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^-
initial:
A^- = 0.1.
HA = 0
OH = 0

change:
HA = +x
OH^- = +x
A^- = -x

equilibrium:
HA = x
OH^- = x
A^- = 0.1-x
etc.
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!

To calculate the value of Ka for formic acid, we need to use the information given about the pH of the sodium formate solution and the knowledge that the anion of a weak acid is a weak base.

First, let's write the dissociation reaction of formic acid (HCOOH):

HCOOH β‡Œ H+ + HCOO-

Since the pH of the solution is given as 8.37, we can determine the concentration of H+ ions using the equation:

pH = -log[H+]

Therefore, [H+] = 10^(-pH) = 10^(-8.37)

Since formic acid is a weak acid, we can assume that the concentration of HCOOH after dissociation is approximately equal to the concentration of H+ ions. Therefore, [HCOOH] β‰ˆ [H+].

Now, we need to determine the concentration of HCOO- (A-) ions. Since sodium formate (NaHCOO) completely dissociates into its ions in solution, the concentration of HCOO- (A-) is equal to the concentration of the sodium formate, which is 0.100 M.

With the concentration of [H+], [HCOOH], and [A-], we can now calculate the value of Ka using the equation:

Ka = [H+][A-] / [HCOOH]

Substituting the values:

Ka = (10^(-8.37))(0.100) / (10^(-8.37))

Simplifying, we find that Ka = 0.100

So, the value of Ka for formic acid is approximately 0.100.