JAMB Chemistry 2018 Paper

Concept:Neutralisation involves reacting equal numbers of moles of hydrogen ions and hydroxide ions according to the balanced chemical equation.Explanation:The balanced equation is:$$2\mathrm{NaOH} + \mathrm{H}_2\mathrm{SO}_4 \rightarrow \mathrm{Na}_2\mathrm{SO}_4 + 2\mathrm{H}_2\mathrm{O}$$This means 2 moles of $\mathrm{NaOH}$ neutralise 1 mole of $\mathrm{H}_2\mathrm{SO}_4$.First, calculate moles of sulphuric acid present:$$\text{Moles of } \mathrm{H}_2\mathrm{SO}_4 = 1.25 \times \frac{10}{1000} = 0.0125 \text{ mol}$$The required moles of sodium hydroxide become:$$\text{Moles of } \mathrm{NaOH} = 2 \times 0.0125 = 0.025 \text{ mol}$$Use the concentration formula to find the volume:$$\text{Volume} = \frac{\text{moles}}{\text{concentration}} = \frac{0.025}{0.5}$$$$\text{Volume} = 0.05 \text{ dm}^3 = 50 \text{ cm}^3$$Answer:50 cm$^3$ of 0.5 molar sodium hydroxide is required.Correct option: D. 50cm$^3$