Question

What is a cell diagram? Write the cell diagram for a galvanic cell consisting of an Al electrode placed in a \(1 \mathrm{M} \mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}\) solution and an Ag electrode placed in a \(1 \mathrm{M} \mathrm{AgNO}_{3}\) solution.

Short answer

A cell diagram represents a galvanic cell's construction. The cell diagram: \( \text{Al} | \text{Al}^{3+} (1 \text{ M}) || \text{Ag}^{+} (1 \text{ M}) | \text{Ag} \).

Step-by-step solution

Understand What a Cell Diagram Is

A cell diagram is a representation of a galvanic cell, showing the components of each half-cell and how they are connected. It uses vertical lines to represent phase boundaries and double vertical lines for a salt bridge. The anode is written on the left side, and the cathode is written on the right side.

Identify the Electrodes and Solutions

In this galvanic cell, you have an aluminum (Al) electrode in a 1 M aluminum nitrate (Al(NO₃)₃) solution and a silver (Ag) electrode in a 1 M silver nitrate (AgNO₃) solution. The aluminum half-cell is the anode because aluminum tends to lose electrons more than silver, making silver the cathode.

Determine the Half-Reactions

The oxidation half-reaction occurs at the anode, where Al is oxidized: \[\text{Al} \rightarrow \text{Al}^{3+} + 3e^{-}\]The reduction half-reaction occurs at the cathode, where Ag⁺ is reduced:\[\text{Ag}^{+} + e^{-} \rightarrow \text{Ag}\]

Formulate the Cell Diagram

Using the standard cell diagram notation, write the components in the order from anode to cathode:\[\text{Al} | \text{Al}^{3+} (1 \text{ M}) || \text{Ag}^{+} (1 \text{ M}) | \text{Ag}\]The single vertical lines '|' denote the separation of different phases, while the double vertical lines '||' represent the salt bridge between the two half-cells.

Key concepts

Galvanic Cell

A galvanic cell is an electrochemical cell that converts chemical energy into electrical energy through a spontaneous redox reaction. It consists of two different metals connected by a salt bridge, with each metal immersed in a solution of its ions. The two metals serve as electrodes, facilitating the flow of electrons generated from chemical reactions in the cell. This cell is named after Luigi Galvani, who first discovered the phenomenon. Understanding how a galvanic cell works is crucial since it forms the basic principle behind most batteries we use in everyday life. These cells work because there is a natural tendency for electrons to flow from one electrode to another, generating electricity.

Electrodes

In a galvanic cell, electrodes are the conductive surfaces that interact with the electrolyte solution. They play a critical role in facilitating the electrochemical reactions. There are two electrodes: the anode and the cathode.

• The Anode: This is where oxidation occurs. In our example, aluminum serves as the anode and is placed in a 1 M \( ext{Al(NO}_3)_3\) solution. It loses electrons during the reaction.
• The Cathode: This is where reduction takes place. Here, silver acts as the cathode in a 1 M \( ext{AgNO}_3\) solution. It gains electrons.

The choice of materials as electrodes affects the overall efficiency and voltage of the galvanic cell. Together, they allow for the circuit to be complete and the energy to be harnessed.

Half-Reactions

Half-reactions simplify the understanding of what occurs in a galvanic cell. They depict how electrons are transferred between species. Each galvanic cell consists of two main half-reactions: one for oxidation and one for reduction.

• For the oxidation half-reaction at the anode, the aluminum metal loses electrons: \[\text{Al} \rightarrow \text{Al}^{3+} + 3e^{-}\]
• For the reduction half-reaction at the cathode, silver ions gain electrons: \[\text{Ag}^{+} + e^{-} \rightarrow \text{Ag}\]

Recognizing these half-reactions helps us write the cell diagram and understand the movement of electrons, showcasing the transformation of reactants to products.

Oxidation

Oxidation is the process where a chemical species loses electrons. It happens at the anode in a galvanic cell. In our example of a galvanic cell, aluminum undergoes oxidation by losing three electrons: \[\text{Al} \rightarrow \text{Al}^{3+} + 3e^{-}\]This loss of electrons leads to the formation of aluminum ions. It's important to note that oxidation does not mean the addition of oxygen; rather, it solely focuses on the loss of electrons. This process results in the release of electrons which then travel through the external circuit towards the cathode, thus generating electrical current.

Reduction

Reduction is the opposite process of oxidation — it involves the gain of electrons. It takes place at the cathode. In our scenario, silver ions gain electrons through the reduction process: \[\text{Ag}^{+} + e^{-} \rightarrow \text{Ag}\]This gain in electrons enables silver ions to transform back into neutral silver atoms. Reduction at the cathode is an essential part of redox reactions in galvanic cells because it completes the circuit, allowing electrical energy to be generated. Reduction is vital for maintaining the flow of electrons, balancing the gain and loss across the cell.