Homework Help: Chemistry -- Please Help!!

Posted by Erin on Monday, April 26, 2010 at 7:06pm.

Find the pH of a mixture of .150 M HF(aq) solution and 0.100 M HClO2(aq)

HF + H2O <--> F- + H3O+
Ka= 3.5*10^-4

So I will show my attempt below...

[HF] [F-] [H3O+]
I .150 0 0
C -x +x +x
E .15-x x x

Ka= [F-][H3O+]/[HF]
3.5*10^-4= x^2/(.150-x)
assume x is small so (.150-x) = .150
7.25*10^-3 = x^2 Take square root of both sides
x= 7.25*10^-3

[H3O+] = 7.25*10^-3
pH=-log[H3O+]=2.14

Is this right?? If it is, why don't we do any work with the .100M HClO2 soution?

Thanks!

Chemistry -- Please Help!! - DrBob222, Monday, April 26, 2010 at 7:17pm
Technically, there is no way to get a firm solution to the problem because the problem doesn't specify the mixture's composition. Your calculation is correct, as far as it goes, and your observation is correct also. According to my tables, HClO2 is a stronger acid than HF and the H^+ content will be dictated more by the HClO2 than by the HF.

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