Question

Buffer capacity is defined as the number of moles of a strong acid or strong base that is required to change the pH of 1 L of the buffer solution by one unit. What is the buffer capacity of a solution that is 0.060 M in acetic acid and 0.060 M in sodium acetate? can anyone help me with this? all the answers on here are wrong for this particular question.

Answer 1

To calculate the buffer capacity , we need to calculate how many moles of base to be used to change the pH by one unit.

We have 1L of buffer 0.060M in acetic acid and 0.060M in acetate ion.  

CH3COOH + OH- -------------------> CH3COO- + H2O

the pH of buffer is given by Hendersen equation

pH = pKa + log [acetate]/[acid]

If the pH has to be increased by 1 unit by addition of base then

log [acetate]/[acid] = 1

or [acetate]/[acid] = 10

CH3COOH + OH- -------------------> CH3COO- + H2O

0.06 0 0.06 0 initial moles

- x - - change

0.06-x 0 0.06+x 0 after reaction

thus [acetate]/[acid] = 10 = [0.06+x]/[0.06-x]

solving x = 0.049

Thus x = 0.049 is the number of moles of base to be added to 1L of buffer to change the pH by one unit.

Hence buffer capacity of the given buffer = 0.049