Gravimetric Stoichiometry: Examining the Law of Conservation of Mass

The Gravimetric Stoichiometry lab was a two-week lab in which we tested one of the fundamental laws of chemistry; the Law of Conservation of Mass. The law states that in chemical reactions, when you start with a set amount of reactant, the product should theoretically have the same mass. This can be hard sometimes because in certain reactions, gases are released and it’s hard to measure the mass of a gas. Some common gases released in chemical reactions include hydrogen, carbon dioxide, oxygen and water vapor. One of the best methods for determining mass in chemistry is gravimetric analysis (Lab Handout). It is essentially using the the mass of the product to figure out the original mass that we are looking for. Thus the purpose of our experiment was to compare the final mass in our reaction to the initial mass and determine the change in mass. In our experiment we utilized the hydrate cobaltous chloride. Hydrates are crystalline compounds in which one or more molecules of water are combined with each unit of a salt. Cobalt (II) chloride hexahydrate is an inorganic compound which is a deep rose color in its hydrated form. As an inducer of
Our procedure though was not without its mistakes. These mistakes are vital because they affect the data we conclude. Theoretically, according to the balanced chemical equation, for every mole of hydrated cobaltous chloride that is being heated, the decomposition ensures that the compound decomposes into one mole of cobalt(II) chloride and six moles of gaseous water vapor. Thus, in theory we should lose the mass equal to six moles of water vapor in each trial. Unfortunately, this is not the case because we don’t have perfect lab conditions and factors such as the time heated, utilization of the same crucible, and the inconsistency of magnitude of the flame from the Bunsen burner all contribute to differences in mass percent change for each