Demonstrations

Aluminum powder is mixed with ferric oxide in a flower pot with a hole in the bottom. The reaction is initiated by reacting glycerine with a small amount of potassium permanganate on the top of the mixture. Because the reaction of glycerine with potassium permanganate generates heat, it "starts" the Thermite reaction, which is extremely exothermic. At the conclusion of the reaction molten iron drops from the flower pot into the pan (containing sand) below. The aluminum is converted into aluminum oxide. The lump of iron is shown at the conclusion being held by a pair of crucible tongs.


A beaker serves as a very crude calorimeter in this demonstration. A digital thermometer is used to measure the temperature change of the solution as ammonium nitrate is added. The drop in temperature indicates that the reaction is endothermic. In order to measure the heat absorbed per mole of ammonium nitrate, the heat capacity of the "calorimeter", the amount of solution, and the amount of ammonium nitrate added would all have to be accurately measured.


Six drops of glycerin are placed on top of a mound of potassium permanganate. The manganese is in a high oxidation state (oxidation state will be discussed in Chapter 18) and therefore can easily be reduced. When the glycerine is first added no reaction is observed. In fact, the reaction begins slowly and heat is generated as the reaction proceeds. After about 20 seconds "smoke" (that is, water vapor) is generated, the heat builds up, and the rate of the reaction increases. When the rate becomes fast enough the reaction proceeds very violently and essentially all of the glycerine is converted to dioxide and water vapor. The permanganate ion is reduced to manganese oxide.