[lucasloredo]

The problem reads as follows:

Calculate the pH of each of the following solutions.
a.) 0.100 M propanoic acid (HC₃H₅O₂, K_a = 1.3 X 10^-5)
b.) 0.100 M sodium propanoate (NaC₃H₅O₂)
c.) Pure H₂O
d.) A mixture containing 0.100 M HC₃H₅O₂ and 0.100 M NaC₃H₅O₂

I've gotten a & b already (the first was easy, just plug and chug basically, then part b was slightly more difficult, having to find the K_b of the reaction then going through the regular motions). However, I can't figure out how to get part C. I have the values here if anyone wants to use them:

For part a.) [H⁺] = 1.13X10^-3 and the pH = 2.95
For part b.) [OH^-] = 8.77X10^-6 and the pH = 8.94

The only thing I could think of for part C was to take the two equations:

HC₃H₅O₂ <-----------> H⁺ + C₃H₅O₂^-
C₃H₅O₂^- <-----------> HC₃H₅O₂ + OH^-

Then cancel out the like terms on each side to give you
H₂O <---------> H⁺ + OH^-

But I'm stuck from there 

Any help would be appreciated!

Thanks,
Lucas

[Borek]

You really don't know what is pH of pure water? That's one of the most basic things about pH scale. You have confused yourself as hell

[lucasloredo]

Haha yes of course i know the pH is going to be 7.00, however we must prove so. That's why I'm stuck! 

[Borek]

Square root of Kw.

[lucasloredo]

Right . . . but don't you think part C. would have to do with the rest of the problem? Like I have to use some of that data to somehow prove the pH of water is 7? Maybe I'll just leave it blank until we talk about it in school ...

[enahs]

http://www.science.uwaterloo.ca/~cchieh/cact/applychem/waterchem.html
Look at the autoionization of water section. And just search google with that term for more examples.

[english]

You really don't know what is pH of pure water? That's one of the most basic things about pH scale. You have confused yourself as hell

LOL

[jennielynn_1980]

Here is some info I used to get me started on a simliar question
One molecule in one million will ionize in water at 25 C and
[H+] = [OH-]
and in water [H+] = 1.00 x 10^-7

Hope that helps