Question

The rusting of iron is represented by the equation 4Fe + 3O2 --> 2Fe2O3. If you have a 3.5-mol sample of iron, how many grams of O2 are needed to rust the iron completely?

34.9 g
84.0 g
16.5 g
48.6 g

Answer 1

84.0 g

Balanced equation: 4Fe + 3O2 --> 2Fe2O3

• 3.5-mol sample of iron

Find moles of oxygen:

• 4Fe : 3O2

• 4 : 3

• (3.5/4)*3 = 2.625 moles

Find mass of O2

• mass = moles * Mr

• mass = 2.625 * 32

• mass = 84 g