The % lithium by mass in a sample of pure lithium carbonate : 18.79%
Further explanation
Proust states the Comparative Law that compounds are formed from elements with the same Mass Comparison so that compounds have a fixed composition of elements
% Lithium (Li) in Li₂CO₃(lithium carbonate) will remain the same even if the mass amount of Li₂CO₃ changes
Ar of Li = 6.941 g/mol
MW of Li₂CO₃ = 73.891 g/mol
[tex]\tt \%Li=\dfrac{2.Ar~Li}{MW~Li_2CO_3}\times 100\%\\\\\5Li=\dfrac{2\times 6.941}{73.891} \times 100\%=18.79\%[/tex]
