For the weak electrolyte , their degree of dissociation increase

Options

A. One increasing dilution
B. On decreasing diluation
C. On increasing pressure
D. None of these

Answer

To solve the question regarding the degree of dissociation of weak electrolytes, we can break down the explanation step by step.

### Step-by-Step Solution:

1. **Understanding Weak Electrolytes**:
- Weak electrolytes are substances that partially ionize in solution. For example, consider a weak electrolyte represented as HA, which dissociates into H⁺ and A⁻ ions in water.

2. **Establishing the Equilibrium**:
- When HA is dissolved in water, it establishes an equilibrium:
\[ HA \rightleftharpoons H^+ + A^- \]
- Let the initial concentration of HA be \( C \), and let \( \alpha \) represent the degree of ionization (the fraction of HA that dissociates).

3. **Setting Up the Concentrations**:
- At equilibrium, the concentrations can be expressed as:
- [HA] = \( C(1 - \alpha) \)
- [H⁺] = \( C\alpha \)
- [A⁻] = \( C\alpha \)

4. **Applying the Equilibrium Constant Expression**:
- The equilibrium constant \( K_a \) for the dissociation of the weak electrolyte is given by:
\[ K_a = \frac{[H^+][A^-]}{[HA]} = \frac{(C\alpha)(C\alpha)}{C(1 - \alpha)} \]
- Simplifying this gives:
\[ K_a = \frac{C\alpha^2}{1 - \alpha} \]

5. **Assuming Small Degree of Ionization**:
- For weak electrolytes, \( \alpha \) is small, so \( 1 - \alpha \) can be approximated as 1. Thus:
\[ K_a \approx C\alpha^2 \]

6. **Solving for Degree of Ionization**:
- Rearranging the equation gives:
\[ \alpha = \sqrt{\frac{K_a}{C}} \]
- This shows that the degree of ionization \( \alpha \) is inversely proportional to the square root of the concentration \( C \).

7. **Conclusion**:
- As the concentration \( C \) decreases (which occurs when the solution is diluted), the degree of ionization \( \alpha \) increases. Therefore, the degree of dissociation of weak electrolytes increases upon dilution.

### Final Answer:
The degree of dissociation of weak electrolytes increases upon dilution.