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The halogens are a useful group for verifying trends in the variation of reactivity with atomic number. However, their toxicity and hazardousness make them difficult to obtain and manipulate. In this paper we propose an easy-to-build apparatus to obtain chlorine, bromine, and iodine. The experiment was developed considering not only theoretical and safety conditions but simplicity and clarity as well. Even so, a trained teaching assistant must lead the experiment. The method requires about half an hour and it has been used successfully for more than ten years.
The experiment is based on electron transfer reactions typical of the group. Normal potentials (as a first approximation) are used to justify complete and balanced redox reactions, which are written down. Results are indicated by the presence of the halogens, which can be easily followed by some of their visual physical properties such as color, aggregation state, and solubility. This information is used to deduce the connection between chemical behavior and the variation of atomic number. Last but not least, teaching laboratory policies are taken into account, including the handling of chemicals after working and before they are disposed of properly.
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