As we continue through lab this semester we will continue to revisit the concepts of stoichiometry and mole-mass relationships. One of the relationships that strengthens our understanding of both the math involved in and the relevance of stoichiometry is mass percent. The mass percent of a compound or element within another compound is often vital to the viability of a reaction. For example, in a hydrate the mass of the salt portion of the molecule is often a low percentage of the overall molecule's mass. Magnesium chloride hexahydrate (MgCl₂•6H₂O) is such a compound. The overall molecular mass is 203.3 g/mol. The salt is only ~46% of that mass. If I were manufacturing this compound I would have to take that into account since a majority of the product mass would not contain the salt compound I need.

Another place where mass percent is important is in medications. Very often the active ingredient in a medication is a very small portion of the overall mass of the tablet or capsule. The rest of the tablet is generally binders, flavors or other medications designed to counteract side effects. The Alka-Seltzer tablets that we will be investigating in this lab contain not only sodium bicarbonate, the acid neutralizing ingredient, but also two other ingredients, aspirin and citric acid. Our purpose in this lab will be to determine the mass percent of the sodium bicarbonate in an Alka-Seltzer tablet and compare our results to the published mass percentages given by the Akla-Seltzer company.

Because the sodium bicarbonate cannot be assessed directly as it reacts with the other ingredients in the tablet to form water and carbon dioxide, we will therefore measure the production of carbon dioxide use stoichiometry to determine the initial mass of the sodium bicarbonate. Thus, we will also have the opportunity to strengthen our understanding of mass to mole relationships. Using a balanced chemical reaction, any chemist should be able to tell you how much product can be made from a given amount of reactant or conversely, as in this case, how much reactant was used to produce a particular amount of product.