Problem 63 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Give the equations for the recovery of lead from Galena by air reduction.

Step-by-Step Solution

Answer

The lead recovery from Galena involves these reactions: \[ 2 \text{PbS} + 3 \text{O}_2 \rightarrow 2 \text{PbO} + 2 \text{SO}_2 \] and \[ 2 \text{PbO} + \text{PbS} \rightarrow 3 \text{Pb} + \text{SO}_2 \].

Step 1: Identify the Composition of Galena

Galena is a mineral composed primarily of lead sulfide (PbS). It is the main source of lead extraction.

Step 2: Write the Initial Reaction Equation

During air reduction, galena reacts with oxygen. First, the lead sulfide (PbS) reacts with oxygen to form lead oxide (PbO) and sulfur dioxide (SO_2). The equation for this reaction is: \[ 2 ext{PbS} + 3 ext{O}_2 ightarrow 2 ext{PbO} + 2 ext{SO}_2 \]

Step 3: Write the Reduction Reaction Equation

The lead oxide (PbO) formed is then reduced by more lead sulfide (PbS) to produce elemental lead (Pb) and sulfur dioxide (SO}_2). The equation for this reaction is: \[ 2 ext{PbO} + ext{PbS} ightarrow 3 ext{Pb} + ext{SO}_2 \]

Key Concepts

Galena

Galena is a significant mineral known for being the primary source of lead. It is recognizable by its shiny metallic luster and silver-gray appearance.
Packed with high densities, Galena's formula is given as lead sulfide (PbS).
This mineral is not only integral to the production of lead but also plays its role in history, being used since ancient times for lead extraction.

• An interesting fact about Galena is that it is one of the earliest minerals to be used by humans.
• It was historically utilized for its lead content in shops and for decorative cosmetics in Ancient Egypt.

Your understanding of Galena as lead sulfide (PbS) sets the stage for understanding how lead is extracted from it through processes like air reduction.

Air Reduction

Air reduction is a chemical process where air, or more specifically, oxygen from the air, is utilized to assist in reducing ores into a purer metallic form.
When extracting lead from Galena, air reduction is a critical step. It involves using the oxygen in the air to transform Galena, which is lead sulfide (PbS), into other compounds that are easier to process into pure lead.

• The initial step involves the conversion of lead sulfide to lead oxide using oxygen, termed as oxidation.
• This process releases sulfur dioxide as a byproduct.

This not only sets the ground for reducing lead oxide into metallic lead in later steps but also helps in isolating impurities.

Chemical Reactions

Chemical reactions are the backbone of extracting lead from Galena.
To recover lead, two main reactions occur during the air reduction process. Understanding these reactions helps to appreciate how elemental lead is ultimately retrieved.

• The first reaction involves lead sulfide reacting with oxygen to form lead oxide and sulfur dioxide, as given by the reaction: \[ 2 \text{PbS} + 3 \text{O}_2 \rightarrow 2 \text{PbO} + 2 \text{SO}_2 \]
• In the second step, lead oxide reacts with additional lead sulfide to produce elemental lead and more sulfur dioxide: \[ 2 \text{PbO} + \text{PbS} \rightarrow 3 \text{Pb} + \text{SO}_2 \]

Each reaction plays a significant role in the conversion process, making it a systematic way to refine galena to obtain pure lead metal.

Lead Sulfide

Lead sulfide (PbS) is the primary compound from which lead metal is extracted.
Often referred to as Galena, this mineral starts the chemical journey from its sulfide form to elemental lead.

• As part of the air reduction process, lead sulfide is first converted to lead oxide.
• This reaction requires oxygen and forms sulfur dioxide as a byproduct.

Later, what remains of the lead sulfide helps reduce lead oxide to the metal we need, illustrating its dual role in the process.
Through this transformation from sulfide to metal, lead sulfide displays its remarkable versatility and essential function in metal extraction.