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

Bleaching powder, chemically known as calcium hypochlorite Ca(OCl)₂, is a widely used chemical compound with strong bleaching, disinfecting, and oxidizing properties. It has a pale yellowish-white appearance and characteristic chlorine-like odour. Bleaching powder plays a significant role in various industries, including textiles, paper, and water treatment. It is valued not only for its ability to remove stains and whiten surfaces but also for its effectiveness as a disinfectant to kill germs and purify water. In this article, we will explore various aspects pertaining to the composition, preparation, uses, and safety of bleaching powder along with highlighting its importance in everyday life and industrial applications.

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This Story also Contains

1. Physical Properties of Bleaching Powder
2. Chemical properties
3. Preparation of Bleaching Powder
4. Uses of Bleaching Powder
5. Some Solved Examples
6. Example 1Question:

Physical Properties of Bleaching Powder

It is a white, odourless powder, which is very soluble in water, which it fuses without decomposition, giving a strongly alkaline solution. Finally, with a molecular formula of Ca(OCl)₂, both the calcium ions and the hypochlorite ions are responsible for the bleaching and disinfecting action. This compound boils at 350 to 100 °C, and its density is about 2.35 g/cm³. One major characteristic of bleaching powder that gives it the advantage of killing bacteria effectively and every sort of any other pathogen is the fact that it is highly oxidizing. This should also take into account the fact that it is stable by virtue of environmental conditions like temperature and humidity which may make it liberate harmful chlorine gas in case it is not stored properly. Advanced Physical Properties of Bleaching Powder Rogers. An appreciation of those advanced physical characteristics is essential for the proper uses of bleaching powder in the various application.

Also, Bleaching powder is hygroscopic; it absorbs water when exposed to the atmosphere. It, therefore, loses its potency over time. The compound reactivity also brings about different natures of the bleaching agents, among which, is sodium hypochlorite, a rather significantly extendable application as household bleach. Some subtleties in using a compound are given in them and have quite a number; therefore, one must have quite a deep knowledge of its properties to be able to use it properly and carefully.

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Chemical properties

Reaction with insufficient and excess dilute acid:

CaOCl₂+H₂SO₄→CaSO₄+CaCl₂+2HCl+O₂

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

6CaOCl₂→5CaCl₂+Ca(ClO₃)₂

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

2CaOCl₂→CoCl₂+CaCl₂+O₂

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:

Ca(OH)₂+Cl₂→CaOCl₂+H₂O

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.

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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.

Some Solved Examples

Example 1
Question:

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 4Cl₂+PbS+4H₂O→PbSO₄+8HCl

Hence, the answer is the option (1).

Example 2
Question:

Cl₂+Hg₂Cl₂→ 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

Cl₂+Hg₂Cl₂→2HgCl₂

Hence, the answer is the option (2).

Example 3
Question:

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

2Ca(OH)₂+2Cl₂→CaCl₂+Ca(OCl)₂+2H₂O

Hence, the correct answer is Option (2)