Question

Find the grams of iron in 79.2 g of Fe2O3.

Answer 1

First you find the RFM (Relative Formula Mass) of Fe2O3
Fe2 = 56 x 2
= 112
O3 = 16 x 3
= 48

112 + 48 = 160

Moles = mass/RFM
           = 79.2/160
           =0.495

Then you rearrange the formula
Mass= moles x RFM
        = 0.495 x 112
        = 55.44 g
(To find mass of Iron have to use RFM of total iron in the substance example Fe2 ^^)