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ExposeExciteIgniteMay2012

6 Magnesium Pencil

6 Magnesium Pencil Sharpener Secrets This is the stuff MacGyver’s dreams were made of. If your students think the sodium and potassium-on-water demonstration is spectacular, wait till they see this one. Magnesium beats the other alkali metals hands down in this eye popping spectacle. Can iron burn? Can you light steel with a battery? Can magnesium burn under water? These questions are not only intriguing, they touch the basics of alkali and alkali-earth chemistry and make great visual demonstrations in the laboratory. We have mentioned before that combustion (burning) is simply a chemical reaction in which a chemical substance reacts rapidly with oxygen to form an oxide, heat and light in an exothermic reaction. It is also known as ‘oxidation’ since an oxide is formed and classified as a redox reaction. Thankfully it requires activation energy to get the process going eg. lightning, flame, spark or friction. Lets look at the first question. A. Can Iron burn? [] What you will need • Steel wool - In paint section at hardware store, Grade: 0000, super fine • Steel nail • Workshop grinding wheel • 9V Battery • Tongs or pair of pliers • Heat resistant mat • Protective wear Figure 7.1 73

Safety / Risk assessment ! Wear protective eye wear and clothing and handle the steel wool with tongs /pliers ! Use a sensible size of steel wool and burn it above the heat resistant mat Here’s how 1. Use a lighter and try to light a steel nail. Why doesn’t it catch fire? Simply because the surface area is too small! 2. Hold the nail to a workshop grinding wheel and see how the friction energy breaks the steel into tiny particles and heats them till they burn white hot. We call the burning particles “sparks” (Figure 7.2). They ignite easily as their surface area/volume ratios are much larger than those of the nail. 4Fe + 3O2 " 2Fe2O3 + energy 3. Take a wad of fluffed out steel wool with a pair of pliers or metal tongs. Hold it over a heat resistant mat and touch the battery’s terminals to the steel wool (Figure 7.3). Due to the high resistance in the thin single strands, the wires will heat up. This energy is sufficient to start the oxidation process of the steel wool. The process races along the strands in the wad until all is oxidized. You will be be left with only iron oxide. Figure 7.2 Figure 7.3 4. Fan the combustion by increasing the oxygen ‘concentration’ by gently blowing on the red steel wool. Why did this happen? We have three changed conditions here that greatly increased the rate of combustion: 74