Write the proton transfer equilibria for the following acids in aqueous solution and identify conjugate acid base pairs in each :
(i)HCN , (ii)`CH_3COOH`

Answer

To solve the problem, we need to write the proton transfer equilibria for the given acids (HCN and CH₃COOH) in aqueous solution and identify the conjugate acid-base pairs for each.

### Step 1: Proton Transfer Equilibrium for HCN

1. **Identify the acid**: HCN (hydrocyanic acid) is a weak acid.
2. **Write the equilibrium reaction**:
- When HCN donates a proton (H⁺) to water (H₂O), it forms its conjugate base (CN⁻) and the hydronium ion (H₃O⁺).
- The reaction can be written as:
\[ \text{HCN} + \text{H}_2\text{O} \rightleftharpoons \text{CN}^- + \text{H}_3\text{O}^+ \]

3. **Identify conjugate acid-base pairs**:
- Conjugate acid-base pair 1: HCN (acid) and CN⁻ (conjugate base).
- Conjugate acid-base pair 2: H₂O (base) and H₃O⁺ (conjugate acid).

### Step 2: Proton Transfer Equilibrium for CH₃COOH

1. **Identify the acid**: CH₃COOH (acetic acid) is also a weak acid.
2. **Write the equilibrium reaction**:
- When CH₃COOH donates a proton (H⁺) to water (H₂O), it forms its conjugate base (CH₃COO⁻) and the hydronium ion (H₃O⁺).
- The reaction can be written as:
\[ \text{CH}_3\text{COOH} + \text{H}_2\text{O} \rightleftharpoons \text{CH}_3\text{COO}^- + \text{H}_3\text{O}^+ \]

3. **Identify conjugate acid-base pairs**:
- Conjugate acid-base pair 1: CH₃COOH (acid) and CH₃COO⁻ (conjugate base).
- Conjugate acid-base pair 2: H₂O (base) and H₃O⁺ (conjugate acid).

### Final Summary

- For **HCN**:
- Equilibrium: \(\text{HCN} + \text{H}_2\text{O} \rightleftharpoons \text{CN}^- + \text{H}_3\text{O}^+\)
- Conjugate acid-base pairs: (HCN, CN⁻) and (H₂O, H₃O⁺)

- For **CH₃COOH**:
- Equilibrium: \(\text{CH}_3\text{COOH} + \text{H}_2\text{O} \rightleftharpoons \text{CH}_3\text{COO}^- + \text{H}_3\text{O}^+\)
- Conjugate acid-base pairs: (CH₃COOH, CH₃COO⁻) and (H₂O, H₃O⁺)