Weak Acid and Strong Acid solution mixed with strong base?

NetherCraft 0

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)

I know that the answer is ClO2-, but I don’t know why. Would someone please explain this to me? Thank you!

I’ve managed to come down to either Cl- or ClO2- but I don’t know why ClO2- is correct.

I understand that:

HClO2 + KOH -> H2O +KClO2

HClO2 + KOH -> H2O +KCl

2 Answers

  • This should also answer the comment on the previous answer.

    The major difference between HClO2 and HCl is that HCl is a strong acid. Strong acids completely dissociate (divide into H+ and Cl-) when added to water. Thus, there is no actual HCl in the solution – only H+ and Cl- ions. On the other hand, HClO2 does not completely dissociate so some of it is ClO2- and some is H+ while some remains HClO2, the intact acid. KOH is a strong base, so it also completely dissociates but into K+ and OH-. The addition of OH- drives to reaction of HClO2 by being strong enough to take its H+ to create water with OH-.

    HCl has already completely divided, so no among of OH- taking H+ can make more Cl- as it is already separated. OH- does take H+ off of HClO2, creating more ClO2 of the remaining intact acid.

  • HClO2 + KOH => H2O + K^+ + ClO2^-

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