By Anonymous on Tuesday, April 11, 2000 - 02:32 pm:
I know ammonium acetate buffer works well at pH5 range. Does it have good buffering power at pH7?
By Marcelo on Tuesday, April 11, 2000 - 03:34 pm:
Dissolving AcONH4 you will have the following acid-base equilibrium
AcOH === AcO- + H+ Ka=4.5 (approx)
NH4+ ===== NH3(aq) + H+ Ka=9.5 (approx)
The theoretical pH will be 7 and the buffering power will be the sum of both contributions. Since maximum buffer power occurs at pH=pKa, you will have good buffering power at pH=4.5 or 9.5 but the worst power at pH=7.
You should use phosphate buffers (2nd pKa=7.2 approx.)
See a classic book of analytical chemistry like Kolthoff-Sandell.
Regards
By Anonymous on Thursday, July 1, 2004 - 02:22 am:
Please, note that "Ka=4.5 (approx)" should be replaced with "pKa=4.5 (approx)". Same for "Ka=9.5 (approx)"
Thank you
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