[iamash]

Hey!
I'm stuck trying to do a question in my textbook. Hope someone can *delete me*
Q: If 25.00mL of 0.20mol/L HCO2H is titrated with 0.20mol/L NaOH, determine the pH after 10.00mL of NaOH has been added.
A(my attempted solution):
I calculated that 0.20*0.010=2.0*10^-3mol of OH- will be added to the beaker, thus the number of moles of CO2H- that will form will also be 2.0*10^-3mol. The final concentration of the CO2H- is (2.0*10^-3mol)/0.035L= 5.7*10^-2mol/L.
I calculated that 0.20*0.025=5.0*10^-3mol of HCO2H is in the beaker before the NaOH is added, thus (5.0*10^-3mol)-(2.0*10^-3mol)=3.0*10^-3mol of HCO2H is in the beaker after the NaOH is added. Thus, concentration of HCO2H= (3.0*10^-3mol)/0.035L= 8.6*10^-2mol/L.
I put the calculated concentrations above into an ICE chart, but I keep getting 2.6*10^-5 for [H+], which yields a pH of 4.6 (the correct answer is 3.57.
Any help is appreciated!

[Borek]

Show the ICE table. What was the initial concentration of H⁺ you used? What was the Ka value you used?

Once you got the concentrations of formic acid and formate, ICE table won't change much, you can plug concentrations directly into the Henderson-Hasselbalch equation.