Problem 86 - A Complete Resource Book in Chemistry for JEE Main

Question

In the presence of cobalt chloride ( \(\mathrm{CoCl}_{2}\) ), bleaching powder decomposes to form (a) \(\mathrm{Cl}_{2} \mathrm{O}\) and \(\mathrm{CaO}\) (b) \(\mathrm{CaCO}_{3}\) and \(\mathrm{O}_{3}\) (c) \(\mathrm{CaCl}_{2}\) and \(\mathrm{O}_{2}\) (d) \(\mathrm{ClO}_{2}\) and \(\mathrm{CaO}\)

Step-by-Step Solution

Answer

The correct answer is option (c): \(\mathrm{CaCl}_2\) and \(\mathrm{O}_2\).

Step 1: Understanding the Reaction

Bleaching powder is chemically known as calcium hypochlorite, (\(Ca(OCl)_2\)). Upon reaction with cobalt chloride (\(\mathrm{CoCl}_2\)), we need to analyze how it decomposes.

Step 2: Identifying Possible Products

We examine the given options for possible reaction products: (a) \(\mathrm{Cl}_2\mathrm{O}\) and \(\mathrm{CaO}\), (b) \(\mathrm{CaCO}_3\) and \(\mathrm{O}_3\), (c) \(\mathrm{CaCl}_2\) and \(\mathrm{O}_2\), (d) \(\mathrm{ClO}_2\) and \(\mathrm{CaO}\). We seek the one that fits the decomposition pattern of bleaching powder.

Step 3: Analyzing the Chemical Reaction

In oxidation reactions, bleaching powder decomposes, releasing oxygen gas and forming calcium chloride. The presence of cobalt chloride, a known catalyst, could promote this decomposition leading to options like \(\mathrm{CaCl}_2\) and \(\mathrm{O}_2\).

Step 4: Fusion of Known Chemistry

Considering the common effect of cobalt chloride and the usual decomposition of \(Ca(OCl)_2\), it often breaks into calcium chloride \((CaCl_2)\) and releases oxygen \((O_2)\). This matches option (c).

Step 5: Conclusion and Selection of Correct Option

After applying the analysis, it is evident that option (c) \(\mathrm{CaCl}_2\) and \(\mathrm{O}_2\) accurately describes the decomposition of bleaching powder in the presence of cobalt chloride as a catalyst.

Key Concepts

Decomposition Reaction

Decomposition reactions are an important type of chemical reaction where a single compound breaks down into two or more simpler substances. This process happens under certain conditions and can often be influenced by catalysts. In the context of our exercise, bleaching powder, which is calcium hypochlorite (0Ca(OCl)_2
41), decomposes to form calcium chloride (0CaCl_2
41) and oxygen gas (0O_2
41). Some key features of decomposition reactions:

• They involve the breakdown of a compound, often requiring energy input like heat, light, or electricity.
• Can be influenced or sped up by catalysts that lower the activation energy needed for the reaction.
• Results in the formation of more than one product from a single reactant.

In many cases, these reactions are used in industrial and laboratory settings to generate desired products or to remove unwanted ones.

Catalysts in Chemistry

Catalysts are crucial substances in chemical reactions. They dramatically enhance the rate of a reaction without being consumed in the process. In the reaction involving bleaching powder, cobalt chloride (0CoCl_2
41) acts as a catalyst. It helps to lower the energy barrier, promoting the decomposition of calcium hypochlorite into calcium chloride and oxygen. Some interesting points about catalysts:

• Catalysts provide an alternate reaction pathway with a lower activation energy.
• They do not alter the equilibrium position of a chemical reaction.
• A small amount of catalyst can affect the rate of reaction for a large amount of reactant.
• Different catalysts are specific to different reactions, affecting only certain types of reactions.

Catalysts are widely used in industry to increase the efficiency of chemical processes, making them more cost-effective and energy-efficient.

Bleaching Powder

Bleaching powder, chemically known as calcium hypochlorite (0Ca(OCl)_2
41), is a widely used industrial and household chemical. Its primary application is in bleaching and disinfecting. Here's why bleaching powder is important:

• It acts as a disinfectant, effectively killing bacteria and viruses, making it a staple in water treatment processes.
• Used in textile industries for bleaching fabrics because it breaks down, lifting colors and stains.
• It is used in the production of chloroform and other chemicals through its decomposition.

The understanding of its decomposition is crucial since it determines its effectiveness and safety in applications.

Oxidation Reactions

Oxidation reactions are fundamental to chemistry and involve the loss of electrons from a molecule, atom, or ion. In the context of our exercise, oxidation occurs when calcium hypochlorite (0Ca(OCl)_2
41) breaks down to release oxygen gas (0O_2
41). Important points about oxidation reactions:

• These reactions are often paired with reduction reactions, collectively known as "redox" reactions.
• They play a critical role in energy extraction processes, such as combustion and cellular respiration.
• Oxidizing agents, like bleaching powder, can gain electrons as they oxidize other substances.
• In industrial applications, controlling oxidation reactions is essential for processes like metal refining and waste treatment.

Oxidation reactions help understand the reactivity and properties of various compounds, predicting the outcomes of chemical reactions effectively.