How do I calculate how much precipitate comes out from this Equation 6-1?

Al(OH)3 is the precipitate, and Al2(SO4)3 is the alum

what I have is a alum dosage in mg/L.

my professor wants us to calculate the amount of precipitate that will come out and compare it with our lab results...

The lab was a Chemical Coagulation/Flocculation Using a Jar Test.

also what units are precipitate?

Chemistry is not my strong suit, but it looks like for every mole of Al2(SO4)3 you put in, you get 2 moles of Al(OH)3 out. So my thought would be to figure out how many moles of Al2(SO4)3 were put in.

Lol do you pay attention in class?

i try, but the professor sucks. noone else in the class knows either when I asked around. i asked the professor how to do it, he wouldnt even gimmi a direct answer.

This organic chem?

You can't use the mole ratio's because the reaction happens both ways.

It's an equilibrium reactions, so you should have an equilibrium constant provided somewhere, or a way of figuring it out. Typically these things require an ICE table.

And the precipitate is most likely going to be in grams. You'll need to figure out the theoretical mass of it, and then when you do the lab you'll filter the solution through a paper cone filter, dry it out, and weigh the filter to figure out how much precipitate is on it.