[chicago504]

I am doing some practice problems and cannot figure out the first question please help... Here it is:
MgF2(arrows going both ways) Mg + 2 F
In a saturated solution of MgF2 at 18 degrees Celsius, the concentration of Mg is 1.21 X 10 ^ -3 molar.  The equilibrium is represented by the equation above.
 
Question #1)
Write the expression for the solubility-product constant Ksp and calculate its value at 18 degrees Celsius.

[Dan]

Read the forum rules, you must attempt the question.

You are asked to start by writing an expression for the solubility product - do it. If you don't know how, it's in your textbook. Your equilibrium equation needs charges too.

[AWK]

Wride down correctly a reaction of solubility process, ie:
PbI₂ => Pb²⁺ + 2^I-
then calculate a concentration of  anion. Put concentrations of ction and anion into a proper Ksp equation