Chemical Effects of Electric Current - Class 8 Notes & Olympiad Questions

Electric Current

Electric current refers to the flow of electric charges through a conductor, which is typically a material that allows the movement of these charges. Electric current plays a fundamental role in various electrical and electronic devices, and it is a crucial concept in understanding how electricity works.

Key Points:

a) Flow of Electric Charges: Electric current is the result of the movement of electric charges within a material. These electric charges are carried by electrons, which are particles with a negative charge. In most conductors, such as metals, electrons are the primary charge carriers responsible for the flow of electric current.

b) Types of Charges: Electric charges come in two types: positive and negative. Positive charges are associated with particles called protons. Negative charges are associated with electrons. Objects with an excess of electrons have a negative charge, while those with a deficit of electrons have a positive charge.

c) SI Unit for Electric Current and Electric Charge: The standard unit for measuring electric current is Ampere (A). The Coulomb, represented by the symbol "C," is the unit used to measure electric charge. One Ampere is defined as the flow of one Coulomb of electric charge per second.

d) Practical Flow of Electrons: In practice, when a circuit is closed, electrons move from the negative terminal of a power source, through the circuit components, and back to the positive terminal of the power source. This flow of electrons creates a flow of electric current through the circuit.

e) Conventional Current Direction: Interestingly, despite the flow of negatively charged electrons, the convention for representing the direction of electric current is from the positive terminal to the negative terminal. This convention was established before the discovery of electrons, and it has remained consistent.

Relationship Between Electric Current, Electric Charge and Time

Definitions

a) Electric Current (I): Electric current is the flow of electric charges wire or a circuit. We measure this flow of charges in Amperes, or simply "Amps" (A).

b) Electric Charge (Q): Electric charges are tiny particles that move around in wires. When these charges move, they create electric currents. We measure the amount of these charges in Coulombs (C).

c) Time (t): Time, measured in seconds (s), dictates the duration over which the charge moves.

The Equation

I = Q/t
Electric Current (Amps) = Electric Charge (Coulombs) / Time (Seconds)

This equation shows that electric current is the rate at which electric charge flows through a conductor. If a certain amount of charge Q passes through a point in a circuit in a time interval t, then the current I is the ratio of Q to t.

Illustrative Examples

1. Consider a scenario where 1 Coulomb of electric charge passes through a circuit point in 1 second. In this case, the resulting electric current would be 1 Ampere.
1 C / 1 s = 1 A

2. Similarly, if 10 Coulombs of charge traverse a circuit point in 5 seconds, the ensuing electric current would be 2 Amperes.
10 C / 5 s = 2 A

Differences between Electric Current and Electric Charge

Conductors and Insulators

Conductors

Conductors are materials that easily allow electric current to flow through them. They enable the movement of electric charge, making them suitable for transmitting electricity. Common examples of conductors include metals like copper, silver, gold, aluminium, and some liquids like saltwater and certain acids.

Key Characteristics of Conductors

a) Metals, due to their crystalline structure and the presence of "free electrons," are the most common and efficient conductors. The free electrons can easily move within the lattice of metal atoms, enabling a continuous flow of electric charge.
b) Conductors exhibit high electrical conductivity, which means they offer minimal resistance to the movement of electric charges. This property is crucial for efficient energy transmission and utilization in various applications.
c) Some liquid solutions containing ions, such as acids, bases, and salts, can also conduct electricity due to the mobility of charged particles within the solution.

Insulators

Insulators are materials that do not allow an electric current to flow through them easily. They resist the movement of electric charge, making them useful for preventing unwanted electrical interactions. Common insulators include materials like wood, plastic, glass, and ceramics. These materials help isolate electrical components and protect against unintended current flow.

Key Characteristics of Insulators

a) Insulators possess electrons that are tightly bound to their respective atoms, making it challenging for these electrons to move within the material.
b) The resistance offered by insulators to the flow of electric charges is considerably higher than that of conductors. This property is harnessed for various purposes, including electrical insulation and safety.

Conductivity Through Liquids

Conductivity through liquids refers to the ability of a liquid to allow an electric current to pass through it. Not all liquids conduct electricity equally well. The conductivity of a liquid depends on its ability to carry electric charges, which are usually carried by ions (positively and negatively charged particles) present in the liquid.

Key Points

a) Pure Water or Distilled Water: Pure water, also known as distilled water, is a poor conductor of electricity. This is because pure water contains very few ions, which are necessary for the flow of electric current. In pure water, only a small number of water molecules dissociate into hydrogen ions (H⁺) and hydroxide ions (OH^-), making it a weak conductor.

b) Presence of Impurities: Most liquids that conduct electricity have impurities in the form of dissolved salts, acids, or bases. These impurities dissociate into ions in the solution, creating a path for electric current to flow. The ions present in the solution can carry the electric charge and enable the flow of current.

c) Conductivity of Solutions: Liquids that are good conductors of electricity are often solutions of acids, bases, or salts. These solutions have a higher concentration of ions compared to pure water, allowing electric current to pass through them more easily. When an electric current is passed through such solutions, the ions move towards the oppositely charged electrode, contributing to the flow of current.

d) LED Bulbs as Conductivity Testers: LED bulbs are sensitive to even small amounts of electric current. They can be used as conductivity testers to detect whether a liquid can conduct electricity or not. When the circuit is complete and electric current flows through the liquid, the LED bulb connected to the circuit will light up if the liquid is a conductor.

Examples of Conductivity: Some examples of liquids and their conductivity include.

1. Tap Water: Contains dissolved minerals and salts, making it a good conductor.
2. Lemon Juice: Contains citric acid, which dissociates into ions, making it a good conductor.
3. Vinegar: Contains acetic acid and is a weak conductor.
4. Cooking Oils: Can conduct electricity if they contain impurities, but generally, they are poor conductors.
5. Milk: Contains dissolved salts and lactose, allowing it to conduct electricity.
6. Honey: Poor conductor due to low ion content.

Chemical Effects of Electric Current

The chemical effects of electric current are a fascinating aspect of the behaviour of electricity in conducting solutions. These effects can be demonstrated through simple experiments and real-world examples.

Experiment to Demonstrate the Chemical Effects of Electric Current:

1. The experiment involves demonstrating the chemical effects of electric current using two carbon rods (or iron nails) as electrodes that facilitate the flow of electric current through the conducting solution (water with added salt or lemon juice). (An electrode is a conductor through which electric current enters or leaves the setup.)

2. When connected to a battery or power supply, the electric current flows through the solution, causing water molecules to break down into hydrogen ions (H⁺) and hydroxide ions (OH^-).

3. At the negative electrode (cathode), hydrogen ions gain electrons and form hydrogen gas (H⁺), while at the positive electrode (anode), hydroxide ions lose electrons and form oxygen gas (O₂).

4. These reactions are part of the electrolysis process, which is a chemical change brought about by the passage of electric current through a conducting solution. It leads to the formation of gas bubbles near the electrodes.

Some of the key Chemical Effects of Electric Current are:

a) Formation of Bubbles: When electric current flows through a conducting solution, it can cause gas bubbles to form at the electrodes (the points where the current enters and exits the solution). These bubbles are a result of the decomposition of the solution's molecules into ions.

b) Deposition of Metals: If a conducting solution contains metal ions, the electric current can cause these ions to migrate to the electrodes and get deposited on them. This process is used for electroplating, where a thin layer of one metal is coated onto another.

c) Change in Solution Colour: Electric current passing through a conducting solution can cause changes in the colour of the solution. This colour change occurs due to the chemical reactions between the solution's components as they gain or lose electrons.

d) Electrolysis: The process of breaking down molecules of a solution into positive and negative ions when an electric current is passed through it is called electrolysis. An electrolyte is a conducting solution that dissociates into ions during electrolysis. Electrolysis has practical applications in various industries, including the extraction and purification of metals.

e) Anode and Cathode Reactions: During electrolysis, the electrode connected to the positive terminal of the battery is called the anode, while the one connected to the negative terminal is called the cathode. Different reactions occur at the anode and cathode, leading to the migration of ions and the changes observed in the conducting solution.

f) Coating with Different Metals (Electroplating): Electroplating is a process that uses the chemical effects of electric current to deposit a layer of metal onto another material. By controlling the type of metal ions in the electrolyte and the current flow, objects can be coated with metals like gold, silver, copper, and more.

Electrolysis

Electrolysis is a chemical process that uses electric current to induce a chemical reaction. This process is used to decompose compounds into their constituent elements or ions. Electrolysis involves the use of an electrolytic cell, which consists of an electrolyte solution and two electrodes connected to an external power source.

The process can be understood through the following steps:

Components of an Electrolytic Cell

1. Electrolyte: The electrolyte is a solution or molten substance that contains ions. It is the substance to be electrolyzed.

2. Cathode: The cathode is the electrode connected to the negative terminal of the power source. It attracts positively charged ions (cations).

3. Anode: The anode is the electrode connected to the positive terminal of the power source. It attracts negatively charged ions (anions).

4. External Power Source: A direct current power source, such as a battery is required to drive the reaction.

Electrolysis Process

1. Preparation: The electrolytic cell is set up with the cathode and anode immersed in the electrolyte. The electrodes are usually made of inert materials like graphite or platinum to prevent them from participating in chemical reactions.

2. Ion Migration: When the power source is connected, an electric current flows through the circuit. Positively charged ions (cations) in the electrolyte are attracted to the cathode, while negatively charged ions (anions) are attracted to the anode.

3. Reduction at the Cathode: At the cathode, cations gain electrons and are reduced, usually leading to the formation of a solid substance or gas.
For example, in the electrolysis of water, hydrogen gas can be formed at the cathode: 2H₂O + 2e^- → H₂ + 2OH^-.

4. Oxidation at the Anode: At the anode, anions lose electrons and are oxidized, leading to the formation of a different compound or gas.
In the case of water electrolysis, oxygen gas is produced at the anode:
4OH^- → 2H₂O + O₂ + 4e^-.

5. Migration of Ions: As the ions are reduced or oxidised at the electrodes, the concentration of ions in the solution changes. This results in the continuous migration of ions from the bulk of the electrolyte to the electrode surfaces.

6. Collection of Products: The products of the electrochemical reactions, which can be gases, solids, or new compounds, are collected or observed at the respective electrodes.

Applications of Electrolysis

Electrolysis has several applications, including:

a) Purification and extraction of metals from their ores.
b) Electroplating: Coating one metal with another by using electrolysis to deposit a layer of metal onto an object.
c) Production of chemicals and industrial processes, like the manufacturing of chlorine gas and sodium hydroxide.

Electroplating

Electroplating is a process that involves depositing a layer of metal onto another material using electricity.
The process of electroplating involves the following steps:

1. Preparation of the Object: The object that needs to be electroplated is thoroughly cleaned and polished to ensure proper adhesion of the plated metal.

2. Choosing the Electrolyte: An electrolyte solution is prepared, containing salts of the metal that will be used for plating. For example, if you want to copperplate an object, the electrolyte will contain copper salt.

3. Setting Up the Electroplating Cell: The object to be plated is connected to the negative terminal of the power source and becomes the cathode. The metal that will be plated onto the object is connected to the positive terminal and becomes the anode. Both the cathode and anode are immersed in the electrolyte solution.

4. Applying Electric Current: When an electric current is applied, metal ions from the electrolyte solution are attracted to the cathode (object to be plated). At the anode (metal to be plated), metal atoms dissolve into the electrolyte as positive ions.

5. Metal Deposition: The metal ions from the electrolyte are reduced at the cathode and get deposited onto the surface of the object. This forms a thin and even layer of the desired metal on the object.

Application of Electroplating

1. Jewellery: Electroplating is commonly used to enhance the appearance of jewellery. For example, a layer of gold or silver can be plated onto less expensive metals to achieve a more luxurious and visually appealing finish.

2. Corrosion Protection: Electroplating is used to protect metals from corrosion. Coating iron or steel with zinc (galvanization) prevents rusting by sacrificing the zinc layer instead of the base metal.

3. Food Containers: Tin plating is applied to iron or steel cans to prevent the contents from coming into contact with the metal, which could affect the taste or safety of the food.

4. Automotive and Bicycle Parts: Chromium plating is used to provide a durable, shiny, and corrosion-resistant surface to parts of cars and bicycles. This enhances their aesthetic appeal and longevity.