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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: OasisJuice on October 18, 2009, 05:33:43 PM

Title: Need help with Chemistry Titration Problem :(
Post by: OasisJuice on October 18, 2009, 05:33:43 PM

A 10.00 mL solution of 0.2500 M CH3COONa is titrated with 0.1300 M HCl to the equivalence point.
CH3COO− + H+ → CH3COOH

volume of HCl required=19.23 mL

Calculate the pH of the solution at the equivalence point.

Now what I did was first
total volume added = 10mL+19.23mL = 29.23mL
Moles of CH3COO- reacted = Moles of CH3COOH made = 0.25M*0.01L = 0.0025mol
Molarity = 0.0025mol/(0.02923L) = 0.08553 M

x^2 / 0.0855 = Ka of CH3COOH

x^2/0.0855 = 1.8197E-5
x=1.555E-6

-log=pOH = 5.81
14-5.81 = 8.19

Which is wrong.  Please help, because I've tried this question over 16 times,:((((

Title: Re: Need help with Chemistry Titration Problem :(
Post by: Borek on October 18, 2009, 07:10:32 PM

CH₃COOH dissociation is not producing OH^-...

And x is not 1.555E-6.

Title: Re: Need help with Chemistry Titration Problem :(
Post by: OasisJuice on October 18, 2009, 09:58:14 PM

Quote from: Borek on October 18, 2009, 07:10:32 PM

CH₃COOH dissociation is not producing OH^-...

And x is not 1.555E-6.

Oh....Well Im not sure what it's producing then...H+ ions?  So then by just solving for x (My calculation's wrong?) and doing the log of that, I would get the answer?

Title: Re: Need help with Chemistry Titration Problem :(
Post by: Borek on October 19, 2009, 03:13:45 AM

Quote from: OasisJuice on October 18, 2009, 09:58:14 PM

Well Im not sure what it's producing then...H+ ions?

Hardly surprising, acetic acid dissociates giving H⁺.

Quote

So then by just solving for x (My calculation's wrong?) and doing the log of that, I would get the answer?

Yes, you just did some mistake in your math.