Concept:A classical chemical buffer solution must consist of a weak acid and its conjugate base (supplied via a highly soluble salt), or a weak base and its conjugate acid.
Formula:$$ \text{Weak Acid (HA)} + \text{Salt of Conjugate Base (A}^- \text{)} $$
Solution:- Acetic acid (\( \text{CH}_3\text{COOH} \)) is a classic weak acid.
- Sodium acetate (\( \text{CH}_3\text{COONa} \)) is a highly soluble salt that fully dissociates to provide the acetate ion (\( \text{CH}_3\text{COO}^- \)), which is the direct conjugate base of acetic acid.
- Mixing these two creates a solution containing both an acid to neutralize added \( \text{OH}^- \) and a base to neutralize added \( \text{H}^+ \). This is the definition of an acidic buffer.
Why other options are incorrect:Acetic acid and ammonia are an acid and a base that will just neutralize each other. Ammonium acetate does not provide the proper counter-ion metal (like Na or K) to act solely as a robust conjugate base salt for acetic acid in a simple binary buffer.
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