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April 21, 2014

Homework Help: CHEMISTRY FOR DR. BOB or anyone else

Posted by Delli on Friday, May 11, 2007 at 12:38pm.

A hypothetical weak acid HA, was combined with NaOH in the following proportions: 0.20 mol HA, 0.08 mol NaOH. The mixture was then diluted to a total volume of 1L, and the pH measured.

(a) If pH=4.80, what is the pKa of the acid

(b) how many additional moles of NaOH should be added to the solution to increase the pH to 5.00

HA + NaOH ==> NaA + HOH

0.2 mol HA to begin.
0.08 mol NaOH used to neutralize.
0.2-0.08 = 0.12 mol HA reamins.
0.08 mol A^- formed.
M = mols/L.
Ka = (H^+)(A^-)/(HA)
You know (H^+), from pH, you know A^- and you know HA. Solve for Ka, then pKa. Post your work if you get stuck.

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