Chemistry HW Help!!!?

Question

1.) From CuSO4*H20, The first weight was 1.57g, when heated, .57g of Suso4 was Left, How many Moles of Water(H20) was Lost?

2.) Magnesium Acetate*H20, the first weight was .84g, when heated, .43g of Magnesium Acetate was left behind. How many Moles of Water(H20) was lost? Thanks! (Show how you got it)

Answer 1

1. First subtract 1.57g -.57g. This gives you 1.00g lost, and we are assuming all mass lost was due to evaporation of water. Next, we take the 1.00g H2O and divide by the molar mass of H2O (approximately 18.00g/mol) and we are left with moles of H2O. The answer should be .0556mol H20.

2. Same idea as number one, subtract .84g-.43g = .41g. Once again, we are assuming the mass lost was due to loss of H2O due to evaporation. This time we will be taking the .41g H2O and dividing by the molar mass so we are left with moles of H2O again. The answer should be .023mol H2O.

Try setting these problems up with the description I've given and see if you can work them out to get the same answers.

Answer 2

Sounds like one gram of water was lost 1.57-.57=1. Divide this by molecular weight of water to get number of moles of water. I am suprised you were not asked to find the x value of CuSO4x H2O which would be the ratio of number of moles of CuSO4 to the number of moles of H2O. This, by now, you should be able to do by repeating above steps to find moles of CuSO4. Turn that in for extra credit and you will look like a real chemist.
Use same logic for 2. and you will have learned something valuable to chemistry.

Answer 3

All you need to do is to determine the mass of water that was lost (the difference between the initial mass and final mass of the compound). And then, use the molar mass of water (18.0 g/mol) to convert that mass to moles.

You should be able to punch those into a calculator to get the answers.