Anhydrous aluminium chloride (AlCl3) is prepared industrially by heating a mixture of alumina (Al2O3) and coke (carbon) in a current of dry chlorine gas. The carbon acts as a reducing agent to help break the strong Al-O bonds, combining with the oxygen to form carbon monoxide. The chemical reaction is: Al2O3 + 3C + 3Cl2 → 2AlCl3 + 3CO. Heating Al2O3 with HCl gas yields hydrated aluminium chloride, not anhydrous.