what is the percent composition by mass of oxygen in ca
Look up relative atomic mass of Ca, Cl and O. Work out formula mass of Ca(ClO3)2 (=207) 1 mol of Ca(ClO3)2 contains 2 mols Cl %Cl = (2 x atomic mass of Cl/207) x 100 = 17.15%. Percent composition can have two meanings: By volume and by weight. It so happens that people usually give the percent composition of the atmosphere by volume, which is 78% nitrogen, 21% oxygen, and 1% other gases, such as carbon dioxide and argon. Erika Â· 2 years ago