There is a scientific law called the Law of Conservation of Mass, discovered by Antoine Lavoisier in 1785. In its most compact form, it states:

matter is neither created nor destroyed.

In 1842, Julius Robert Mayer discovered the Law of Conservation of Energy. In its most compact form, it it now called the First Law of Thermodynamics:

energy is neither created nor destroyed.

In the early 20th century, Albert Einstein announced his discovery of the equation E=mc² and, as a consequence, the two laws above were merged into the Law of Conservation of Mass-Energy:

the total amount of mass and energy in the universe is constant.

What does this mean to us? Well, these laws allow us to balance chemical equations, calculate product amounts and determine whether reactions will be spontaneous or not. Our entire system of stoichiometry is based on the veracity of these laws. The purpose of the lab experiment you will be performing is to allow you to convince yourself of at least the first of these laws, the law of conservation of mass.

If you were to design an experiment to confirm this law, you would want to observe two things: 1) A reaction is taking place; and 2) The total mass of all reactants is equal (within experimental error) to the total mass of all the products. In order to observe a reaction taking place, there must be a color change, or the emission of a gas or some other chemical change that can be visually monitored. There are several types of reactions that we can observe, such as wood burning, that are difficult to quantify because their products escape as soon as they are produced. Wood for example burns into water and carbon dioxide which escape as gases as soon as they are formed. The other by-product of this reaction is extreme heat which makes trapping the gases difficult and beyond the technology available to us in the CHM1045L laboratory.

Another type of reaction that produces both a color change and the production of a gas is the reaction of copper II sulfate and zinc metals in aqueous HCl. The reaction can be monitored by observing the leaching of copper from the solution (loss of blue color) and the production of hydrogen gas. This reaction satifies both of the previously stated requirements for our desired experimental reaction. By quantifying the reactants and products of this reaction, we will be able to confirm for ourselves that a reaction did take place and that the total mass remained unchanged (within experimental error).

As always in lab, there are other purposes being served along with the learning of a new concept. We will also be revisiting the use of the analytical balance and producing our first chemical solution. You will notice the phrase "within experimental error" being used a couple of times above. This is because with any experiment there is a certain amount of reactant and product lost when they are transferred from flask to flask or spilled, splashed or dropped as part of the human error in the experiment. These "errors" must be taken into account when reporting the results of any experiment. Statistics are often used to indicate the relative importance of the error. For example, losing 100 grams of product would seem tremendous unless it was compared to an expected product mass of 2.5 x 10⁶ g. Then this error seems very small indeed. We will use this experiment to practice our knowledge and use of statistics to report the error in the mass of products created from the mass of reactants used.