Question

Which of the following aqueous salt solutions has the least pH value ?

• A. \(\text{Na}_2\text{CO}_3\)
• B. \(\text{CuCl}_2\)
• C. \(\text{CH}_3\text{COONa}\)
• D. \(\text{NaNO}_3\)

Hint:

A salt of a strong acid and a weak base gives an acidic solution, so CuCl2 has the lowest pH.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The pH of a salt solution depends on which ions undergo hydrolysis. A salt of a strong acid and a weak base is acidic. A salt of a weak acid and a strong base is basic. A salt of a strong acid and a strong base is neutral.

Step 2: Key Formula or Approach:
Classify each salt by its parent acid and base.

Step 3: Detailed Explanation:
\(\text{Na}_2\text{CO}_3\): strong base NaOH and weak acid \(\text{H}_2\text{CO}_3\). The carbonate ion hydrolyses and gives a basic solution, pH above 7.
\(\text{CuCl}_2\): weak base \(\text{Cu(OH)}_2\) and strong acid HCl. The \(\text{Cu}^{2+}\) ion hydrolyses to give \(\text{H}^+\), so the solution is acidic, pH below 7.
\(\text{CH}_3\text{COONa}\): strong base and weak acid, so it is basic.
\(\text{NaNO}_3\): strong base and strong acid, so it is neutral, pH about 7.
The lowest pH belongs to the acidic salt.

Final Answer:
\(\text{CuCl}_2\) gives the most acidic solution, so it has the least pH. This is option (B). \[ \boxed{\text{CuCl}_2 \text{ (B)}} \]