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Calcium hypochlorite is an inorganic compound with formula Ca(ClO)2. As a mixture with lime and calcium chloride, it is marketed as chlorine powder or bleaching powder for water treatment and as a bleaching agent.[1] This compound is relatively stable and has greater available chlorine than sodium hypochlorite (liquid bleach).[2] It is a white solid, although commercial samples appear yellow. It strongly smells of chlorine, owing to its slow decomposition in moist air. It is not highly soluble in hard water, and is more preferably used in soft to medium-hard water. It has two forms: dry and hydrated.

Uses

Sanitation

Calcium hypochlorite is commonly used to sanitize public swimming pools and disinfect drinking water. Generally the commercial substance is sold with a purity of a 68% (with other additives and contaminants varying based upon the product's intended purpose). For instance as a swimming pool chemical it is often mixed with cyanuric acid stabilizers and anti-scaling agents (in order to reduce the loss of chlorine from ultraviolet radiation and to prevent calcium hardening). Calcium hypochlorite is also used in kitchens to disinfect surfaces and equipment.[3] Other common uses include bathroom cleansers, household disinfectant sprays, algaecides, herbicides, and laundry detergents.

Organic chemistry

Calcium hypochlorite is a general oxidizing agent and therefore finds some use in organic chemistry.[4] For instance the compound is used to cleave glycols, α-hydroxy carboxylic acids and keto acids to yield fragmented aldehydes or carboxylic acids.[5] Calcium hypochlorite can also be used in the haloform reaction to manufacture chloroform.[6]

Production

Calcium hypochlorite is produced industrially by treating lime (Ca(OH)2) with chlorine gas. The reaction can be conducted in stages to give various compositions, each with different concentration of calcium hypochlorite, together with unconverted lime and calcium chloride. The full conversion is shown[1]

2 Cl
2
+ 2 Ca(OH)
2
Ca(OCl)
2
+ CaCl
2
+ 2 H
2
O

Bleaching powder is made with slightly moist slaked lime. It is not a simple mixture of calcium hypochlorite, calcium chloride, and calcium hydroxide. Instead, it is a mixture consisting principally of calcium hypochlorite Ca(OCl)2, dibasic calcium hypochlorite, Ca3(OCl)2(OH)4, and dibasic calcium chloride, Ca3Cl2(OH)4.[7]

Properties

Calcium hypochlorite reacts with carbon dioxide to form calcium carbonate and release dichlorine monoxide:

2Ca(ClO)
2
+ 2CO
2
→ 2CaCO
3
+ 2Cl
2
+ O
2

A calcium hypochlorite solution is basic. This basicity is due to the hydrolysis performed by the hypochlorite ion, as hypochlorous acid is weak, but calcium hydroxide is a strong base. As a result, the hypochlorite ion is a strong conjugate base, and the calcium ion is a weak conjugate acid:

ClO
+ H2O → HClO + OH

Similarly, calcium hypochlorite reacts with hydrochloric acid to form calcium chloride, water and chlorine:

Ca(OCl)2 + 4 HCl → CaCl2 + 2 H2O + 2 Cl2

Safety

Calcium hypochlorite is stored dry and cold, away from any organic material and metals. The hydrated form is safer to handle.

References

  1. ^ a b Vogt, H.; Balej, J; Bennett, J. E.; Wintzer, P.; Sheikh, S. A.; Gallone, P.; Vasudevan, S.; Pelin, K. (2010). "Chlorine Oxides and Chlorine Oxygen Acids". Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH. doi:10.1002/14356007.a06_483.pub2. 
  2. ^ Gerald F. Connell. "KEY OPERATING STRATEGIES FOR CHLORINE DISINFECTION OPERATING SYSTEMS" (PDF). Retrieved 19 October 2014. 
  3. ^ Chemical Products Synopsis: Calcium Hypochlorite (Technical report). Asbuiy Park, NJ: Mannsvile Chemical Products. 1987. 
  4. ^ Nwaukwa, Stephen; Keehn, Philip (1982). "The oxidation of aldehydes to acids with calcium hypochlorite [Ca(OCl)2]". Tetrahedron Letters. 23 (31): 3131–3134. doi:10.1016/S0040-4039(00)88577-9. 
  5. ^ Nwaukwa, Stephen; Keehn, Philip (1982). "Oxidative cleavage of α-diols, α-diones, α-hydroxy-ketones and α-hydroxy- and α-keto acids with calcium hypochlorite [Ca(OCl)2]". Tetrahedron Letters. 23 (31): 3135–3138. doi:10.1016/S0040-4039(00)88578-0. 
  6. ^ Cohen, Julius (1900). Practical Organic Chemistry for Advanced Students. Newyork: Macmillan & Co. p. 63. 
  7. ^ W.L Smith, Inorganic bleaches, Production of Hypochlorite in Handbook of Detergents,Part F, (2009) Ed. U Zoller and Paul Sosis, CRCPress, ISBN 978-0-8247-0349-3

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