Posted by Natash on .
the pH of a .100 M solution of sodium formate = 8.37. Calculate the value of Ka of formic acid.
okay so I know that the anion of a weak acid is itself a weak base
so A- +H2O---> OH- + HA
pOH =14-8.37 so conc of OH is 10^-5.63
Ka=[OH][HA]/[A-] so we know the conc of OH and A- and then im stuck helppp
Convert to (OH^-) = ?? I get 2.34 x 10^-6 but check me out on that. (HA) is the same. (A^-) is 0.1. Solve for Ka.
I know that part, but why are the conc. of OH and HA the same ?
When one 1 mole of A^- hydrolyzes, it produces 1 mole of HA and 1 mole of OH^-. Or you can make up an ICE chart from your equation.
A^- + HOH ==> HA + OH^-
A^- = 0.1.
HA = 0
OH = 0
HA = +x
OH^- = +x
A^- = -x
HA = x
OH^- = x
A^- = 0.1-x
Don't hesitate to follow through if you still don't understand.
OHHHH got it, without the ICE chart I sort of get confused. Thanx!