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Topic: Diluting a buffer has no effect on its pH?!  (Read 28564 times)

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mrflow3r

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Diluting a buffer has no effect on its pH?!
« on: December 11, 2005, 05:08:35 PM »
Hello there, my text book says 'diluting a buffer has no effect on its pH', but I don't understand why though.

This is the Ka expression of a buffer solution
Ka = [Conjugate base][H3O+ ]/[Conjugate acid]

My textbook says pH doesn't change since both [conjugate base] and [conjugate acid] are diluted equally.
But if you dilute this solution, wouldn't that change the concentration of everything including H3O+?

Thank you, I appreciate your help.

Offline Borek

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Re:Diluting a buffer has no effect on its pH?!
« Reply #1 on: December 11, 2005, 06:18:01 PM »
That's only approximation, but it holds very well.

Check this pH of buffers lecture.

If you dilute 1M solution of acetic buffer 50/50 to 0.001M change in pH is less then 0.03 pH unit (assuming that the ionic strength of the solution have not changed).
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