Question

A popular buffer solution consist of carbonate (CO3 2-) and hydrogen carbonate (HCO3-) conjugate acid-base pair. Which, if any of the following such buffers has the highest buffer capacity?

A. 0.9M CO3 2- and 0.1M HCO3-
B. 0.1M CO3 2- and 0.9M HCO3-
C. 0.5M CO3 2- and 0.5M HCO3-
D. 0.1M CO3 2- and 0.1M HCO3-
E. They all have the same buffer capacity.

HOW DO I FIGURE THIS....

Answer 1

Do you know what buffer capacity is? It's defined as the mols of strong acid or strong base that can be added to 1 L of a buffer solution and without changing the pH more than +/- 1.
The buffer capacity depends mostly upon two things.
1. The concn of base and acid components.
2. on the RATIO of the base/acid pair.
The maximum buffering capacity is delivered when the RATIO is 1.0. So you want C or D; those are the only ones with ratio of 1.0. Of the two which do you think would provide more capacity? The higher concn, of course.