Suppose that you have 135 mL of a buffer that is 0.360 M in both propanoic acid ( C 2 H 5 COOH ) and its conjugate base ( C 2 H 5 COO − ) . Calculate the maximum volume of 0.240 M HCl that can be added to the buffer before its buffering capacity is lost.

202.50 ml is the maximum volume of 0.240 M HCl that can be added to the buffer before its buffering capacity is lost.

Explanation:

Data given:

volume of buffer = 135 ml or 0.135 litres

molarity of the buffer = 0.360  M

volume of the acid = ?

molarity of the acid = 0.24 M

the number of moles of conjugate base is

M X V = number of moles

0.360 X 0.135

0.0486 moles of conjugate base

The maximum amount of acid added will equal the amount of conjugate base from the buffer.

So, the volume of acid will be calculated by using the formula:

Molarity =

 volume =

              = 0.2025 l

202.50 ml is the volume of acid added.