Asked by Leroy

What is the PH of an aqueous solution consisting of 0.070 M formic acid (HCOOH) and 0.070 M sodium formate (HCOONa)?
Answered by DrBob222
Use the Henderson-Hasselbalch equation.
pH = pKa + log (base)/(acid)
pH = ?
pKa = look up
(base) = 0.07
(acid) = 0.07

Answered by Leroy
I am not really sure how the find the
pKa. Do I need to find the conjugate acid -base pair first?
Answered by DrBob222
pKa = -log Ka
Answered by Leroy
I am not understand how to use log on my calculate, so no answer is calculating.

can you explain how to use log?
Answered by Leroy
pKa = 7.6 for HCOOH
so pH= 7.6 + log [.07]/[.07}
pH = 7.6

is this correct or at least moving in the right direction?
Answered by DrBob222
Some is correct. I don't know how your calculator works (calculators aren't standard) but I can tell you how to proceed.
First, where did you get the pKa for formic acid? I looked it up on the web and found 3.77. You can get slightly different numbers depending upon where you look but that's fiarly close. The Ka is about 1.7E-4. So
pH = pKa + log (base)/(acid_
pH = 3.77 + log (0.07/0.07)
pH = 3.77 + log 1
and log 1 I thought everyone knew is zero and you really don't need a calculator for that.
Then pH = 3.77 + 0 = 3.77. Right?
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