Review the equilibrium and choose the correct statement `HCIO_(4) + H_(2)O hArr H_(2)O^(+) CIO_(4)^(-)`

Options

A. `HCIO_(4)` is the conjugate base of `H_(2)O`
B. `H_(3)O^(+)` is the conjugate base of `H_(2)O`
C. `H_(2)O` is the conjugate acid of `H_(3)O^(+)`
D. `CIO_(4)^(-)` is the conjugate base of `HCIO_(4)`

Answer

To solve the question regarding the equilibrium reaction \( \text{HClO}_4 + \text{H}_2\text{O} \rightleftharpoons \text{H}_3\text{O}^+ + \text{ClO}_4^- \), we need to analyze the roles of each species involved in the reaction.

### Step-by-Step Solution:

1. **Identify the Acid and Base**:
- In the reaction, \( \text{HClO}_4 \) (perchloric acid) donates a proton (H⁺) to water (\( \text{H}_2\text{O} \)).
- Therefore, \( \text{HClO}_4 \) acts as an acid because it donates a proton.
- Water (\( \text{H}_2\text{O} \)) accepts a proton, so it acts as a base.

2. **Determine the Products**:
- When \( \text{HClO}_4 \) donates a proton, it forms \( \text{ClO}_4^- \) (the conjugate base of \( \text{HClO}_4 \)).
- Water, after gaining a proton, becomes \( \text{H}_3\text{O}^+ \) (the hydronium ion), which is the conjugate acid of water.

3. **Identify Conjugate Acid-Base Pairs**:
- The conjugate base of the acid \( \text{HClO}_4 \) is \( \text{ClO}_4^- \).
- The conjugate acid of the base \( \text{H}_2\text{O} \) is \( \text{H}_3\text{O}^+ \).

4. **Evaluate the Statements**:
- **Statement 1**: "HClO4 is a conjugate base of water" - Incorrect, because \( \text{HClO}_4 \) is an acid, not a base.
- **Statement 2**: "Hydronium ion is a conjugate base of water" - Incorrect, because \( \text{H}_3\text{O}^+ \) is the conjugate acid of water.
- **Statement 3**: "Water is a conjugate acid of hydronium ion" - Incorrect, because water is acting as a base in this reaction.
- **Statement 4**: "ClO4^- is a conjugate base of HClO4" - Correct, because \( \text{ClO}_4^- \) is formed when \( \text{HClO}_4 \) donates a proton.

5. **Conclusion**:
- The correct statement is: **ClO4^- is a conjugate base of HClO4**.