Few drops of HCI is addded to acetic acid buffer. The `p^(H)` is maintained constant by

Options

A. `CH_(3)COOH`
B. `CH_(3)COO^(-)`
C. `Na^(+) `
D. `CH_(3)COONa`

Answer

To solve the question regarding how the pH is maintained constant when a few drops of HCl are added to an acetic acid buffer, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Buffer System**:
- An acetic acid buffer consists of acetic acid (CH₃COOH) and its conjugate base, sodium acetate (CH₃COO⁻Na⁺). This buffer system helps maintain a relatively constant pH when small amounts of acids or bases are added.

2. **Addition of HCl**:
- When a few drops of hydrochloric acid (HCl) are added to the acetic acid buffer, it dissociates in solution to produce hydronium ions (H₃O⁺) and chloride ions (Cl⁻):
\[ \text{HCl} \rightarrow \text{H}^+ + \text{Cl}^- \]
- The hydronium ions (H₃O⁺) are the species that can affect the pH of the solution.

3. **Reaction with Acetate Ions**:
- The acetate ions (CH₃COO⁻) present in the buffer will react with the added hydronium ions (H₃O⁺) to form acetic acid (CH₃COOH):
\[ \text{H}_3\text{O}^+ + \text{CH}_3\text{COO}^- \rightarrow \text{CH}_3\text{COOH} + \text{H}_2\text{O} \]
- This reaction effectively neutralizes the added H₃O⁺ ions, minimizing the change in pH.

4. **Maintaining pH**:
- Because the acetate ions can react with the added hydronium ions to form more acetic acid, the concentration of free H₃O⁺ ions does not increase significantly. Therefore, the pH remains relatively constant despite the addition of HCl.

5. **Conclusion**:
- The pH is maintained constant by the presence of acetic acid (CH₃COOH) and acetate ions (CH₃COO⁻). The buffer system's ability to react with added acids (like HCl) is what allows it to resist changes in pH.

### Final Answer:
The pH is maintained constant by **CH₃COOH (acetic acid)**.

---