Problem 33 - Chemistry in 30 days

Question

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

Step-by-Step Solution

Answer

(b) FeS + dil. H2SO4

Step 1: Identify the Correct Reaction

To prepare hydrogen sulfide ( H_2S ) in the laboratory, we need to identify the reaction that naturally produces this gas. Among the given options, the reaction that classically generates H_2S involves the use of a metal sulfide with a dilute acid. This is typically the reaction where iron sulfide ( FeS ) reacts with dilute sulfuric acid ( dil. H_2SO_4 ).

Step 2: Evaluate Reaction (b)

For the reaction FeS + ext{dil.} H_2SO_4 ightarrow H_2S + FeSO_4 , this involves iron sulfide reacting with dilute sulfuric acid. In this process, H_2S gas is produced as one of the products. This is the standard laboratory method.

Step 3: Eliminate Other Options

Let's briefly evaluate the other options: (a) FeSO_4 + H_2SO_4 does not react to produce H_2S . (c) FeS + ext{conc.} H_2SO_4 leads to different reactions and not primarily H_2S . (d) Combining elementary H_2 and S directly doesn't produce H_2S under standard conditions.

Step 4: Conclusion

Given that the reaction of FeS with dilute sulfuric acid is a standard laboratory technique for preparing H_2S , option (b) is the correct method.

Key Concepts

Iron Sulfide

Iron sulfide, with the chemical formula \( \text{FeS} \), is a compound consisting of iron and sulfur. It is often found in nature as the mineral pyrrhotite. Iron sulfide has interesting properties that make it valuable in various chemical reactions, especially in the laboratory.

In our context, iron sulfide is crucial for preparing hydrogen sulfide gas. When \( \text{FeS} \) interacts with an acid, it releases \( \text{H}_2\text{S} \), a gas with a characteristic rotten egg smell. This gas is not only used in laboratory experiments but also plays roles in various industrial processes.

When handling iron sulfide, it is important to remember proper storage and handling techniques. Keeping it in a dry, cool place prevents unwanted reactions with moisture or other substances that could alter its properties.

Dilute Sulfuric Acid

Dilute sulfuric acid (\( \text{dil. } \text{H}_2\text{SO}_4 \)) is a substance produced by mixing sulfuric acid with water. This creates a less concentrated solution that is useful for various reactions.

The role of dilute sulfuric acid in the preparation of hydrogen sulfide is to react with iron sulfide. This reaction liberates \( \text{H}_2\text{S} \) gas. This process is typical due to its reliability and straightforwardness.

Using a dilute acid is important because it ensures a controlled release of \( \text{H}_2\text{S} \) without excessive heat or violent reactions. This allows safer handling within a laboratory setting.

• Since it is corrosive, even when diluted, handling should always involve appropriate safety equipment like gloves and goggles.
• Proper ventilation is crucial to avoid inhaling any released gases during reactions.

Chemical Reactions

Chemical reactions involve the reorganization of atoms within substances to form new compounds. When iron sulfide and dilute sulfuric acid react, they undergo a chemical transformation that produces hydrogen sulfide gas, \( \text{H}_2\text{S} \), and iron sulfate, \( \text{FeSO}_4 \). The word equation for this reaction can be represented as:

Iron Sulfide + Dilute Sulfuric Acid → Hydrogen Sulfide + Iron Sulfate

1. This reaction is characterized by a color change and the release of gas, making it easy to observe in a laboratory setting.
2. Recognizing the type of reaction, which is a double displacement, helps in predicting the outcomes.
3. Understanding these processes is vital for conducting experiments safely and effectively.

Chemical reactions can be influenced by factors such as temperature, concentration of reactants, and the presence of catalysts, so precise control and understanding are key to achieving desired results.

Laboratory Techniques

Mastering laboratory techniques is essential for conducting successful experiments, especially when handling substances that can produce hazardous gases like \( \text{H}_2\text{S} \).

When preparing hydrogen sulfide gas, it's important to follow specific steps to ensure safety and accuracy.

• Always conduct experiments in a well-ventilated area or under a fume hood to avoid exposure to harmful gases.
• Use appropriate glassware and measuring equipment to ensure the correct proportions of iron sulfide and dilute sulfuric acid.
• Wear personal protective equipment such as gloves, goggles, and lab coats to minimize the risk of chemical exposure.

By following these techniques, students and chemists can safely perform reactions while obtaining valuable insights into chemical processes and behaviors.