Calculating pH

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Marc Farah 3D
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Calculating pH

Postby Marc Farah 3D » Wed Nov 30, 2016 1:36 pm

In the course reader it says if H30+ is less than 10^-7, then the solution is considered neutral becausee we know that as a result of autoprotolysis there are 10^-7 mol L^-1 H30+. What exactly does this mean?

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Re: Calculating pH

Postby Tyler_Ash_3C » Wed Nov 30, 2016 4:30 pm

If the concentration of H3O+ is 10^-7, then pH= -log(10^-7). Using the log rule dealing with exponents, pH= 7 log(10), and pH=7, which proves that the solution would be neutral. Autoprotolysis refers to the transfer of a proton between two identical molecules. In this case two molecules of H2O yield H3O+ and OH- because a proton is transferred from one water molecule to another. Autoprotolysis can be explained in more detail using the ionization constant of water (Kw):

[H3O+][OH-] = 1.0x10^-14
[H3O+] = [OH-]
[H3O+]^2 = 1.0x10^-14
[H3O+]= 10^-7

So: pH= -log(10^-7)
as explained above, pH=7, so the solution is neutral

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