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

(b) \( \mathrm{HgS} \)

Step 1: Identify the reactants

The reactants given in the problem are hydrogen sulfide (\( \mathrm{H}_{2}\mathrm{S} \)) and mercuric ions (\( \mathrm{Hg}_2^{2+} \)). The chemical interaction will occur between these two compounds.

Step 2: Write the chemical reaction

When hydrogen sulfide (\( \mathrm{H}_{2}\mathrm{S} \)) reacts with mercurous ions (\( \mathrm{Hg}_2^{2+} \)), the reaction can be written as: \[ \mathrm{Hg}_2^{2+} + \mathrm{H}_{2}\mathrm{S} \rightarrow \mathrm{HgS} + 2\,\mathrm{H}^{+} \] The product formed is mercuric sulfide (\( \mathrm{HgS} \)).

Step 3: Analyze the reaction products

The above reaction shows that \( \mathrm{HgS} \) is formed as a product. Additionally, there are no other mercury compounds like \( \mathrm{Hg}_{2}\mathrm{S} \) formed in the simplistic assumption; \( \mathrm{Hg}_2^{2+} \) results solely in \( \mathrm{HgS} \).

Step 4: Determine the correct option based on the products

The problem lists several potential options for the product of the reaction. Based on the balanced reaction we derived earlier, the product is only \( \mathrm{HgS} \). The correct answer from the given options is (b) \( \mathrm{HgS} \).

Key Concepts

Mercuric Ions

Mercuric ions, represented as \( \mathrm{Hg}_2^{2+} \), are a common form of mercury in inorganic chemistry. These ions consist of two mercury atoms sharing a 2+ charge, forming a diatomic ion. Unlike the more stable mercuric ion \( \mathrm{Hg}^{2+} \), \( \mathrm{Hg}_2^{2+} \) is found in dimers or pairs. This dual-atom structure means that when involved in chemical reactions, they behave somewhat differently than single atom ions.

• Mercuric ions are a key player in many chemical reactions due to their oxidizing properties.
• They often appear in tests and experiments for detecting other substances, especially when using reactions that produce a visible precipitate.

Understanding mercuric ions' behavior is critical in fields that focus on heavy metal chemistry, as they can readily transform and form compounds with various substances.

Chemical Reaction

A chemical reaction occurs when one or more substances, the reactants, transform into different substances, the products. In the context of the reaction between mercuric ions \( \mathrm{Hg}_2^{2+} \) and hydrogen sulfide \( \mathrm{H}_2\mathrm{S} \), this process is a prime example of a sulfide precipitation reaction.

Characteristics of Chemical Reactions

• In a chemical reaction, the atoms in the reactants are rearranged to form the products.
• The properties of the products differ from those of the reactants.
• They often involve exchanges of energy, usually in the form of heat, light, or electricity.

In our case, the compounds interact to produce mercury sulfide \( \mathrm{HgS} \), a solid precipitate, showcasing a typical reaction type where visible change occurs.
Chemical reactions are guided by specific rules and principles, such as the conservation of mass and charge, which are vital for balancing equations and ensuring the reaction's feasibility.

Hydrogen Sulfide

Hydrogen sulfide \( \mathrm{H}_2\mathrm{S} \) is a simple binary compound of hydrogen and sulfur. It is known for its distinctive rotten egg smell and occurs naturally in various environments, like volcanic gases and some mineral springs.

Properties and Uses

• It is highly corrosive and dangerous, especially in confined spaces due to its toxicity.
• Despite its drawbacks, \( \mathrm{H}_2\mathrm{S} \) is used in chemical research and industrial applications, particularly in the production of metal sulfides.

In chemical reactions, hydrogen sulfide acts as a source of sulfide ions \( \mathrm{S}^{2-} \), which readily react with metals to form metal sulfides. This ability to form insoluble compounds makes \( \mathrm{H}_2\mathrm{S} \) crucial in processes like the precipitation reaction demonstrated with mercuric ions.