Question

In the extractive of sodium by Down's process cathode and anode are respectively: (a) Nickel and chromium (b) Iron and graphite (c) Copper and nickel (d) Copper and chromium

Short answer

(b) Iron and graphite.

Step-by-step solution

Understand Down's Process

Down's process is used for the extraction of sodium from its compounds. It involves the electrolysis of molten sodium chloride (NaCl) where the sodium ions ( ext{Na}^+) are reduced at the cathode and chlorine ions ( ext{Cl}^-) are oxidized at the anode.

Identify Cathode Material

In Down's process, the cathode is made of iron. This material is used because it is a good conductor of electricity and resistant to the high temperatures and reactive environment within the electrolytic cell.

Identify Anode Material

The anode used in Down's process is made of graphite. Graphite is chosen because it is a good conductor of electricity and can withstand the corrosive environment where chlorine is produced during the electrolysis.

Associate Materials with Given Choices

Based on the information that the cathode is iron and the anode is graphite, match these materials to the given multiple-choice options. The correct pair is option (b): Iron and graphite.

Key concepts

Down's Process

Down's process is a method specifically designed for extracting sodium from its compounds, particularly sodium chloride. It’s a type of electrochemical process that has been refined over the years to efficiently produce sodium metal. Invented by James C. Down in the early 20th century, this technique revolutionized sodium extraction by providing a method that could be used on a commercial scale.

• Importance of Down's Process: Provides a direct and practical method of obtaining pure sodium.
• Historical Context: A breakthrough in industrial chemistry enabling large-scale production.

By understanding the nuances of this process, students can appreciate how electrochemical principles are applied in real-world industry.

Electrolysis

Electrolysis is an essential part of Down's process. It refers to the chemical decomposition of substances when an electric current is passed through them. In the case of Down's process, molten sodium chloride undergoes electrolysis, which means that electricity is used to break it down into its component elements.

• Basic Principle: Electricity is utilized to induce a chemical reaction.
• Product Formation: Leads to the extraction of sodium and chlorine gas.

During electrolysis, sodium ions migrate towards the cathode, where they gain electrons to form sodium metal. Simultaneously, chloride ions move towards the anode to release electrons and form chlorine gas. This step is crucial, as it sets the stage for obtaining pure sodium from sodium chloride.

Sodium Extraction

Sodium extraction in Down's process is a fascinating application of electrochemistry. The goal is to extract sodium in its elemental form for various industrial applications. During extraction, sodium ions (\( \text{Na}^+ \)) are reduced at the cathode by gaining electrons, thus turning into solid sodium metal.

• Cathode Reaction: \( \text{Na}^+ + e^- \rightarrow \text{Na} \)
• Result: Production of solid sodium that can be harvested for use.

Extracted sodium is critically important in industries ranging from energy production (in molten state as coolants in nuclear reactors) to manufacturing of chemicals and pharmaceuticals. Understanding this process can help students grasp key industrial applications of chemistry.

Molten Sodium Chloride

Molten sodium chloride is the raw material used in Down's process. It is essentially salt that has been heated past its melting point to form a liquid. This state is crucial because the ions in molten sodium chloride can move freely, making it possible for electricity to pass through and for electrochemical reactions to occur.

• State of Matter: Changing from solid to liquid facilitates ion movement.
• Role in Electrolysis: Enables the electrolysis process to operate efficiently by allowing ions to reach the electrodes.

Heating sodium chloride until it is molten is an essential preparatory step in Down's process, highlighting the importance of various physical states in chemical processes.