Bromine dissolves in water

Bromine water

Bromine water is a saturated aqueous solution of bromine in water.

properties

Since bromine is only sparingly soluble in water, a brown-colored, dilute bromine solution is created. Due to the disproportionation to bromide and hypobromite, bromine water reacts slightly acidic:

$ \ mathrm {Br_2 \ + \ H_2O \ longrightarrow \ Br ^ - \ + \ BrO ^ - \ + \ 2 \ H ^ +} $

The reaction is accelerated by light. Bromine water is therefore stored in brown, less translucent bottles.

use

Bromine water is used in the laboratory for the rapid detection of C = C multiple bonds in organic compounds such as alkenes or alkynes. If an organic compound is introduced as a gas (e.g. ethene) into bromine water or shaken as a liquid with bromine water, whereby the solution becomes colorless, the sample substance contains at least one C = C double bond. This evidence is based on an electrophilic addition. The bromide ions, which are positively and negatively charged as a result of polarization and heterolytic cleavage, form bonds with the p electrons that were previously involved in the double bond.

$ \ mathrm {H_2C {=} CH_2 \ + \ Br_2 \ longrightarrow \ Br {-} CH_2 {-} CH_2 {-} Br} $
Bromine adds to ethene. 1,2-Dibromoethane is formed.

The reaction of bromine water with an alkane takes place only with a catalyst and / or under high-energy light. The bromine water is also decolorized, but HBr is also formed, since the reaction mechanism is now a radical substitution. It is very easy to differentiate between alkanes and alkenes.

$ \ mathrm {C_2H_6 \ + \ Br_2 \ longrightarrow \ C_2H_5Br \ + \ HBr} $
Substitution reaction of ethane and bromine. Bromethane and hydrogen bromide are formed.

safety instructions

The escaping bromine fumes are very poisonous. They must not be inhaled, as the bromine fumes corrode the alveoli and the airways. For details see article Brom.