(d) Why is sodium metal not obtained when an aqueous solution of NaCl undergoes electrolysis?

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Understand the process of electrolysis: Electrolysis involves passing an electric current through a solution to cause a chemical change. In the case of NaCl, the solution is aqueous, meaning water is present.

Identify the ions present in the solution: In an aqueous NaCl solution, the ions present are Na⁺, Cl⁻, H⁺ (from water), and OH⁻ (from water).

Determine the possible reactions at the cathode: At the cathode, reduction occurs. The possible reductions are Na⁺ + e⁻ → Na (sodium metal) and 2H₂O + 2e⁻ → H₂ + 2OH⁻ (hydrogen gas).

Compare the reduction potentials: The reduction potential for Na⁺ to Na is more negative than that for water to hydrogen gas. This means that water is more easily reduced than Na⁺ in an aqueous solution.

Conclude why sodium metal is not obtained: Since water is reduced preferentially over Na⁺, hydrogen gas is produced at the cathode instead of sodium metal during the electrolysis of aqueous NaCl.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Electrolysis

Electrolysis is a chemical process that uses electrical energy to drive a non-spontaneous reaction. In the context of aqueous solutions, it involves the decomposition of compounds into their constituent elements or ions when an electric current is passed through the solution. The process occurs at electrodes, where oxidation and reduction reactions take place, leading to the formation of different products depending on the ions present.

Ionic Compounds in Aqueous Solution

When ionic compounds like NaCl dissolve in water, they dissociate into their respective ions, Na⁺ and Cl⁻. In an aqueous solution, water molecules also participate in the electrolysis process, which can lead to the production of hydrogen gas at the cathode and oxygen gas at the anode. The presence of water and its competing reactions significantly influences the products formed during electrolysis.

Electrode Reactions and Product Formation

During electrolysis, the reactions that occur at the electrodes depend on the relative reactivity of the ions present. In the case of NaCl electrolysis, water is more easily reduced than sodium ions, leading to the production of hydrogen gas instead of sodium metal. Similarly, at the anode, chloride ions are oxidized to form chlorine gas, rather than oxidizing water to produce oxygen, which further explains why sodium metal is not obtained.

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