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pH calculation questions » pH of buffer solution

Use acetic acid and sodium acetate to prepare 0.01 M buffer solution with pH 4.50. pKa=4.75.

We can easily calculate ratio of concentrations of acid and conjugate base, by plugging known values of pH and pKa into the Henderson-Hasselbalch equation and rearranging:

eq. 15.215.2

[A-]/[HA] = 10pH-pKa = 104.50-4.75 = 0.562

0.01 M buffer means sum of concentrations of acetic acid and acetate is 0.01 M:

[HA] + [A-] = 0.01 M

We have two equations in two unknowns, solving them requires just a basic algebra skills and yields

[HA]=0.0064 M

[A-]=0.0036 M

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