Consider the three solutions of 1 M concentration
1. Sodium acetate `(CH_3COONa)`
2. Acetic acid + Sodium acetate
`(CH_3COOH+CH_3COONa)`
3. Acetic acid `(CH_3COOH)`
The pH of these solutions will be lie in the following sequence

Options

A. `3 gt 2 gt 1`
B. `2 gt 1 gt 3`
C. `1 gt 2 gt 3`
D. `3 gt 1 gt 2`

Answer

To determine the sequence of pH values for the three solutions of 1 M concentration, we will analyze each solution step by step.

### Step 1: Analyze Sodium Acetate Solution `(CH3COONa)`

- Sodium acetate is a salt formed from a weak acid (acetic acid) and a strong base (sodium hydroxide).
- In solution, sodium acetate dissociates into sodium ions `(Na^+)` and acetate ions `(CH3COO^-)`.
- The acetate ion can hydrolyze in water to produce hydroxide ions `(OH^-)`:

\[ CH_3COO^- + H_2O \rightleftharpoons CH_3COOH + OH^- \]

- This reaction results in an increase in pH, making the solution basic (pH > 7).

### Step 2: Analyze Acetic Acid + Sodium Acetate Solution `(CH3COOH + CH3COONa)`

- This solution is a buffer solution because it contains both a weak acid (acetic acid) and its conjugate base (acetate ion).
- The pH of a buffer solution can be calculated using the Henderson-Hasselbalch equation:

\[ pH = pK_a + \log\left(\frac{[A^-]}{[HA]}\right) \]

- Here, `[A^-]` is the concentration of the acetate ion and `[HA]` is the concentration of acetic acid. Since both are present in equal concentrations (1 M), the pH will be around the pKa of acetic acid, which is approximately 4.76. Thus, the pH will be less than 7 but higher than that of pure acetic acid.

### Step 3: Analyze Acetic Acid Solution `(CH3COOH)`

- Acetic acid is a weak acid and does not dissociate completely in water.
- The pH of a 1 M acetic acid solution can be calculated using the dissociation constant `(K_a)`:

\[ CH_3COOH \rightleftharpoons H^+ + CH_3COO^- \]

- The pH of this solution will be less than 7, as it is an acidic solution.

### Summary of pH Sequence

1. **Sodium Acetate `(CH3COONa)`**: pH > 7 (basic solution)
2. **Acetic Acid + Sodium Acetate `(CH3COOH + CH3COONa)`**: pH < 7 but > pH of pure acetic acid (buffer solution)
3. **Acetic Acid `(CH3COOH)`**: pH < 7 (acidic solution)

### Final Sequence of pH Values

The sequence of pH values from highest to lowest is:

1. Sodium Acetate `(CH3COONa)` (pH > 7)
2. Acetic Acid + Sodium Acetate `(CH3COOH + CH3COONa)` (pH < 7 but > pH of pure acetic acid)
3. Acetic Acid `(CH3COOH)` (pH < 7)