Which of the compounds is more soluble in an acidic solution than in pure water? CuCl CuCN Zn(OH)2 KClO4 SrS
The Correct Answer and Explanation is:
Correct Answer: Zn(OH)₂ and SrS
Explanation:
To determine which compounds are more soluble in an acidic solution than in pure water, consider how they react with hydrogen ions (H⁺) from acids. Compounds that contain basic anions or behave like bases will generally be more soluble in acidic solutions because they react with H⁺, forming neutral or less soluble species and shifting equilibrium to dissolve more of the solid.
1. Zn(OH)₂ (Zinc hydroxide)
Zinc hydroxide is a sparingly soluble base. In water, it partially dissociates into Zn²⁺ and OH⁻.
In an acidic solution, H⁺ reacts with OH⁻ to form water:
OH⁻ + H⁺ → H₂O
This removal of OH⁻ shifts the equilibrium to dissolve more Zn(OH)₂. Therefore, Zn(OH)₂ is more soluble in acidic solution.
2. SrS (Strontium sulfide)
Strontium sulfide dissociates into Sr²⁺ and S²⁻ ions. The sulfide ion (S²⁻) is a strong base and reacts with H⁺ in acid:
S²⁻ + 2H⁺ → H₂S (gas)
This reaction reduces the concentration of S²⁻, shifting the equilibrium toward more dissolution of SrS. Hence, SrS is also more soluble in acidic solution.
Why the Others Are Not More Soluble:
- CuCl (Copper(I) chloride): It contains Cl⁻, which is the conjugate base of a strong acid (HCl) and does not react with H⁺, so its solubility does not increase significantly in acid.
- CuCN (Copper(I) cyanide): CN⁻ can react with H⁺ to form HCN, but CuCN is highly insoluble and forms complex ions. The situation is complex and does not guarantee increased solubility in acid due to the stability of the solid and potential formation of complex ions.
- KClO₄ (Potassium perchlorate): ClO₄⁻ is the conjugate base of a very strong acid (HClO₄) and does not react with H⁺. Its solubility remains unchanged in acidic conditions.
Conclusion: Zn(OH)₂ and SrS are more soluble in acidic solutions because they contain basic anions (OH⁻ and S²⁻) that react with H⁺, enhancing dissolution.
