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May 25, 2013

# Homework Help: Chemistry

Posted by Michael on Tuesday, July 12, 2011 at 8:17pm.

If a buffer is prepared using equal amounts of acetic acid and sodium acetate predict what the pH of the solution will be.

• Chemistry - DrBob222, Tuesday, July 12, 2011 at 8:27pm

This is NOT a very good question because it doesn't specify what is meant by equal amounts. Is that equal amounts of mass, equal amounts of moles, or just what? If it is equal amounts of moles, then
It will be pKa of acetic acid.
pH = pKa + log(base)/(acid)
If base = acid, then B/A = 1, log 1 = 0 and pH = pKa + 0 = pKa.

If equal amounts mass, the easy way is to assume some convenient amount of acetic acid and sodium acetate. I would pick 50 g, then
moles acetic acid = 50/molar mass acetic acid.
moles sodium acetate = 50/molar mass sodium acetate, then
pH = pKa + log (moles NaAc/moles HAc) and solve for pKa. I estimate about 4.6 for the pH.

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