Question

Sketch a schematic representation of a typical galvanic cell, using a reaction of your choice. Indicate the direction of electron flow in your cell. How are the solutions placed in electrical contact to allow charge to balance between the chambers of the cell?

Short answer

A Daniell cell consists of a container divided into two sections: one for the copper-copper(II) sulfate electrode and one for the zinc-zinc sulfate electrode, with copper and zinc metal rods submerged in their respective electrolyte solutions. Electrons flow from the zinc metal (anode) to the copper metal (cathode), indicated by arrows on a connecting wire. To balance charges between the chambers and maintain electrical contact, a salt bridge, typically a U-shaped tube filled with agar gel containing an inert salt like potassium nitrate, connects the two electrolyte solutions allowing ions to move between them.

Step-by-step solution

Choose a redox reaction

For this example, we will use the Daniell cell, which involves a copper-copper(II) sulfate electrode and a zinc-zinc sulfate electrode. The redox reaction occurring in this cell is: \(Zn(s) + Cu^{2+}(aq) \rightarrow Zn^{2+}(aq) + Cu(s)\) ##Step 2: Sketch the galvanic cell##

Draw the basic components

To create a schematic representation of the Daniell cell, we will draw a container divided into two sections: one for the copper-copper(II) sulfate electrode and one for the zinc-zinc sulfate electrode. The copper and zinc metal rods are placed in their respective chambers and are submerged in their appropriate electrolyte solutions (copper(II) sulfate and zinc sulfate). ##Step 3: Indicate electron flow##

Show the electron flow

In the Daniell cell, electrons flow from the zinc metal (anode) to the copper metal (cathode). To indicate this, we will draw a wire connecting both metal rods and mark the flow of electrons with arrows pointing from the zinc to the copper. ##Step 4: Balance charges between the chambers##

Introduce a salt bridge

To maintain electrical contact and balance charges between the two chambers, we will use a salt bridge. This salt bridge connects the two electrolyte solutions and allows ions to move between them to compensate for the changes in the ionic concentrations of the solutions. The salt bridge can be represented by a U-shaped tube filled with agar gel containing an inert salt (e.g., potassium nitrate). Upon completing these steps, we have successfully sketched a schematic representation of a typical Daniell cell, indicated the direction of electron flow, and described how the solutions maintain electrical contact through a salt bridge to balance charges between the chambers of the cell.

Key concepts

Redox Reaction

Understanding redox reactions is fundamental to grasping the principles that govern a galvanic cell. Redox reactions involve the transfer of electrons between two substances. They consist of two half-reactions: oxidation and reduction. During oxidation, a substance loses electrons, while in reduction, a substance gains electrons.

Take the Daniell cell as an example. The reaction occurring in this galvanic cell can be divided into two half-reactions:

• Oxidation: \(Zn(s) \rightarrow Zn^{2+}(aq) + 2e^{-}\)
• Reduction: \(Cu^{2+}(aq) + 2e^{-} \rightarrow Cu(s)\)

Zinc metal is oxidized, releasing electrons into the circuit, while copper ions in the solution are reduced, receiving electrons from the circuit. The electrons given up by the zinc travel through an external circuit to the copper, driving the redox reaction forward.

Electron Flow in Galvanic Cell

The flow of electrons is the lifeblood of a galvanic cell and is critical for its operation. In this electrochemical cell, the spontaneous redox reaction generates an electric current as electrons move through an external circuit from the anode to the cathode.

In the case of the Daniell cell, the anode is made of zinc. As zinc undergoes oxidation, it releases electrons, which then flow through the connecting wire towards the cathode, made of copper. The cathode where the reduction takes place, receives these electrons, which complete the circuit. This flow from anode to cathode is driven by the potential difference between the two electrodes, resulting in a current that can do electrical work.

It is crucial that students can identify the direction of electron flow not only for understanding the cell's operation but also for correctly sketching the schematic of a galvanic cell in their exercises.

Salt Bridge

The salt bridge is an essential component of a galvanic cell, yet it is often misunderstood. It is not merely a physical connection between the two half-cells, but a pathway that allows ions to flow and thereby maintain electrical neutrality in the system.

As electrons leave the anode and flow to the cathode, positive ions build up in the anodic compartment and negative ions accumulate in the cathodic compartment. If this were to continue without a salt bridge, the reaction would soon halt due to charge imbalance. The salt bridge prevents this by allowing ions, typically an inert salt like potassium nitrate, to move between the two solutions. This migration of ions compensates for the electron flow, preventing charge buildup and allowing the redox reaction to continue.

Incorporating a salt bridge in the sketch of a Daniell cell is to faithfully represent this critical component that ensures charge balance and continuity of the electrochemical reaction.