Calculate the amount (in moles) of iron 3 nitrate in a 2.16g sample.

Formula of Iron 3 Nitrate is Fe(NO3)3. Moles = mass/Mr.

Already given mass = 2.16g

Want to work out amount in moles.

Need to calculate Mr of Iron 3 nitrate, put into equation with mass -> find moles.

Using periodic table Mr is always the bottom number (mass of an atom relative to carbon which is always taken as 12)

Mr of iron (Fe) is 56

Mr of oxygen (O) is 16

Mr of nitrogen (N) is 14

In the formula Fe(NO3)3 there are: 

1 molecule of iron -> 1 x 56 = 56

3 molecules of nitrogen (due to 3 outside the bracket) -> 3 x 14 = 42

3 (inside bracket) x 3 (outside bracket) = 9 molecules of oxygen. 9 x 16 = 144

56 + 42 + 144 = Mr of Iron 3 nitrate = 242

As above, moles = mass/mr

So moles of iron 3 nitrate = 2.16/242 = 8.93x10-3