Question

A good buffer generally contains relatively equal concentrations of a weak acid and its conjugate base. If youwanted to buffer a solution at pH = 4.00 or pH = 10.00,how would you decide which weak acid-conjugate baseor weak base-conjugate acid pair to use? The secondcharacteristic of a good buffer is good buffering capacity.What is the capacity of a buffer? How do the followingbuffers differ in capacity? How do they differ in pH?
0.01 M acetic acid/0.01 M sodium acetate
0.1 M acetic acid/0.1 M sodium acetate
1.0 M acetic acid/1.0 M sodium acetate

Short answer

The acid component which has $K_a=1\times {10}^{-4}$should take as$p{K}_a=-log{K}_a$ for pH=4. The acid component has $K_a=1\times {10}^{-10}$or base component of$K_b=1\times {10}^{-4}$ for pH=10. The mole number of strong acid or base needs to change the pH by 1 unit called buffer capacity.

Step-by-step solution

Buffer solution and Henderson-Hasselbalch equation

A buffered solution is an aqueous mixture that contains weak conjugate bases or acids, or conversely.The pH of buffer solution can be denoted as,

$pH=p{K}_a+\log \frac{\left[base\right]}{\left[acid\right]}$

pH of buffer solution equal to pKa

The acid component which has$K_a=1\times {10}^{-4}$ should take asdata-custom-editor="chemistry" $p{K}_a=-log{K}_a$ for pH=4. The acid component hasdata-custom-editor="chemistry" $K_a=1\times {10}^{-10}$ or base component of data-custom-editor="chemistry" $K_b=1\times {10}^{-4}$for pH=10. The mole number of strong acid or base needs to change the pH by 1 unit called buffer capacity.

Highest and lowest capacity of the buffer

The buffer solution hasthe same pH when the acid concentration and conjugate base are 1:1. When there is a large concentration, there will be a high buffer capacity. The buffer which has the highest capacity is 1 M whereas the lowest capacity is 0.01 M.