Is calcium carbonate soluble or insoluble
The correct answer and explanation is:
Calcium carbonate (CaCO₃) is insoluble in water. While it is a common compound found in nature in the form of limestone, marble, and chalk, its solubility in water is extremely low. This is due to the strong ionic bonds between calcium ions (Ca²⁺) and carbonate ions (CO₃²⁻), which make it difficult for the compound to dissolve in water.
The solubility of calcium carbonate can be explained using its solubility product constant (Ksp). The Ksp for calcium carbonate is very small, indicating that only a very small amount of it can dissolve in water before it reaches equilibrium. For calcium carbonate, the dissolution process involves the following equilibrium:
CaCO3(s)⇌Ca2+(aq)+CO32−(aq)\text{CaCO}_3 (s) \rightleftharpoons \text{Ca}^{2+} (aq) + \text{CO}_3^{2-} (aq)
Because the Ksp value is very low, the concentration of calcium ions and carbonate ions in solution remains very small. This means that under normal conditions, calcium carbonate will mostly remain undissolved in water.
However, its solubility can increase in the presence of acidic conditions. For example, when calcium carbonate reacts with acids such as hydrochloric acid (HCl), it dissolves to form calcium chloride (CaCl₂), carbon dioxide (CO₂), and water:
CaCO3(s)+2HCl(aq)→CaCl2(aq)+CO2(g)+H2O(l)\text{CaCO}_3 (s) + 2 \text{HCl} (aq) \rightarrow \text{CaCl}_2 (aq) + CO_2 (g) + H_2O (l)
In environments with low pH, like in rainwater with dissolved CO₂ (forming carbonic acid), calcium carbonate can also slowly dissolve. This explains processes like the weathering of limestone or the formation of caves and stalactites. In summary, calcium carbonate is insoluble in water under normal conditions but can dissolve under acidic conditions.