Question

Okay I've got a HUGE chem test tomorrow and I desperately need help! Please help!!!!

73. Hematite (Fe2O3) and magnetite (Fe3O4) are two ores used as sources of iron. Which ore provides the greatest percentage of iron per kilogram?

78. A hydrate contains .050 mole of H2O to every .00998 mole of ionic compound XYY the formula of the hydrate XY.

79. Calculate the mass of the water of hydration if a hydrate looses .025 mole of H2O when heated.

I absolutely have no idea how to start any of these, please help!

Answer 1

73. Because this is chemistry you're intimidated. % anything = (mass of that/total mass)*100
%Fe in Fe2O3 = (2*atomic mass Fe/molar mass Fe2O3)*100 = ?
Works the same way for Fe3O4.

78. Sorry, I don't understand this one. Neither XYY nor XY makes sense to me. Read that sentence; something seems to be missiing. My guess; however, is that you want to know the formula of the hydrate and that is 1 mol compound:Y mols H2O. To get that 0.05mols/0.00998 - 5.01 mols H2O which rounds to 5.0. So the formula is, for example, CuSO4.5H2O which is in the ration of 1 mol salt to 5 mol H2O.

79.
So it loses 0.025 mols H2O. Convert that to grams H2O. g = mols x molar mass = ?