Acetic acid has a pKa of 4.74. Buffer A: 0.10 M HC2H3O2, 0.10 M NaC2H3O2 Buffer B: 0.30 M HC2H3O2, 0.30 M NaC2H3O2 Buffer C: 0.50 M HC2H3O2, 0.10 M NaC2H3O2 Which of the above buffers has the highest buffer capacity? [ Select ] Which of the above buffers has the lowest buffer capacity? [ Select ]

Buffer B has the highest buffer capacity.

Buffer C has the lowest buffer capacity.

Explanation:

An effective weak acid-conjugate base buffer should have pH equal to of the weak acid. For buffers with the same pH, higher the concentrations of the components in a buffer, higher will the buffer capacity.

Acetic acid is a weak acid and is the conjugate base So, all the given buffers are weak acid-conjugate base buffers. The pH of these buffers are expressed as (Henderson-Hasselbalch):

Buffer A:    

Buffer B:  

Buffer C:  

So, both buffer A and buffer B has same pH value which is also equal to . Buffer B has higher concentrations of the components as compared to buffer A, Hence, buffer B has the highest buffer capacity.

The pH of buffer C is far away from . Therefore, buffer C has the lowest buffer capacity.

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explanation: