Question

The pH of an aqueous solution of a salt is 9. The types of acid and base from which this salt is formed are:

• A. weak acid and weak base
• B. weak acid and strong base
• C. strong acid and weak base
• D. strong acid and strong base

Answer 1

The Correct Option is B

Step 1: Understanding the relationship between pH and salt formation:
The pH of a solution indicates its acidity or alkalinity. A pH of 9 suggests that the solution is slightly alkaline (basic). Salts can be formed by the reaction between an acid and a base, and the pH of the resulting salt solution depends on the strengths of the acid and the base involved.

Step 2: Identifying the nature of the salt:
- If the salt is formed from a strong acid and a strong base, the solution typically has a neutral pH of around 7.
- If the salt is formed from a strong acid and a weak base, the solution will be slightly acidic (pH < 7).
- If the salt is formed from a weak acid and a strong base, the solution will be slightly basic (pH > 7).

Since the pH of the solution is 9, which is slightly alkaline, it indicates that the salt was formed from a weak acid and a strong base. A common example of such a salt is sodium acetate (formed from acetic acid, a weak acid, and sodium hydroxide, a strong base).

Step 3: Conclusion:
The salt is formed from a weak acid and a strong base, as indicated by the slightly basic pH of 9. This is a typical outcome when a salt from a weak acid and a strong base is dissolved in water.