Molar mass, M, is the mass of one mole of something. But the main thing to remember is: Molar mass is just the same as the relative molecular mass, Mr
The only difference is you stick a 'g mol-1' for grams per mole on the end...
E.g. Find the molar mass of CaCO3
Relative formula mass of CaCOS3 = 40 + 12 + (3X16) = 100
So the molar mass is 100g mol-1
Here's another formula. This one's really important - you need it all the time: Moles = mass/Mr
E.g. How many moles of aluminium oxide are present in 5.1g of Al2O3?
Molar Mass of Al2O3 = (2x27) + (3 x 16) = 102 g mol-1
Number of moles of Al2O3 = 5.1/102 = 0.05 moles
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