solubility expression: question stem confusion or process error?

[epsilonprodigy]

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Question from a GS exam:

A student adds magnesium sulfate to a solution that is 10-4 M in each of the ions F- and CO32- until the Mg2+ concentration is also 10-4 M. Which of the following salts will precipitate from the final mixture?
(Data: Ksp MgF2 = 10-8; Ksp MgCO3 = 10-5)


In the solution, when showing the concentration of fluorine anion in solution, they square the term. In other words, they say that the concentration of fluorine anion in solution is (1E-4)^2. But in the question stem, they say that the solution has a concentration of (1E-4) fluorine anion.

I understand that MGF2 is a "4x^3" salt and all of that, but can't figure out why they squared the term when they specifically said that 10^-4 IS the concentration of fluorine anion.

 

[Pre-Med Village]

You have to square the fluoride concentration in the Ksp expression for MgF2 because dissociation would produce two fluoride anions. That must be what the explanation refers to.