Which of the following solutions has the highest pH?

Options

A. `0.2 M HClO_(4)`
B. `0.20 M CH_(3)COOH`
C. `0.020 M HCl`
D. `0.2 M NaCl`

Answer

To determine which of the given solutions has the highest pH, we need to analyze the nature of each solution provided. The solutions in question are:

1. 0.2 M HClO4 (Perchloric acid)
2. 0.2 M CH3COOH (Acetic acid)
3. 0.2 M HCl (Hydrochloric acid)
4. 0.2 M NaCl (Sodium chloride)

### Step-by-Step Solution:

**Step 1: Identify the nature of each solution.**
- HClO4 and HCl are strong acids, meaning they completely dissociate in water.
- CH3COOH is a weak acid, meaning it does not completely dissociate in water.
- NaCl is a salt formed from a strong acid (HCl) and a strong base (NaOH), and it does not affect the pH of the solution significantly.

**Step 2: Determine the pH of strong acids.**
- For strong acids like HCl and HClO4, the pH can be calculated using the formula:
\[ \text{pH} = -\log[\text{H}^+] \]
Since both HCl and HClO4 are strong acids at 0.2 M, their pH will be approximately:
\[ \text{pH} \approx -\log(0.2) \approx 0.7 \]

**Step 3: Determine the pH of the weak acid (CH3COOH).**
- The pH of a weak acid can be calculated using the dissociation constant (Ka), but generally, we know that weak acids have a higher pH than strong acids. Therefore, the pH of 0.2 M CH3COOH will be greater than that of HCl and HClO4, but still less than 7.

**Step 4: Determine the pH of the neutral salt (NaCl).**
- NaCl is a neutral salt, and its solution will have a pH of around 7 at room temperature. This is because it does not produce any H+ or OH- ions in solution.

**Step 5: Compare the pH values.**
- Strong acids (HCl and HClO4) have pH values less than 1.
- The weak acid (CH3COOH) has a pH greater than 1 but still less than 7.
- The neutral salt (NaCl) has a pH of approximately 7.

**Conclusion:**
Among the given solutions, the one with the highest pH is the 0.2 M NaCl solution, which is neutral.

### Final Answer:
The solution with the highest pH is **0.2 M NaCl**.

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