From: ::Rose::
Date: 11 Jun 2008, 18:26
Q1. A buffer Solution contains HCOOH and HCOONa. Calculate the pH of a buffer solution containing equal volumes of 2.5mol dm-3 HCOONa and 1.0mol dm-3 HCOOH (Ka=1.6 x 10(to the -4) mol dm-3.
[Salt] = 2.5 M
[Acid] = 1.0 M
[Acid ka] = 1.6 x 10-4 M
First convert Ka into pKa
pKa of acid = -log(1.6 x 10-4) = 3.8
Now use the Henderson-Hasselbalch equation:
pH = pKa + log [salt]/acid]
pH = 3.8 + log 2.5/1.0
pH = 4.2
(I have rounded everything to 1 d.p, square brackets [] refers to concentration)
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1 comment:
Very useful information. I also found the derivation of the Henderson Hasselbalch approximation which might help some readers.
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