Cathode and Anode: Definitions, Functions, and Practical Examples
The Difference Between Cathode And Anode is a frequent topic in exams because these concepts are central to understanding electrochemical cells, batteries, and electrolysis. Knowing their definitions and distinctions is vital for scoring in Chemistry and Physics questions.
Definition of Anode
An anode is the electrode where oxidation occurs, meaning it is the site where electrons are released by a chemical species and enter the external circuit. In both electrochemical and electrolytic cells, the anode's polarity depends on the cell type.
In an electrolytic cell, the anode is positively charged, while in a galvanic cell, it carries a negative charge. The process at the anode always involves the loss of electrons. For detailed charge concepts, see Basic Properties Of Electric Charge.
Definition of Cathode
A cathode is the electrode at which reduction takes place, meaning it is where electrons are accepted from the external circuit by a chemical species. The cathode's polarity also varies with the cell type.
In an electrolytic cell, the cathode is negative, while in a galvanic cell, it has a positive charge. The main event at the cathode is the gain of electrons. For comparison of other electrical parameters, refer to Difference Between Amperes And Volts.
Difference Table
| Anode | Cathode |
|---|---|
| Site of oxidation reactions | Site of reduction reactions |
| Loses electrons to external circuit | Gains electrons from external circuit |
| Positive in electrolytic cells | Negative in electrolytic cells |
| Negative in galvanic cells | Positive in galvanic cells |
| Attracts anions in electrolytic cells | Attracts cations in electrolytic cells |
| Repels cations in electrolytic cells | Repels anions in electrolytic cells |
| Produces electrons in reactions | Consumes electrons in reactions |
| Symbol often ‘A’ | Symbol often ‘K’ |
| Connected to power supply positive in electrolysis | Connected to power supply negative in electrolysis |
| Source of electrons in galvanic cells | Sink for electrons in galvanic cells |
| Example: Zinc electrode in Zn–Cu cell | Example: Copper electrode in Zn–Cu cell |
| Can be made of active or inert material | Can be made of active or inert material |
| Participates in oxidation half-cell reactions | Participates in reduction half-cell reactions |
| Potential is lower in galvanic cells | Potential is higher in galvanic cells |
| Often corrodes in electrochemical reactions | Often gets plated in electroplating |
| Direction of electron flow is from anode | Direction of electron flow is to cathode |
| In batteries, delivers electrons to circuit | In batteries, receives electrons from circuit |
| Oxidation: $M \to M^{n+} + ne^-$ | Reduction: $X^{n+} + ne^- \to X$ |
| Basis for the term "anions" | Basis for the term "cations" |
| Linked with energy source in electrolysis | Linked with electrolyte deposition in electrolysis |
Key Differences
- Anode is the site of oxidation, cathode for reduction
- Anode loses electrons, cathode gains electrons
- Polarity depends on the cell type
- Anode attracts anions, cathode attracts cations
- Electron flow always from anode to cathode
- Active in corrosion and electroplating processes
Examples
In a Daniel (Zn–Cu) cell, the zinc rod acts as the anode and undergoes oxidation, while the copper rod is the cathode and undergoes reduction. For instrument readings see Galvanometer Explained.
In the electrolysis of molten NaCl, the anode is connected to the positive terminal and chlorine forms by oxidation, while sodium ions are reduced at the cathode.
Applications
- Understanding battery function in electronics
- Electroplating metal objects in industries
- Electrolysis for extraction of reactive metals
- Corrosion prevention with sacrificial anodes
- Working of electrolytic refining of metals
- Operation principles of fuel cells and batteries
One-Line Summary
In simple words, anode is where oxidation and electron loss occur, whereas cathode is where reduction and electron gain take place.
FAQs on Understanding the Difference Between Cathode and Anode
1. What is the difference between cathode and anode?
Cathode and anode are two types of electrodes that differ in polarity and function.
Key differences:
- Cathode: Electrode where reduction occurs (gains electrons).
- Anode: Electrode where oxidation occurs (loses electrons).
- In an electrolytic cell: Cathode is negative, anode is positive.
- In a galvanic/voltaic cell: Cathode is positive, anode is negative.
2. How do you remember the difference between cathode and anode?
A common way to remember is Red Cat and An Ox:
- Red Cat: Reduction at the Cathode (gains electrons).
- An Ox: Anode is where Oxidation occurs (loses electrons).
3. In which types of cells are cathode and anode positive or negative?
The polarity depends on the type of cell:
- Electrolytic cell: Anode is positive, cathode is negative (because an external source pushes electrons in).
- Galvanic/Voltaic cell: Anode is negative, cathode is positive (as the cell generates electricity spontaneously).
4. What is the function of the cathode and anode in electrolysis?
In electrolysis:
- Cathode: Site of reduction, where cations gain electrons and are deposited/reduced.
- Anode: Site of oxidation, where anions lose electrons and undergo discharge.
5. Why does oxidation occur at the anode and reduction at the cathode?
Oxidation refers to the loss of electrons (Leo the lion says Ger – Loss of Electrons is Oxidation, Gain is Reduction). At the anode, electrons are lost; at the cathode, they are gained. This rule holds for all electrochemical cells.
6. What is the role of cathode and anode in a galvanic cell?
In a galvanic cell:
- Anode: Where oxidation happens (negative electrode; gives up electrons).
- Cathode: Where reduction takes place (positive electrode; receives electrons).
7. How can you identify the anode and cathode during an experiment?
To identify them:
- Observe which electrode attracts cations (positive ions) – that is the cathode.
- The electrode attracting anions (negative ions) is the anode.
8. What happens at the anode and cathode during electrolysis of water?
During water electrolysis:
- Anode (positive): Oxidation of water to oxygen gas (O2).
- Cathode (negative): Reduction of water to hydrogen gas (H2).
- Anode: 2H2O → O2 + 4H+ + 4e-
- Cathode: 2H2O + 2e- → H2 + 2OH-
9. What is the charge on anode and cathode in electrolytic cells and galvanic cells?
Charges depend on the cell type:
- Electrolytic cell: Anode (+), Cathode (-)
- Galvanic/Voltaic cell: Anode (-), Cathode (+)
10. Can cathode and anode change their role depending on the type of cell?
Yes, the polarity (positive or negative) of cathode and anode changes with the cell type, but:
- Cathode is always where reduction happens.
- Anode is always where oxidation occurs.
11. What are examples of cathode and anode in everyday life?
Cathode and anode are found in:
- Batteries: Anode (zinc, negative), cathode (carbon, positive in dry cells)
- Electroplating: The item to be coated is the cathode
- Electrolysis: Water splitting (anode produces oxygen, cathode produces hydrogen)
