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Commonly the most dangerous chemical found in a household, bleach is an inorganic
aqueous solution of 5.25%
sodium hypochlorite. Bleach is a clear to yellowish liquid with a distinct
chlorine like odor. Often mistakenly referred to as "chlorine bleach" because of its strong smell, bleach does not release a considerable amount of chlorine gas during its normal mode of action. Bleaches often include
sodium hydroxide to maintain a pH-dependent equilibrium between the
hypochlorite and
chlorine the solution contains. Household bleach normally has a very
alkali pH of around 12.5, and it is highly
corrosive. Different solution strengths are marketed for different uses. High strength bleach is usually a 10% sodium hypochlorite
solution, and some industrial bleaches may be up to 50%.
Pool chlorine is usually 12%.
Household bleach is an
unstable solution. Chlorine evaporates from it at a rate of 0.75 gram active per day. When heated to temperature above 40C, or placed in direct sunlight, bleach disintegrates into its component chemicals. It is
vigorously reactive with many chemicals, is a strong
oxidator and reacts with flammable compounds and reductors.
Given these facts, why would any one want to have bleach around?
The key is
disinfection. Every day, millions of households throughout the
world rely on sodium hypochlorite bleach for their disinfection, deodorizing and
cleaning needs. Bleach has long been recognized as having outstanding disinfective properties. The
Institute Pasteur lists it as the most effective
disinfectant against all known pathogenic
bacteria,
fungi and
viruses. Its
low cost and ready availability makes it an invaluable weapon for the maintenance of
human health and proper preventative
hygiene, throughout the world. It is also used in the removal of
mold and
mildew.
NASA relied on bleach during the
Apollo program to assure destruction of any potentially harmful organisms introduced from space by returning
spacecraft. It has the advantage that
microorganisms cannot build up any
resistance to it. It can be produced, stored and transported, and used easily and safely.
Dosage calculation is simple. Sodium hypochlorite bleach is as chemically
effective as chlorine gas for disinfection and it leaves residual disinfectant products when used. In Canada, "
Javex" brand bleach has been sold continuously since 1935. It definitely has a commercial future.
How does bleach disinfection work?
By adding hypochlorite to water, hypochlorous acid (HOCl) is formed:
NaOCl + H2O = HOCl + NaOH-
Hypochlorous acid is divided into hydrochloric acid (HCl) and oxygen (O). The oxygen atom is a very strong oxidator.
What else is it good for?
Bleach is also used as a
whitener,
stain remover and
sanitizer for
laundry. When used as a supplement to laundry
detergent, It is highly effective at removing a wide range of tough stains e.g.
blood,
body soil,
coffee,
grass,
mustard, and
red wine. Conversely, one of the hazards of laundry bleach use is the tendency for it to
blanch bright colors and
weaken fibers. If directly dripped on fabrics, it can cause spotting or even
holes. Bleach is more commonly used when washing white clothing as a
brightening agent.
Not happy with the title of "World's Most popular Germ-Killer", bleach is also used in great quantities by industries worldwide. An enormous
commercial market for industrial
bleach exists, where it used for
waste water treatment,
drinking water disinfection and
textile and
paper manufacturing. It is used to treat
sewage and industrial wastes to reduce odors and increase digesting efficiency. Hypochlorite bleach neutralizes
sulphur hydrogen gas (SH) and
ammonia (NH3). It detoxifies
cyanide baths in metal finishing industries and treats cyanide
effluents created by
gold mining. Bleach is also used to recover precious metals from manufacturing solutions.
Air scrubbing systems use bleach to destroy
pathogens and neutralize gases. Without bleach, much of the
food processing done in
North America would not be possible. It is used to clean dairy equipment and food processing equipment, in fruit, vegetable, mushroom, hog, beef, poultry, fish and
maple syrup processing. One of the first uses for commercial uses bleach was its use as a
cotton whitener. It remains one of the most important chemicals used in
textile manufacturing. Bleach is also used to whiten
paper,
soap,
straw,
wood and many other
organic products.
The common smell of
swimming pools is created by bleach. It is used in swimming pool water disinfection, both as a daily regimen and as a shock treatment. An interesting tidbit is that if a pool smells of
chlorine, it probably isn't very clean. When bleach reacts with
ureum (a mixture of urine and sweat), hypochlorous acid and ureum react to form
chloramines. These chloramines irritate mucous membranes and cause the so-called 'chlorine smell'.
Who came up with this wonderful stuff?
French chemist Claude Louis Berthollet, while working in the town of
Javel on the outskirts of
Paris, discovered sodium hypochlorite in 1787. Berthollet focused much of his work on the use of
dyes, and was primarily interested in bleaches when used to whiten textiles. His discovery was quickly put to
commercial use.
The Javel Company introduced bleach to France, naming the product 'eau de Javel'. It was so popular that bleach is still known by that colorful name in
France today. Another enterprising French scientist,
Louis Pasteur, discovered the potent effectiveness of bleach when used against disease-causing bacteria. After Pasteur detailed the unsurpassed
disinfection spectrum of bleach, its use as a disinfectant skyrocketed.
How is bleach made?
Sodium hypochlorite bleach is usually created in one of these two ways:
The
cheapest and
safest was is by creating a concentrated brine solution by dissolving
salt (
sodium chloride) in softened water (H20). By running electricity through this solution, sodium hypochlorite forms in water. This solution contains 150 g active chlorine (Cl2) per liter. During the electrolyzing reaction, explosive
hydrogen gas is also formed. This is the safest way? Actually, yes.
The far more
dangerous way to make bleach, which was also the method used by Berthollet, is by adding
chlorine gas (Cl2) to caustic soda (NaOH). When this is done, sodium hypochlorite, water (H2O) and
salt (NaCl) are produced according to the following reaction:
Cl2 + 2NaOH + = NaOCl + NaCl + H2O
This solution is also known as "Eau de Labarraque", and "Eau de Javel".
What are the danger of misusing bleach?
Bleach is made up of
sodium,
oxygen and
chlorine, some of the most
reactive of all chemicals. When bleach reacts with another substance, or is broken down in any way, these chemicals are released in ways that are rarely beneficial to
biology.
The most important thing to remember about
bleach around the house are other cleaning substances that it reacts with dangerously.
Ammonium, found in some cleaning products, mixed with
sodium hypochlorite evolves
nitrogen trichloride. Nitrogen trichloride smells like chlorine and is nearly as deadly. Deadly
chlorine gas is created when bleach and
hydrochloric acid are mixed, but few people use acid around the house for cleaning. As a strong
base, bleach should not be mixed with a strong
acid. That sort of thing is basic chemistry, what with the
hydrogen ions being passed around in an energetic manner.
Bleach decomposes slowly when stored properly, but
decomposition is speeded up by temperatures above 40 degrees C and light. While decomposing, bleach becomes chlorine gas, oxygen gas, and
sodium chlorate.
There are lots of other things you shouldn't mix bleach with.
Nitrogen compounds (e.g., ammonia, urea, amines, isocyanurates) can form toxic, reactive
chloramines and nitrogen gas.
Methanol and bleach can form
methyl hypochlorite, which is explosive. Metals, like
copper,
nickel and
cobalt, speed up the decomposition of NaOCl, while others will rapidly
corrode because of oxygen reactions.
Assume the worst when using bleach, because it will react with almost anything.
So, you messed up. How can bleach kill you?
The previously mentioned
nitrogen trichloride and
chlorine gases cause burning in the throat and coughing. High levels of
exposure can lead to swelling and obstruction of the airway. In serious cases
noncardiogenic pulmonary edema can occur. Bleach will react with
skin and eyes causing
corrosive burns and tissue
necrosis. In small amounts it is a
skin irritant, and inhaled aerosols can inflame the lungs. It is very
harmful when ingested, as it reacts with the
acidic environment of the digestive tract. Extensive damage to the mouth, throat, eyes, lungs, esophagus, nose, and stomach are possible. Damage can continues to occur to the esophagus and stomach for several weeks after the
alkali was swallowed, and death may occur as long as a month later. If bleach is swallowed,
vomiting should
not be induced. Give milk or water and seek emergency medical care immediately. If bleach is on the
skin, wash with lots of water. Ingested bleach can cause a severe change in
blood pH which can damage all
internal organs, but it is rare. Deaths caused by the misuse of bleach are
extremely rare.
Sodium hypochlorite is a known
mutagenic, but bleach is not a
mutagen,
carcinogen,
teratogen or
skin sensitizer. The IARC (the International Agency for Research on Cancer) has concluded that
chlorinated drinking water is not a "classifiable" human
carcinogen. Bleach decomposition creates tiny amounts of
absorbable organic halides (AOX), which have potential negative health effects in humans. That being said, the majority of these AOXs are easily
degradable, are primarily
water soluble and not
bio-accumulative. Highly chlorinated species, such as
dioxins, are not formed.