= Production of household bleach
Household bleach mainly contains sodium hypochloride, NaOCl (eau de Javel). It is an unstable white powder that dissolves in water to give a yellow stable solution.
It also contains small amounts of NaoH, $H_2O_2$ and $Ca(OCl)_2$. The first method of producing bleach involved a reaction between chloride gas $Cl_2$ and sodium carbonate ($Na_2CO_3$). Later, sodium carbonate was replaced by caustic soda (soda lye), NaOH, a cheaper substance that also made the production more efficient.
In this reaction, $Cl_2(g)$ is reaction with a solution of NaOH giving a spontaneous reaction:
$$
Cl_2 (g) + 2NaOH(aq) \rightarrow NaCl(aq) + NaClO(aq) + H_2O
$$
The raw materials of the reaction, chloride and caustic soda come from the electrolysis of brine.