16.3 Buffer Effectiveness: Buffer Range and Buffer Capacity

- What factors influence the effectiveness of a buffer? The relative amounts of the acid and conjugate base and the absolute concentrations of the acid and conjugate base.
Capacity of a Buffer: How much added acid or base it can effectively neutralize
Range of a buffer: the ph range over which a particular acid and its conjugate base can be effective.
- a buffer is most effective when the concentrations of acid and conjugate base are equal. a buffer becomes less effective as the difference in the relative amounts of acid and conjugate base increases. we can say that an effective buffer must have a base/acid ratio in the range of 0.10 to 10. in order for a buffer to be reasonably effective, the relative concentrations of acid and conjugate base should not differ by more than a factor of 10.
- a buffer is most effective when the concentrations of acid and conjugate base are high. The more dilute the buffer components, the less effective the buffer
- we can calculate the ph range over which a particular acid and its conjugate base can be used to make an effective buffer.
- Lowest oh for effective buffer occurs when the base is one tenth as concentrated as the acid (ph=pka-1)
- highest ph for the effective buffer occurs when the base is 10 times as concentrated as the acid (ph=pka+1)
- for example, the buffering system with a weak acid pka of 5.0 can be used to prepare a buffer in the range of 4.0-6.0
Buffer Capacity: is the amount of acid or base that you can add to a buffer without causing a large change in ph. Buffer capacity increases with increasing absolute concentrations of the buffer components. The more concentrated the weak acid and conjugate base that compose the buffer, the higher the buffer capacity. Overall, buffer capacity increases as the relative concentrations of the buffer components become more similar to each other. As the ratio of the buffer components gets closer to 1, the overall capacity of the buffer becomes greater.

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Topics involving aqueous solutions: buffers and solubility equilibria