Decomposition of Sodium Hypochlorite (NaOCl) and the Formation of Sodium Chlorate
The presence of transition metal ions (copper and nickel) is known to catalyze the
decomposition of liquid sodium hypochlorite, contributing to the loss of bleach
strength and the formation of oxygen. Loss of bleach strength means more product
will be needed when the bleach is used as a disinfectant. Oxygen build-up can pose
problems when storing sodium hypochlorite in storage containers or bleach transport
piping due to pressure build-up.
All bleach decomposition is dependant on temperature. For any given temperature,
the higher the strength, the faster it decomposes and the higher the level of oxygen
and chlorate formation. In summary, for every 10° C increase in storage temperature,
the sodium hypochlorite will decompose at an increased rate factor of approximately
Powell offers two free interactive tools showing the rate of decomposition of both
filtered and non-filtered sodium hypochlorite at varying strengths and temperature
as selected by the user. They also calculate the formation of oxygen and sodium
chlorate in sodium hypochlorite over time.
All sodium hypochlorite decomposition is dependant on temperature. For any given
temperature, the higher the strength the faster it decomposes. In order to completely
understand the decomposition of bleach with respect to strength versus temperature,
please refer to the AWWA research document "Minimizing Chlorate when Hypochlorite
is the Chlorinating Ion." In summary, for every 10°C increase in storage
temperature, the sodium hypochlorite will decompose at an increased rate factor
of approximately 3.5.
Sodium hypochlorite filtered with the
Powell Bleach Filter System contains only trace amounts of transition metal
ions, significantly reducing the rate of decomposition and virtually eliminating
the formation of oxygen.
For more information about sodium hypochlorite, visit the
Technical Information section.