Understanding the Dissolution of Powdered Chalk (Calcium Carbonate) in Water

Chalk, primarily composed of calcium carbonate (CaCO3), is commonly used in various applications ranging from educational settings to industrial processes. A key question often arises regarding its solubility in water: will powdered chalk dissolve in water, and if not, what happens to it when it is added to water?

Insolubility of Calcium Carbonate in Water

Calcium carbonate is known for its low solubility in water. The solubility product (Ksp) of calcium carbonate in pure water at 25°C is approximately 3.3 × 10-9, which translates to a saturation concentration of about 12–13 ppm (parts per million). This means that only a very small amount of calcium carbonate will dissolve in water under normal conditions.

Chemical Equations and Reactions

The dissolution of calcium carbonate in water can be described by the following equation:

CaCO3(s) ? Ca2 (aq) CO32-(aq)

However, this equilibrium lies far to the left, indicating that the majority of calcium carbonate will remain in its solid form when added to water. If the water contains carbonic acid (H2CO3), the reaction will proceed further to produce calcium bicarbonate (Ca(HCO3)2), which is more soluble in water:

CaCO3(s) H2CO3(aq) ? Ca(HCO3)2(aq)

Insolubility in Pure Water

In pure water, the dissolution of calcium carbonate is negligible. Adding small amounts of chalk powder to water will result in the formation of a suspension rather than a solution. The chalk particles will settle at the bottom of the container as particles become saturated, ultimately forming a sediment.

Effect of Acids and Carbonic Acid

Calcium carbonate is highly reactive with acids, such as hydrochloric acid (HCl), which can cause the calcium carbonate to dissolve completely. The reaction produces calcium chloride (CaCl2) and carbon dioxide (CO2), both of which are soluble in water:

CaCO3(s) 2HCl(aq) ? CaCl2(aq) H2O(l) CO2(g)

When calcium carbonate is continuously agitated in water, more of it can dissolve, especially if the water contains carbon dioxide. In biological systems, such as in the deep ocean, the solubility of calcium carbonate is significantly enhanced due to the presence of dissolved carbon dioxide, leading to the formation of calcium bicarbonate.

Conclusion

In summary, powdered chalk made of calcium carbonate will not dissolve significantly in pure water under normal conditions. However, the addition of acids or the presence of dissolved carbon dioxide can enhance its solubility, allowing for the dissolution of calcium carbonate. Understanding these reactions and principles is crucial for various applications involving calcium carbonate.

Related Keywords: calcium carbonate, chalk, water solubility