Question

Calculate the equilibrium constant for the weak acid, CH3CH2CO2H, if the aqueous solution of CH3CH2CO2H that has an initial concentration of 1.97E-2 M has a [H+] of 5.00E-4.

CH3CH2CO2H <=> CH3CH2CO2 + H


i know that to figure out the equilibrium constant it is kc = products/reactants
and i have to do something with the ICE table...but i don't know how to apply it...

Answer 1

Let's call CH3CH2COOH, just to save some time typing, HP.
HP ==> H+ + P^-

Ka = (H^+)(P^-)/(HP)

Initial concns:
(HP) = 1.97E-2
(H^+)= 0
(P^-) = 0

Equilibrium concns:
(H^+) = 5.00E-4
(P^-) = 5.00E-4
(HP) = 1.97E-2 - 5.00E-4

Plug those equilibrium values into the Ka expression and solve for K.