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Home Q & A Board Science-Related Homework Help Chemistry (Moderator: Laser_3)
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juelz juelz
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11 years ago
A solution of formic acid is titrated with NaOH until the solution is 0.45 M in formic acid and 0.55 M in sodium formate. Calculate the pH of this solution.


I think I'm supposed to use the Henderson-Hasselbalch equation, which in this case would be pH= pKa + log ([CH3COO-]/[CH3COOH]), but I'm not sure. If so, how would I calculate the pKa?


Thanks in advance!
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#1
11 years ago
Yes, use the H-H equation. The pKa is a constant value. The value is 3.74 for formic acid.

pH = 3.74 + log (0.55/0.45) = 3.82
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#2
11 years ago
Henderson-Hasselbalch Equation:
pH= pKa + log([A-]/[HA])

pKa of formic acid is 3.698970004...
 so the value would make:
pH= 3.70+ log (0.55/0.45)
pH= 3.79
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