Question

Phathalic acid, H2C8H4O4, is a diprotic acid and has a concentration of 2.9 M. Ka1 = 0.0012 and Ka2 = 3.9 x 10-6. Estimate the concentration of [HC8H4O4-] and [C8H4O4-2] at equilibrium. Determine Kb1 and Kb2. Determine the pH of the solution at each proton dissociation. 11. Calculate the molar solubility of calcium hydroxide (Ksp = 4.8 x 10^6 I NEED TO KNOW HOW DID THEY GET THIS ANSWER PLEASE 0.0012 = x2/2.9 x = 0.059 M equilibrium concentration of HC8H4O4- = 0.059 M

Answer 1

H2C8H4O4   ----------------------> HC8H4O4-   + H+

2.9 M                                                0                  0

2.9 - x                                               x                  x

Ka1 = [HC8H4O4- ][H+] / [H2C8H4O4]

0.0012 = x^2 / 2.9 - x

x = 0.059

[HC8H4O4-] = 0.059 M

[C8H4O4-2] = Ka2 = 3.9 x 10^-6 M

[C8H4O4-2] always equals to second ionization constant.

Ka1 = 0.0012

Kb1 = Kw / Ka1 = 1.0 x 10^-14 / 0.0012

        = 8.33 x 10^-12

Kb1= 8.33 x 10^-12

and Ka2 = 3.9 x 10^-6

Kb2 = Kw / Ka2 = 1.0 x 10^-14 / 3.9 x 10^-6

       = 2.56 x 10^-9

Kb2 = 2.56 x 10^-9

11) Ca(OH)2 ------------------> Ca+2   + 2OH-

                                                   S            2S

Ksp = (S)(2S)^2

Ksp = 4S^3

4.8 x 10^-6 = 4S^3

S = 0.0106 M

molar solubility =0.0106 M