JAMB Chemistry 2024 Paper

Concept:A solution is described by comparing its actual concentration with the known solubility at the same temperature.If the actual concentration is lower than the solubility, more solute can still dissolve, so the solution is unsaturated.Explanation:First, find the molar mass of $\mathrm{KNO}_3$.Molar mass $= 39 + 14 + (3 \times 16) = 101\ \mathrm{g/mol}$.Then convert the given mass concentration to molar concentration.Molar concentration $= \frac{\text{mass concentration}}{\text{molar mass}}$.So, molar concentration $= \frac{303\ \mathrm{g/dm^3}}{101\ \mathrm{g/mol}} = 3.00\ \mathrm{mol/dm^3}$.The solubility of $\mathrm{KNO}_3$ at $30^\circ\mathrm{C}$ is $3.10\ \mathrm{mol/dm^3}$.Compare the two values: $3.00\ \mathrm{mol/dm^3} < 3.10\ \mathrm{mol/dm^3}$.Since the solution contains less solute than the maximum it can hold at that temperature, it is not saturated.More $\mathrm{KNO}_3$ can still dissolve in the solution.Therefore, the solution is unsaturated at $30^\circ\mathrm{C}$.Answer:B. unsaturated.