What is the percent by mass of water in iron (ii) sulfate heptahydrate, feso4•7h2o (or what percent of the molar mass of feso4•7h2o is due to the waters of crystallization) ?

45.360% First, lookup the atomic weights of all involved elements: Atomic mass Iron = 55.845 Atomic mass Sulfur = 32.065 Atomic mass Hydrogen = 1.00794 Atomic mass oxygen = 15.999 Now calculate the molar mass of FeSO4•7H2O 55.845 + 32.065 + 11 * 15.999 + 14 * 1.00794 = 278.01016 g/mol And the mass of 7H2O 14 * 1.00794 + 7 * 15.999 = 126.10416 Now calculate what percentage of 278.01016 is 126.10416 126.10416 / 278.01016 = 0.453595509 = 45.3595509% = 45.360%