Problem 73 - A Complete Resource Book in Chemistry for JEE Main

Question

\(\mathrm{Cl}_{2} \mathrm{O}\) is best prepared by passing dry (a) hydrogen chloride and oxygen over hot silver oxide (b) chlorine gas over hot \(\mathrm{HgO}\) (c) chlorine and oxygen over hot silver chlorate (d) hydrogen chloride over phosphorus pentoxide

Step-by-Step Solution

Answer

Option (b): chlorine gas over hot HgO.

Step 1: Identify the Reaction for Cl_2 O Preparation

We begin by identifying the most suitable chemical reaction that results in the production of chlorine monoxide Cl_2 O among the given options.

Step 2: Evaluate Option (a)

For Option (a), hydrogen chloride and oxygen passed over hot silver oxide does not produce Cl_2 O as these reactants do not conveniently form chlorine monoxide under these conditions.

Step 3: Evaluate Option (b)

Option (b) proposes passing chlorine gas over hot mercury oxide HgO. This does produce Cl_2 O as chlorine reacts with heated HgO, forming chlorine monoxide and mercury Hg as by-products.

Step 4: Evaluate Option (c)

In Option (c), chlorine and oxygen over hot silver chlorate are conditions that typically do not directly produce chlorine monoxide without additional reagents or catalysts, making this a less viable option for direct Cl_2 O synthesis.

Step 5: Evaluate Option (d)

Option (d) involves passing hydrogen chloride over phosphorus pentoxide, which does not provide a pathway to form Cl_2 O, as these reactants primarily serve to remove water from the system rather than forming chlorine monoxide.

Key Concepts

Chemical Reactions Evaluation

Chemical reactions evaluation is an important step in ensuring we choose the most effective method for preparing a specific compound. When deciding on the best reaction, consider:

• The reactants involved and their typical behavior.
• The reaction conditions, such as temperature and pressure.
• The by-products formed during the reaction.
• The efficiency and feasibility of the reaction.

These factors help determine whether a reaction is suitable for the desired outcome.
In our exercise, the goal is to prepare chlorine monoxide, or \( \text{Cl}_{2}\text{O} \). This involves evaluating multiple potential reactions, each with unique reactants and conditions. The decision requires a careful analysis of which option will most reliably produce the desired compound while minimizing unwanted side products.

Chlorine and Mercury Oxide Reaction

The reaction of chlorine gas with hot mercury oxide (\( \text{HgO} \)) is a well-known method for producing chlorine monoxide. This combination is effective due to the following reasons:

• Chlorine gas is highly reactive and can easily interact with other compounds.
• When chlorine reacts with heated mercury oxide, it facilitates the breakdown of \( \text{HgO} \), leading to the formation of \( \text{Cl}_{2}\text{O} \).
• This reaction also produces mercury (\( \text{Hg} \)) as a by-product, which can be captured safely if handled properly.

This method is favored because it efficiently converts reactants to chlorine monoxide, making it a preferred choice in industrial and laboratory settings where \( \text{Cl}_{2}\text{O} \) is needed.

Chlorine Compounds Synthesis

Synthesis of chlorine compounds like chlorine monoxide requires thorough understanding of reaction mechanisms and conditions. To synthesize chlorine monoxide effectively, here’s what to consider:

• Selection of suitable reactants that can undergo transformation to \( \text{Cl}_{2}\text{O} \).
• Reaction conditions that favor the formation of the desired compound without promoting unnecessary by-products.
• Catalysts or additional reagents that might be required to enable or speed up the reaction.

In our case, passing chlorine gas over hot mercury oxide is ideal due to minimal additional requirements beyond heat. This compound, \( \text{Cl}_{2}\text{O} \), is useful in various applications, such as in the formulation of bleaching agents and disinfectants, highlighting the importance of efficient synthesis methods.