Given:
Mr of MgSO4.7H2O = 246
Mr of Oxygen = 16
Percentage by mass of Oxygen = TotalmassofOxygenTotalmassofMgSO4.7H2O×100
% by mass of Oxygen = 11molesofoxygenMgSO4.7H2O×100 (4moles of oxygen + 7 moles of oxygen from 7H2O )
= 11X16246×100
= 176246×100
= 71.544%
= 71.5%
