Electrolysis of brine
Brine is a concentrated or saturated solution of sodium chloride in water. The process of electrolysis uses electricical energy to produce a chemical reaction in the sodioum chloride solution which results in the formation of sodium hydroxide, chloirine and hydrogen gas. The equation for this chemical reaction is as follows.
Sodium chloride + Water =electrolysis=> Sodium hydroxide + Hydrogen + Chlorine
NaCl + H2O =electrolysis=> NaOH + H2 + Cl2
The manufacture of sodium hydroxide or caustic soda is an important industrial process
The electrochemistry involved in the reaction involves an reduction oxidation reaction, which is sometimes called a redox reaction.
Electrolysis of salt solution, NaCl
In a solution of brine there are three chemical species: The sodium ion, Na+, the chloride ion, Cl- and water, H2O. The easiest chemcial species to oxidise is the chloride ion. The eaasiest chemical species to reduce is the water.
The anode is the electrode where oxidation or the loss of electrons take place. In an electolytic cell the anode is positive in charge. The chloride ion is oxidised to chlorine gas.
Cl- =oxidation=> ½Cl2 + e-
H2O + e- =reduction=> ½H2 + OH-
In water the sodium ion is not reduced as it is much easier to reduce water. The sodium ion becomes a spectator ion and is not involved in the reaction.
The overall chemical equation for the electrolysis of brine is
NaCl + H2O =electrolysis=> H2 + Cl2 + NaOH
In industry the hydrogen gas must be separated from the chlorine gas or they will explode when exposed to UV light producing hydrogen chloride. H2 + Cl2 =UV=> 2HCl
Sodium hydroxide is caustic in nature and must be handled with care. It is used in industry in the manufacture of soap by saponification. It is also used to make pulp and in the production of paper.