Moles

Compounds.

To find the mass of one mole of a compound,
just add up all the RAMs of the elements of the compound,
taking account of the formula.
The number you get is called the Relative Formula Mass.
It is the mass of one mole of the compound in grams.
The Relative Formula Mass can be written as Mr or RFM.

For example, the mass of one mole of carbon dioxide (CO2) is
(1 x RAM of carbon) + (2 x RAM of oxygen)
= (1 x 12) + (2 x 16)  =  44 g.
So, one mole of carbon dioxide has a mass of 44 g.
The Relative Formula Mass of carbon dioxide is 44.
This may also be called the Relative Molecular Mass (RMM),
since carbon dioxide is a molecule


The mass of one mole of calcium carbonate (CaCO3) is
(1 x RAM of calcium) + (1 x RAM of carbon) + (3 x RAM of oxygen)
= (1 x 40) + (1 x 12) + (3 x 16)  =  100 g.
So, one mole of calcium carbonate has a mass of 100 g.
The Relative Formula Mass of calcium carbonate is 100.

If you are not sure why CaCO3
means 1 calcium + 1 carbon + 3 oxygens, see balancing equations.


The mass of one mole of magnesium oxide (MgO) is
(1 x RAM of magnesium) + (1 x RAM of oxygen)
= (1 x 24) + (1 x 16)  =  40 g.
So, one mole of magnesium oxide has a mass of 40 g.
The Relative Formula Mass of magnesium oxide is 40.

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