Understanding the Nature of CH₃COONa Aqueous Solution

The question asks about the nature of an aqueous solution of CH₃COONa. To determine this, we need to understand the parent acid and base from which this salt is formed.

Composition of CH₃COONa Salt

Sodium acetate (CH₃COONa) is a salt formed from the reaction between acetic acid (CH₃COOH) and sodium hydroxide (NaOH):

• Acetic acid (CH₃COOH) is a weak acid.
• Sodium hydroxide (NaOH) is a strong base.

So, CH₃COONa is a salt of a weak acid and a strong base.

Hydrolysis of CH₃COONa in Water

When a salt of a weak acid and a strong base is dissolved in water, hydrolysis occurs. Hydrolysis is the reaction of an ion with water. In this case, the anion from the weak acid, CH₃COO⁻ (acetate ion), reacts with water, while the cation from the strong base, Na⁺ (sodium ion), does not hydrolyze significantly.

The hydrolysis reaction for the acetate ion is:

\( \text{CH}_3\text{COO}^- \text{(aq)} + \text{H}_2\text{O (l)} \rightleftharpoons \text{CH}_3\text{COOH (aq)} + \text{OH}^- \text{(aq)} \)

Impact on Solution pH

As shown by the hydrolysis reaction, the reaction of acetate ions with water produces hydroxide ions (OH⁻). The increase in the concentration of hydroxide ions in the solution leads to a decrease in the hydrogen ion (H⁺) concentration and thus increases the pH.

Since the concentration of OH⁻ ions increases, the solution becomes alkaline (or basic).

Salts of a weak acid and a strong base typically form alkaline solutions due to the hydrolysis of the anion.

Conclusion

Based on the hydrolysis of the acetate ion (CH₃COO⁻) from the salt CH₃COONa, the aqueous solution contains excess hydroxide ions (OH⁻), making it alkaline.