Question

Choose the best answer below. If an equal number of moles of lactic acid, HC3H5O3, and potassium hydroxide, KOH, are added to water, is the resulting solution acidic, basic, or neutral? The Ka of lactic acid is 1.4 x10-5.

Answer 1

Solution is basic.

Step-by-step explanation:

When you add the same moles to a weak acid and strong base, you produce a neutralization reaction and a salt. For this case:

CH₃CHOHCOOH + KOH → KCH₃CHOHCOO + H₂O

If we work in a titration, this is the equivalence point where:

moles of base = moles of acid

For this reaction we are only having lactates ions on solution. All the moles from the lactic acid and the hydroxide will be neutralized to make water. As both numbers are the same, the number is the moles of the formed lactate.

If we think the equilibrium equation for lactate, we have:

CH₃CHOHCOO⁻ + H₂O ⇄ CH₃CHOHCOOH + OH⁻

In conclussion, the solution is basic, because we give OH⁻ to medium.

Notice, that in a titratrion of a weak acid and a strong base, the pH at the equivalence point is always basic.