}} = 0.08 \, \text{mol} \]
Step 2: Convert volume to dm\(^3\).
The volume is 250 cm\(^3\), which is equal to: \[ \text{Volume in dm}^3 = \frac{250}{1000} = 0.25 \, \text{dm}^3 \]
Step 3: Calculate molarity.
\[ M = \frac{0.08 \, \text{mol}}{0.25 \, \text{dm}^3} = 0.32 \, \text{mol dm}^{-3} \]
Step 4: Conclusion.
The molarity of the solution is 0.32 mol dm\(^{-3}\).