## autoprotolysis

Jasleen Kahlon
Posts: 52
Joined: Wed Nov 21, 2018 12:19 am

### autoprotolysis

I understand that autoprotolysis is the transfer of an H+ from an acid to a base in an equation (I think), I'm unclear on how pKW = pH + pOH is derived from it though.

Nicholas Chin 1G
Posts: 100
Joined: Thu Jul 11, 2019 12:17 am

### Re: autoprotolysis

Autoprotolysis is not just the transfer of a H+ ion between an acid and a base, it's the transfer of an H+ between two identical molecules, one that can act as an acid and a base (like H2O). If you then take the equilibrium constant of the equation 2 H2O -> OH- + H30+, you'll get Kw = [OH-][H30+].

christabellej 1F
Posts: 109
Joined: Sat Aug 17, 2019 12:17 am

### Re: autoprotolysis

Autoprotolysis is the reaction of 2 H2O --> OH - + H3O+. Like any reaction, you can write the K expression (products over reactants), and get Kw = [OH-][H3O+], since H2O is a liquid and so isn't counted in the K expression. Now , you can use the properties of logs, and do logKw = log[OH-] + log[H3O+]. If you make the entire equation negative, you get -logKw=-log[OH-] - log[H3O+]. This will get you pKw = pOH + pH.

Posts: 106
Joined: Sat Aug 24, 2019 12:17 am
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### Re: autoprotolysis

Autoprotolysis is when H+ ions are transferred from 2 molecules of the same species. When you write out the chemical equation for this transfer, you can write a K equation for it.

Posts: 106
Joined: Sat Aug 24, 2019 12:17 am
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### Re: autoprotolysis

Autoprotolysis is when H+ ions are transferred from 2 molecules of the same species. When you write out the chemical equation for this transfer, you can write a K equation for it.

Sara Richmond 2K
Posts: 110
Joined: Fri Aug 30, 2019 12:16 am

### Re: autoprotolysis

Autoprotolysis is the transfer of H+ ions within two identical molecules such as two H2O molecules. In this reaction two H2O molecules react to form one molecule of H30 and one molecule of OH

Sara Richmond 2K
Posts: 110
Joined: Fri Aug 30, 2019 12:16 am

### Re: autoprotolysis

Jasleen Kahlon wrote:I understand that autoprotolysis is the transfer of an H+ from an acid to a base in an equation (I think), I'm unclear on how pKW = pH + pOH is derived from it though.

The PkW=Pka+Pkb equation is derived from autoprotolysis because autoprotolysis is the simplest example of acid and conjugate base pairs.

Orrin Zhong 4G
Posts: 51
Joined: Sat Jul 20, 2019 12:16 am

### Re: autoprotolysis

From Kw = [H+][OH-], you can negative log both sides => -log[Kw] = -log([H+][OH-]), and using the log rules, you can get =log[Kw] = -log[H+] + -log[OH-]. Since "p-" in chemistry denotes "-log" (as in pH = -log[H+]), you can get the equation pKw = pH + pOH.