Halogens are the group VII elements, mainly Fluorine, Chlorine, Bromine and Iodine.
Going down the group some distinct properties can be seen:
- The reactivity down the group decreases a lot, due to an increase in the radius of the atom.
- Fluorine and Chlorine are gases, with Bromine being liquid and Iodine being a solid.
Displacement Reactions
A set of reactions which are very important in the halogens group is the displacement reactions, where a reactive halogen will replace a less reactive one, such as the displacement of Bromide ions with Chlorine.
Fluorine is never used due to its reactivity, and therefore Chlorine is the most reactive followed by Bromine followed by Iodine.
Preparation of Chlorine
Chlorine can be prepared by removing the hydrogen from hydrochloric acid using an oxidisign agent. Any oxidizing agent such as manganese dioxide, potassium dichoroamte and potassium permanganate can be used. The oxygen of the oxidizing agents combines with the hydrogen of the hydrochloric acid leaving behind chlorine.
A test for Chlorine is its bleaching action on litmus paper. It first turns blue litmus paper red, and then it bleaches it.
Bleaching action of Chlorine
Chlorine bleaches organic colours by the process of oxidation in presence of moisture:
- Chlorine first dissolves in water to give a mixture of Hydrochloric acid and Hypochlorous acid.
- The hypochlorous acid is very unstable and decomposes to give hydrochloric acid and nascent oxygen.
- The nascent oxygen oxidizes the colouring matter to colourless matter, resulting in bleaching
Colouring Matter + Nascent Oxygen → Colourless Matter