Problem 11 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one of the following does not produce metallic sulphide with \(\mathrm{H}_{2} \mathrm{~S}\) ? (a) \(\mathrm{COCl}_{2}\) (b) \(\mathrm{CuCl}_{2}\) (c) \(\mathrm{ZnCl}_{2}\) (d) \(\mathrm{CdCl}_{2}\)

Step-by-Step Solution

Answer

(a) \(\mathrm{COCl}_2\) does not produce metallic sulfide with \(\mathrm{H}_2\mathrm{S}\).

Step 1: Identifying the Reaction

The reaction in question involves a metal chloride reacting with hydrogen sulfide (\(\mathrm{H}_2\mathrm{S}\)) to form a metallic sulfide and hydrochloric acid \(\mathrm{HCl}\). The general reaction is \(\mathrm{MCl}_2 + \mathrm{H}_2\mathrm{S} \rightarrow \mathrm{MS} + 2\mathrm{HCl}\), where \(\mathrm{M}\) is the metal.

Step 2: Analyzing Chemical Properties

For the reaction to occur, \(\mathrm{MCl}_2\) must be a metal chloride that can form a metallic sulfide \(\mathrm{MS}\) upon reaction with \(\mathrm{H}_2\mathrm{S}\). We need to analyze if each option is capable of forming \(\mathrm{MS}\).

Step 3: Checking COCl2 Behavior

\(\mathrm{COCl}_2\), known as phosgene, is not a metal chloride. It is an organochlorine compound and does not react with \(\mathrm{H}_2\mathrm{S}\) to form a metallic sulfide because it does not contain a metal.

Step 4: Checking CuCl2, ZnCl2, CdCl2

\(\mathrm{CuCl}_2\), \(\mathrm{ZnCl}_2\), and \(\mathrm{CdCl}_2\) are chlorides of copper, zinc, and cadmium respectively. These are metal chlorides that can react with \(\mathrm{H}_2\mathrm{S}\) to form \(\mathrm{CuS}\), \(\mathrm{ZnS}\), and \(\mathrm{CdS}\), all of which are metallic sulfides.

Step 5: Conclusion

Since \(\mathrm{COCl}_2\) is not a metal chloride, it cannot produce a metallic sulfide when reacted with \(\mathrm{H}_2\mathrm{S}\). Therefore, it is the correct answer.

Key Concepts

Metallic Sulfides

Metallic sulfides are compounds formed by the combination of metal ions with sulfur. They have significant relevance in both chemistry and industry due to their unique properties.

• **Formation**: Typically, metallic sulfides are formed by the reaction of metal compounds, like chlorides, with hydrogen sulfide (\(\mathrm{H}_2\mathrm{S}\)). An example of this type of reaction would be: \(\mathrm{ZnCl}_2 + \mathrm{H}_2\mathrm{S} \rightarrow \mathrm{ZnS} + 2\mathrm{HCl}\).
• **Characteristics**: Metallic sulfides exhibit distinct properties such as varying colors and unique magnetic and electrical characteristics. These properties make them an interest in fields like material science and geology.
  For example, zinc sulfide (\(\mathrm{ZnS}\)) is known for its luminescent property.
• **Applications**: Many metallic sulfides are useful in industrial processes. Some, like copper sulfide (\(\mathrm{CuS}\)), find use in metallurgy while others serve as pigments or semiconductors in electronics.

Metallic sulfides, thus, play an essential role in many everyday applications and scientific phenomena.

Hydrogen Sulfide Reactions

Hydrogen sulfide (\(\mathrm{H}_2\mathrm{S}\)) is a colorless gas known for its distinctive rotten egg smell. It plays a crucial role in various chemical reactions, especially those involving the formation of metallic sulfides.

• **Reactivity**: \(\mathrm{H}_2\mathrm{S}\) readily reacts with metal ions to form metal sulfides and is also a common reactant in redox and precipitation reactions. The process of forming metal sulfides often produces hydrochloric acid as a by-product. For example, \(\mathrm{CuCl}_2 + \mathrm{H}_2\mathrm{S} \rightarrow \mathrm{CuS} + 2\mathrm{HCl}\).
• **Safety and Environmental Concerns**: Due to its potential toxicity and flammability, \(\mathrm{H}_2\mathrm{S}\) must be handled with care in both industrial and laboratory settings.
  Despite its risks, it is invaluable for synthesizing various chemical compounds.
• **Biological Relevance**: Remarkably, \(\mathrm{H}_2\mathrm{S}\) is also produced naturally in the human body and plays roles in signaling and cellular processes, showing its importance beyond traditional industrial uses.

Understanding hydrogen sulfide reactions is vital for chemistry students, particularly in the context of forming metal sulfides.

Metal Chlorides

Metal chlorides are a diverse group of compounds where a metal is bonded to chlorine atoms. They are key players in numerous chemical reactions, including those producing metallic sulfides.

• **Structure and Composition**: Metal chlorides consist of metals bonded with chlorine, depicted generally as \(\mathrm{MCl}_n\) where \(\mathrm{M}\) is the metal. Metal chlorides can exist in different oxidation states, with binary chlorides like \(\mathrm{CuCl}_2\) and \(\mathrm{ZnCl}_2\) being common.
• **Chemical Behavior**: These chlorides can react with hydrogen sulfide to form metallic sulfides. The general reaction is \(\mathrm{MCl}_2 + \mathrm{H}_2\mathrm{S} \rightarrow \mathrm{MS} + 2\mathrm{HCl}\), where \(\mathrm{MS}\) is the resultant metallic sulfide. This is the typical reaction observed in many metal chlorides including copper and zinc.
• **Industrial Applications**: Metal chlorides have extensive applications
  in industries. For instance, they often serve as catalysts, in water treatment, or as precursors in the production of other vital chemical compounds. Some, like \(\mathrm{CuCl}_2\), are also of interest for their role in conducting electric current.

The understanding of metal chlorides' properties and reactions forms a cornerstone in both inorganic chemistry studies and practical applications.