Consider the acid-base nature of calcium chloride, CaCl
, when it is dissolved in water. (1) What are the acid-base properties of the cation? (2) What are the acid-base properties of the anion? (3) Would an aqueous solution of calcium chloride be acidic, basic or neutral?
The Correct Answer and Explanation is:
When calcium chloride (CaCl2) dissolves in water, it dissociates into calcium ions (Ca²⁺) and chloride ions (Cl⁻). Let’s analyze the acid-base properties of each ion:
- Acid-Base Properties of the Cation (Ca²⁺):
The calcium ion (Ca²⁺) is a highly charged metal ion and can interact with water molecules. It tends to polarize water molecules, making the hydrogen atoms more likely to dissociate into protons (H⁺). This creates a slightly acidic environment, as Ca²⁺ can lead to the production of H⁺ ions by the following reaction: \text{Ca}^{2+} + 6H_2O \rightarrow \text{[Ca(H2O)6]}^{2+} \rightarrow \text{[Ca(H2O)5]^{2+}} + H_2O \rightarrow H^+ + OH^- Although calcium ions do not directly release protons themselves, they can increase the concentration of protons (H⁺) through this interaction with water, making the solution weakly acidic. However, since this is not a strong acid-base reaction, the acidity is relatively low. - Acid-Base Properties of the Anion (Cl⁻):
The chloride ion (Cl⁻) is the conjugate base of a strong acid (HCl). As a result, it does not readily react with water to produce OH⁻ ions, meaning it has no significant basicity. Chloride ions are neutral in solution and do not affect the pH of the solution. - Acid-Base Nature of the Aqueous Solution of Calcium Chloride:
In an aqueous solution, the calcium cation (Ca²⁺) is slightly acidic, while the chloride anion (Cl⁻) is neutral. As a result, the overall solution of calcium chloride will be slightly acidic but not strongly so. The contribution of Ca²⁺ is small compared to other acids, so the solution will be nearly neutral with a slight tendency to lower the pH.
Conclusion:
An aqueous solution of calcium chloride (CaCl2) is typically neutral to slightly acidic due to the weakly acidic nature of Ca²⁺.
