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Determine the pH of the buffer. Express your answer using two decimal places.?
A buffer is created by combining 160.0 mL of 0.25 molL−1 HCOOH (Ka=1.8×10−4) with 75.0 mL of 0.25 molL−1 NaOH.
1 Answer
- hcbiochemLv 71 year ago
Equilibrium: HCOOH <--> H+ + HCOO-
Ka = 1.8X10^-4 = [H+][HCOO-]/[HCOOH]
Moles HCOOH initially present = 0.1600 L X 0.25 mol/L = 0.0400 mol
Moles OH- added = 0.0750 L X 0.25 mol/L = 0.01875 mol
The OH- reacts quantitatively with HCOOH forming HCOO-. So, moles HCOO- formed = moles OH- added = 0.01875.
Remaining moles HCOOH = 0.04000 - 0.01875 = 0.02125 mol
Ka = 1.8X10^-4 = [H+] (0.01875) / 0.02125
[H+] = 2.04X10^-4
pH = 3.69
