[Edher]

Saludos,

     Need a hint.

A typical Ca+2 concentration in seawater is 0.010M. Will the precipitation of             Ca(OH)2 be complete from a seawater sample in which [OH-] is maintained at 0.040 M?

This is what I did,

CaOH2 <--> Ca+2   +  2OH-

Qsp=[Ca+][2OH-]²

(0.010)(2*0.040)² = 6.4x10^-5

6.4x10^-5  x   100 = 0.16%
       0.040

The book says that the precipitation wasn't complete. Is this because 0.16% exceeds 0.1%?

Edher

[Borek]

Qsp=[Ca+][2OH-]²

You are wrong here. It should be

Qsp=[Ca+][OH-]²

As you made a mistake here, rest of your calculation is faulty.

You must compare result of your calculations with Qsp value taken from the tables, to see whether precipitation started ro not.

I don't get what are these % for? All concentrations used here are M.