Question 10.11: What is the pH of a buffer solution that is 0.5 M in formic ......

General, Organic, And Biological Chemistry [1102665]

What is the pH of a buffer solution that is 0.5 M in formic acid (HCHO $_{2}$ ) and 1.0 M in sodium formate (NaCHO $_{2}$ )? The pK $_{a}$ for formic acid is 3.74.

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The concentrations for the buffering species are
HCHO $_{2}$ = 0.5 M CHO $_{2} ^{-}$ = 1.0 M
Substituting these values into the Henderson–Hasselbalch equation gives

pH = pK_{a}+log\frac{[CHO_{2}^{-}]}{[HCHO_{2}]}=3.74+log\frac{1.0}{0.5}\\\quad\quad\quad = 3.74 + log 2 = 3.74 + 0.30 \\\quad\quad\quad = 4.04

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