Question

In the Castner's process of extraction of sodium cathode is (a) nickel rod (b) iron rod (c) graphite rod (d) copper rod

Short answer

(c) graphite rod

Step-by-step solution

Understanding Castner's Process

Castner's process is a method used to extract sodium by electrolysis of molten sodium hydroxide (NaOH). It requires an appropriate choice of cathode material to prevent unwanted chemical reactions.

Identifying Suitable Cathode Materials

The choice of cathode in the electrolysis process is crucial. Materials like nickel, iron and copper can interact negatively with the molten sodium formed during electrolysis. Graphite, however, is chemically inert and resistant to high temperatures, making it a suitable choice.

Analyzing Options

Evaluating the given options: (a) nickel rod, (b) iron rod, (c) graphite rod, and (d) copper rod. Since graphite is stable and inert, it minimizes any potential reactions with sodium in molten form.

Concluding the Best Choice

Considering all options and the nature of the Castner's process, the cathode should be a material that is inert and resistant to sodium, which is achieved with a graphite rod due to its properties.

Key concepts

Electrolysis

Electrolysis is a fascinating chemical process used to drive a non-spontaneous reaction using electricity. In simple terms, it's a method that uses an electric current to cause a chemical change. For the extraction of elements, such as in Castner's process, electrolysis plays a central role.
This procedure involves passing an electric current through molten compounds to decompose them into their constituent elements.
In the context of sodium extraction, electrolysis breaks down sodium hydroxide into sodium metal and oxygen gas under high temperatures and controlled conditions.

• The source compound is electrically conductive, typically in a liquid molten state.
• The setup involves a cathode (negative electrode) and an anode (positive electrode), where reduction and oxidation reactions occur.
• Ultimately, this efficient process provides a way to isolate elements that occur in compounds only, such as sodium.

Because electricity is directly used to cause changes, electrolysis is instrumental in mining, refining, and many other chemical applications.

Sodium Extraction

Sodium extraction is a specific application of electrolysis aimed at obtaining pure sodium metal from its compounds. Sodium isn't found freely in nature due to its high reactivity, particularly with water, so it must be extracted from compounds like sodium hydroxide.
The Castner's process was a groundbreaking method developed to achieve this goal.

In Castner's process:

• Molten sodium hydroxide (NaOH) is subjected to electrolysis.
• At the cathode, reduction takes place: it’s here the sodium ions gain electrons and form sodium metal.
• The overall chemical reaction for the process can be shown as:
  \( 2 ext{NaOH} ightarrow 2 ext{Na} + ext{H}_2 ext{O} + rac{1}{2} ext{O}_2 \).
• This process mainly requires stable equipment and carefully chosen materials to withstand high temperatures and reactive chemicals.
• It’s an essential industrial process because sodium is crucial in various applications, from chemical manufacturing to metal refining.

Understanding such an extraction method emphasizes the importance of electrochemical technologies in modern chemistry.

Cathode Materials

In the realm of electrolysis, particularly in processes like sodium extraction, the choice of the cathode material is critical. The cathode is the electrode where reduction occurs; negative charged ions gain electrons.
For efficiency and safety, the selected material must remain largely inert and resist high temperatures and the reactivity of the metal being extracted.

Ideal characteristics for cathode materials include:

• Chemical Inertness: The material should not react with the substances being electrolyzed. Graphite is often chosen due to its high chemical stability.
• Heat Resistance: High temperatures can be common, so the material must cope without degrading.
• Electrical Conductivity: To facilitate the flow of electric current with minimal resistance.

In Castner's process, the cathode needs to withstand the formation of molten sodium. Options like nickel and copper aren’t suitable due to possible undesirable reactions. Graphite fits the criteria well, making it a reliable choice in electrolysis for sodium extraction. The choice exemplifies how understanding the properties of materials helps in optimizing chemical processes.