The value of the ionic product of water depends

Options

A. on volume of water
B. on temperature
C. changes on adding acid or alkali
D. always remain constant

Explanation

To determine what the ionic product of water (Kw) depends on, we can analyze the given options step by step.

### Step-by-Step Solution:

1. **Understanding Ionic Product of Water (Kw)**:
- The ionic product of water is defined as the product of the concentrations of hydrogen ions [H⁺] and hydroxide ions [OH⁻] in pure water at equilibrium.
- Mathematically, it is expressed as:
\[ K_w = [H^+][OH^-] \]

2. **Analyzing the Options**:
- **Option 1: Volume of Water**:
- The ionic product of water does not depend on the volume of water. It is a constant value at a given temperature. Therefore, this option is incorrect.

- **Option 2: Temperature**:
- The ionic product of water is temperature-dependent. As temperature increases, the equilibrium shifts according to Le Chatelier's principle, leading to an increase in the concentration of both H⁺ and OH⁻ ions. Thus, this option is correct.

- **Option 3: Adding Acid or Alkali**:
- When an acid is added, the concentration of H⁺ ions increases, which causes a corresponding decrease in OH⁻ ions to maintain the ionic product constant. Therefore, the ionic product of water remains unchanged despite the addition of acids or alkalis. This option is incorrect.

- **Option 4: Always Constant**:
- While Kw is constant at a specific temperature, it changes with temperature. Therefore, this option is also incorrect.

3. **Conclusion**:
- After analyzing all the options, we conclude that the ionic product of water (Kw) primarily depends on temperature. The correct answer is **Option 2: Temperature**.

### Final Answer:
The value of the ionic product of water depends on **temperature**.