How to find molecular mass?

How to find mass of hydrate, anhydrous salt, ect?

• Lab report: molar mass of unknown is 120.359 Mass of crucible and lid after heating=24.278g Mass of crucible, lid, hydrated before heating=29.378g Mass of crucible, lid, anhydrated(1st)=26.288g Mass of crucible, lid, anhydrated(2nd)=26.281g Mass of hydrate=5g Can you guys help me to find the mass of anhydrous salt (anhydrated), mass of water driven off, % water, moles of anhydrous salt, moles of water, mole ratio, and formula ("xH2O). ASAP please~ thank you!

• Answer:

  Your descriptions of the various masses does not make a whole lot of sense, but lets see what we can do if we make a few assumptions. Looks like you actually had 5.100 g of hydrate because that's the weight difference. Then you heated it and you lose 3.093 g. So you have 3.093 g of water = 0.1717 mol And you have 5.1 - 3.093 = 2.007 g of compound 2.007 g x 1 mol / 120.359 g = 0.01668 mol 0.1717 / 0.01668 = 10.3 Pretty close to 10. (that's the "x" in "x H2O") Probably magnesium sulfate decahydrate but I thought magnesium sulfate formed a septahydrate ... oh well.