[Azred]

Originally posted by Nanobyte: So, would you say: 6M H3PO4 x .75L solution= 4.5mol H3PO4 / 2mol H3PO4=2.25mol and then just multiply 2.25 to the products and figure the masses?

Yes. You would have 2.25 mol of the calcuim phosphate; use this to calculate the actual mass of calcium phosphate. Then, you can calculate the mass of only the calcium (mass of Ca/mass of calcium phosphate) to figure out how much calcium hydroxide is needed on the left, and finally the mass of the resulting water.
So far so good!

Originally posted by Nanobyte: I do not understand how you can get the # of moles of one element from a compound. Would you get the mass of (OH)3 multiply it to the mass you get from converting mL into grams? I'm still a little fuzzy on this one.

.25 L * 2.5 M = .625 mole Al(OH₃), then multiply by 3 to get 1.875 mole OH. To make water, you need 1.875 mole H. You know the concentration of sulfuric acid and the number of moles; alter the formula to become volume (in L)= moles / concentration.

Originally posted by Nanobyte: So, are you saying it can't be done?

It does appear to be missing a piece of information. Go back to the original problem and make sure everything is there.
I did have a professor who would put problems on his test that were impossible to solve because you would be missing a piece of information; the correct answer to those problems was "not enough information given". What a sneak!