[RobbieWinkler]

Hey guys, I have a stoichiometry test tommorow, and i'm still a little bit shaky. If anyone could help me work out this problem as sort of an example and what I should do, that would be great!

            When 9.00 g of Al react with an excess of H3PO4, 30.0 g of AlPO4 are produced. What is the precentage yield of this reaction?
                                     2Al(s)  + 2H3PO4(aq) --> 2AlPO4(aq)  + 3H2(g)

   Any help is much appreciated!

[constant thinker]

Is there something specific you want to know.

The way I usually tackle stoichiometry problems is I identify what I want to know, and what I need to solve for what I want to know.

What you want to know. Percent yield
You know that percent yield is calculated with the formula, "(actual yield/theoretical yield)*100=% yield"

We have the actual which is 30.0g, so we need to find the theoretical yield.

General steps for finding the theoretical yield.
Identify limiting reagent (we can deduce Al is limiting from the fact that phosphoric acid is in excess).
Convert grams of given limiting reagent to moles.
Multiply by the ratio of reagent to product you want to identify percent yield for (in this case it's 2Al:2AlPO₄ so a ratio of 2/2).
Now you have the number of moles of product theoretically produced.
Now convert moles of product into grams.
Plug the information into the percent yield formula.

Now try this specific problem out. Show all the work, and I'll help you (or someone will) if you get stuck or don't get the right answer.

You should get something around 73.74% yield (unless wikipedia was wrong on the molar mass of aluminum phosphate).

[Edit]Spelling mistake & answer. I decided that maybe you're telling the truth and you are asking for a test and this isn't just homework.