Introduction
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 is 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.
Our entire system of stoichiometry is based on the veracity of these laws. The purpose of this lab experiment is to verify 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, the emission of a gas, or some other chemical change that can be visually monitored. There are reactions that we observe quite often, such as wood burning, that could be used but that are difficult to quantify because their products escape as soon as they are produced. When wood burns it is converted into water and carbon dioxide which escape as gases as soon as they are formed. More importantly, the other by-product of this reaction is extreme heat, which makes trapping the gases difficult and beyond the technology available in most introductory chemistry laboratories.
Since it produces both a color change and a gas, the reaction of copper (II) sulfate and zinc metal in aqueous HCl is useful for our purposes. The reaction can be monitored by observing the loss of blue color in the solution, by the production of hydrogen gas, and by the formation of solid copper. By quantifying the reactants and products of this reaction, we will be able to confirm that the total mass remained unchanged (within experimental error) while visually confirming that a reaction did in fact occur.