Question

How many molecules are there in 79g of Fe2O3? how many atoms is this?

Answer 1

160g ---------- 6·10²³molecules
79g ---------- x

x = 2.9625·10²³ molecules

1molecule = 5 atoms
2.9625·10²³ molecules = 2.9625·10²³·5 = 14.8125·10²³ atoms

Answer 2

Molar mass of iron(III) oxide is 160g/mol

160g ----------- of iron(III) oxide is ---------------- 6.02*10²³molecules
79g ----------- of iron(III) oxide is ---------------- x

x = [6.02*10²³*79g]/160g ≈ 2.97*10²³ molecules