[Kogelbauer]

Hi all

Got a bit confused over this buffer question although it looks fairly straightforward. Thanks for any help

You are asked to prepare a solution containing zinc at pH9. In order to control the pH you choose a glycine buffer. Describe how you would prepare the actual buffer using glycine and a strong acid or base, so that it can buffer 0.1mol/L of base with a maximum change of 0.05pH units

[Borek]

Write Henderson-Hasselbalch equation for the buffer before addition of base and after addition of base. See what is unknown, what is known. Are these two equations enough to solve the problem?

[Kogelbauer]

I tried doing that but I cant get the same answers as in the solutions. What I have done is:

pH = pKa2 + log[Salt]/[Acid]

9 = 9.78 +  log[Salt]/[Acid]

[Salt]/[Acid] = 0.166

Then for the second equation

9.05 = 9.78 + log[Salt]+0.1 / [Acid]-0.1

0.1862 = [Salt]+0.1 / [Acid]-0.1

[Acid] = 5.87M

[Borek]

I got a very similar result - 5.86M and 0.97M. If your book states something else, it is most likely wrong.

Somehow I wonder if they really wanted the concentrations to be that large. Perhaps it should be not 0.1M of base, but 0.01M or 0.001M?

What is the answer given by the book?

[Kogelbauer]

Cheers mate Legend