⚡ Chemical Effects of Electric Current
Electrolysis • Electrolytes • Electrodes • Ions • Faraday's Laws • Electroplating • Cells • Primary Cells • Defects of Simple Cell
⚡ Chemical Effect of Electric Current
When electric current passes through certain liquids or solutions, chemical changes take place. This phenomenon is called the chemical effect of electric current.
🧪 Basic Terms
Electrolysis
The chemical decomposition or chemical change produced by passing electric current through an electrolyte is called electrolysis.
Electrolyte
A liquid or solution that conducts electricity through ions and undergoes chemical change is called an electrolyte.
Electrodes
Conducting plates immersed in an electrolyte to allow current to enter and leave the electrolyte are called electrodes.
Anode
In an electrolytic cell, the anode is connected to the positive terminal of the DC supply.
Cathode
In an electrolytic cell, the cathode is connected to the negative terminal of the DC supply.
Ions
Charged particles produced in an electrolyte. Positive ions are called cations and negative ions are called anions.
🔬 Electrolysis – Animated Circuit Diagram
The animation below shows a DC source connected to two electrodes immersed in an electrolyte. Positive ions move towards the cathode and negative ions move towards the anode.
SUPPLY
Animated representation of ion movement during electrolysis
⚖️ Electrochemical Equivalent (ECE)
The mass of a substance liberated or deposited during electrolysis by the passage of one coulomb of electricity is called its electrochemical equivalent (ECE).
🔢 Coulomb
The coulomb (C) is the SI unit of electric charge. The quantity of electricity passing through a conductor is related to current and time.
1 Faraday's First Law of Electrolysis
The mass of a substance liberated or deposited at an electrode is directly proportional to the quantity of electricity passed through the electrolyte.
m ∝ I × t
m = Z × I × t Faraday's First Law
Where:
| Symbol | Meaning |
|---|---|
| m | Mass of substance liberated/deposited |
| Z | Electrochemical equivalent |
| I | Current in amperes |
| t | Time in seconds |
| Q | Quantity of electricity in coulombs |
2 Faraday's Second Law of Electrolysis
When the same quantity of electricity is passed through different electrolytes, the masses of substances liberated are proportional to their respective electrochemical equivalents.
⭐ Exam Point
First Law: Mass depends on quantity of electricity.
Second Law: For the same quantity of electricity, mass depends on the electrochemical equivalent of the substance.
⚙️ Applications of Electrolysis
Depositing a protective or decorative metal coating.
Purification of metals using electrolysis.
Some metals are extracted from compounds using electrolysis.
Electrolytic process used for reproducing objects or printing forms.
Electrolytic action is used to form the dielectric layer.
Electrolysis is used in several industrial chemical processes.
✨ Electroplating
Electroplating is the process of depositing a layer of one metal on the surface of another object by electrolysis.
⚡ Electroplating Circuit Diagram
Anode (+): Metal to be deposited
Cathode (-): Article to be coated
Electrolyte: Solution containing ions of plating metal
✓ Conditions for Electroplating
- The article must have a clean surface.
- The article to be coated is connected as the cathode.
- The anode is generally made from the metal to be deposited.
- The electrolyte should contain ions of the coating metal.
- DC supply is used for electroplating.
🛡️ Cathodic Protection
Cathodic protection is a method used to reduce corrosion by making the metal structure to be protected act as the cathode of an electrochemical cell.
🔋 Electrical Cells
An electrochemical cell converts chemical energy into electrical energy during discharge. A cell generally consists of electrodes and an electrolyte.
Dry Cell
Uses a paste-type electrolyte and can generally be operated in different positions without leakage.
Wet Cell
Uses a liquid electrolyte. Lead-acid batteries are a common example.
Secondary Cell
Rechargeable cell in which the chemical reaction can be substantially reversed by applying electrical energy.
🔋 Primary Cells
Primary cells are generally non-rechargeable cells. Their chemical reaction is not practically reversible by normal charging.
Voltaic Cell
Uses zinc and copper electrodes with an acidic electrolyte.
Leclanché Cell
Carbon-zinc cell using ammonium chloride electrolyte and manganese dioxide.
Dry Cell
Common carbon-zinc cell with a moist paste electrolyte.
Alkaline Cell
Uses an alkaline electrolyte, commonly potassium hydroxide.
Mercury Cell
Historically used in small electronic equipment; mercury disposal requires environmental care.
Silver Oxide Cell
Used for compact applications such as watches and small electronic devices.
Lithium Cell
Provides relatively high cell voltage and long shelf life depending on chemistry.
🔋 Simple Voltaic Cell
A simple voltaic cell uses zinc and copper electrodes with an electrolyte such as dilute sulphuric acid. During operation, chemical reactions produce a potential difference between the electrodes.
Simple Voltaic Cell – illustrative diagram
🔋 Leclanché Cell / Carbon-Zinc Cell
The Leclanché cell uses zinc as the negative electrode and a carbon rod as the positive electrode. Manganese dioxide acts as a depolarizing material.
🔋 Dry Cell
A dry cell is a type of primary cell in which the electrolyte is present as a moist paste. The common carbon-zinc dry cell has a zinc container as the negative electrode and a carbon rod as the positive electrode.
🔋 Alkaline Cell
Alkaline cells commonly use zinc as the negative electrode, manganese dioxide as the positive active material and potassium hydroxide as the electrolyte.
⚠️ Defects of a Simple Cell
1. Local Action
Local action occurs because impurities in commercial zinc can form small local cells on the zinc surface. This causes unwanted chemical action and reduces the useful output of the cell.
2. Polarisation
During operation of a simple cell, hydrogen may accumulate on the copper electrode. This increases internal resistance and reduces the effective cell output.
📚 Quick Revision Points
- Electrolysis: Chemical change caused by electric current through an electrolyte.
- Electrolyte: Solution/liquid conducting electricity mainly through ions.
- Cation: Positively charged ion.
- Anion: Negatively charged ion.
- Electroplating: Depositing a metal coating by electrolysis.
- First Law: m = ZIt.
- Charge: Q = It.
- Electroplating article: Connected as cathode.
- Electroplating anode: Generally the metal being deposited.
- Primary cell: Generally non-rechargeable.
- Secondary cell: Rechargeable.
📝 Important MCQs
A) Induction
B) Electrolysis
C) Magnetisation
D) Rectification
A) Positive terminal
B) Negative terminal
C) Earth
D) Neutral point
A) m = ZIt
B) V = IR
C) P = VI
D) Q = CV
A) Anode
B) Cathode
C) Electrolyte
D) Insulator
A) Ampere
B) Volt
C) Coulomb
D) Ohm
⚡ Chemical Effects of Electric Current
Electrolysis • Faraday's Laws • Electroplating • Cells