Question

Consider the molecular view of an electrochemical cell involv- ing the overall reaction: $$ \mathrm{Zn}(s)+\mathrm{Ni}^{2+}(a q) \longrightarrow \mathrm{Zn}^{2+}(a q)+\mathrm{Ni}(s) $$ Draw a similar sketch of the cell after it has generated a substantial amount of electrical current.

Short answer

After generating substantial current, the zinc electrode will have decreased in size due to the loss of Zn atoms, the nickel electrode will have increased in size due to Ni deposition, and the concentration of Zn2+ in solution will have increased while the concentration of Ni2+ will have decreased.

Step-by-step solution

Understand the Original System

Begin by understanding the original electrochemical cell, which consists of a zinc electrode (where the solid zinc is oxidized to Zn2+ ions, releasing electrons) and a nickel electrode (where Ni2+ ions are reduced to solid nickel, gaining electrons).

Identify the Anode and the Cathode

Identify that the anode is the electrode where oxidation takes place, which is the zinc electrode. The cathode is the electrode where reduction takes place, which is the nickel electrode.

Describe the Process of Oxidation

At the anode, solid Zn is oxidized to form Zn2+ ions which go into solution, and two electrons are released per zinc atom.

Describe the Process of Reduction

At the cathode, Ni2+ ions in the solution are reduced to solid nickel metal by gaining two electrons each.

Sketch the 'After' Situation

When drawing the electrochemical cell after substantial use: - Show the zinc electrode smaller than the beginning due to oxidation and loss of mass.- Show the nickel electrode larger than the beginning due to nickel plating onto it.- Indicate the movement of Zn2+ ions into the solution and Ni2+ ion concentration decreasing.- Show the electron flow from the zinc electrode to the nickel electrode.

Key concepts

Oxidation and Reduction Reactions

Understanding oxidation and reduction reactions, commonly known as redox reactions, is crucial when studying electrochemical processes. In essence, these reactions involve the transfer of electrons between substances. Oxidation refers to the loss of electrons, while reduction indicates the gain of electrons. It's helpful to remember this with the simple mnemonic 'LEO the lion says GER': Lose Electrons Oxidization and Gain Electrons Reduction.

In the exercise given, zinc (Zn) atoms lose electrons to form Zn²⁺ ions, undergoing oxidation. Conversely, Ni²⁺ ions gain electrons to become solid nickel (Ni), thus being reduced. Every redox reaction is a tandem act; oxidation cannot occur without reduction happening simultaneously. The substance that gives away electrons (Zn) is called the reducing agent, and the one that accepts electrons (Ni²⁺) is termed the oxidizing agent. Recognizing these reactions in an electrochemical cell allows us to understand how chemical energy is converted into electrical energy.

Galvanic Cells

A galvanic cell, also known as a voltaic cell, is a device that generates electrical energy from spontaneous redox reactions. It consists of two electrodes - made of different metals or metal compounds - immersed in electrolyte solutions and connected by an external circuit and a salt bridge. These cells harness the energy released from redox reactions to produce electricity.

In the context of the exercise, the mentioned electrochemical cell is a type of galvanic cell where the zinc electrode undergoes oxidation, and the nickel electrode undergoes reduction. The key here is that the redox reactions are spontaneous, meaning they release energy that can be directed to do work, such as powering a light bulb. Understanding the principles of galvanic cells helps us comprehend the fundamentals of batteries and how simple combinations of metals and solutions can create portable sources of power.

Anode and Cathode Identification

To identify the anode and cathode within an electrochemical cell correctly, one needs to pinpoint where oxidation and reduction occur, respectively. The anode is the electrode where oxidation happens, and it's characterized by the release of electrons. On the other hand, the cathode is the electrode where reduction occurs, and it is known for the gain of electrons. It's important to note that in galvanic cells, the anode has a negative charge due to the excess of electrons that are released during the oxidation process, while the cathode has a positive charge as it attracts and gains electrons.

In the presented exercise, the zinc electrode is the anode because it loses electrons (oxidation), and the nickel electrode is the cathode because it gains electrons (reduction). An easy way to remember this is 'An Ox' and 'Red Cat' – Anode Oxidation and Reduction Cathode. The identification of anode and cathode is paramount for understanding how the cell functions and which direction the electrons will flow.

Electron Flow in Electrochemical Cells

The flow of electrons is what generates electricity in electrochemical cells. Electrons move from the anode to the cathode within the external circuit. This movement is crucial for the cell's operation, as it's the flow of electrons that allows the redox reactions to continue. To put it simply: no electron flow, no electricity, no reaction.

In our example exercise, electrons are released by the zinc atom at the anode when it becomes Zn²⁺. These electrons travel through the external circuit to the nickel cathode, driving the reduction reaction that forms solid nickel. It's this continuous flow of electrons that results in the production of electrical current. Over time, as the exercise indicates, the physical characteristics of the electrodes change — the zinc electrode diminishes in size due to the loss of zinc atoms, while the nickel electrode grows as nickel plates onto it.