what distiingushes in the different types of bleaching powder?
Answers
4.1.2 Sodium hypochlorite. 4.1.3 Bleaching powder. 4.1.4 Chlorine. 4.1.5 Chlorine dioxide.4.2 Peroxide-based bleaches. 4.2.1 Hydrogen peroxide. 4.2.2 Sodium percarbonate. 4.2.3 Sodium perborate.4.3 Miscellaneous bleaches.4.4 Reducing bleaches.
Most industrial and household bleaches belong to three broad classes:
Chlorine-based bleaches, whose active agent is chlorine, usually from the decomposition of some chlorine compound like hypochlorite or chloramine.
Peroxide-based bleaches, whose active agent is oxygen, almost always from the decomposition of a peroxide compound like hydrogen peroxide.
Sulfur dioxide based bleaches, whose active agent is sulfur dioxide, possibly from the decomposition of some oxosulfur anion.
Chlorine-based bleaches
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Chlorine-based bleaches are found in many household "bleach" products, as well as in specialized products for hospitals, public health, water chlorination, and industrial processes.
The grade of chlorine-based bleaches is often expressed as percent active chlorine. One gram of a 100% active chlorine bleach has the same bleaching power as one gram of elemental chlorine.
Mixing these bleaches with an acid such as vinegar can liberate chlorine gas, which is a respiratory irritant that attacks mucous membranes and burns the skin. Mixing these bleaches with other common household chemicals, such as ammonia, can produce other toxic gases.
The most common chlorine-based bleaches are:
Sodium hypochlorite (NaClO), usually as a 3–6% solution in water, usually called "liquid bleach" or just "bleach". Historically called "Javel water". It is used in many households to whiten laundry, disinfect hard surfaces in kitchens and bathrooms, treat water for drinking and keep swimming pools free of infectious agents.
Bleaching powder (formerly known as "chlorinated lime"), usually a mixture of calcium hypochlorite (Ca(ClO)
2), calcium hydroxide (lime, Ca(OH)
2), and calcium chloride (CaCl
2) in variable amounts.[16] Sold as a white powder or in tablets, is used in many of the same applications as sodium hypochlorite, but is more stable and contains more available chlorine.
Chlorine gas (Cl
2). It is used as a disinfectant in water treatment, especially to make drinking water and in large public swimming pools. It was used extensively to bleach wood pulp, but this use has decreased significantly due to environmental concerns.
Chlorine dioxide (ClO
2). This unstable gas is generated in situ or stored as dilute aqueous solutions. It finds large-scale applications for the bleaching of wood pulp, fats and oils, cellulose, flour, textiles, beeswax, skin, and in a number of other industries.
Other examples of chlorine-based bleaches, used mostly as disinfectants, are chloramine, halazone, and sodium dichloroisocyanurate.[17]
Peroxide-based bleaches
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Peroxide-based bleaches are characterized by the peroxide chemical group, namely two oxygen atoms connected by a single bond, (–O–O–). This bond is easily broken, giving rise to very reactive oxygen species, which are the active agents of the bleach.
The main products in this class are:
Hydrogen peroxide itself (H
2O
2). It is used, for example, to bleach wood pulp and hair or to prepare other bleaching agents like the perborates, percarbonates, peracids, etc.
Sodium percarbonate (Na
2H
3CO
6), an adduct of hydrogen peroxide and sodium carbonate ("soda ash" or "washing soda", Na
2CO
3). Dissolved in water, it yields a solution of the two products, that combines the degreasing action of the carbonate with the bleaching action of the peroxide.
Sodium perborate (Na
2H
4B
2O
8). Dissolved in water it forms some hydrogen peroxide, but also the perborate anion (B(OOH)(OH)−
3) which can perform nucleophilic oxidation.[18]
Peracetic (peroxoacetic) acid (H
3CC(O)OOH). Generated in situ by some laundry detergents, and also marketed for use as industrial and agricultural disinfection and water treatment.[19]
benzoyl peroxide ((C
6H
5COO)
2). It is used in topical medications for acne[17] and to bleach flour.[20]
Ozone (O
3). While not properly a peroxide, its mechanism of action is similar. It is used in the manufacture of paper products, especially newsprint and white Kraft paper.[21]
Potassium persulfate ( K2S2O8) and other persulfate salts. It, alongside ammonium and sodium persulfate, are common in hair lightening products.[22]
Permanganate salts such as Potassium permanganate (KMnO4).
In the food industry, other oxidizing products like bromates are used as flour bleaching and maturing agents.
Reducing bleaches
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Sodium dithionite (also known as sodium hydrosulfite) is one of the most important reductive bleaching agents. It is a white crystalline powder with a weak sulfurous odor. It can be obtained by reacting sodium bisulfite with zinc
2 NaHSO3 + Zn → Na2S2O4 + Zn(OH)2