Problem 84 - A Complete Resource Book in Chemistry for JEE Main

Question

Bleaching powder is used as a disinfectant for purification of water. When water-borne germs are killed, the disinfectant activity is destroyed. This is due to its disproportionation into (a) \(\mathrm{CaCl}_{2}\) and \(\mathrm{Ca}\left(\mathrm{ClO}_{3}\right)_{2}\) (b) \(\mathrm{CaO}, \mathrm{Cl}_{2}\) and \(\mathrm{CaCl}_{2}\) (c) \(\mathrm{CaO}\) and \(\mathrm{Cl}_{2}\) (d) \(\mathrm{CaCl}_{2}\) and \(\mathrm{Cl}_{2}\)

Step-by-Step Solution

Answer

Option (a) is correct: CaCl\(_2\) and Ca(ClO\(_3\))\(_2\) are the disproportionation products.

Step 1: Understand Bleaching Powder

Bleaching powder is chemically known as calcium hypochlorite, Ca(OCl)\(_2\). It is used as a disinfectant because it releases chlorine which kills water-borne germs.

Step 2: Define Disproportionation Reaction

A disproportionation reaction is a redox reaction in which an element forms two or more different products, where the element is simultaneously oxidized and reduced.

Step 3: Analyze the Options

Each given option represents different possible products from the disproportionation of bleaching powder. We need to determine which of these is correct based on the known reaction processes of bleaching powder.

Step 4: Determine the Reaction Products

The disproportionation of Ca(OCl)\(_2\) usually leads to the formation of CaCl\(_2\) (calcium chloride) and Ca(ClO\(_3\))\(_2\) (calcium chlorate). This means that option (a), CaCl\(_2\) and Ca(ClO\(_3\))\(_2\), correctly describes the products of this disproportionation reaction.

Step 5: Conclusion

The correct option is (a) because bleaching powder disproportionates into CaCl\(_2\) and Ca(ClO\(_3\))\(_2\), which supports its use as a disinfectant.

Key Concepts

Disinfection Chemistry

Disinfection chemistry is crucial for maintaining safe and healthy water supplies. This process involves using chemical agents to kill or inactivate harmful microorganisms, such as bacteria, viruses, and protozoans. When it comes to water treatment, ensuring the elimination of these water-borne pathogens is essential to prevent disease outbreaks. One of the most common disinfectants used in water purification processes is chlorine, which can be released from compounds such as bleaching powder. Chlorine functions by attacking the essential structures and enzymes within microbial cells, leading to their demise. This action helps protect public health by reducing or eliminating the risk of infections from water-borne diseases. Bleaching powder, also known as calcium hypochlorite, is an effective disinfectant because it liberates chlorine. The chlorine not only neutralizes germs but also acts as a residual disinfectant, meaning it continues to protect the water supply as it moves through pipes and storage facilities. Its widespread availability and efficacy make bleaching powder a popular choice in disinfection chemistry.

Water Purification

Water purification is all about making water safe for drinking and other purposes. It involves removing contaminants such as dirt, bacteria, viruses, chemicals, and toxins. There are various methods for purifying water, including physical, chemical, and biological processes.

• Filtration: This physical process removes solid particles and debris from water.
• Coagulation and Flocculation: These chemical methods help aggregate suspended particles for easy removal.
• Disinfection: Chemicals like chlorine are used to kill harmful microorganisms. This process is critical in ensuring water safety.

Bleaching powder plays a significant role in the chemical disinfection stage of water purification. By releasing chlorine, it provides an effective means to quickly and efficiently disinfect water at treatment plants. Additionally, its ongoing action ensures that even if pathogens enter the water later, they can still be neutralized, maintaining the purified status of the water as it reaches consumers.

Disproportionation Reaction

A disproportionation reaction is a fascinating type of redox reaction where a single substance is simultaneously oxidized and reduced, forming two distinct products. In the context of bleaching powder, this involves the chemical known as calcium hypochlorite, Ca(OCl) egin{align*} _2 ext{.} ext{} ext{Instead of decomposing into simpler forms, each chlorine atom in calcium hypochlorite undergoes a change.} Bleaching powder undergoes disproportionation to form:

• Calcium chloride, CaCl
_2 ext{} ext{, which results from the reduction of hypochlorite.}
• Calcium chlorate, Ca(ClO
) _3 ext{} )_2 ext{} ext{, formed due to the oxidation of hypochlorite.}

These distinct products demonstrate how a single chemical compound can undergo a multi-pathway reaction, forming both reduced and oxidized species. Understanding disproportionation reactions aids in comprehending various chemical processes, especially those involved in environmental and industrial applications, including water purification and treatment.