In the buffer solution
A)
CH3CO2H is a base, and H3O+ is its conjugate acid.
B)
H3O+ is an acid, and CH3CO2 – is its conjugate base.
C)
H3O+ is an acid, and CH3CO2H is its conjugate base.
D)
CH3CO2H is an acid, and CH3CO2 – is its conjugate base.
The Correct Answer and Explanation is :
The correct answer is:
D) CH3CO2H is an acid, and CH3CO2– is its conjugate base.
Explanation:
A buffer solution contains a weak acid and its conjugate base, or a weak base and its conjugate acid. The main function of a buffer is to resist changes in pH when small amounts of acid or base are added.
In this case, CH3CO2H (acetic acid) is a weak acid, and CH3CO2– (acetate ion) is its conjugate base. Here’s how this works:
- Acetic Acid (CH3CO2H):
- Acetic acid is a weak acid, meaning it only partially dissociates in water:
[
\text{CH3CO2H} \rightleftharpoons \text{CH3CO2}^- + \text{H}^+
] - When acetic acid donates a proton (H⁺), it forms the acetate ion (CH3CO2–). Therefore, acetic acid acts as the acid in this system.
- Acetate Ion (CH3CO2–):
- The acetate ion (CH3CO2–) is the conjugate base of acetic acid. This means it can accept a proton (H⁺) to reform acetic acid:
[
\text{CH3CO2}^- + \text{H}^+ \rightleftharpoons \text{CH3CO2H}
] - In the context of a buffer, the acetate ion helps neutralize added acids (H⁺), preventing a significant decrease in pH.
In a buffer solution of acetic acid and acetate, the equilibrium between acetic acid and acetate maintains a relatively constant pH. If a small amount of acid (H⁺) is added, the acetate ion will absorb it, shifting the equilibrium to produce more acetic acid and minimizing the pH change. Similarly, if a small amount of base (OH⁻) is added, acetic acid will donate a proton to neutralize it, again maintaining the pH.
Thus, acetic acid (CH3CO2H) is the acid, and acetate (CH3CO2–) is its conjugate base in this buffer system.