Gen Chem Question from Kaplan

[esperi]

Question from Kaplan Practice Test:

How many moles of AgIO3 (Ksp=3.1x10^-8) will dissolve in 1 Liter of a 10^-5 M solution of NaIO3?

a. sqrt(3.1x10^-8)
b. [sqrt(3.1x10^-8)] [10^-5]
c. [sqrt(3.1x10^-8)] / [10^-5]
d. [10^-5] - [sqrt(3.1x10^-8)]
e. [sqrt(3.1x10^-8)] - [10^-5]

Kaplan says the answer is E, but I don't get why.

I get how Ksp=[Ag+][IO3-]= X^2= 3.1x10^-8, thus X= sqrt(3.1x10^-8). But why subtract [10^-5] from it ??? Anyone care to explain? Would appreciate it very much!

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[DentalBoston]

It's been a while sine I've done any general chem but since IO3 is a common ion in both you have to take that into account by subtracting the 10^-5. I'm sure if you have a chem book you can review the entire idea by looking up common ion effect.