Which of the following aqueous solutions will form a basic solution?
a) AlCl⁻
b) NaBr
c) CH₃COONa
d) K₂SO₄
The Correct Answer and Explanation is:
The correct answer is c) CH₃COONa (sodium acetate).
Explanation:
To determine which of the given aqueous solutions will form a basic solution, we need to analyze the components of each salt. Basicity in an aqueous solution generally arises from the hydrolysis of the anion of a salt, which can accept protons from water, thus increasing the concentration of hydroxide ions (OH⁻) in the solution.
- AlCl₃ (aluminum chloride): When dissolved in water, it dissociates into Al³⁺ and Cl⁻ ions. The aluminum ion (Al³⁺) is a weak acid because it can hydrolyze in water to form Al(OH)₃ and release H⁺ ions, resulting in an acidic solution. Thus, it does not contribute to basicity.
- NaBr (sodium bromide): This salt dissociates into Na⁺ and Br⁻ ions. The Na⁺ ion is neutral and does not affect pH, while Br⁻ is the conjugate base of a strong acid (HBr) and does not hydrolyze in water. Therefore, NaBr solutions are neutral and do not form a basic solution.
- CH₃COONa (sodium acetate): Sodium acetate dissociates into Na⁺ and CH₃COO⁻ ions. The acetate ion (CH₃COO⁻) is a conjugate base of acetic acid (a weak acid). In water, acetate can react with water in a hydrolysis reaction, producing CH₃COOH and OH⁻ ions:
[
CH₃COO⁻ + H₂O \rightleftharpoons CH₃COOH + OH⁻
]
This reaction results in an increase in OH⁻ concentration, making the solution basic. - K₂SO₄ (potassium sulfate): Upon dissolving, it dissociates into K⁺ and SO₄²⁻ ions. The K⁺ ion is neutral, and the sulfate ion (SO₄²⁻) is the conjugate base of a strong acid (H₂SO₄), which also does not hydrolyze in water. Thus, K₂SO₄ solutions are neutral.
In summary, only CH₃COONa forms a basic solution upon dissociation in water due to the hydrolysis of the acetate ion, which increases the hydroxide ion concentration in the solution.