Question

A solution containing HCl and the weak acid HClO2 has a pH of 2.4. Enough KOH (aq) is added to the solution to increase the pH to 10.5. The amount of which of the following species increases as the KOH (aq) is added? A)Cl- (aq) B)H+ (aq) C)ClO2- (aq) d)HClO2 (aq)

Answer 1

Answer:

$\boxed{\rm \text{[ClO _{2}^{-} ] increases}}$

Explanation:

At the beginning, you have two reactions happening:

$\rm HCl + H _{2} O \, \longrightarrow \, H _{3} O ^{+} + Cl ^{-} \\\rm HClO _{2} + H _{2} O \, \rightleftharpoons \, H _{3} O ^{+} + ClO _{2}^{-}$

As you add KOH(aq), it does two things:

1. It increases the volume of the solution.
2. It reacts with the hydronium ions to form water.

A) The HCl is completely ionized. The Cl⁻ does not react, but it is diluted when the volume of the solution increases. [Cl⁻] decreases.

B) The KOH reacts with the H⁺ and removes it from the solution. [H⁺] decreases.

C) When all the H⁺ from the HCl has been neutralized, the KOH starts neutralizing the H⁺ from the HClO₂. According to Le Châtelier's Principle, more HClO₂ will dissociate to replace the decreased H⁺. [HClO₂] decreases.

D) As HClO₂ reacts, it forms ClO₂⁻. $\boxed{\rm \textbf{[ClO _{2}^{-} ] increases}}$