Calculate the molarity of a solution containing 5 g of NaOH in 500 mL of solution.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 0.25 M
Molarity (M) is the number of moles of solute dissolved in one litre of solution. The molar mass of NaOH is 23 + 16 + 1 = 40 g mol−1, and 500 mL = 0.500 L.
\( \displaystyle n_{\ce{NaOH}}=\frac{5\ \mathrm{g}}{40\ \mathrm{g\,mol^{-1}}}=0.125\ \mathrm{mol} \)
\( \displaystyle M=\frac{\text{moles of solute}}{\text{volume of solution in litres}}=\frac{0.125\ \mathrm{mol}}{0.500\ \mathrm{L}} \)
\( \displaystyle M=0.25\ \mathrm{mol\,L^{-1}}=0.25\ \mathrm{M} \)