Problem 154 - A Complete Resource Book in Chemistry for JEE Main

Question

The following methods are not advisable to extract zinc from its oxide ore. (a) Reduction with aluminium (b) Reduction with \(\mathrm{H}_{2}\) (c) Electrolytic reduction (d) Reduction with carbon

Step-by-Step Solution

Answer

Reduction with 12 \( \mathrm{H}_{2} \) and carbon are not advisable for zinc oxide.

Step 1: Understand the Chemical Properties of Zinc Oxide

Zinc oxide (ZnO) is a stable compound with a high melting point. It requires a reduction process that can break the Zn-O bonds effectively to yield metallic zinc.

Step 2: Analyze Reduction with Aluminium

Reduction with aluminium is known as aluminothermic reduction, a method often used for metals with high melting points. Aluminium is a powerful reducing agent and can effectively reduce zinc oxide to zinc.

Step 3: Analyze Reduction with \\( \mathrm{H}_{2} \\\)

Hydrogen gas (12\( \mathrm{H}_{2} \)) is a reducing agent, yet it is ineffective for reducing zinc oxide at typical conditions because it cannot sufficiently reduce ZnO at the necessary temperatures.

Step 4: Analyze Electrolytic Reduction

Electrolytic reduction involves electric current to extract metals from their compounds. This process is not typically used for zinc oxide, as it is more commonly applied to ores that are already in metallic form or need purification.

Step 5: Analyze Reduction with Carbon

Carbon can be used to reduce some metal oxides (like iron oxides) but is typically ineffective for zinc oxide. The zinc-containing compound is reduced only partially in standard conditions often resulting in contamination and low yield.

Key Concepts

Reduction Methods

The extraction of zinc from zinc oxide involves several reduction methods. Choosing the right method is crucial for efficiency.

• Aluminothermic Reduction: This method uses aluminum as a reducing agent due to its strong reducing capabilities. It's very effective for high melting point metals.
• Hydrogen Reduction: Hydrogen gas can act as a reducing agent, though it's often not effective under normal conditions for zinc oxide.
• Electrolytic Reduction: An electric current is used to extract metals from their ores, often suitable for ores in a metallic state.
• Carbon Reduction: Carbon is frequently used for iron but is ineffective for reducing zinc oxide due to partial reduction and contamination issues.

Each method has its benefits and drawbacks, and the right choice often depends on the specific metal and compound involved.

Chemistry of Zinc

Zinc is a versatile and important element in both industrial and biological contexts. It is in group 12 on the periodic table and is a transition metal.

• Zinc forms compounds primarily in the +2 oxidation state, such as zinc oxide (ZnO), which is a highly stable compound.
• Its stability is due to the strong Zn-O bonds, making certain reduction methods less effective.
• The melting point and reactivity of zinc play a significant role in its extraction from oxide ores.

These chemical properties are pivotal in understanding which reduction methods are viable for zinc oxide extraction.

Electrolytic Reduction

Electrolytic reduction is a technique that uses an electric current to facilitate the extraction of metals from their ores. This method is more common for purifying metals rather than extracting from oxides.

• It works well for metals that are already in a metallic state, providing high purity results.
• For zinc oxide, electrolytic reduction isn't cost-effective and doesn't provide the desired yield due to the stability of Zn-O bonds.
• Instead, it is often used to refine zinc itself from metallic impurities.

Understanding the application of this method is crucial in metal extraction processes where high purity is required.

Aluminothermic Reduction

The aluminothermic reduction process utilizes the strong reducing power of aluminum to extract metals from their oxides.

• Aluminum's high affinity for oxygen enables it to break strong oxide bonds, such as those in zinc oxide.
• This method is advantageous for metals with high melting points, including zinc, making it a suitable choice.
• The reaction between aluminum and zinc oxide is highly exothermic, providing the necessary energy for the reduction process, thus yielding pure metallic zinc.

Aluminothermic reduction is particularly useful in extracting metals that are otherwise challenging due to their strong oxide bonds.