Bleaching Powder and Sodium Hydroxide - Overview, Preparation, Formula, Uses, FAQs

Physical Properties of Bleaching Powder

• It is a white, odourless powder.

• Highly soluble in water and forms a strongly alkaline solution when dissolved.

• It fuses without decomposition on heating.

• Chemical formula: {Ca}(\mathrm{OCl})_2$.

• Both calcium ions $\left(\mathrm{Ca}^{2+}\right)$ and hypochlorite ions $\left(\mathrm{OCl}^{-}\right)$ contribute to its bleaching and disinfecting action.

• Boiling point ranges approximately from 350°C to 100°C.

• Density is around $2.35 \mathrm{~g} / \mathrm{cm}^3$.

• It is a strong oxidizing agent, which makes it highly effective in killing bacteria and other pathogens.

• It is hygroscopic means it absorbs moisture from the atmosphere.

• Due to moisture absorption, it gradually loses its potency on exposure to air.

• It can decompose on exposure to heat, humidity, or light, releasing harmful chlorine gas if not stored properly.

• Its stability depends on environmental conditions such as temperature and humidity.

• It must be stored in airtight containers away from direct sunlight to maintain effectiveness.

• It shows reactivity similar to other bleaching agents like sodium hypochlorite, which is commonly used as household bleach.

• Proper knowledge of its properties is essential to ensure safe and effective use in bleaching, disinfection, and water treatment.

Chemical Properties

Reaction with insufficient and excess dilute acid:

$\mathrm{CaOCl}_2+\mathrm{H}_2 \mathrm{SO}_4 \rightarrow \mathrm{CaSO}_4+\mathrm{CaCl}_2+2 \mathrm{HCl}+\mathrm{O}_2$

Autoxidation: When it undergoes autoxidation, it loses its available chlorine due to which affects its bleaching process.

$6 \mathrm{CaOCl}_2 \rightarrow 5 \mathrm{CaCl}_2+\mathrm{Ca}\left(\mathrm{ClO}_3\right)_2$

Catalytic decomposition: The catalytic decomposition of bleaching powder occurs as follows:

$2 \mathrm{CaOCl}_2 \rightarrow \mathrm{CoCl}_2+\mathrm{CaCl}_2+\mathrm{O}_2$

Preparation of Bleaching Powder

Bleaching powder, or calcium hypochlorite (Ca(OCl)₂), is prepared on an industrial scale through the reaction of chlorine gas with dry slaked lime (calcium hydroxide). The chemical equation for this reaction is:

$\mathrm{Ca}(\mathrm{OH})_2+\mathrm{Cl}_2 \rightarrow \mathrm{CaOCl}_2+\mathrm{H}_2 \mathrm{O}$

Chlorine gas (Cl₂) is generated in chemical plants, often as a by-product of other reactions and slaked lime (Ca(OH)₂) is a solid, dry material that reacts readily with chlorine. In this process, Chlorine gas is passed over dry slaked lime in specially designed chambers. The reaction takes place at room temperature and requires controlled conditions to ensure the complete reaction and stability of the product. Finally, the chlorine gas reacts with slaked lime to form a mixture of calcium hypochlorite (Ca(OCl)₂) and calcium chloride (CaCl₂), along with a small amount of water.

Related Topics

• Introduction to P Block Elements
• K₂Cr₂O₇
• Borax Formula
• Boric Acid
• Sulfuric Acid
• Phosphoric Acid

Uses of Bleaching Powder

Bleaching powder is a chemical with numerous applications due to its strong oxidizing, disinfecting, and bleaching properties. Below mentioned are some of its applications across various fields:

1. Water Treatment: It is widely used to purify drinking water by killing bacteria, viruses, and other microorganisms, and to maintain hygienic conditions in swimming pools.

2. Bleaching Agent: In the textile industry, it is used to bleach cotton and linen, while in the paper industry, it whitens paper pulp during manufacturing.

3. Disinfectant: It disinfects surfaces in hospitals, households, and public spaces and is also used in wastewater treatment to sterilize sewage and industrial waste.

4. Chemical Manufacturing: Bleaching powder serves as a precursor in the production of chemicals like chloroform (CHCl₃) and other chlorinated compounds.

5. Agriculture: It disinfects agricultural fields and storage areas, protecting crops and grains from pests and fungal infections.

6. Odor Removal: It neutralizes unpleasant odors in garbage dumps and restrooms due to its strong oxidizing nature.

7. Public Health: It is deployed during outbreaks of waterborne diseases like cholera to disinfect water supplies and contaminated areas.

8. Household Applications: It is used to whiten laundry, sanitize kitchen and bathroom surfaces, and remove mold and mildew from walls and tiles

Also read -

Some Solved Examples
Question 1: When PbS is oxidized by Cl₂ it forms

1) (correct)PbSO₄

2)SO₂

3)SO₃

4)S

Solution:

Cl₂ oxidizes PbS to PbSO_4,

The reaction is given as $4 \mathrm{Cl}_2+\mathrm{PbS}+4 \mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{PbSO}_4+8 \mathrm{HCl}$

Hence, the answer is the option (1).

Question 2: $\mathrm{Cl}_2+\mathrm{Hg}_2 \mathrm{Cl}_2 \rightarrow$ Product

The product is

1)Hg

2) (correct)HgCl₂

3)[HgCl₄]^2-

4)HgCl
Solution:

As we have learnt,

Reaction with Mercury (I) Chloride with Chlorine -Chlorine oxidizes Mercurous ions to mercuric ions

$\mathrm{Cl}_2+\mathrm{Hg}_2 \mathrm{Cl}_2 \rightarrow 2 \mathrm{HgCl}_2$

Hence, the answer is the option (2).

Question 3: With which substance should chlorine be treated to get bleaching powder

1)Sodium hydroxide

2) (correct)Calcium hydroxide

3)Potassium hydroxide

4)Sodium carbonate

Solution

As we have learnt,

When calcium hydroxide is treated with chlorine gas, it yields bleaching powder.

The reaction is given as

$2 \mathrm{Ca}(\mathrm{OH})_2+2 \mathrm{Cl}_2 \rightarrow \mathrm{CaCl}_2+\mathrm{Ca}(\mathrm{OCl})_2+2 \mathrm{H}_2 \mathrm{O}$

Hence, the correct answer is Option (2)

Question 4: When PbS is oxidised by $\mathrm{Cl}_2$ it forms
1) (correct) $\mathrm{PbSO}_4$

2) $\mathrm{SO}_2$

3) $\mathrm{SO}_3$

4) $S$

Solution:

$\mathrm{Cl}_2$ oxidises PbS to $\mathrm{PbSO}_4$,
The reaction is given as $4 \mathrm{Cl}_2+\mathrm{PbS}+4 \mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{PbSO}_4+8 \mathrm{HCl}$
Hence, the answer is option (1).

Practice More Questions With Link given Below