Calcium hypochlorite

Calcium hypochlorite
Names
Other names
Hypochlorous acid calcium salt
Bleaching powder, Calcium oxychloride or chloride of lime
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.007
EC Number 231-908-7
RTECS number NH3485000
UN number 1748
Properties
Ca(OCl)2
Molar mass 142.98 g/mol
Appearance white/gray powder
Density 2.35 g/cm3 (20 °C)
Melting point 100 °C (212 °F; 373 K)
Boiling point 175 °C (347 °F; 448 K) decomposes
21 g/100 mL, reacts
Solubility reacts in alcohol
Hazards
Safety data sheet ICSC 0638
O (O)
C (C)
Xn (Xn)
N (N)
R-phrases (outdated) R8, R22, R31, R34, R50
S-phrases (outdated) (S1/2), S26, S36/37/39, S45, S61
NFPA 704
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
850 mg/kg (oral, rat)
Related compounds
Other anions
 Calcium chloride
Other cations
 Sodium hypochlorite
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Calcium hypochlorite is an inorganic compound with formula Ca(ClO)2. It is the main active ingredient of commercial products called bleaching powder, chlorine powder, or chlorinated lime, used for water treatment and as a bleaching agents.[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 (anhydrous); and hydrated (hydrous).

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 65 to 73% with other chemicals present, such as calcium chloride and calcium carbonate, resulting from the manufacturing process. As a swimming pool chemical, it is blended with other chemicals less often than other forms of chlorine, due to dangerous reactions with some common pool chemicals. In solution, calcium hypochlorite could be used as a general purpose sanitizer,[3] but due to calcium residue, sodium hypochlorite (bleach) is usually preferred.

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
2O

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

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. 1 2 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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