Answer:
The concentration of H₃O⁺ ions increase whereas the concentration of the OH⁻ decreases.
Explanation:
The water, H₂O, has its own equilibrium thus:
2H₂O(l) ⇄ OH⁻(aq) + H₃O⁺(aq)
Where the water equilibrium constant, Kw, is defined as:
Kw = 1x10⁻¹⁴ = [OH⁻] [H₃O⁺]
The addition of a base represents the increasing of [OH⁻]. that means the concentration of OH⁻ ions.
Based on LeCh principle, in an equilibrium, the addition of a product produce the decreasing in concentration of the other products trying to counteract the effect, that means the concentration of H₃O⁺ ions decreases.