Question

Answer the following questions based on Figure \(20.28 .\) a. Which electrode grows? Write the reaction that occurs at this electrode. b. Which electrode disappears? Write the reaction that occurs at this electrode.

Short answer

a. The electrode that grows is the one undergoing reduction, gaining electrons. The general reaction is \[M^n+ + ne^- \rightarrow M\] b. The electrode that disappears is the one undergoing oxidation, losing electrons. The general reaction is \[M \rightarrow M^n+ + ne^-\] Please refer to Figure 20.28 for specific element and reactions mentioned in the figure.

Step-by-step solution

Identify the Half-Reactions

Referring to Figure 20.28, start by identifying the half-reactions occurring at each electrode. These reactions should specify the loss or gain of electrons and the chemical species involved.

Determine the Growth and Depletion of Electrodes

Knowing the half-reactions, determine which electrode gains mass (i.e., grows) and which electrode loses mass (i.e., disappears). When a metal electrode is reduced, its mass increases due to the deposition of metal ions from the solution. When it is oxidized, its mass decreases as the metal atoms lose electrons and turn into metal ions, leaving the electrode.

Write the Reactions Occurring at Each Electrode

Based on the growth and depletion of electrodes, write the reactions occurring at each electrode. Specifically, for the growing electrode, write the reduction half-reaction, where an element gains electrons. For the disappearing electrode, write the oxidation half-reaction, where an element loses electrons. Please note that without specific information about Figure 20.28, it is impossible to provide detailed steps for this specific exercise. However, using the outlined steps above, you should be able to analyze any electrochemical cell described in a given figure and determine the electrode growth, depletion, and reactions occurring at each electrode.

Key concepts

Half-Reactions in Electrochemistry

Electrochemistry is a branch of chemistry that deals with the interrelation of electrical and chemical changes in substances. One of its fundamental components is the concept of half-reactions. Understanding half-reactions is crucial for students as it breaks down the complex processes of electrochemical reactions into simpler, more manageable steps.

Half-reactions essentially divide the overall reaction of an electrochemical cell into two parts: one that involves the loss of electrons (oxidation) and the other that involves the gain of electrons (reduction). Each half-reaction represents what happens at one electrode of an electrochemical cell. They are a valuable tool for balancing chemical equations for redox reactions since they allow us to focus on the change happening to each reactant individually.

When you're presented with an electrode process, simply remember that there are two half-reactions at play. The electrodes are where these reactions occur, with electrons being transferred from the reducing agent to the oxidizing agent. In essence, every exchange of electrons that powers your device or carries out a reaction in a lab, hinges on these half-reactions.

Oxidation and Reduction

Delving into the realms of oxidation and reduction will reveal the core of numerous chemical reactions, especially in the field of electrochemistry. These processes are two halves of a whole, always occurring simultaneously. Oxidation involves the loss of electrons, while reduction refers to the gain of electrons. It’s crucial to recognize that one cannot exist without the other; they are like dance partners in the ballet of chemistry.

These reactions are often summed up by the mnemonic 'OIL RIG' - Oxidation Is Loss, Reduction Is Gain (of electrons). Understanding the flow of electrons helps us determine what gets oxidized and what gets reduced in a chemical reaction. For instance, in a battery, the material that gives up electrons (oxidizes) does so at the anode, while the material that gains electrons (reduces) does so at the cathode. Mastering the concepts of oxidation and reduction will not only aid in solving electrochemistry exercises but will also give insight into how batteries function, how metals corrode, and how we can prevent or encourage these processes.

Electrode Processes

Electrochemistry revolves around electrode processes. A deeper look into these processes reveals that the behavior of an electrochemical cell - like a battery or an electrolysis apparatus - is dictated by the events happening at the electrodes.

Electrodes are conductive materials, typically metals or graphite, that serve as the sites for oxidation or reduction reactions in an electrochemical cell. At the cathode, reduction occurs where ions gain electrons and deposit onto the electrode, typically leading to growth in mass. Conversely, at the anode, oxidation takes place where atoms or ions lose electrons. This often results in the electrode material dissolving into the solution, meaning a loss of mass.

Being able to write the half-reactions at each electrode is vital, as it tells us not just the fate of electrons, but also how the mass of the electrodes will change. Whenever working on problems related to electrode processes, remember to consider the direction of electron flow, the substances gaining or losing electrons, and the subsequent material changes of the electrodes. Powering a light bulb or plating a layer of chrome onto steel, each transforms energy and matter through the dance of electrode processes.