8. What is the pH of a solution of 0.200M H3C6H5O7 (citric acid)? Ka = 3.5 x 10-4

Ionization equilibrium: H3C6H5O7 (aq) H+ (aq) + H2C6H 5O7- (aq)

I.C.E. table:

H3C6H5O7 (aq) H+ (aq) H2C6H5O7- (aq)
INTIAL
0.200M
0M
0M
CHANGE
-xM
+xM
+xM
EQUILIBRIUM
(0.200-x)M
xM
xM

Now substitute the equilibrium concentrations into the Ka expression! Which of the following represents the correct substitution?

a) 3.5 x 10-4 = {(x)(0.200-x)} / {x2}
b) 3.5 x 10-4 = {(0.200-x)} / {x2}
c) 3.5 x 10-4 = {x2} / {(0.200-x)}
d) 3.5 x 10-4 = {x2} / {(x)(0.200-x)}