Homework Help: Chemistry

Posted by anonymous on Monday, April 20, 2009 at 11:42pm.

Known:
Cyanaocetic acid
Ka=3.55*10^-3
ionization equation: HC3H2NO2<==> H^+ + C3H2NO2^-
Unknown: pH of 0.4M of Cyanaocetic acid

I can't figure out how to calculate this. I only knew how to calculate the pH value of an acid with a known Ka, but not in this case.

Also, I want to know the second ionization equation of succinic acid because I need to find the Ka expression of this.
Can someone please help me out. Thanks in advance for helping out.

Chemistry - DrBob222, Monday, April 20, 2009 at 11:50pm
If you know how to calculate the pH of solution of a known Ka, then why not this one. It's the same thing. For simplicity, let's call this long molecule just HC.
HC ==> H^+ + C^-
Now (H^+)(C^-)/(HC) = Ka.
Do an ICE chart, calculate (H^+) and pH from there.

Succinic acid.
http://en.wikipedia.org/wiki/Succinic_acid

If we call succinic acid H2Su, then
H2Su ==> H^+ + HSu^- and
k1 = ......
Then
HSu^- ==> H^+ + Su^=
an k2 = ,......
I assume you can take it from there.
Chemistry - anonymous, Monday, April 20, 2009 at 11:56pm
What's an ice chart? I don't think I had learned about that..
Chemistry - DrBob222, Tuesday, April 21, 2009 at 12:00am
Show me how you do the pH of an acid with a Ka.
Chemistry - anonymous, Tuesday, April 21, 2009 at 12:13am
For example,
Given:
1.000M of Cyanoacetic acid
pH value of 2
HC3H2NO2<==> H^+ + C3H2NO2^-
Unknown: Ka
pH=-LOG[H^+]
[H^+]=10^(-2)
[H^+}=0.01
Ka=(0.01)(0.01)/(1-0.01)
=1.01*10^-4?
Is it right?
Actually I don't know why [H^+] and [C3H2NO2^-] have the same value, also why [HC3H2NO2] equals initial concentration minus [H^+]?
Thanks alot
Chemistry - anonymous, Tuesday, April 21, 2009 at 12:18am
I think I said something wrong.. I mean I know how to calculate the Ka with a known pH value...sorry..

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