Which mixture constitutes an effective acidic buffer solution capable of maintaining a stable pH when small amounts of acid or base are added?
Answer and explanation
Correct answer: B. Equimolar mixture of acetic acid (CH3COOH) and sodium acetate (CH3COONa)
- Step 1: An acidic buffer solution consists of a weak acid and its conjugate base (salt with a strong base).
- Step 2: In a mixture of acetic acid (, weak acid) and sodium acetate (, conjugate salt), added ions are neutralized by acetate ions (), and added ions are neutralized by undissociated acetic acid ().
- Step 3: Strong acid-salt mixtures (, ) and strong base mixtures () cannot function as buffers because strong acids/bases are fully dissociated and lack a reserve reservoir to neutralize added ions without shifting pH.
Answer
Equimolar mixture of acetic acid (CH3COOH) and sodium acetate (CH3COONa)
Why not the others: 'HCl and NaCl' is a strong acid mixture with zero buffering capacity; 'NaOH and NaCl' is a strong base mixture; 'HNO3 and NH4NO3' contains a strong acid that dominates pH without buffering against added acid.
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