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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: DustinByfuglien on December 14, 2021, 10:16:51 PM

Title: Why do we calculate OH- concentrations for an acid dissociation?
Post by: DustinByfuglien 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!

Title: Re: Why do we calculate OH- concentrations for an acid dissociation?
Post by: Borek 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.