Question

A 1.0 L buffer solution is 0.300 M HC2H3O2 and 0.045 M LiC2H3O2. Which of the following actions will destroy the buffer?

Answer 1

Answer:

b) Adding 0.075 moles of HCl

Explanation:

A buffer is defined as the aqueous mixture of a weak acid and its conjugate base or vice versa (Weak base with its conjugate acid).

The buffer of the problem is the acetic acid / lithium acetate.

The addition of any moles of the acid and the conjugate base will not destroy the buffer, just would change the pH of the buffer. Thus, a and c will not destroy the buffer.

The addition of an acid (HCl) or a base (NaOH), produce the following reactions:

HCl + LiC₂H₃O₂ → HC₂H₃O₂ + LiCl

The acid reacts with the conjugate base to produce the weak acid.

And:

NaOH + HC₂H₃O₂  →NaC₂H₃O₂ + H₂O

The base reacts with the weak acid to produce conjugate base.

As the buffer is 1.0L, the moles of the species of the buffer are:

HC₂H₃O₂ = 0.300 moles

LiC₂H₃O₂ = 0.045 moles

The reaction of HCl with LiC₂H₃O₂ consume all LiC₂H₃O₂ -because there are an excess of moles of HCl that react with all LiC₂H₃O₂-

As you will have just HC₂H₃O₂ after the reaction, the addition of b destroy the buffer.

In the other way, 0.0500 moles of NaOH react with the HC₂H₃O₂ but not consuming all HC₂H₃O₂, thus d doesn't destroy the buffer.