JAMB Chemistry 2024 Paper

Concept:The gas that turns lime water milky is carbon dioxide, $\mathrm{CO}_{2}$.Explanation:When $\mathrm{CO}_{2}$ passes through lime water, it reacts with calcium hydroxide to form insoluble calcium carbonate, which appears milky.The reaction is:$$\mathrm{Ca(OH)_{2} + CO_{2} \rightarrow CaCO_{3} \downarrow + H_{2}O}$$Carbon dioxide is produced from trioxocarbonate(IV) salts when they react with acids or decompose on heating.Therefore, the gas is likely from a trioxocarbonate(IV).Chlorides, trioxonitrate(V), and tetraoxosulphate(VI) do not release carbon dioxide.Answer:A. Trioxocarbonate(IV)