Buffer Capacity
Introduced| English |
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| buffer capacity/ˈbʌfə kəˈpæsɪti/ |
How much can it take?
- Every protector has a limit before it gives out.
- A dilute mixture tires quickly; a concentrated one holds firm.
- Its reserves decide how much shock it can absorb.
- Beyond that limit, the pH finally lurches.
The reserve strength
- Buffer capacity 缓冲容量 is how much acid or base a buffer can absorb.
- A higher capacity resists larger additions.
- Exceed it, and the pH swings sharply.
Once a buffer's capacity is exceeded, the pH changes sharply.
The buffer fails and can no longer resist the change.
More concentrated, more capacity
- Higher concentrations of both components give a larger capacity.
- More reserve means more added acid or base can be neutralized.
- Dilute buffers run out quickly.
A more concentrated buffer has a...
More of both components means more can be absorbed.
A dilute buffer runs out of capacity more quickly than a concentrated one.
Less reserve means it is overwhelmed sooner.
Buffer capacity increases with the ____ of the buffer components.
Higher concentrations provide more reserve.
Balanced is best
- Capacity is greatest when acid and base are about equal.
- A lopsided buffer runs out on one side first.
- So near $\text{pH} = \text{p}K_a$, the capacity peaks.
Buffer capacity is greatest when the ratio of acid to base is about...
A balanced 1:1 buffer handles both directions best.
Which buffer resists more added acid: $1.0\ \text{M}$ or $0.01\ \text{M}$ (same ratio)?
- The $1.0\ \text{M}$ buffer has far more reserve.
- So it resists more added acid -- a higher capacity.
What raises buffer capacity?
Sort each buffer by whether it resists more or less added acid/base.
Two buffers have the same pH. Do they necessarily have the same capacity?
Same pH (ratio) can hide very different concentrations.
Buffer capacity is about the amount of buffer (its concentration), not just the ratio -- two buffers can share a pH but have very different capacities. It peaks at a 1:1 ratio ($\text{pH} = \text{p}K_a$). And once the capacity is exceeded, the buffer fails and the pH jumps.
Buffer capacity is how much acid or base a buffer can absorb before failing. It rises with the concentration of both components and peaks when they are balanced ($\text{pH} = \text{p}K_a$). Two buffers can share a pH yet differ greatly in capacity.