Question

In one type of alkaline cell used to power devices such as portable radios, \(\mathrm{Hg}^{20}\) ions are reduced to metallac mercury when the cell is bcing discharged. Does this reduction occur at the anode or the cathode? Explain.

Short answer

The reduction occurs at the cathode.

Step-by-step solution

Understand Reduction and Oxidation

In electrochemical cells, reduction refers to the gain of electrons, while oxidation refers to the loss of electrons. The mnemonic to remember is OIL RIG: Oxidation Is Loss, Reduction Is Gain.

Identify the Electrodes

In any electrochemical cell, the anode is where oxidation occurs, and the cathode is where reduction occurs.

Apply Information to the Problem

The exercise states that \(\text{Hg}^{2+} \) ions are reduced to metallic mercury. Since reduction is occurring, it must happen at the cathode.

Conclusion

From the information above, it can be concluded that the reduction of \(\text{Hg}^{2+} \) ions to metallic mercury occurs at the cathode.

Key concepts

Oxidation

Oxidation is a key process in electrochemical cells and involves the loss of electrons from an atom or molecule. Think of it as a substance becoming more positive. For example, when a metal like zinc undergoes oxidation, it loses electrons and becomes a positive ion (Zn to Zn^{2+} ). Remember the mnemonic OIL RIG: Oxidation Is Loss. This helps you recall that oxidation is the process where electrons are given up. It's crucial to know that oxidation always occurs at the anode in electrochemical cells.

Reduction

Reduction is the opposite of oxidation: it involves the gain of electrons. When a substance undergoes reduction, it gains negative electrons and thus becomes more negative. For example, the reduction of Hg^{2+} ions to metallic mercury ( Hg ) is accomplished through the gain of two electrons, transforming the oxidized Hg^{2+} into its elemental form Hg. Use the second part of the mnemonic OIL RIG: Reduction Is Gain, to help remember this concept. Reduction always occurs at the cathode in electrochemical cells.

Anode

The anode in an electrochemical cell is where oxidation takes place. At the anode, electrons are lost by the substance undergoing oxidation. These electrons then flow away from the anode, into the circuit, contributing to the electrical current that powers devices. For example, in a common alkaline cell, substances like zinc are oxidized at the anode, losing electrons and creating an electric current. If you're using an anode, always think of it as the site of electron loss.

Cathode

The cathode is the electrode where reduction happens. At the cathode, electrons are gained by the substance getting reduced. For instance, in the exercise example, Hg^{2+} ions gain electrons and are reduced to metallic mercury at the cathode. This gain of electrons is what makes the cathode a crucial part of the electrochemical process. Any time you read about a cathode, think of a place where electrons are accepted and reduction is taking place.

Electrodes

Electrodes are conductive materials that serve as the sites for oxidation and reduction in electrochemical cells. There are two types of electrodes: the anode and the cathode.

• Anode: This is where oxidation occurs, meaning it's the site where electrons are lost.
• Cathode: This is where reduction occurs, meaning it's where electrons are gained.

Together, these electrodes enable the flow of electrons through the cell, creating an electric current. In the context of the exercise, the electrodes facilitate the reduction of Hg^{2+} ions at the cathode, completing the circuit and powering the device.