How would I work out 'Calculate the mass of iron formed from 8g of iron (III) oxide, Fe2O3: (Ar values: Fe=56, O=16)?

Question

anonymous · Answer

First write equation and balance it, to find ratio of moles.$$2Fe _{2}O _{3}\rightarrow 4Fe+3O _{2}$$
As you can see , the ratio between Fe2O3 and Fe is 2:4 or 1:2.
What you do now is find the mol of 8 g wanted in question. That can be calculated by the formula$$mol=\frac{ Given Mass }{ MolarMass }=\frac{ 8 }{ 56(2)+16(3) }=0.05mol$$
By ratio and proportion, 0.05*2/1=0.1mol of Fe$$GivenMass=mol*MolarMass=0.1*56=5.6g$$