A 2.144-g sample of phosgene, a compound used as a chemical warfare agent during World War I, contains 0.260 g of carbon, 0.347 g of oxygen, and 1.537 g of chlorine. What is the empirical formula of this substance?

First convert each mass to moles by dividing by the molar mass.

0.347g Oxygen = 0.022 moles

0.260g Carbon = 0.022 moles

1.537g Chlorine = 0.043 moles

Divide each by smallest mole vale (0.022)

Oxygen = 0.022/0.022 = 1

Carbon = 0.022/0.022 = 1

Chlorine = 0.043/0.022 = 2

Therefore the empirical formula is COCl2