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Topic: Why do we calculate OH- concentrations for an acid dissociation?  (Read 732 times)

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Offline DustinByfuglien

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Why do we calculate OH- concentrations for an acid dissociation?
« on: December 14, 2021, 10:16:51 PM »
I've been stumped on this one for a while now and I can't seem to find an answer anywhere. That leads me to believe that I'm totally missing something.

I need to know why/how we can calculate OH- concentration for a reaction that does not include OH-.

For example if 0.077M of HCl dissociates in water.

HCl ---> H+ + Cl-

I know that since this is a strong acid, the concentration of the H+ will equal the concentration of the acid. My question is how can we use the Kw equation (Kw = [H+][OH-]) to find OH- when it is not present in the reaction equation.

Thanks in advance!

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Re: Why do we calculate OH- concentrations for an acid dissociation?
« Reply #1 on: December 15, 2021, 02:52:20 AM »
In water there is always a reaction

H2O :lequil: H+ + OH-

taking place. So even if the acid dissociation reaction doesn't change concentration of OH- directly, it does that through a reaction that occurs next.
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