Where do the OH ions go as additional acid is added?

Answer 1

Firstly, let's correct the question: If there's a concentration of OH- ions present, then your solution is a base, so in fact you would simply be adding acid, not additional acid, which implies that your solution is already acidic.

As you add acid to a base, the OH- ions in the base and the H+ ions from the acid combine to form H2O, also known as water.

If you add so much acid that there is the same concentration of H+ as OH- ions, then your solution is now Ph neutral. In other words, it's neither an acid nor a base.

IMPORTANT: Ph neutral DOES NOT MEAN that there are no OH- or H+ ions present at all in the solution because they've all "paired off" - both ions are always present in the solution, constantly pairing and splitting. It's just that the concentration of both is now equal, so in effect they "cancel each other out".

If you continue to add acid, the H+ concentration increases beyond the OH- concentration, and the solution starts becoming acidic (this is also the point at which you would be correct in saying that you're adding additional acid)