Although chlorine is commonly used as a bleaching agent, chlorine and bleach are not interchangeable. While bleach is a broad category for any chemical that can remove or lighten colour, chlorine is a specific chemical element that exists in nature and has many uses, including chlorine bleach. Further examination of the two substances reveals more of their types, differences and uses.
Definition of Chlorine
Chlorine is a chemical element that exists in the earth and oceans as a yellow-green gas, but can be converted to a liquid with the correct temperature and pressure. It was discovered in 1772 by Karl Wilhelm Scheele, and, in the decades following, was found to have many useful properties.
In its gaseous form, chlorine was first added to a solution of potash and later limestone to make a powerful bleach powder for cloth and paper.
Chlorine gas mixed with sodium hydroxide creates sodium hypochlorite, which, mixed with water in a 5.25 per cent solution, is chlorine bleach in the form most commonly used in modern times.
Released into the air, chlorine reacts with water to form hydrochloric acid, which can then be broken down to make products that lower the pH of water.
Uses of Chlorine
Aside from being essential to the lives of plants and animals, chlorine has many manufactured uses as well. Primarily, it is added to drinking water and swimming pools as a disinfectant. Chlorine in drinking water (added as 0.2 ppm to 3 ppm) kills bacteria linked to life-threatening diseases such as cholera. In swimming pool water, it kills bacteria and algae.
Chlorine is also a stain remover. Natural stains are chemical compounds called chromophores, and when chlorine reacts with water, the atomic oxygen created reacts with the chromophores to remove the colour of the stain.
Dangers of Chlorine
Exposure to chlorine gas can be dangerous and cause negative health effects. It is corrosive, and even small amounts may cause irritation of the throat, coughing, and eye and skin irritation. Higher amounts of gas may cause burning eyes and skin, blue colouring of the skin, narrowing of the bronchi, fluid build-up in the lungs, and pain in the chest. A byproduct of chlorine, dioxin, has caused much environmental debate.
Definition of Bleach
A bleach is any chemical used to lighten or remove colour. Though bleach usually brings to mind the chlorine bleach used for washing powder, bleaches exist in many forms, among them sunlight and lemon juice. Other bleaches include oxygen bleach, sodium persulfate, calcium peroxide, zinc peroxide, bromate, chlorine dioxide and sodium persilicate. Most bleaches are oxidising agents, but others, such as sodium dithionite, remove colour through the process of reduction.
How Bleach Works
The final outcome of using either oxidising or reducing bleach is the same: they both get stains out of clothing. But the process is different for each type. Oxidising bleach breaks the chemical bonds of the chromophore, or the area of the molecule with colour. This makes a shorter molecule, and because a shorter chromophore absorbs light of a shorter wavelength than visible light, it does not appear coloured to the human eye. Reducing bleach changes the double bonds of the chromophore to single bonds, which eliminates the molecule's ability to absorb visible light. Hence, again it appears colourless.
Uses of Bleach
Aside from making stains appear colourless, bleach has many other uses as well. Oxidising bleaches like hydrogen peroxide are used to lighten hair, and sodium carbonate peroxide or carbamide peroxide is used to whiten teeth. Benzoyl peroxide is used as a bleaching agent to whiten wheat flour, and sulphur dioxide is a reducing bleach that helps to preserve dried fruit. Oxidising bleach, most often sodium hypochlorite or calcium hypochlorite, is also used as a disinfectant in households, drinking water and swimming pools.
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