Question

If $2.0$ g of NaOH is dissolved in $500\ \text{cm^3$ of water, what is molarity of solution ?}

• A. $0.25\ \text{mol dm}^{-3}$
• B. $0.1\ \text{mol dm}^{-3}$
• C. $0.4\ \text{mol dm}^{-3}$
• D. $0.50\ \text{mol dm}^{-3}$

Hint:

Always convert volume into dm$^3$ before calculating molarity.

Answer 1

The Correct Option is B

Step 1: Calculation of moles of NaOH.
Molar mass of NaOH $= 40\ \text{g mol}^{-1}$.
\[ \text{Moles of NaOH} = \frac{2.0}{40} = 0.05\ \text{mol} \]
Step 2: Conversion of volume into dm$^3$.
\[ 500\ \text{cm}^3 = 0.5\ \text{dm}^3 \]
Step 3: Calculation of molarity.
\[ \text{Molarity} = \frac{0.05}{0.5} = 0.1\ \text{mol dm}^{-3} \]
Step 4: Conclusion.
Therefore, the molarity of the solution is $0.1\ \text{mol dm^{-3}$}.