February 02, 2023, 10:21:11 AM
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Topic: ICE charts, what do I do when the equilibrium for the acid is negative?  (Read 947 times)

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Offline _Alexis_

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Hello, this is for Biochemistry, but the math is basically high school Chemistry. Unfortunately, I've forgotten a lot of the logic when it comes to ICE problems. I'm trying to find the PH of a buffer after some strong base has been added to acetic acid. What do I do if more mols of the strong base are more than acetic acid? I wrote the formula (PH= pka + log(B/A)) afterward, but a negative value cannot be logged.

Here is what the ICE chart looks like:
      CH3COOH + KOH <-> CH3COO- + H2O
I         0.005      0.00525       0              -
C     -0.00525    -0.00525    +0.00525    -
E       -0.00025     0              0.00525

As you can see, I have a negative value for CH3COOH. That negative value cannot be put into log, so what do I do?

Offline mjc123

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Re: ICE charts, what do I do when the equilibrium for the acid is negative?
« Reply #1 on: September 03, 2022, 07:14:56 PM »
Have you heard of the concept of the limiting reagent? What happens when all the acetic acid has reacted?

Offline _Alexis_

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Re: ICE charts, what do I do when the equilibrium for the acid is negative?
« Reply #2 on: September 03, 2022, 07:46:31 PM »
Yes. Does this mean I solve and add together the PH together of (0.005 mols) CH3COO- and KOH (0.00025mols)


Offline mjc123

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Re: ICE charts, what do I do when the equilibrium for the acid is negative?
« Reply #3 on: September 03, 2022, 07:56:08 PM »
No. [OH-] will give you [H+] directly.
PS You do not have a buffer here!

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