Dissociation and pH ?

Question

For Propanoic acid (HC3H5O2, Ka = 1.3 x 10^-5)

1) Determine concentration of species present

2) Determine pH

3) Determine percent dissociation of a 0.100 M solution

Just the general concept of the steps with terms that I can recognize would be great.

Answer 1

HC3H5O2 <------> C3H5O2- + H+

initial conc.

0.100

at equilibrium

0.100-x ,, , , , , , , , , x . . . . . . x

1.3 x 10^-5 = x^2 / 0.100-x

x = [C3H5O2-] = [H+] = 0.0011 M

[HC3H5O2 ] = 0.100 - 0.0011 =0.0989 M

pH = - log 0.0011 =3.0

0.0011 x 100 / 0.100 =1.1 %