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ellis182
03-16-2005, 08:38 AM
Guys just a really easy question i need clarification with..

How many moles of O-atoms in 25.7g of CaSO4?

I know moles = mass/molar mass

so..

25.7/(40.8 + 32.07 + 4x16) = .188

Is this the answer or do i multiply .188 by 4 because there is 4 oxygen atoms in CaSO4?



Also..

How many molecules in 13.72g oh hydrazine? N2H4? i dont even know where to start!

If anyone could help me at all it would be much appreciated!

ellis182
03-16-2005, 11:28 AM
Ok i have figured out the first one! the 0.188 is multiplied by 4. However, anyone help with question number 2?

Holden_Caulfield
03-17-2005, 09:13 PM
Also..

How many molecules in 13.72g oh hydrazine? N2H4? i dont even know where to start!

If anyone could help me at all it would be much appreciated!

Hydrazine mol. mass : 14*2 + 4 = 32

Number of moles = 13.72/32 = 0.5-2.28/32 =0.5-0.57/8~0.5-0.07=0.43

Number of molecules ~ 0.43*6*10^23=2.58*10^23