Calcium hypochlorite


Calcium hypochlorite is an inorganic compound with formula 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 agent. This compound is relatively stable and has greater available chlorine than sodium hypochlorite. 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 substances are sold with a purity of 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, but due to calcium residue, sodium hypochlorite is usually preferred.

Organic chemistry

Calcium hypochlorite is a general oxidizing agent and therefore finds some use in organic chemistry. For instance the compound is used to cleave glycols, α-hydroxy carboxylic acids and keto acids to yield fragmented aldehydes or carboxylic acids. Calcium hypochlorite can also be used in the haloform reaction to manufacture chloroform.
Calcium hypochlorite can be used to oxidize thiol and sulfide byproducts in organic synthesis and thereby reduce their odour and make them safe to dispose of.

Production

Calcium hypochlorite is produced industrially by treating lime 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
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 Ca2, dibasic calcium hypochlorite, Ca324 2 · 2 Ca, and dibasic calcium chloride, Ca3Cl24.

Calcium oxychlorides

A confusion sometimes reigns between calcium oxychlorides and calcium hypochlorite. Indeed, the name calcium oxychloride does not immediately refer to calcium hypochlorite, but is only applicable to the mixed calcium basic chloride compounds remaining unreacted in the bleaching powder, such as, e.g. CaCl2 · 2 Ca2.
Calcium oxychloride may also be formed in concrete in roads and bridges when calcium chloride is used as deicing agent during winter. Calcium chloride then reacts with calcium hydroxide present in cement hydration products and forms a deleterious expanding phase also named CAOXY by concrete technologists. The stress induced into concrete by crystallisation pressure and CAOXY salt expansion can considerably reduce the strength of concrete.

Chemical properties

Calcium hypochlorite exhibits both acido-basic and oxydo-reduction properties. It is a relatively strong base.
Calcium hypochlorite solution is basic as the hypochlorite anion can accept a proton from a water molecule leaving a hydroxyl anion in solution. This basicity is due to the propensity for the hypochlorite anion to accept a proton to become hypochlorous acid, a weak acid:
The hypochlorite anion is also a strong oxidizing agent containing a chlorine atom at the valence I which reacts under acidic conditions with the reduced chloride species present in hydrochloric acid to form calcium chloride, water and gaseous chlorine. The overall reaction is:

Safety

Calcium hypochlorite is stored dry and cold, away from any acid, organic materials, and metals. The hydrated form is safer to handle.
If mixed with an acid it releases highly toxic chlorine gas.