Taking Autoprotolysis into Account

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Sarah H Brown 1L
Posts: 56
Joined: Fri Sep 26, 2014 2:02 pm

Taking Autoprotolysis into Account

Postby Sarah H Brown 1L » Tue Dec 09, 2014 10:56 pm

Under what conditions do you take the autoprotolysis of water into account?

Shreyesi Srivastava 2D
Posts: 11
Joined: Fri Sep 26, 2014 2:02 pm

Re: Taking Autoprotolysis into Account

Postby Shreyesi Srivastava 2D » Tue Dec 09, 2014 11:26 pm

Autoprotolysis is taken into account in two different ways for strong acids and weak acids.

For strong acids and strong bases, you only have to take autoprotolysis in to account when the concentration of the strong acid or base is less than 10^-6 mol/L.

The process is similar for weak acids. You have to use your two known equations: Kw=[H3O+][OH-] and Ka= [H3O+][A-]/[HA].

Some weak acids go through very like deprotonation that you must take autoprotolysis into account when finding pH.

A full detailed example of how to derive Ka using this method is in our book on pg. 466.

Hope that helps!

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