Problem 155 - A Complete Resource Book in Chemistry for JEE Main

Question

When \(\mathrm{H}_{2} \mathrm{~S}\) is passed through \(\mathrm{Hg}_{2}{\underline{\phantom{xx}}}^{2+}\), we get (a) \(\mathrm{Hg}_{2} \mathrm{~S}\) (b) \(\mathrm{HgS}\) (c) \(\mathrm{HgS}+\mathrm{Hg}_{2} \mathrm{~S}\) (d) \(\mathrm{HgS}+\mathrm{Hg}\)

Step-by-Step Solution

Answer

The correct answer is (a) \( \mathrm{Hg}_{2} \mathrm{~S} \).

Step 1: Write the reaction equation

When hydrogen sulfide, \( \mathrm{H}_{2} \mathrm{~S} \), is passed through \( \mathrm{Hg}_{2}^{2+} \), it reacts with mercury ions. The general reaction with mercury ions can be represented as: \[ \mathrm{Hg}_2^{2+} + \mathrm{H}_2\mathrm{S} \rightarrow \mathrm{HgS} + 2\mathrm{H}^+ \] However, since \( \mathrm{Hg}_2^{2+} \) indicates two mercury atoms are involved, it suggests the formation of mercurous sulfide, \( \mathrm{Hg}_2\mathrm{S} \). The equation is: \[ \mathrm{Hg}_2^{2+} + \mathrm{H}_2\mathrm{S} \rightarrow \mathrm{Hg}_2\mathrm{S} + 2\mathrm{H}^+ \]

Step 2: Analyze the reaction products

The product \( \mathrm{Hg}_2\mathrm{S} \) suggests the formation of mercurous sulfide. Since the reaction involves \( \mathrm{Hg}_2^{2+} \) ions reacting with sulfide ions, the expected principal product should indeed be \( \mathrm{Hg}_2\mathrm{S} \). Therefore, the first option matches the chemical reaction best: \( \mathrm{Hg}_2\mathrm{S} \).

Step 3: Determine the correct answer

From the analysis in Step 2, we conclude that when \( \mathrm{H}_{2} \mathrm{~S} \) is passed through \( \mathrm{Hg}_{2}^{2+} \), the primary compound formed is \( \mathrm{Hg}_{2} \mathrm{~S} \). Thus, the correct answer is (a) \( \mathrm{Hg}_{2} \mathrm{~S} \).

Key Concepts

Mercury Compounds

Mercury compounds are fascinating substances within the realm of chemistry. Mercury, a heavy, silvery metal, forms a variety of compounds, most notably in the +1 and +2 oxidation states. One common example is mercurous chloride (Hg₂Cl₂), used historically as a medicine, although it's toxic.
In terms of chemistry, mercury has a unique ability to form diatomic ions, notably as

• Mercurous ion (\[ \mathrm{Hg}_2^{2+} \]), which consists of two mercury atoms sharing a positive charge.
• This formation contributes to mercury's distinct reactivity, especially in inorganic reactions where it combines with other elements to create complex compounds.

Mercury compounds are significant in both industrial and environmental contexts. They are used in various applications but need careful handling due to toxicity.

Sulfide Ion Reactions

Sulfide ions are simple and reactive anions formed from sulfur. They play a crucial role in various chemical reactions due to their ability to bond with metals.
In sulfide ion reactions, a metal ion reacts with sulfide (\[\mathrm{S}^{2-}\]) to form a metal sulfide compound. This reaction is quite common in inorganic chemistry and forms

• precipitates.
• For instance, when hydrogen sulfide (\[\mathrm{H}_2\mathrm{S}\]) is passed through solutions containing certain metal ions, sulfide ions are released.

The sulfide ions react readily with the metal ions, like mercury in this case, to create compounds such as mercurous sulfide (\[\mathrm{Hg}_2\mathrm{S}\]), evident from the given reaction.

• This process is valuable for the synthesis of various metal sulfides, which can have distinct colors and properties.

Stoichiometry

Stoichiometry is a foundational concept in chemistry that deals with the quantitative relationships between reactants and products in a chemical reaction.
Understanding stoichiometry allows us to predict the quantities of substances consumed and produced. In the reaction

• between mercury ions (\[\mathrm{Hg}_2^{2+}\]) and hydrogen sulfide (\[\mathrm{H}_2\mathrm{S}\]), stoichiometry helps us determine that mercurous sulfide (\[\mathrm{Hg}_2\mathrm{S}\]) forms alongside hydrogen ions (\[\mathrm{H}^+\]).
• Balancing the chemical equation is crucial to ensure that atoms are conserved in the reaction.

For example, knowing that each \[\mathrm{Hg}_2^{2+}\] ion reacts with a molecule of \[\mathrm{H}_2\mathrm{S}\] to form \[\mathrm{Hg}_2\mathrm{S}\] enlightens us on the stoichiometric relationship between mercury and sulfide ions.

• Thus, stoichiometry is a key tool for chemists in both laboratory and industrial settings.

Inorganic Chemistry

Inorganic chemistry is the branch of chemistry that deals with inorganic compounds. Unlike organic chemistry, which focuses on carbon-containing molecules, inorganic chemistry encompasses a wide range of substances, including metals, minerals, and salts.
One significant aspect of inorganic chemistry is the study of reactions and compounds not involving carbon-hydrogen bonds. Inorganic reactions can span from simple ion exchanges to complex coordination reactions.
For example, the reaction between \[\mathrm{Hg}_2^{2+}\] and \[\mathrm{H}_2\mathrm{S}\] falls under inorganic chemistry. It showcases how non-organic molecules interact to form new compounds, revealing behaviors and patterns unique to inorganic chemicals.
Inorganic chemistry also includes the exploration of the properties and application of these compounds, which can be found in industries such as

• manufacturing,
• pharmacy, and even in materials used for electronics.

Studying such reactions provides insight into the fabric of materials and natural processes.