Question

question 36 (1 point)
if additional acid is added to an acid-base system at equilibrium, which occurs?
○ concentration of hydronium ions increase and concentration of hydroxide ions decrease
○ concentration of hydronium ions decrease and concentration of hydroxide ions increase
○ concentration of both hydronium and hydroxide ions increase
○ concentration of both hydronium and hydroxide ions decrease
○ concentration of hydronium ions increase and concentration of hydroxide ions remain the same

Explanation:

1. Recall the autoionization of water: $\ce{H2O <=> H+ + OH-}$ (or $\ce{H3O+ + OH-}$), and the ion - product constant $K_w = [\ce{H3O+}][\ce{OH-}]$, which is a constant at a given temperature.
2. When additional acid is added to an acid - base system at equilibrium, the acid donates $\ce{H+}$ (or $\ce{H3O+}$) ions. So the concentration of hydronium ions ($[\ce{H3O+}]$) increases.
3. Since $K_w = [\ce{H3O+}][\ce{OH-}]$ and $K_w$ is constant, if $[\ce{H3O+}]$ increases, then $[\ce{OH-}]$ must decrease to maintain the constant value of $K_w$.

Answer:

A. concentration of hydronium ions increase and concentration of hydroxide ions decrease