In this experiment you have an opportunity to learn about several topics in Chemistry. First, you will learn about a type of chemical reaction called an oxidation-reduction reaction. Second, you will learn about the air you breathe and find out that it is actually a mixture of different gases. Finally, you will be able to make a rough measurment of what fraction of the air is oxygen.
Iron is a very important element. It is most often used to make steel, an alloy of iron, manganese, chromium, and carbon. The steel is used to make everything from cars, to knives and forks, to bridges and large buildings. When iron rusts it changes color and begins to flake apart. Iron objects that are allowed to rust no longer function the way they were intended. Bridges may crumble if rust damage is not taken care of in time. Or maybe your bicycle chain will get so rusty you can’t pedal anymore. In 2002 a federal study backed by the U.S. Federal Highway Administration and carried out by NACE, the Corrosion Society, found that annual costs due to corrosion were $276 billion. This is more than a quarter of a trillion dollars. (source: http://www.nace.org/Publications/Cost-of-Corrosion-Study/ accessed Mar 6, 2013). In other words, rust is a big deal with huge real-world costs.
Rusting is a complex chemical reaction involving iron, oxygen, and water. In order for the reaction to work, water must be present: iron that never gets wet rusts extremely slowly or not at all. Iron that is wet and is exposed to air will quickly obtain a surface layer of rust. If the water is salty, the reaction may be even faster because the salt serves as an electrolyte which makes it easier for the iron atoms to give electrons to the oxygen atoms. Chemical educators classify this reaction as an oxidation-reduction reaction. Some may add that it is an example of a synthesis reaction. Here is one way to write the reaction symbolically:
In this reaction the iron gives electrons to the oxygen changing from the pure metal (Fe) to the ion iron(III) (Fe3+). The oxygen gains electrons and changes from pure oxygen (O2) to the oxide ion (O2–). The oxygen in this reaction comes from the air. Air is actually a mixture of many small components but only three major components. The Earth’s atmosphere is 78% nitrogen gas (N2), 21% oxygen gas (O2) and 1% argon gas (Ar). In this activity you will be able to measure the oxygen content of the air by causing iron to rust in a container that is closed off from the rest of the atmosphere by a water barrier. As the oxygen is used up water will rise in the container to take its place. The fraction of the container that is filled with water when the iron has reacted with all of the oxygen trapped in the container is the same as the fraction of the air that is oxygen.
Read all instructions completely before beginning your experiment. By knowing why you are doing each step you will be able to do it better. There are few hazards in this activity but as always, be careful when carrying out chemistry experiments. Keep the materials away from mouth, nose and eyes and do not eat or drink while working on the experiment. The rust may be handled but wash hands thoroughly after handling the rusty steel wool. When you are finished, throw the rusty steel wool away in the trash. Place the other items in your recycle bin.
Write the usual Real Life Chemistry report for this experiment.