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the dreaded mole.
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ellis182:
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!
AWK:
1 OK
--- Quote ---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!
--- End quote ---
Calculate moles of hydrazine as in the first problem, then multiply by Avogadro number
Pirt:
Hey ellis you are right about how to do it.
heres how i worked it out, hope this helps.
the weight on 1mole of CaSO4 is 136.9g.
therefore if you work out how much mass is needed as a ratio
1st part ratio between mass you have and mass for one mole is:
25.7 / 136.9 = 0.188
Ca : S : O
40.8 : 32.1 : 64 <------ mass in g for 1 mole
Divide mass for 1 mole by the ratio above (0.188)
7.67 : 6 : 12 <-------- mass in g for 0.188 moles
now you have the mass of O in your compound which is 12g so you can do
12/16 = 0.75 moles [mass / RMM = no moles]
Hope this helps
Prit
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