What is the pH of a solution containing 0.22 M HCOOH (formic acid) and 0.49 M HCOOK (potassium formate)?   For HCOOH, Ka = 1.7 x 10-4

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e-devam | High School Teacher | (Level 2) Adjunct Educator

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Formic acid is a weak acid having Ka value of `1.7xx10^-4` . Potassium formate is its salt with a strong base, potassium hydroxide. A weak acid and its salt constitute a buffer solution, the pH of which is governed by the Hendersen-Hasselbalch equation, given by

`pH=pK_a+ log( [C_(HCOO^-)]/[C_(HCOOH)])`

Putting the values, what we have

`pH=-log[1.7xx 10^(-4)] + log[0.49/0.22]`

`=3.77+0.35`

`=4.12`

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