Question

\(\mathrm{Pb}\) and \(\mathrm{Sn}\) are extracted from their chief ore by: (a) Carbon reduction and self reduction (b) Self reduction and carbon reduction (c) Electrolysis and self reduction (d) Self reduction and electrolysis

Short answer

(b) Self reduction and carbon reduction.

Step-by-step solution

Identify the Chief Ore of Lead (Pb)

Lead is commonly extracted from the ore known as Galena (PbS). We determine the process involved in the extraction based on the chemical properties of the compound.

Determine the Reduction Method for Lead

Galena is primarily reduced by a self-reduction process, where the sulfide ore is first converted to its oxide and then reduced to lead using carbon in the form of coke.

Identify the Chief Ore of Tin (Sn)

Tin is generally extracted from Cassiterite (SnO2). Recognizing the constitution of the ore provides insight into the extraction method.

Determine the Reduction Method for Tin

Cassiterite is reduced using carbon reduction, where the oxide is directly reduced to Tin using carbon.

Analyze the Extraction Methods Combination

Lead's extraction involves self-reduction, and Tin's extraction involves carbon reduction, matching the combination found in option (b).

Key concepts

Lead Extraction

Lead is typically extracted from its most common ore, galena, which is scientifically known as PbS, or lead(II) sulfide. This process involves two key steps.
First, galena undergoes a transformation where the sulfide is converted to oxide form. This is followed by a reaction in which carbon, often in the form of coke, reduces the lead oxide to metallic lead.

This method is known as self-reduction.

• Galena (PbS) is first roasted in air, converting some of the sulfide to oxide (PbO).
• A portion of the remaining sulfide reacts with the oxide to form metallic lead and sulfur dioxide.

Self-reduction is quite efficient in lead extraction because it simplifies the process by using the ore's own chemical compounds. This method effectively harnesses the chemical energy stored in the ores themselves, resulting in the formation of metallic lead, which can be further refined and used in various applications.
Understanding the chemistry behind these reactions can provide a deeper insight into industrial processes used in lead production.

Tin Extraction

The extraction of tin primarily utilizes its oxide ore known as cassiterite, or SnO2. Cassiterite is abundant and is the main source of tin. The extraction process for tin involves a straightforward reduction method using carbon. This process is conducted at high temperatures.

• First, the cassiterite ore is reduced directly by carbon to produce metallic tin.
• The chemical reaction is simple: SnO2 + 2C → Sn + 2CO.

Carbon reduction in tin extraction is highly effective due to its relatively low cost and simplicity. The carbon, typically in forms such as charcoal or coke, serves as a reducing agent, removing the oxygen from tin oxide, leaving pure tin metal.

The metal thus produced is usually in a crude form, requiring further refining to achieve the purity needed for industrial applications, such as solder, plating, and alloys.

Reduction Methods

Reduction methods are integral to the extraction of metals from their ores. These methods employ reducing agents to convert metallic compounds (usually oxides or sulfides) into a purer metallic form. Two main reduction methods are commonly used with different ores:

• Self-reduction involves the ore reacting internally to shed non-metallic elements, utilizing the presence of other minerals or compounds.
• Carbon reduction uses carbon as the reducing agent, typically in the form of coke or charcoal, to facilitate the removal of oxygen from metal oxides.

Self-reduction is often useful for metals that are stable as sulfides or compounds within the ore and do not require additional materials to initiate the reduction process. On the other hand, carbon reduction is more suitable for metal oxides because of the strong reducing capability of carbon at elevated temperatures.

Choosing the correct reduction method is crucial as it affects the purity, cost, and efficiency of the metal extraction process. Understanding these concepts is essential for anyone studying metallurgy or chemical engineering, as they form the basis of industrial extraction techniques.