chemistry problem help please?

Question

The solid Ag2CrO4 forms when 2.7*10-5 g of AgNO3 is dissolved in 15 mL of 2.1*10^-3 M K2CrO4. (Assume no volume change.) What is the Qsp and Ksp?

Answer 1

First of all lets find out how many moles of AgNO3 you have
mole=mass/MW =(2.7*10^-5)/169.87= 1.59*10^-7

AgNO3 -> Ag(+) + NO3(-)

so moles Ag(+)= moles AgNO3 =1.59*10^-7
The concentration is mole/V =(1.59*10^-7)/0.015 =1.06*10^-5

K2CrO4 ->2K(+) + CrO4(-2)

So [CrO4(-2)]= [K2CrO4]= 2.1*10^-3

For Ag2CrO4
Ag2CrO4 <=> 2Ag(+) + CrO4(-2)
Therefore
Qsp=([Ag+]^2)*[CrO4(-2)] =((1.06*10^-5)^2)*2.1*10^-3 = 2.36*10^-13
If it is just at saturation of the solution then Ksp=Qsp. You don't give more info so I assume that this is the case.