[polly]

hi

trying to get my head around what they mean by the exact proton balance condition and I have searched the internet and the recommended textbook (Physical Chemistry-Atkins....not good for my problems)

Does anybody have an ENGLISH way of explaining what it actually is? All i have to go on is a bunch of equations that mean very little.

This is what I have as an example of one equation:

[H3O⁺]=C_A/2+SQRT(C_A²/4+K_W)

I know I can use it to calculate pH of an acid (because I am solving for the [hydronium ion])
But what is the point of this condition

Anything as a means of an answer is welcome
cheers

[Borek]

I suppose that you are referring to the way exact pH calculations should be performed, ie without ignoring H⁺ from water autodissociation.

Please read these pages:

http://www.chembuddy.com/?left=pH-calculation&right=general-pH-calculation

http://www.chembuddy.com/?left=pH-calculation&right=pH-acid-base-solution

http://www.chembuddy.com/?left=pH-calculation&right=pH-strong-acid-base

Now, take a look at the equation 7.4 on the last page listed. If you solve it using quadratic formula and discriminant you will get your equation (hopefully in correct form).

You will find it also here:

http://www.chembuddy.com/?left=BATE&right=pH-cheat-sheet

as a ready to use formula (point 9 in the monoprotic acid part of the first cheat sheet).

[polly]

 

Thanks mate...i think i should forward this to my teacher so that the undergrads next years dont face the same problem.