How to calculate moles from given mass of a substance?

How to calculate moles from given mass of a substance?Practice questions/worksheet for IB and IGCSE students

Mole(n)= Mass of a substance(m)/ Molar mass(Mr)

so moles of a substance , n= m / Mr

The first question is solved for you.

For calculating Molar mass, you need to add the relative atomic masses of all the atoms in a 

compound or ion. For example Mr of Na₂O = (23x2)+16 = 62 ,

because  Ar( relative atomic mass) of Na=23,

Ar( relative atomic mass) of O= 16

so  moles of 100 g Na₂O= 100/ 62= 1.61 moles

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