Question

A solution is prepared by dissolving 0.23 mol of chloroacetic acid and 0.27 mol of sodium chloroacetate in water sufficient to yield 1.00 L of solution. The addition of 0.05 mol of HCl to this buffer solution causes the pH to drop slightly. The pH does not decrease drastically because the HCl reacts with the _______ present in the buffer solution. The
`K_a` of chloroacetic acid is 1.36 x 10⁻³.

a. H₂O

b. Na⁺

c. chloroacetate ion

d. chloroacetic acid

e. This is a buffer solution: the pH does not change upon addition of acid or base.

Answer 1

c. chloroacetate ion

Step-by-step explanation:

The chloroacetic acid, ClCH₂CO₂H, is a weak acid with Ka = 1.36x10⁻³. When this weak acid is in solution with its conjugate base, ClCH₂CO₂⁻ (From sodium chloroacetate) a buffer is produced. The addition of a strong acid as the HCl produce the following reaction

HCl + ClCH₂CO₂⁻ → ClCH₂CO₂H + Cl⁻.

Where the acid reacts with the chloroacetate ion to produce more chloroacetic acid

That means, the HCl reacts with the chloroacetate ion present in the buffer solution

Right answer is:

c. chloroacetate ion