Laboratory preparation of nonmetals
Preparation of bromine
In a ground flask containing 250 ml hang of a mixture of 10 g finely minced potassium bromide and 10 g of powdered potassium dichromate. Place the flask in the terminals and put on a stand with asbestos mesh. The flask join declining ground-cooler. As a model using a small ground-glass flask. Then pour the contents of the flask 30 ml conc. sulfuric acid and the apparatus closed immediately. When the vigorous reaction ceased, have driven nepředestilovaný bromine by heating the flask to about 60 ° C. The resulting product is distilled again.
Brom strongly etching the skin and mucous membranes, so we work in a fume hood or outdoors.
A possible alternative for the preparation of a solution of bromine in water, the reaction of bromide and bromate in an acidic environment (created bromine water).
Preparation of iodine
In a conical flask Pour 10 g of potassium iodide and dissolve it in 12 ml of water. Into such a solution introducing a stream of chlorine. The reaction should be carried out under cooling with ice, it is strongly exothermic and could leak iodine vapor. The introduction of chlorine exit to a solution of iodine excluded fawn. A thick, pasty crude sharply sucked on a Buchner funnel, dried between sheets of filter paper and purified by sublimation.
Preparation of amorphous silicon by reduction with magnesium
A mixture of 10 g of powdered magnesium and 30-40 g silica powder is placed into a tube of glass těžkotavitelného. Tube first and then heat the whole very hot gas burning her bottom. After completion of the reaction tube let cool, then crack the tube. The reaction product immersed in water and slowly pouring hydrochloric acid (1:1). It develops a certain amount of silane samozápalného, ??so everything is done in a fume hood. After silicon decanted water and let about 24 hours in conc. hydrochloric acid. Thus prepared silica contains a large amount of silica. The product is placed in a platinum dish, add conc. hydrofluoric acid so as to cover the silica fume and evaporate about 2 hours until the acid does not remove the major part. Thereafter dilute mixture of water four times and add conc. sulfuric acid and the mixture was evaporated until it starts releasing white fumes of sulfur trioxide.
The mixture is cooled, dilute sixfold amount of water, the silicon was washed with water and dry.