[weber90]

Two solutions at 25 degrees C are mixed, one contains Fe3+ and one containing IO3- ions.  At the instant of mixing,[Fe3+]=1.0 x 10-4 M and [IO3-]=1.0 x 1--5 M.  Which one of the following statements is true?

a. A precipitate forms because[Fe+3][IO3-]3>Ksp
b. A precipitate forms because[Fe+3][IO3-]3<Ksp
c. No precipitate forms because [Fe+3][IO3-]3>Ksp
d. No precipitate forms because [Fe+3][IO3-]3=Ksp

My answer: I don't think a precipitate will form but I'm not sure if>Ksp or =Ksp

[Albert]

If [Fe3+] = 10-4M;  [IO3 -] = 10-5M  and Kps = 10-14 = [Fe3+][IO3 -]3

Hence: Q = [10-4][10-5]3 = 10-19 and Q< Kps

Accordingly, what do you expect to be the 'behaviour' of the solution?

[weber90]

So are you saying a precipitate will form because Q is< Ksp

             

[Albert]

So are you saying a precipitate will form because Q is< Ksp

             

I think you'd better check your book: if Q<Ksp, there'll be no precipitate.

[weber90]

thanks for all your help so far, i have been over and over my book the last 2 weeks.   If the product of the ion concentrations exceeds the Ksp of the salt, the salt starts to precipitate. So if Q<ksp it will not precipitate, so the answer would be (d)                                

[Albert]

so the answer would be (d)                                

The answer is NOT among those you wrote in the opening post. However, I agree with you, because, generally speaking, there's no precipitate whenever Q is minor or equal to Ksp.