chemistry
posted by kelly .
The formula for epsom salt is MgSO4 . 7H20 If 1.250 g of the compound is dissolved in water, calculate the number of milliliters of .200 M Ba(NO3)2 that would be required to precipitate all of the sulfate ions as barium sulfate. I got that right with an answer of 25.4 milliliters.
Then it asks to make the same determination for 1.000 g of alum, which is AlK(SO4)2 .12H2O. I'm not sure .. is the mole to mole ratio 1:2? How do I figure this part out? Any answers would be greatly appreciated.

1:2 or 2:1 depending upon which way you do it.
moles alum = 1.000/molar mass alum.
moles BaSO4 = 2 x moles alum
M Ba(NO3)2 = moles Ba(NO3)2/L Ba(NO3)2
Solve for L and convert to mL. 
so is the answer 1000ml?

or 21.075ml?

I get 21.08 which would round to 21.1 mL to three s.f.

what is the chemical equation of this problem