How Is Calcium Hypochlorite Produced and Used in Daily Life?
Calcium hypochlorite can be defined as a chemical compound having the formula Ca(ClO)2.
Commonly, it is referred to as either calcium oxychloride or bleaching powder. It can be said as an ionic compound, made up of two hypochlorite anions (ClO–) and a calcium cation (Ca2+). Despite being stable at room temperatures, calcium hypochlorite decomposes slowly in moist environments, giving it a characteristic 'chlorine' smell. The common name of calcium hypochlorite can be given as bleaching powder.
Calcium hypochlorite is a compound known to be an active ingredient in most commercial bleaching agents such as chlorinated lime and chlorine powder bleaching powder.
Calcium Hypochlorite Chemical Equation
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Commercially, calcium hypochlorite is available in its hydrated and anhydrous forms and is one of the primary ingredients of both bleaching powder and chlorine powder. The Ca(ClO)2 compound is produced on an industrial scale through the chlorine gas reaction with calcium hydroxide.
The chemical equation representation for this reaction can be given as follows.
2Ca(OH)2 + 2Cl2 → Ca(ClO)2 + H2O + CaCl2
In general, the bleaching powder is a calcium hypochlorite mixture, and its dibasic form can be given as (Ca(ClO2).2Ca(OH)2). In contrast, the dibasic form of calcium chloride can be given as (CaCl2.2Ca(OH)2). Because it contains two ClO– ions, this compound contains a high chlorine availability to that of sodium hypochlorite (NaOCl).
Structure of Calcium Hypochlorite
The Ca(ClO)2 molecule's structure consists of one Ca+ ion and two ClO– ions. The representation can be given as follows.
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Each chlorite ion holds a -1 charge, whereas the calcium ion holds a +2 charge. Thus, one calcium cation can form ionic bonds with the help of two hypochlorite ions.
Properties of Calcium Hypochlorite
Chemical Data
Physical Properties
At room temperatures, the calcium hypochlorite compound is a white or grey solid.
It has a water solubility of 21g/100 mL, and when dissolved, it reacts with the water.
It has a hard water solubility of relatively low to that of its solubility in either soft or medium-hard water.
Ca(ClO)2 compound has a strong chlorine smell (due to its reactions with water molecules present in air).
Chemical Properties
Calcium hypochlorite compound acts as a strong base because it accepts H+ readily. Also, when dissolved in water, the hypochlorite anion accepts a proton from H2O by liberating OH– ion.
The chemical equation for this reaction can be given by ClO- + H2O → HClO + OH-
This is also a compound, which is a powerful oxidizing agent because it can accept an electron readily.
Calcium hypochlorite is a compound that reacts with hydrochloric acid by yielding water, calcium chloride (CaCl2), and also chlorine gas (Cl2).
The chemical equation for this reaction can be given as 4HCl + Ca(ClO)2 → CaCl2 + Cl2 + H2O.
Production of Calcium Hypochlorite
Calcium hypochlorite is a compound that is industrially produced by treating lime (Ca(OH)2) with chlorine gas. This reaction is conducted in stages to produce various compositions, each with a different calcium hypochlorite concentration, together with the unconverted calcium chloride and lime. The chemical representation can be shown as,
2 Cl2 + 2 Ca(OH)2 → Ca(CIO)2 + CaCl2 + 2 H2O
Bleaching powder is prepared with a moist slaked lime slightly. It is also not a simple mixture of calcium chloride, calcium hydroxide, and calcium hypochlorite. However, instead, it is a mixture that principally contains the dibasic calcium hypochlorite, calcium hypochlorite Ca(ClO)2, Ca3(ClO)2(OH)4 (can also be written as Ca(ClO)2 · 2 Ca(OH)2), and the dibasic calcium chloride, Ca3Cl2(OH)4 (calcium hydroxy chloride, which is also written as CaCl2 · 2 Ca(OH)2).
Calcium Hypochlorite Uses
The Ca(ClO)2 compound is often used to disinfect large volumes of water by making it safe to drink. It can also be used widely in swimming pools to sanitize water bodies and destroy the germs present in it. A few other primary calcium hypochlorite uses are listed below.
Because it is a good oxidizing agent, this is quite useful in the field of organic chemistry.
It can be used to obtain fragmented aldehydes or carboxylic acids by cleaving the glycols and keto acid bonds.
The Ca(ClO)2 compound is used in the haloform reaction, yielding chloroform.
It can be used to disinfect both drinking water and wastewater because it has a high chlorine availability.
Calcium hypochlorite is used in some bleaching solutions as well.
FAQs on Calcium Hypochlorite: Structure, Uses, and Chemical Equation
1. What is the chemical formula and common name for calcium hypochlorite?
The chemical formula for calcium hypochlorite is Ca(OCl)₂. It is most commonly known as bleaching powder. Other names include calcium oxychloride and chloride of lime.
2. What are the primary uses of calcium hypochlorite in daily life and industry?
Calcium hypochlorite is a versatile chemical with several important applications. Its primary uses include:
- Water Treatment: It is widely used as a disinfectant for drinking water, swimming pools, and sewage to kill harmful bacteria and pathogens.
- Bleaching Agent: In the textile and paper industries, it is used to bleach cotton, linen, and wood pulp.
- Sanitisation: It serves as a general-purpose sanitizer for cleaning public spaces, bathrooms, and food processing equipment.
- Oxidizing Agent: In chemical synthesis, it is used as a strong oxidizing agent.
3. How does the structure of calcium hypochlorite relate to its function as a bleaching agent?
The structure of calcium hypochlorite is ionic, consisting of one calcium cation (Ca²⁺) and two hypochlorite anions (OCl⁻). Its function is directly tied to the hypochlorite ion. When dissolved in water, this ion forms hypochlorous acid (HOCl), which is a powerful oxidizing agent. This acid easily releases nascent oxygen [O], which breaks the chemical bonds of chromophores (colour-producing molecules), rendering them colourless. Therefore, the presence of the OCl⁻ ion is key to its bleaching and disinfecting properties.
4. Why is calcium hypochlorite considered a hazardous substance that requires careful handling?
Calcium hypochlorite is considered hazardous primarily because it is a strong oxidizing agent and is highly reactive. It can cause fires or explosions if it comes into contact with organic materials or other reactive chemicals. Furthermore, if it is mixed with an acid, it will rapidly release highly toxic and corrosive chlorine gas (Cl₂). It should always be stored in a cool, dry place away from incompatible substances.
5. What happens chemically when calcium hypochlorite is dissolved in water?
When calcium hypochlorite, an ionic salt, is dissolved in water, it dissociates into its constituent ions: a calcium ion (Ca²⁺) and two hypochlorite ions (OCl⁻). The hypochlorite ions then react with water in an equilibrium reaction to form hypochlorous acid (HOCl) and hydroxide ions (OH⁻). It is this hypochlorous acid that acts as the primary disinfectant and bleaching agent. The overall reaction is: Ca(OCl)₂ + 2H₂O ⇌ Ca(OH)₂ + 2HOCl.
6. What is the key difference between calcium hypochlorite and sodium hypochlorite?
While both are used as bleaches and disinfectants, the key differences are:
- Physical State: Calcium hypochlorite is a solid (available as powder or granules), making it easier to transport and store. Sodium hypochlorite is typically sold as a liquid solution (household bleach).
- Stability: Calcium hypochlorite is generally more stable and has a longer shelf life than its sodium counterpart.
- Effect on Water: Calcium hypochlorite adds calcium ions to water, increasing its hardness. Sodium hypochlorite adds sodium ions and does not affect hardness.
7. Why does bleaching powder (calcium hypochlorite) have a strong smell of chlorine?
The distinct smell is not actually from chlorine gas itself but from the slow decomposition of the compound. When exposed to moisture and carbon dioxide (CO₂) in the air, calcium hypochlorite undergoes a chemical reaction that releases hypochlorous acid (HOCl). This acid is volatile and has a sharp smell similar to chlorine, and it is also the active substance responsible for bleaching. The continuous, slow release of this acid causes the persistent smell associated with bleaching powder.
8. Is calcium hypochlorite completely soluble in water?
Pure calcium hypochlorite is moderately soluble in water. However, commercial-grade bleaching powder is often a mixture and contains impurities like calcium hydroxide (Ca(OH)₂) and calcium chloride (CaCl₂), which are byproducts of its manufacturing process. Calcium hydroxide, in particular, has low solubility, which is why a milky or cloudy solution with some undissolved solid at the bottom is often observed when bleaching powder is mixed with water.
