Problem 197 - A Complete Resource Book in Chemistry for JEE Main

Question

How is \(\mathrm{H}_{2} \mathrm{~S}\) prepared in laboratory? (a) \(\mathrm{FeS}+\mathrm{dil} \mathrm{H}_{2} \mathrm{SO}_{4}\) (b) \(\mathrm{FeSO}_{4}+\mathrm{H}_{2} \mathrm{SO}_{4}\) (c) \(\mathrm{FeS}+\) conc. \(\mathrm{H}_{2} \mathrm{SO}_{4}\) (d) elementary \(\mathrm{H}_{2}+\) elementary \(\mathrm{S}\)

Step-by-Step Solution

Answer

The correct choice is (a) \(\mathrm{FeS} + \mathrm{dil} \; \mathrm{H}_{2} \mathrm{SO}_{4} \).

Step 1: Identify the Reactants

To prepare hydrogen sulfide (\(\mathrm{H}_{2}\mathrm{S}\)), we need to recognize the suitable reactants. Upon examining the options, we can see that iron sulfide (\(\mathrm{FeS}\)) is commonly used because it directly provides sulfur combined with another element, which can react to form \(\mathrm{H}_{2}\mathrm{S}\).

Step 2: Choose the Appropriate Acid

For the preparation of \(\mathrm{H}_{2}\mathrm{S}\) in the laboratory, a dilute acid is preferable as it reacts with iron sulfide (\(\mathrm{FeS}\)) to yield \(\mathrm{H}_{2}\mathrm{S}\). In the provided options, \(\mathrm{dil} \; \mathrm{H}_{2} \mathrm{SO}_{4}\) is the dilute version of sulfuric acid.

Step 3: Determine the Chemical Reaction

Once the correct reactants are selected, verify the chemical reaction: \( \mathrm{FeS} + \mathrm{dil} \; \mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{FeSO}_{4} + \mathrm{H}_{2} \mathrm{S} \). This reaction outlines the preparation process where iron(II) sulfate and hydrogen sulfide are produced.

Step 4: Conclusion: Select the Correct Option

Based on the chemical reaction, the correct option for the preparation of hydrogen sulfide in the laboratory is \(\mathrm{FeS} + \mathrm{dil} \; \mathrm{H}_{2} \mathrm{SO}_{4}\), which corresponds to option (a).

Key Concepts

Iron Sulfide

Iron sulfide is a compound made up of iron and sulfur with the chemical formula \( \mathrm{FeS} \). In the laboratory setting, iron sulfide serves as a key reactant in the preparation of hydrogen sulfide gas (\( \mathrm{H}_{2}\mathrm{S} \)). The compound effectively supplies the needed sulfur element that combines with hydrogen ions to form \( \mathrm{H}_{2}\mathrm{S} \).
When iron sulfide reacts with an acid, it acts as a source of sulfide ions. This reaction is beneficial due to the straightforward nature of iron sulfide’s properties. Its stability and availability make it an ideal choice for conducting experiments involving gases such as \( \mathrm{H}_{2}\mathrm{S} \).

• Iron sulfide is typically acquired as a powder or small granules.
• It must be stored in a dry environment to avoid premature reactions.
• Being handled in controlled conditions ensures safe usage and prevents unwanted chemical reactions.

Understanding iron sulfide's role is essential for realizing its function in gas production processes, particularly in educational laboratory environments.

Dilute Sulfuric Acid

Dilute sulfuric acid (\( \mathrm{dil} \; \mathrm{H}_{2}\mathrm{SO}_{4} \)) plays a crucial role in chemical reactions where a mild acidic environment is required. It comes from concentrated sulfuric acid which is mixed with water to achieve the desired dilution. In laboratory settings, it acts as a reactant to facilitate specific chemical transformations.
The acid's primary role in this context is to react with iron sulfide (\( \mathrm{FeS} \)) to produce hydrogen sulfide gas along with iron(II) sulfate. Dilute sulfuric acid is preferred over the concentrated version because it allows for a controlled reaction, minimizing risks associated with excessive heat or violent reactions.

• Dilution of sulfuric acid should be done cautiously to prevent splattering and ensure safety.
• Using dilute acid helps in achieving precise reaction outcomes.
• It is important to follow all safety protocols while handling any form of sulfuric acid to avoid skin or eye irritation.

The correct usage of dilute sulfuric acid is imperative for achieving the desired chemical changes without any harmful side effects.

Chemical Reactions in Laboratory

Chemical reactions in a laboratory are foundational to understanding larger scientific concepts. These reactions, such as the one between iron sulfide and dilute sulfuric acid, illustrate fundamental principles of chemistry.
In a typical laboratory setting, experiments are set up to observe reactive processes, with attention to safety and precision. Specifically, the reaction \( \mathrm{FeS} + \mathrm{dil} \; \mathrm{H}_{2}\mathrm{SO}_{4} \rightarrow \mathrm{FeSO}_{4} + \mathrm{H}_{2}\mathrm{S} \) is a transformation process that demonstrates the interaction of solids and liquids to form a gas and an aqueous compound.

• This setup allows students to witness the conversion of reactants to products in real time.
• Laboratory conditions must ensure proper ventilation, especially when gases are produced.
• All chemical reactions should be conducted under expert supervision to mitigate risks and ensure accurate observations.

Through these experiments, students learn to analyze reaction pathways, calculate yields, and understand stoichiometry, all while fostering a deeper appreciation of chemical science.