Which statements is wrong about pH ?

Options

A. pH of pure water is not zero
B. Adding 1 N solution `CH_3COOH and 1 N` NaOH pH will be seven
C. pH of dilute and hot `H_2SO_4` is less then 7
D. Mixing solution of `CH_3COOH and HCI` pH will be less than 7

Answer

To determine which statement is wrong about pH, we will analyze each option provided in the question step by step.

### Step 1: Understand what pH is
- **Definition**: pH is defined as the negative logarithm (base 10) of the hydrogen ion concentration in a solution. It is a measure of the acidity or basicity of that solution.
- **Formula**: \( \text{pH} = -\log[\text{H}^+] \)

### Step 2: Evaluate the first statement
- **Statement**: "pH of pure water is not zero."
- **Analysis**: Pure water is neutral and has a pH of 7 at 25°C. Therefore, this statement is true.

### Step 3: Evaluate the second statement
- **Statement**: "Adding one normal solution of acetic acid and one normal NaOH pH will be 7."
- **Analysis**: Acetic acid (CH₃COOH) is a weak acid, while NaOH is a strong base. When mixed, the weak acid will not completely neutralize the strong base, resulting in a basic solution. Thus, the pH will be greater than 7. Therefore, this statement is false.

### Step 4: Evaluate the third statement
- **Statement**: "The pH of dilute and hot H₂SO₄ is less than 7."
- **Analysis**: H₂SO₄ is a strong acid, and solutions of strong acids have a pH less than 7. Therefore, this statement is true.

### Step 5: Evaluate the fourth statement
- **Statement**: "Mixing a solution of acetic acid and HCl, pH will be less than 7."
- **Analysis**: HCl is a strong acid, and acetic acid is a weak acid. Mixing these two will result in an acidic solution, thus the pH will indeed be less than 7. Therefore, this statement is true.

### Conclusion
After evaluating all the statements, we find that the only incorrect statement is the second one: "Adding one normal solution of acetic acid and one normal NaOH pH will be 7."

### Final Answer
The wrong statement about pH is option number 2.

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