I need some help with 3 homework questions. We're really behind due to missing so much school because of Hurrican Gustav and Hurricane Ike; therefore, I'm having a hard time catching up. Any help would be greatly appreciated.

1. Calculate the percent yield of an analysis if 1.9365g of AgCl (MM 143.32g/mol) was precipitated in a gravimetric experiment if 1.2000g of a soluble sample that contained 40.25% Cl- was used as the starting material.

--Ok, I know for gravimetric analysis you need to know the starting material and ending material which would be 1.2g of sample and 1.9365 g AgCl product. After this step, I'm lost.

2.A mixture containing only Al2O3 (MM 101.96 g/mol) and Fe2O3 (MM 159.69 g/mol) weighs 2.0190g. When heated under a stream of H2, Al2O3 is unchanged, but Fe2O3 decomposes to Fe(s) and water vapor. If the residue weighs 1.7740g, what is the %Fe2O3 in the original sample?

Fe2O3--->2Fe(s) + 3H20(g)

Hint: Think about what's left in the residue and where the change in mass comes from!

--This one has me 100% lost. I don't even know where to start.

3. When a 100.0mL portion of a solution containing 0.5000g of AgNO3 (MM 169.87 g/mol) is mixed with 100.0 mL of a solution containing 0.3000g of K2CrO4 (MM 194.19 g/mol), a bright red precipitate of Ag2CrO4 (MM 331.73 g/mol) forms. Calculate the molar concentration of the excess reactant that remains in solution.

--I have no idea what to do if there's 2 starting materials.

Thanks for all of your time