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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.