Cell Notation: Videos & Practice Problems

An electrochemical cell can be succinctly represented using cell notation, which outlines the redox reaction without the need for elaborate diagrams. The cell notation consists of phase boundaries, indicated by a single line, and a physical boundary, represented by two lines, separating the anode and cathode. The anode, where oxidation occurs, is the site where electrons are lost, while the cathode is where reduction takes place, gaining electrons. For instance, in a galvanic cell with a chromium anode and a copper cathode, the half-reactions are combined to yield the overall redox reaction. The cell notation follows the pattern of placing lower oxidation states at the ends and higher oxidation states in the middle, with the anode (A) and cathode (C) components separated by the physical boundary (B). This method provides a quick and efficient way to communicate the essential details of an electrochemical cell to others in the field.

Cell Notation

Cell notation, also known as a cell diagram, provides a concise way to represent the overall redox reaction occurring in an electrochemical cell. It incorporates two types of boundaries: phase boundaries and physical boundaries. Phase boundaries are depicted as a single line, indicating the coexistence of two phases of the same substance at equilibrium, while physical boundaries are represented by two solid lines, marking the separation between the anode and cathode.

In a typical electrochemical cell, such as a galvanic or voltaic cell, the anode is positioned on the left and the cathode on the right. In this setup, the anode carries a negative charge and is the site of oxidation, where electrons are lost. Conversely, the cathode is positively charged and serves as the site of reduction, where electrons are gained. For example, in a cell with a chromium electrode, chromium (Cr) at the anode undergoes oxidation, releasing electrons into the circuit, while copper ions (Cu²⁺) at the cathode gain these electrons to form solid copper (Cu).

The half-reactions can be summarized as follows: at the cathode, Cu²⁺ + 2e^- → Cu, and at the anode, Cr → Cr²⁺ + 2e^-. The electrons produced during oxidation at the anode and consumed during reduction at the cathode must balance, leading to the overall redox reaction: Cu²⁺ (aq) + Cr (s) → Cu (s) + Cr²⁺ (aq).

To express this in cell notation, we follow a simple format: A | B | C, where A represents the anode compartment, B denotes the physical boundary, and C signifies the cathode compartment. The lower oxidation states are placed at the ends, while the higher oxidation states are positioned in the center. For instance, the cell notation for the described electrochemical cell would be written as Cr (s) | Cr²⁺ (aq) || Cu²⁺ (aq) | Cu (s). This notation effectively summarizes the components and reactions occurring in the cell without the need for a detailed diagram, making it a practical tool for chemists.

Cell Notation Example

In an electrochemical cell, the cell notation is a concise way to represent the components and reactions occurring within the cell. The notation follows a specific format, typically denoted as a | b | c, where a represents the anode, b is the phase boundary, and c is the cathode. Understanding the oxidation states of the substances involved is crucial for determining the correct placement in the notation.

In the given redox reaction, we observe the transformation of tin (Sn) and aluminum (Al). The oxidation state of tin changes from +2 (in the form of Sn²⁺) to 0 (as solid tin, Sn), indicating that it is being reduced. This reduction occurs at the cathode, where the higher oxidation state (Sn²⁺) is located in the interior of the compartment, while the lower oxidation state (solid Sn) is on the end.

Conversely, aluminum undergoes oxidation, changing from 0 (as solid aluminum, Al) to +3 (in the form of Al³⁺). This increase in oxidation state signifies that aluminum is the anode, with the higher oxidation state (Al³⁺) found in the interior and the lower oxidation state (solid Al) on the end.

Thus, the complete cell notation for this electrochemical cell can be represented as:

Al | Al³⁺(aq) || Sn²⁺(aq) | Sn

This notation effectively summarizes the components and their respective oxidation states, providing a clear representation of the electrochemical processes taking place within the cell.

Write the half reactions as well as the overall net ionic equation for the following line notation: 
                     Fe (s) | Fe²⁺ (aq) || Mg²⁺ (aq) | Mg (s)

• A. Anode: Fe (s) → Fe²⁺ (aq) + 2e^-Cathode: Mg²⁺ (aq) + 2e^- → Mg (s)Overall: Fe (s) + Mg²⁺ (aq) → Fe²⁺ (aq) + Mg (s)
• B. Anode: Fe (s) → Fe²⁺ (aq) + 2e^-Cathode: Mg²⁺ (aq) + 2e^- → Mg (s)Overall: Fe²⁺ (aq) + Mg (s) → Fe (s) + Mg²⁺ (aq)
• C. Anode: Fe (s) → Fe²⁺ (aq) + 2e^-Cathode: Mg (s) → Mg²⁺ (aq) + 2e^-Overall: Fe (s) + Mg²⁺ (aq) → Fe²⁺ (aq) + Mg (s)
• D. Anode: Fe²⁺ (aq) + 2e^- → Fe (s)Cathode: Mg²⁺ (aq) + 2e^- → Mg (s)Overall: Fe (s) + Mg²⁺ (aq) → Fe²⁺ (aq) + Mg (s)

Answer: (A)

The cell notation for a redox reaction is given as the following at (T= 298 K). Calculate the cell potential for the reaction at 25ºC.
Zn (s) | Zn²⁺ (aq, 0.37 M) || Ni²⁺ (aq, 0.059 M) | Ni (s)
Standard Reduction Potentials
Zn²⁺ (aq) + 2 e^–  →. Zn (s)            E°_red = - 0.7621
Ni²⁺ (aq) + 2 e^–­  →  Ni (s)             E°_red = - 0.2300

• A. 0.3130 V
• B. 0.4033 V
• C. 0.5085 V
• D. 0.1199 V

Answer: (C)

What is the [Cu²⁺] for the following cell notation diagram if the cell potential is 0.4404 V?
Cu | Cu²⁺ (aq, ? M) || Ag⁺(aq, 0.50 M) | Ag
Standard Reduction Potentials
Cu²⁺ (aq) + 2 e^–  →. Cu (s)               E°_red = + 0.3394
Ag⁺ (aq) + e^–­  →  Ag (s)                    E°_red= + 0.8000

• A. 0.87 M
• B. 1.20 M
• C. 3.32 M
• D. 0.11 M

Answer: (B)

Here’s what students ask on this topic:

How do you write cell notation?

Writing cell notation involves representing the components of an electrochemical cell and the direction of electron flow. Here's how you do it:

1. Anode to Cathode: Write the anode (oxidation half-cell) on the left and the cathode (reduction half-cell) on the right. The vertical line, "|", represents a phase boundary, and the double vertical line, "||", represents the salt bridge or a porous membrane separating the two half-cells.
2. Anode Half-Cell: Start with the anode material (the solid electrode), followed by the phase boundary line. Next, write the anode's aqueous ions with their concentration in parentheses. If there's a solid and a gas involved, write the gas before the solid.
3. Cathode Half-Cell: After the double line for the salt bridge, write the cathode's aqueous ions and their concentration, followed by the phase boundary line, and then the cathode material (the solid electrode).
4. Electron Flow: Electrons flow from the anode to the cathode, but in cell notation, you don't explicitly write the direction of electron flow.

For example, for a cell with zinc and copper:

$\mathrm{Zn}\left(s\right)\left|{\mathrm{Zn}}^2\right(\mathrm{aq})||{\mathrm{Cu}}^2(\mathrm{aq}\left)\right|\mathrm{Cu}\left(s\right)$

How do you read cell notation?

Cell notation, also known as line notation, is a shorthand way to represent the components of an electrochemical cell. Here's how to read it:

1. Anode and Cathode: The anode (negative electrode where oxidation occurs) is written on the left, and the cathode (positive electrode where reduction occurs) is on the right.
2. Electrode Material: The material of the electrode is written first, typically a metal.
3. Ion Concentration: After the electrode material, the concentration of the ions in solution is given in parentheses.
4. Double Vertical Lines: These represent a salt bridge or a porous membrane, which separates the two half-cells.
5. Single Vertical Lines: These denote a phase boundary within a half-cell, such as between a solid electrode and an aqueous solution.

For example, in the cell notation:

$\mathrm{Zn}\left(s\right)\left|{\mathrm{Zn}}^{\mathrm{2+}}\right(\mathrm{aq},1M)||{\mathrm{Cu}}^{\mathrm{2+}}(\mathrm{aq},1M\left)\right|\mathrm{Cu}\left(s\right)$

Zinc is the anode, and copper is the cathode. The zinc electrode is solid, as denoted by (s), and it's in a 1M solution of Zn²⁺ ions. The double vertical lines indicate the separation between the anode and cathode half-cells, and the copper cathode is solid, as denoted by (s), and it's in a 1M solution of Cu²⁺ ions.

What is the correct line notation for the following voltaic cell?

To write the correct line notation for a voltaic cell, you'll need to know the specific details of the cell's components, such as the anode and cathode materials, and the electrolytes involved. However, I can give you a general format for a voltaic cell's line notation:

Anode | Anode Ion (Concentration) || Cathode Ion (Concentration) | Cathode

Here's how to break it down:

1. Start with the anode (the electrode where oxidation occurs) on the left.
2. Separate the anode material and its aqueous ions with a single line (|), which represents a phase boundary.
3. Use a double line (||) to represent the salt bridge or membrane that separates the two half-cells.
4. After the double line, list the cathode ion and its concentration.
5. End with the cathode material (the electrode where reduction occurs) on the right.

For example, if you have a zinc-copper voltaic cell with Zn as the anode and Cu as the cathode, and both are in solutions of their respective sulfates, the line notation would be:

$\mathrm{Zn}\left(s\right)\left|{\mathrm{Zn}}^{\mathrm{2+}}\right(\mathrm{aq})||{\mathrm{Cu}}^{\mathrm{2+}}(\mathrm{aq}\left)\right|\mathrm{Cu}\left(s\right)$

Remember to include the physical state of the materials (s for solid, aq for aqueous).