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Topic: Calculating pH of buffer solution  (Read 5901 times)

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kad3285

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Calculating pH of buffer solution
« on: July 07, 2005, 10:25:08 AM »
I need some help calulating the pH of a 100mL solution, at .025M (w/ pkb=4.76) and .075 M ammonium acetate with 1mL of .1 F HCl is added...

I am a little confused with calculating the pH after the addition of another solution.  

Can someone point me in the right direction?

« Last Edit: July 07, 2005, 10:37:02 AM by kad3285 »

Offline lemonoman

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Re:Calculating pH of buffer solution
« Reply #1 on: July 07, 2005, 10:36:42 AM »
Think of it as a titration of base with acid.  Then, at the end, there will be either an excess of base (CH3COO-), excess of acid (H+), or an excess of neither (perfect equivalence point).

Then you can figure things out from there, whether you want to treat the solution as basic or acidic.

Good luck!

P.S. Try searching the forum for similar questions - Buffers are a popular topic in Highschool, and it's almost certain to have been covered before.  To start off, try

http://www.chemicalforums.com/index.php?board=6;action=display;threadid=3626

and then do a search here

http://www.chemicalforums.com/index.php?action=search
« Last Edit: July 07, 2005, 10:39:40 AM by lemonoman »

kad3285

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Re:Calculating pH of buffer solution
« Reply #2 on: July 07, 2005, 10:41:54 AM »
This is what I did to find the standard

pH = 4.76 + log (.025)/(.075) = 4.283
.

Now I just treat the addition of HCl as a dilution right?
« Last Edit: July 07, 2005, 11:09:38 AM by kad3285 »

Offline Borek

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Re:Calculating pH of buffer solution
« Reply #3 on: July 07, 2005, 12:25:45 PM »
Now I just treat the addition of HCl as a dilution right?

No. Adding hydrochloric acid you are converting conjugated base (acetate) into acid (acetic acid).

Take a look here:

http://www.chembuddy.com/?left=pH-calculation&right=pH-buffers-henderson-hasselbalch

and here:

http://www.chembuddy.com/?left=pH-calculation-questions&right=pH-buffer-q1
« Last Edit: July 07, 2005, 12:27:00 PM by Borek »
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