JAMB Chemistry 2024 Paper

Concept:Permanent hardness in water is caused by dissolved calcium and magnesium salts that remain even after boiling.Explanation:Hard water contains dissolved metal ions, mainly $\mathrm{Ca}^{2+}$ and $\mathrm{Mg}^{2+}$.Temporary hardness is due to bicarbonates, which decompose and precipitate when heated.Permanent hardness is caused by chlorides and sulphates of calcium and magnesium.These salts, such as $\mathrm{CaSO}_4$ and $\mathrm{MgSO}_4$, do not decompose or precipitate on heating.Therefore, boiling cannot remove permanent hardness.Among the given ions, only $\mathrm{Ca}^{2+}$ and $\mathrm{Mg}^{2+}$ are responsible for permanent hardness.Answer:B. $\mathrm{Ca}^{2+}$ and $\mathrm{Mg}^{2+}$