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

Q: what is the chemical formula of bleaching powder?

Chemical formula of Bleaching powder is CaOCl 2 and it is known as Calcium Oxychloride. It is made with slaked lime and chlorine gas.

Edited By Team Careers360 | Updated on Jul 02, 2025 04:26 PM IST

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.

This Story also Contains

Physical Properties of Bleaching Powder
Chemical properties
Preparation of Bleaching Powder
Uses of Bleaching Powder
Some Solved Examples
Example 1Question:

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

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:

Cl₂oxidizes 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)

Frequently Asked Questions (FAQs)

1. what is the chemical formula of bleaching powder?

Chemical formula of Bleaching powder is CaOCl₂ and it is known as Calcium Oxychloride. It is made with slaked lime and chlorine gas.

2. Bleaching powder is acidic or basic?

Bleaching powder contains a basic character.

3. Does bleaching powder have a pH value?

Yes, bleaching powder has a pH value, and it's basic with a pH of around 11–13.

4. What is the significance of sodium hydroxide?

Sodium hydroxide (NaOH), is a chemical with significant industrial and practical applications. It is crucial in manufacturing soaps, detergents, paper, and textiles and is widely used in water treatment, petroleum refining, and food processing.

5. How does bleaching powder differ from household bleach?

Bleaching powder (Ca(OCl)2) is a solid compound, while household bleach is typically a solution of sodium hypochlorite (NaClO) in water. Bleaching powder is more stable for storage but needs to be dissolved before use, whereas household bleach is ready to use but has a shorter shelf life.

6. Why is sodium hydroxide also called caustic soda?

Sodium hydroxide is called caustic soda because of its highly corrosive nature. The term "caustic" refers to its ability to burn or corrode organic tissues. It can cause severe chemical burns if it comes into contact with skin or eyes.

7. What is the pH of a sodium hydroxide solution?

A sodium hydroxide solution is strongly basic, with a pH greater than 7. The exact pH depends on the concentration, but a 0.1 M NaOH solution has a pH of about 13. As the concentration increases, the pH approaches 14, which is the upper limit of the pH scale.

8. How does sodium hydroxide react with acids?

Sodium hydroxide reacts with acids in a neutralization reaction, producing water and a salt. For example, with hydrochloric acid:

9. Why is sodium hydroxide used in the production of biodiesel?

Sodium hydroxide is used as a catalyst in biodiesel production. It facilitates the transesterification reaction between vegetable oils or animal fats and an alcohol (usually methanol). This reaction converts the triglycerides in the oils into fatty acid methyl esters (biodiesel) and glycerol.

10. What is the shelf life of bleaching powder and how should it be stored?

The shelf life of bleaching powder is typically 6-12 months when stored properly. To maximize shelf life:

11. How does bleaching powder compare to other chlorine-based disinfectants?

Bleaching powder compares to other chlorine-based disinfectants as follows:

12. What is the role of bleaching powder in emergency water disinfection?

In emergency situations, bleaching powder can be used to disinfect water quickly and effectively. A small amount of bleaching powder added to water can kill harmful microorganisms, making the water safe to drink. This is particularly useful in disaster relief efforts or in areas without access to clean water. The dosage must be carefully controlled to ensure safety while maintaining effectiveness.

13. What is the difference between the bleaching action of chlorine-based bleaches and peroxide-based bleaches?

Chlorine-based bleaches (like bleaching powder) and peroxide-based bleaches differ in their bleaching mechanisms:

14. What is the difference between anhydrous sodium hydroxide and its hydrates?

Anhydrous sodium hydroxide (NaOH) contains no water molecules, while its hydrates (like NaOH·H2O) contain a specific number of water molecules in their crystal structure. Anhydrous NaOH is more hygroscopic and reactive, while hydrates are more stable but less concentrated in terms of hydroxide content.

15. How is bleaching powder prepared industrially?

Bleaching powder is prepared industrially by passing chlorine gas over dry slaked lime (calcium hydroxide). The reaction can be represented as:

16. What is the environmental impact of bleaching powder production and use?

The production and use of bleaching powder can have several environmental impacts:

17. What is the chemical formula of sodium hydroxide?

The chemical formula of sodium hydroxide is NaOH. It's a strong base composed of sodium cations (Na+) and hydroxide anions (OH-).

18. How is sodium hydroxide produced industrially?

Sodium hydroxide is primarily produced through the chloralkali process. This involves the electrolysis of a sodium chloride (NaCl) solution, which produces chlorine gas, hydrogen gas, and sodium hydroxide. The overall reaction is:

19. What is the role of bleaching powder in the paper industry?

In the paper industry, bleaching powder is used to whiten paper pulp. It oxidizes and breaks down lignin, the brown compound in wood that gives unbleached paper its color. This process not only whitens the paper but also helps to soften and separate wood fibers, improving the paper's quality and appearance.

20. What are the main uses of bleaching powder?

Bleaching powder has several uses, including:

21. How does bleaching powder act as a disinfectant?

Bleaching powder acts as a disinfectant by releasing hypochlorite ions (OCl-) when dissolved in water. These ions oxidize and destroy the cell membranes of microorganisms, effectively killing them. The process also produces hypochlorous acid (HOCl), which further enhances its disinfectant properties.

22. What is bleaching powder and why is it called so?

Bleaching powder is a chemical compound with the formula Ca(OCl)2. It's called "bleaching powder" because of its ability to bleach or whiten materials by oxidizing colored compounds. The active ingredient, calcium hypochlorite, releases chlorine when dissolved in water, which acts as a powerful bleaching agent.

23. How does bleaching powder remove stains?

Bleaching powder removes stains through oxidation. When dissolved in water, it releases hypochlorite ions (OCl-) which break down the chemical bonds in colored molecules. This process either destroys the chromophores (color-producing components) or converts them into colorless compounds, effectively removing the stain.

24. What is the difference between bleaching powder and chlorine gas in water treatment?

While both bleaching powder and chlorine gas are used for water treatment, they differ in their application and storage. Bleaching powder is a solid that's easier to store and transport, making it suitable for smaller-scale operations. Chlorine gas is more commonly used in large-scale water treatment plants but requires special handling due to its hazardous nature.

25. Why is sodium hydroxide considered a strong base?

Sodium hydroxide is considered a strong base because it completely dissociates in water, releasing all of its hydroxide ions (OH-). This results in a high concentration of OH- ions in solution, which gives it its strong basic properties and ability to neutralize acids effectively.

26. What safety precautions should be taken when handling sodium hydroxide?

When handling sodium hydroxide:

27. What is the role of sodium hydroxide in soap making?

In soap making, sodium hydroxide acts as a catalyst in the saponification process. It reacts with fats or oils (triglycerides) to produce glycerol and fatty acid salts (soap). The strong base breaks down the triglycerides and converts the fatty acids into their salt form, which has cleansing properties.

28. What is the difference between technical grade and food grade sodium hydroxide?

Technical grade and food grade sodium hydroxide differ in their purity levels:

29. What is the role of sodium hydroxide in the production of biodegradable plastics?

Sodium hydroxide plays a role in producing biodegradable plastics like polylactic acid (PLA):

30. What is the role of sodium hydroxide in fracking fluids?

In hydraulic fracturing (fracking), sodium hydroxide is used to:

31. How does sodium hydroxide contribute to the extraction of alumina from bauxite ore?

Sodium hydroxide is crucial in the Bayer process for extracting alumina from bauxite:

32. What are the environmental concerns associated with sodium hydroxide production?

Environmental concerns with sodium hydroxide production include:

33. How does the concentration of a sodium hydroxide solution affect its properties?

As the concentration of a sodium hydroxide solution increases:

34. How does sodium hydroxide contribute to aluminum recycling?

In aluminum recycling, sodium hydroxide is used to remove paint and other coatings from aluminum scrap. The process, called caustic cleaning, involves immersing the aluminum in a hot NaOH solution. This dissolves the coatings and any oxide layers, leaving clean aluminum that can be melted and reused.

35. How does sodium hydroxide affect proteins?

Sodium hydroxide denatures proteins by disrupting their secondary and tertiary structures. It does this by:

36. What is the difference between the action of bleaching powder and sodium hydroxide on organic matter?

Bleaching powder primarily oxidizes organic matter, breaking down colored compounds and killing microorganisms. Sodium hydroxide, on the other hand, hydrolyzes organic matter, breaking down fats and proteins. While bleaching powder is mainly used for disinfection and bleaching, sodium hydroxide is used for cleaning and breaking down organic materials.

37. How does temperature affect the reactivity of sodium hydroxide?

Temperature increases the reactivity of sodium hydroxide by:

38. How does sodium hydroxide contribute to the production of paper?

Sodium hydroxide plays several roles in paper production:

39. How does sodium hydroxide react with amphoteric metals like aluminum?

Sodium hydroxide reacts with amphoteric metals like aluminum in a unique way. While most metals don't react with bases, aluminum does. The reaction produces hydrogen gas and a soluble aluminate ion:

40. How does bleaching powder affect the chlorine demand of water?

Bleaching powder affects the chlorine demand of water by:

41. How does the presence of carbon dioxide affect a sodium hydroxide solution?

Carbon dioxide reacts with sodium hydroxide solution to form sodium carbonate:

42. What are the potential health effects of long-term exposure to low levels of bleaching powder?

Long-term exposure to low levels of bleaching powder can potentially cause:

43. How does sodium hydroxide affect the solubility of different substances?

Sodium hydroxide affects solubility in various ways:

44. What is the role of bleaching powder in the textile industry beyond whitening?

In the textile industry, bleaching powder serves multiple purposes:

45. How does the concentration of sodium hydroxide affect its ability to absorb carbon dioxide?

The concentration of sodium hydroxide affects its CO2 absorption as follows: