 Quantitative chemical analysis involves the scientific concepts and technological skills needed to determine the quantity of a substance in a sample.

(pronounced as “stoy-kee-ah-meh-tree”)  Stoichiometry is the study of the amount of reactants and products involved in chemical reactions. It is the quantitative description of the proportions by moles of the substances in a chemical reaction. These proportions can also be expressed as grams or molecules.

 Consider a chemical reaction as a recipe. For example, to build a car, you need a body (B), an engine (E) and tires (T). The completed car would have the "formula" BET 4. The balanced equation for the production of 1 car is: B + E + 4T  BET 4

 How many engines and tires do you need in order to produce 50 cars?  According to the balanced equation, stoichiometry tells you that for every car, 1 engine and 4 tires are needed.  So, for 50 cars, you need 50 engines and 200 tires.

 Stoichiometry allows you to compare the amounts of any materials in the same chemical equation using their coefficients from the equation.  The coefficients of the balanced chemical equation indicate the numbers of moles (or molecules) of reactants and products in a chemical reaction. An equation is a chemist’s recipe. It indicates the amounts of reactants to mix and the amounts of products to expect.

 When doing experiments, it is unscientific and dangerous for you to mix chemicals in a haphazard manner.  Before any practical laboratory work is done, you must always start with a balanced reaction equation.  When you know the quantity of one substance in a reaction, you can calculate the quantity of any other substance consumed or created in the reaction.

 Ammonia is widely used as a fertilizer. It is produced industrially by the reaction of nitrogen with hydrogen. How many moles of product could 10 moles of nitrogen produce? Using the coefficients from the balanced chemical equation, you can see that 1 mol of nitrogen reacts with 3 mol of hydrogen to form 2 mol of ammonia. N2 and H2 will always react to form ammonia in this 1:3:2 ratio of moles. So if you started with 10 mol of N2 it would take 30 mol of H2 and would produce 20 mol of NH 3

 When heated, potassium chlorate decomposes into potassium chloride and oxygen: 2KClO 3  2KCl + 3O 2 How many moles of oxygen are produced by the decomposition of 2.8 mol of potassium chlorate? 2 mol of potassium chlorate give 2 mol of potassium chloride and 3 mol of oxygen. You can use mole ratios of the coefficients: for every 2 mol of KClO 3 that decomposes, 3 mol of O 2 is formed. The ratio can be represented as: Since 1 mol of KClO3 produces 1.5 mol of O2, you now multiply by 2.8 mol. So, 4.2 mol of O2 are produced from 2.8 mol of KClO 3.