Calculate the mass of iron, which is formed by the interaction of 20 g of iron (III) oxide with 50 g of aluminum.

Given:

m (Fe2O3) = 20 g

m (Al) = 50 g

Find:

m (Fe) -?

Solution:

Fe2O3 + 2Al = 2Fe + Al2O3, – we solve the problem, relying on the composed reaction equation:

1) Find the amount of iron oxide and aluminum that have reacted:

n (Fe2O3) = m: M = 20 g: 160 g / mol = 0.125 mol

n (Al) = m: M = 50 g: 27 g / mol = 1.85 mol

We start from a lower value to get more accurate calculations. We work with Fe2O3:

2) We compose a logical expression:

if 1 mol of Fe2O3 gives 2 mol of Fe,

then 0.125 mol of Fe2O3 will give x mol of Fe,

then x = 0.25 mol.

3) Find the mass of precipitated iron:

m (Fe) = n * M = 0.25 mol * 56 g / mol = 14 g.

Answer: m (Fe) = 14 g.