Question

A formic acid buffer system contains 0.250 moles of formic acid and 0.250 moles of sodium formate. Which of the following additions to the system would exhaust the buffer and cause it to go over the buffer capacity? 0.325 moles of NaOH; 0.175 moles of HCl; 0.160 moles of KOH; 0.250 moles of NaOH and 0.250 moles of HCl

Answer 1

Buffer capacity :

Buffer capacity is the ability of a buffer to resist a change in pH when adding a strong acid or a strong base.

Now Buffers that are equimolar in weak acid and weak base require a greater amount of strong acid or strong base to bring about a one unit change in pH.

So as given

0.25 moles of formic acid and sodium formate

Equimolar buffer

Now to exhaust the buffer and cause it to go over the buffer capacity which of the following is added

Among all the given options except 0.325 moles of NaOH, 0.250 moles of NaOH and 0.250 moles of HCl all others have less no of moles so they will not be considered for addition

Among 0.325 moles NaOH, 0.25 moles NaOH and 0.25 moles HCl

0.325 moles NaOH is more than the given number of moles while others are equal to the given no of moles. So as 0.325 moles of NaOH is more it can be added to the buffer system

Answer is 0.325 moles NaOH