Aluminium oxide contains 52.90% Aluminium. Carbondioxide contains 27.27% carbon. Calculate the percentage of aluminium in aluminium carbide assuming that the law of reciprocal proportions is true.

% of ' Al'=52.90 then % of ' O 'in Al2O3=100-52.9=47.1% % of ' C 'in CO2=27.27% then % of ' O 'in CO2=100-27.27=72.73%Let fixed mass of oxygen be 47.1g         52.9g of combine with 47.1g of oxygen        Then amount of carbon that combine with 47.1g of oxygen is = 47.1×27.2772.73=17.6 g  ratio of mass of Al to C is 52.917.6=3:1Total mass of Aluminium carbide is 52.9+17.6=70.5g∴ percentage of Aluminium =52.970.50×100=75%