The pH of `H_(2)O` is

Options

A. 7
B. `gt 7`
C. `lt 7`
D. 0

Explanation

To determine the pH of pure water (H₂O), we can follow these steps:

### Step-by-Step Solution:

1. **Understanding pH**:
The pH scale measures the concentration of hydrogen ions (H⁺) in a solution. It is defined as:
\[ \text{pH} = -\log[\text{H}^+] \]

2. **Dissociation of Water**:
Water can dissociate into hydrogen ions and hydroxide ions:
\[ \text{H}_2\text{O} \rightleftharpoons \text{H}^+ + \text{OH}^- \]

3. **Ionization Constant of Water (Kₗ)**:
The ionization constant of water at 25°C (298 K) is given by:
\[ K_w = [\text{H}^+][\text{OH}^-] = 10^{-14} \]

4. **Equal Concentrations in Pure Water**:
In pure water, the concentrations of H⁺ and OH⁻ ions are equal:
\[ [\text{H}^+] = [\text{OH}^-] \]
Let’s denote this concentration as \( x \). Therefore:
\[ K_w = x^2 \]

5. **Calculating the Concentration of H⁺**:
Since \( K_w = 10^{-14} \):
\[ x^2 = 10^{-14} \]
Taking the square root of both sides gives:
\[ x = 10^{-7} \]
Thus, the concentration of H⁺ ions in pure water is \( 10^{-7} \) M.

6. **Calculating pH**:
Now, substituting this value into the pH formula:
\[ \text{pH} = -\log(10^{-7}) = 7 \]

7. **Conclusion**:
Therefore, the pH of pure water at 25°C is 7.

### Final Answer:
The pH of H₂O is **7**.

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