Bleach as a Sanitizer (Temperature)
Name: Sabrina J. B.
I have been told that in order for chlorine bleach to be an effective
sanitizer, it must be used in lower temperatures such as 75-90 degrees. Is this true,
and if so, why?
I am not sure where/how the temperature interval was measured, but it does make chemical
sense. If the temperature is too high, the bleach decomposes thermally before it has a
chance to sanitize. If the temperature is too low, the reaction between the bleach and
microbes et.al. is too slow to be practical. In the presence of light, e.g. as a
swimming pool algaecide the photochemical decomposition also is important. The
exact temperature interval, and what is being sanitized against what, is chemically
complicated, but some temperature range of utility makes sense.
As is true for all gases, the chlorine gas (the sanitizing component of the bleach)
becomes less soluble in water as the temperature rises. The hotter the water, the less
chlorine present to do the work.
The liquid bleach available for households and laundries is a solution of sodium
hypochlorite NaOCL, at a pH of about 11 or higher. The high ph ensures that the
chemical equilibrium favors the OCl minus 1, not the less stable HOCl. At higher
temperatures the OCL disproportionates or breaks down into less stable compounds.
This means that liquid bleach works better at room temperatures and also has an
acceptable shelf life unless heated. I hope that this helps you out.
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Update: June 2012