In a saturated solution of magnesium phosphate, [mg2+] = 2.4 *10^-5 m and [po4^3-] =1.6 *10^-6. what is the solubility of magnesium phosphate?

Ksp of AxBy (for example Mg3(PO4)2; A=Mg x=3 B=PO4 y=2) =([A]^x)*
([B]^y)
 for this question Ksp=([Mg]^3)*([PO4]^2)={(2.4*10^-5)^3}*
{[1.6*10^-6)^-6}=3.5*10^-26  
From the question you first need to determine the chemical formula from the charges, Mg^2+ and PO4^3- to make the charges=0 you need to make them equal and opposite, 2*x+(-3)*y=0 the easiest way to do this is by multiplying the two charges together to determine what value will make them cancel out. 2*3=6 therefore x and y should give values of 6 to cancel out to 0. 2*x+(-6)=0 x=3; 6+(-3)y=0 y=2 this makes our chemical formula Mg3(PO4)2. From here we can use the solubility formula to determine the Ksp, since we were given the concentrations, and we now how the chemical formula, when the molecule dissociates 3Mg + 2PO4 is produce the 3 and 2 become the exponents in the equation.