Why do the experiment?

Many students will have done this experiment before they started the Diploma programme so some teachers are surprised I include it. It is very simple (so there is no separate worksheet) but I find it worthwhile for three reasons. The first is to show that using simple materials can sometimes be better. Traditionally a porcelain crucible is used but I used to find that these often cracked in the heat and were expensive to replace. In addition it was also necessary to keep lifting the crucible lid with tongs in order to let air in. Now I use two metal beer bottle caps which cost nothing and actually do a better job! The second important reason for the experiment is that it is useful early on in the programme to train students how to evaluate an experiment. The third, and possibly the most important reason, is that it covers one the mandatory laboratory component areas, Topic 1.2. 'The obtaining and use of experimental data for deriving empirical formulas from reactions involving mass changes'.