Question

What is the reaction occurring at the anode in Down? process for the extraction of sodium? (a) \(2 \mathrm{Cl}^{-} \rightarrow \mathrm{Cl}_{2}+2 \mathrm{e}^{-}\) (b) \(\mathrm{NaOH} \rightarrow \mathrm{Na}++\mathrm{OH}^{-}\) (c) \(4 \mathrm{OH}^{-} \rightarrow 2 \mathrm{H}_{2} \mathrm{O}+\mathrm{O}_{2}+4 \mathrm{e}^{-}\) (d) \(\mathrm{Na}^{+}+\mathrm{e}^{-} \rightarrow \mathrm{Na}\)

Short answer

The reaction at the anode is (a) \(2 \mathrm{Cl}^{-} \rightarrow \mathrm{Cl}_{2}+2 \mathrm{e}^{-}\).

Step-by-step solution

Understanding the Down's Process

The Down's process is used for the extraction of sodium from molten sodium chloride. In this electrochemical process, sodium ions are reduced to sodium metal, and chloride ions are oxidized to chlorine gas.

Identify Anode and Cathode Reactions

In general electrochemical cells, the anode is where oxidation occurs, and the cathode is where reduction takes place. We focus on identifying the correct oxidation reaction occurring at the anode.

Analyze Given Reaction Options

We have four options to consider:(a) \(2 \mathrm{Cl}^{-} \rightarrow \mathrm{Cl}_{2}+2 \mathrm{e}^{-}\)(b) \(\mathrm{NaOH} \rightarrow \mathrm{Na}^{+} + \mathrm{OH}^{-}\)(c) \(4 \mathrm{OH}^{-} \rightarrow 2 \mathrm{H}_{2}\mathrm{O} + \mathrm{O}_{2} + 4 \mathrm{e}^{-}\)(d) \(\mathrm{Na}^{+} + \mathrm{e}^{-} \rightarrow \mathrm{Na}\)

Identify Oxidation Reaction at the Anode

Oxidation reactions involve the loss of electrons. In option (a), \(2 \mathrm{Cl}^{-} \rightarrow \mathrm{Cl}_{2} + 2 \mathrm{e}^{-}\), chloride ions lose electrons to form chlorine gas, which is consistent with an anode reaction.

Conclusion

Based on our analysis, the reaction occurring at the anode in the Down's process is the oxidation of chloride ions to chlorine gas, described by option (a).

Key concepts

Anode Reaction

In the Down's Process, the anode is a key component of this electrochemical system. The anode is a positively charged electrode where oxidation, the process of losing electrons, takes place. Identifying the reaction happening at the anode is crucial for understanding the overall mechanism of sodium extraction. In this particular setup, chloride ions (\( \text{Cl}^{-} \)) from molten sodium chloride are oxidized at the anode. They lose electrons to form chlorine gas (\( \text{Cl}_2 \)), as represented by the reaction:

• \( 2 \text{Cl}^{-} \rightarrow \text{Cl}_2 + 2 \text{e}^{-} \)

This is consistent with the principle that oxidation reactions involve the removal of electrons. Understanding the anode's role helps one grasp how different ions are transformed and moved in electrochemical processes.

Sodium Extraction

The Down's Process is primarily known for extracting sodium metal from its compound, sodium chloride. This process involves electrolysis—a method that uses electricity to drive a chemical reaction.
At the core of this process is the transformation of sodium ions into solid sodium metal. The reaction occurring at the cathode builds upon the fact that sodium ions gain electrons to undergo reduction.

• \( \text{Na}^{+} + \text{e}^{-} \rightarrow \text{Na} \)

Through these steps, sodium extracted in its metallic form is obtained from the more stable ionic compound it exists within. This process is significant in industrial applications where sodium needs to be isolated for further utilization.

Oxidation Reaction

Oxidation reactions are at the heart of what happens at the anode during the Down's process. Oxidation refers to the loss of electrons by a molecule, atom, or ion. In the context of sodium extraction, we specifically look at the oxidation of chloride ions.
The oxidation reaction can be detailed as follows:

• \( 2 \text{Cl}^{-} \rightarrow \text{Cl}_2 + 2 \text{e}^{-} \)

Here, chloride ions each lose an electron, leading to the formation of chlorine gas. Recognizing the role of oxidation in electrochemical processes emphasizes the importance of electron transfer in chemical transformations. This electron transfer is fundamental to the production and recovery of different substances, including sodium.

Chlorine Gas Formation

The formation of chlorine gas is a secondary yet crucial outcome of the Down's process. When chloride ions (\( \text{Cl}^{-} \)) undergo oxidation, they not only lose electrons but also combine to form chlorine gas. This transformation is chemically represented as:

• \( 2 \text{Cl}^{-} \rightarrow \text{Cl}_2 + 2 \text{e}^{-} \)

Chlorine gas, produced at the anode, is then collected separately. The generation of chlorine gas is vital as it indicates the completion of the oxidation reaction and reflects the efficiency of the Down's process.
Chlorine gas itself has widespread industrial usage, including being a precursor in the manufacture of many everyday chemical compounds. Appreciating this aspect of chlorine generation allows one to see the interconnected nature of chemical processes both in labs and industry.