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April 20, 2014

Homework Help: CHEMISTRY FOR DR. BOB or anyone else

Posted by Delli on Friday, May 11, 2007 at 12:39pm.

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

Duplicate post. answered the original.

Sorry bout that. I didn't notice part b.
Assuming not all of the HA is neutralized and that you still have a buffered solution,
Use the Henderson-Hasselbalch equation.
pH = pKa + log [(base)/(acid)].
OR just use the simple Ka expression you used for part a, plug in (H^+) equivalent to pH = 5.00.

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