Invert the cylinder and submerge it in water (in a drinking glass or in a shallow bowl, as illustrated in the video below).Make sure the steel wool does not fall out (if it does, fluff it up more and put it back). Then, open the tube and discard the vinegar in the sink or in your waste container. Close it with the cap and invert the cylinder a couple of times. Pour vinegar into the cap and transfer it into the tube. Divide the steel wool in your kit into four parts, “fluff it up”, and place it in a 15 ml tube.The vinegar acts as a catalyst – similar to salty wet conditions that will make your car rust faster in a New England winter than, say, in the Arizona desert. To make the reaction sufficiently fast, we will use a loosely packed sample of steel wool (the high surface area is advantageous in the reaction with a gas) that has been soaked vinegar (which is an acetic acid solution with additional molecules that give it flavor). We monitor the volume changes by running the reaction in an upside-down graduated tube submerged in water. The trick is to make the reaction fast enough so that most of the oxygen is used up within our lab session, and to run it in a way that we can observe the volume changes. If we run the reaction long enough to remove all of the oxygen, the volume change will indicate how much oxygen was present in the sample at the beginning. Oxygen in the gas state reacts with iron to form a solid product (rust), leading to a reduction in volume we can observe (the chemical equation is a simplification, but captures the important result that dioxygen is removed from air and becomes part of a solid):
The chemical reaction is the formation of rust. During that time, the air has to stay trapped so you can monitor by how much the volume of your sample decreases, and to prevent fresh air from replenishing the oxygen in you sample. In order to measure the oxygen content of your air sample, you will trap a defined volume of air in a 15 mL tube and run a chemical reaction that uses up the oxygen within about 40 minutes. \( \newcommand\)Ī chemical reaction that uses up the oxygen in air trapped in a 15 mL tube
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