Help with law of multiple proportions.

AP Chemistry help please!?

• A compound made of iron and oxygen weighs 12.8g. Upon heating it now weighs 11.52g. When reduced to pure iron it weighed 8.96g. a) mass of oxygen in the 1st compound b)mass of oxygen in 2nd compound c) ratio of mass of oxygen in 1st compound to mass of oxygen in 2nd compound d) how demonstrates law of multiple proportions e) if there was still oxygen present in pure iron what would be effect on ratio, explain. Help much appreciated. Confused on how heating reduces mass of FeO.

• Answer:

  Assuming that the mass of 8.96g is indeed that of pure iron: a) Mass of oxygen in the 1st compound 12.8g - 8.96g = 3.84g b) Mass of oxygen in the 2nd compound 11.52g - 8.96g = 2.56g c) Ratio of mass of oxygen in 1st compound to mass of oxygen in 2nd compound 3.84g:2.56g = 3:2 d) The ratio of whole numbers for oxygen in the 1st and 2nd compounds indicates that oxygen combines with iron in discrete proportional units. e) If the iron after reduction still contains oxygen the ratio between oxygen and iron in the beginning and intermediate compounds would be changed. For example, if the pure iron has no oxygens after reduction the initial compound (12.8g) will have an oxygen:iron ratio of (3:2), if the "pure" iron still contains oxygen, the oxygen:iron ratio of the initial compound may be (4:2) or (5:2). Heating reduces the mass of the iron-oxygen compound by removing one oxygen from the compound and forming a different iron-oxygen compound: 2Fe2O3 (heat) → 4FeO + O2 (reduction) → 4Fe + 3O2 Note: depending on the reduction reaction, the oxygen may be now in a different compound.