pH of solutions of four sodium salts NaW, NaX, NaY and NaZ were found to be 7.0, 9.0, 10.0 and 11.0 respectively. If each solution has concentration 0.1 M, the weakest acid is :

Options

A. HW
B. HX
C. HY
D. HZ

Answer

To determine the weakest acid among the sodium salts NaW, NaX, NaY, and NaZ based on their pH values, we can follow these steps:

### Step 1: Understand the relationship between pH and acidity
The pH of a solution indicates its acidity or basicity. A lower pH means a more acidic solution, while a higher pH indicates a more basic solution.

### Step 2: Analyze the given pH values
The pH values of the solutions are:
- NaW: pH = 7.0 (neutral)
- NaX: pH = 9.0 (basic)
- NaY: pH = 10.0 (more basic)
- NaZ: pH = 11.0 (very basic)

### Step 3: Identify the nature of the salts
All the sodium salts (NaW, NaX, NaY, NaZ) are formed from a strong base (NaOH) and a weak acid. The degree of basicity of each salt solution indicates the strength of the corresponding weak acid.

### Step 4: Determine the strength of the acids
- The salt with a pH of 7.0 (NaW) indicates that the weak acid (HW) is relatively stronger compared to the others, as it does not produce a basic solution.
- The salts with pH values of 9.0 (NaX), 10.0 (NaY), and 11.0 (NaZ) indicate that their corresponding acids (HX, HY, HZ) are weaker, with HZ being the weakest since it results in the highest pH.

### Step 5: Conclusion
Since the pH increases from NaW to NaZ, it indicates that the strength of the acids decreases in the order:
- HW (strongest acid) > HX > HY > HZ (weakest acid)

Thus, the weakest acid among the given sodium salts is **HZ**.

### Final Answer:
The weakest acid is **HZ**.

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