From the periodic table:
mass of calcium = 40 grams
mass of sulfur = 32 grams
mass of oxygen = 166 grams
Therefore:
molar mass of CaSO4 = 40 + 32 + 4(16) = 136 grams
number of moles can be calculated as follows:
number of moles = mass / molar mass
number of moles = (7.3 x 10^-3) / (136) = 5.367 x 10^-5 moles
