Relative Formula Mass (RFM)
Relative Formula Mass is basically the sum of all the mass of the atoms added up together in a compound. It's pretty easy! If you can do the question below, you can pretty much work out the RFM. Let's say:
1 can of
red paint weighs 18kg
yellow paint weighs 16kg
blue paint weighs 10kg
How much does 2 cans of red, 3 cans of yellow and 6 cans of blue paint weigh?
2*18+3*16+6*10=164 kg
If you got that, you are home free!
Here are the steps to RFM:
1) Find the Molar Masses of the atoms in the compound
Look for the RAM of the corresponding atoms in the periodic table! That's your molar mass!
2) Multiply subscripts to get how many of a particular atom is in the compound
Do the stuff that's in the brackets first!
3) Add and multiply accordingly!
Remember the cans of paint? It's the same logic!
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Here is a sample question:
Fe2(SO4)3
1) Work out the molar masses
Fe: 52
S: 36
O:12
2) Work out the quantities:
Fe: 2
S: 3*1=3
O:4*3=12
3) Multiply and add
2*Fe+3*S+12*O
=2*52+3*36+12*12
=400 That's it! That is the relative formula mas? Questions? Send me an email!
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