Magnesium, the element, is produced commercially by electrolysis from a molten salt (the 'electrolyte') using a cell similar to the one shown here. (c) Recall that in an electrolytic cell the anode is given the + sign and the cathode is given the – sign, which is the opposite of what we see in batteries. What half-reaction occurs at the anode in this electrolytic cell?

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Identify the anode and cathode in the electrolytic cell. The anode is the carbon electrode connected to the positive terminal, and the cathode is the steel electrode connected to the negative terminal.

Determine the species present in the electrolyte. The electrolyte contains molten salt, which includes magnesium ions (Mg2+) and chloride ions (Cl-).

Recall that oxidation occurs at the anode. Therefore, the half-reaction at the anode involves the loss of electrons by chloride ions.

Write the oxidation half-reaction for chloride ions at the anode: 2Cl- -> Cl2(g) + 2e-.

Confirm that chlorine gas (Cl2) is produced at the anode, as indicated by the diagram showing Cl2(g) out.

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Key Concepts

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

Electrolytic Cell

An electrolytic cell is a device that uses electrical energy to drive a non-spontaneous chemical reaction. In this setup, an external voltage source is applied to facilitate the movement of ions in the electrolyte, leading to the oxidation and reduction reactions at the electrodes. The anode is positively charged, where oxidation occurs, while the cathode is negatively charged, where reduction takes place.

Half-Reaction

A half-reaction is a representation of either the oxidation or reduction process occurring in an electrochemical cell. It shows the species involved, their charges, and the electrons exchanged. In the context of the electrolytic cell described, the half-reaction at the anode involves the oxidation of chloride ions (Cl-) to form chlorine gas (Cl2), which is released as a product.

Electrode Reactions

Electrode reactions are the chemical processes that occur at the electrodes of an electrochemical cell. At the anode, oxidation occurs, where electrons are lost, while at the cathode, reduction occurs, where electrons are gained. Understanding these reactions is crucial for predicting the products of electrolysis, such as the formation of chlorine gas at the anode in this specific electrolytic cell.

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Textbook Question

Bars of iron are put into each of the three beakers as shown here. In which beaker—A, B, or C—would you expect the iron to show the most corrosion ? [Section 20.8]

Textbook Question

Magnesium, the element, is produced commercially by electrolysis from a molten salt (the 'electrolyte') using a cell similar to the one shown here. (a) What is the most common oxidation number for Mg when it is part of a salt?

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Textbook Question

Magnesium, the element, is produced commercially by electrolysis from a molten salt (the 'electrolyte') using a cell similar to the one shown here. (b) Chlorine gas is evolved as voltage is applied in the cell. Knowing this, identify the electrolyte.

Textbook Question

(b) On which side of an oxidation half-reaction do the electrons appear?