Complete the description of how a buffer behaves.
A buffer contains a weak acid together with its ______, and its pH equals the ______ when the two are present in equal amounts. Diluting the buffer leaves the pH almost ______ but reduces its ______.
Word bank: conjugate base · pKa · unchanged · capacity · concentration
Hints
- The Henderson-Hasselbalch equation contains a RATIO, not two separate concentrations.
- Diluting changes both concentrations equally, so the ratio survives.
Show the answer
A buffer contains a weak acid together with its conjugate base, and its pH equals the pKa when the two are present in equal amounts. Diluting the buffer leaves the pH almost unchanged but reduces its capacity.
Only the ratio of base to acid enters the equation, so dilution leaves the pH nearly untouched. What dilution does destroy is capacity, there is simply less material available to absorb added acid or base.
Practise Buffers, Hydrolysis and Titration
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