lead poisoning in children used to be treated with intraveno

lead poisoning in children used to be treated with intravenous injections of EDTA. If the concentration fo EDTA in the blood of a patient is 2.55 x 10^-8 M and the formation constant for the complex, [Pb(EDTA)]2-, is 2.00 x 10^18, what is the concentration ratio of the free (and potentially toxic) Pb2+ (aq) in the blood to the much less toxic Pb 2+ - EDTA complex?

Solution

Pb2+ + EDTA ---> [Pb(EDTA)]2-

y 2.55*10^-8 x   

k = 2*10^18 = x/y*(2.55*10^-8)

x/y = 5.1*10^10

y/x = 1.96*10^-11.....................ans