Question

Suppose that you have 135 mL of a buffer that is 0.300 M in both formic acid (HCOOH) and its conjugate base (HCOO-). Calculate the maximum volume of 0.290 M HCl that can be added to the buffer before its buffering capacity is lost.

Answer 1

HCOOH (aq) <=======> HCOO-(aq) + H⁺

The maximum amount of strong acid that can be added before losing its buffer capacity is equal to the total amount of conjugate base present in the buffer.

Step-1 Calculate the moles of conjugate base (HCOO-)

Moles of conjugate base = Volume of conjugate base in L x Molarity of conjugate base

= 0. 135*0.300 M

= 0.0405 moles

Step-2 Calculate the volume of HCl

Moles of acid that can be added will be equal to the moles of conjugate base, so moles of HCl = 0.0405 mol.

Molarity of HCl solution that is being added = 0.290 M

The maximum volume of 0.290M HCl that can be added = moles of HCl/ Molarity of HCl solution

= 0.0405Moles/0.290 M

= 0.1397L

= 139.7 ml

The maximum volume of 0.290 M HCl that can be added to the buffer before its buffering capacity is lost is = 139.7 ml