1. Introduction to Electric Current and Circuits

We have learnt in earlier classes that materials which allow electric current to pass through them are good conductors of electricity. On the other hand, materials which do not allow electric current to pass through them easily are poor conductors of electricity. For example, metals such as copper and aluminium conduct electricity, whereas materials such as rubber, plastic and wood do not conduct electricity.

So far we have used our tester to test materials which were in solid state. But what about liquids? Do liquids also conduct electricity? In this chapter, we will discuss whether liquids conduct electricity and what happens when electric current passes through them.

2. Do Liquids Conduct Electricity?

To check if a liquid allows electric current to pass through it or not, we can use the same tester. However, when we use a tester, we check if the bulb glows or not. If the bulb glows, it means the liquid conducts electricity. If it does not glow, it means the liquid does not conduct electricity.

When the liquid between the two ends of the tester allows the electric current to pass, the circuit of the tester becomes complete. The current flows in the circuit and the bulb glows. When the liquid does not allow the electric current to pass, the circuit of the tester is not complete and the bulb does not glow.

In some situations even though the liquid is conducting, the bulb may not glow. This may happen because the current flowing through the circuit is too weak. The filament of the bulb needs to get heated to a high temperature to glow. If the current is weak, the filament does not get heated sufficiently and it does not glow.

3. Detecting Weak Currents: Using LED

To detect weak currents, we can use an LED (Light Emitting Diode) in place of the electric bulb. LED glows even when a weak electric current flows through it. There are two wires (called leads) attached to an LED. One lead is slightly longer than the other. Remember that while connecting to a circuit, the longer lead is always connected to the positive terminal of the battery and the shorter lead is connected to the negative terminal of the battery.

Using Magnetic Compass

We can also use another effect of electric current to make a tester. We know that electric current has a magnetic effect. Even if a small current flows in the wire, a magnetic needle kept nearby shows deflection. So, we can make a tester using the magnetic effect of current. This tester is more sensitive and can detect even very weak currents.

4. Good and Poor Conductors of Liquids

We tested various liquids like lemon juice, vinegar, tap water, vegetable oil, milk, and honey. We found that some liquids are good conductors of electricity and some are poor conductors.

Actually, under certain conditions most materials can conduct. That is why it is preferable to classify materials as good conductors and poor conductors instead of conductors and insulators.

Distilled water versus Tap water: Distilled water is free of salts and is a poor conductor. The water that we get from taps, hand pumps, wells and ponds is not pure. It may contain several salts dissolved in it. Small amounts of mineral salts are naturally present in it. This water is thus a good conductor of electricity. On the other hand, distilled water is free of salts and is a poor conductor.

Most liquids that conduct electricity are solutions of acids, bases and salts.

5. Chemical Effects of Electric Current

A British chemist, William Nicholson (1753-1815), had shown that if electrodes were immersed in water, and a current was passed, bubbles of oxygen and hydrogen were produced. Oxygen bubbles formed on the electrode connected to the positive terminal of the battery and hydrogen bubbles formed on the other electrode.

The passage of an electric current through a conducting solution causes chemical reactions. As a result, bubbles of a gas may be formed on the electrodes. Deposits of metal may be seen on electrodes. Changes of colour of solutions may occur. The reaction would depend on what solution and electrodes are used. These are some of the chemical effects of electric current.

6. Electroplating

One of the most common applications of chemical effects of electric current is electroplating. It is the process of depositing a layer of any desired metal on another material by means of electricity.

The Process

To understand electroplating, let us take the example of copper plating. We need copper sulphate solution and two copper plates. When electric current is passed through the copper sulphate solution, copper sulphate dissociates into copper and sulphate. The free copper gets drawn to the electrode connected to the negative terminal of the battery and gets deposited on it. But what about the loss of copper from the solution?

From the other electrode (the copper plate connected to the positive terminal), an equal amount of copper gets dissolved in the solution. Thus, the loss of copper from the solution is restored and the process continues. This means that copper gets transferred from one electrode to the other.

7. Uses of Electroplating

• Protection from Corrosion: Chromium plating is done on many objects such as car parts, bath taps, kitchen gas burners, bicycle handlebars, wheel rims and many others. Chromium has a shiny appearance. It does not corrode. It resists scratches. However, chromium is expensive and it may not be economical to make the whole object out of chromium. So the object is made from a cheaper metal and only a coating of chromium over it is done.
• Decoration: Jewellery makers electroplate silver and gold on less expensive metals. These ornaments have the appearance of silver or gold but are much less expensive.
• Food Storage: Tin cans, used for storing food, are made by electroplating tin onto iron. Tin is less reactive than iron. Thus, food does not come into contact with iron and is protected from getting spoilt.
• Strength and Protection: Iron is used in bridges and automobiles to provide strength. However, iron tends to corrode and rust. So, a coating of zinc is deposited on iron to protect it from corrosion and formation of rust. This process is called galvanization (though galvanization can also be done by dipping, electroplating is one method).

8. Pollution from Electroplating Industries

In the electroplating factories the disposal of the used conducting solution is a major concern. It is a polluting waste and there are specific disposal guidelines to protect the environment. The conducting solutions are often acidic or contain heavy metals, which can be harmful to soil and water bodies if not treated properly before disposal.

9. Conduction in Water and Safety

We should never handle electrical appliances with wet hands or while standing on a wet floor. As we discussed, tap water contains dissolved salts and is a good conductor. This increases the risk of electric shock. Water from natural sources like rivers, ponds, and rain is also a conductor. Only pure distilled water is an insulator. This is why electrical repairs are never done outdoors during rain.

10. Ions and Charge Carriers

In solids like metals, electricity is carried by the flow of electrons. However, in liquids (electrolytes), electricity is carried by ions. When a salt like sodium chloride (NaCl) is dissolved in water, it separates into positively charged sodium ions (Na+) and negatively charged chloride ions (Cl-). These ions are free to move in the solution. When a voltage is applied, positive ions move towards the negative electrode (cathode) and negative ions move towards the positive electrode (anode). This movement of ions constitutes the electric current in liquids.

11. Electrolysis

The process of decomposition of a chemical compound in a solution when an electric current passes through it is called electrolysis. The solution that conducts electricity is called the electrolyte. The rods or plates through which current enters and leaves the electrolyte are called electrodes. The electrode connected to the positive terminal of the battery is the anode, and the one connected to the negative terminal is the cathode.

12. Purification of Metals

Besides electroplating, electrolysis is also used for the purification of metals. For example, impure copper can be purified to get pure copper. A thick rod of impure copper is made the anode, and a thin strip of pure copper is made the cathode. The electrolyte is acidified copper sulphate solution. When current is passed, pure copper from the anode dissolves into the electrolyte and an equivalent amount of pure copper from the electrolyte deposits on the cathode. The impurities settle down at the bottom of the anode as 'anode mud'.

Good conductors are materials that allow electric current to pass through them easily. Most metals like copper, silver, aluminium, and iron are good conductors. This property makes them ideal for making electrical wires and components in circuits.

Poor conductors, also known as insulators, are materials that do not allow electric current to pass through them easily. Examples include rubber, plastic, wood, and glass. They are used to cover electrical wires to prevent electric shocks.

Just like solids, liquids can also be classified as good conductors and poor conductors. However, unlike metals where electrons carry the charge, in liquids, ions are responsible for conducting electricity. Salt solutions are typical examples of conducting liquids.

A tester can be made using an electric cell, a bulb, and connecting wires. When the free ends of the tester are dipped in a liquid, if the bulb glows, the liquid is a conductor. If it does not glow, the liquid is a poor conductor.

Sometimes a liquid may conduct weak current that is insufficient to heat the filament of a standard bulb to incandescence. In such cases, the bulb will not glow even though the liquid is conducting. To detect such weak currents, an LED or a magnetic compass can be used.

LEDs are semiconductor devices that glow even with very weak electric currents. They consume less power and are more durable than traditional bulbs. They have two leads; the longer lead (anode) is connected to the positive terminal, and the shorter lead (cathode) to the negative terminal.

Electric current has a magnetic effect. A compass needle placed near a wire carrying current will deflect. This principle is used to make sensitive testers. The stronger the current, the greater the deflection of the needle.

Distilled water is pure water free from dissolved salts and minerals. Because it lacks ions, it is a poor conductor of electricity. However, it can become conducting if salts, acids, or bases are dissolved in it.

Tap water, well water, and pond water contain small amounts of dissolved mineral salts. These salts provide ions that make the water a good conductor of electricity. This is why handling electrical appliances with wet hands is dangerous.

An electrolyte is a liquid or solution that conducts electricity due to the presence of free ions. Common examples include solutions of sodium chloride (salt), copper sulphate, sulphuric acid, and sodium hydroxide.

Liquids that do not conduct electricity are called non-electrolytes. Examples include distilled water, alcohol, petrol, kerosene, and vegetable oil. These liquids do not contain free ions to carry the electric charge.

Most liquids that conduct electricity are aqueous solutions of acids, bases, or salts. When these substances dissolve in water, they dissociate into positive and negative ions, which are free to move and carry electric current.

When electric current passes through a conducting solution, it causes chemical reactions. This is known as the chemical effect of electric current. It can result in the formation of gas bubbles, metal deposition on electrodes, or changes in the colour of the solution.

When electric current is passed through acidified water, it decomposes into hydrogen and oxygen gases. Hydrogen bubbles form at the cathode (negative electrode), and oxygen bubbles form at the anode (positive electrode). This process was demonstrated by William Nicholson.

Electrodes are conductors (rods, plates, or wires) submerged in an electrolyte through which electric current enters or leaves. They are essential components of an electrolytic cell. Carbon rods and metal plates are commonly used as electrodes.

The anode is the electrode connected to the positive terminal of the battery or power source. In an electrolytic cell, oxidation usually occurs at the anode. Negative ions (anions) are attracted to the anode.

The cathode is the electrode connected to the negative terminal of the battery. Reduction usually occurs at the cathode. Positive ions (cations) in the electrolyte are attracted to the cathode and move towards it.

Electroplating is the process of depositing a thin layer of a desired metal onto another material by means of electricity. It is one of the most widely used applications of the chemical effect of electric current. It is done for protection or decoration.

In electroplating, the object to be coated is made the cathode (negative). The metal to be deposited is made the anode (positive). The electrolyte is a soluble salt of the metal to be deposited. This arrangement ensures the metal ions move to the object.

When current flows through copper sulphate solution, copper dissociates. Free copper is drawn to the negative electrode (cathode) and deposited. An equal amount of copper dissolves from the positive electrode (anode) into the solution to maintain the balance.

Chromium plating is used on objects like car bumpers, taps, and bicycle parts because chromium is shiny, hard,scratch-resistant, and does not corrode. It provides a durable and attractive finish to steel or iron objects.

In jewellery making, a thin layer of gold is electroplated onto cheaper metals like silver or copper. This gives the jewellery the appearance of gold while keeping the cost low. It is a common commercial application.

Tin cans used for storing food are made by electroplating tin onto iron. Tin is less reactive than iron. This prevents the food from coming into direct contact with the iron, which could rust and spoil the food.

Galvanization is the process of coating iron or steel with a layer of zinc to prevent rusting. While typically done by hot-dipping, electroplating can also be used to achieve a uniform zinc coating on bridges and automobile parts.

Electroplating is cost-effective because it allows manufacturers to use cheaper, stronger metals (like steel or iron) for the core of the product while giving it the surface properties (like shine and corrosion resistance) of more expensive metals (like chromium or gold).

The conducting solutions used in electroplating often contain acids and harmful heavy metals. Disposal of these solutions is a major environmental concern. Strict guidelines must be followed to treat this waste before disposal.

Passing current through a cut potato using copper wires produces a greenish-blue spot around the positive electrode. This is due to a chemical reaction between the copper wire, potato starch, and the current, identifying the positive terminal.

The conductivity of liquids depends on the movement of ions. When potential difference is applied across the electrodes, positive ions (cations) move toward the cathode, and negative ions (anions) move toward the anode.

Dissociation is the breaking up of a compound into simpler constituents (ions) that are usually capable of recombining under other conditions. For example, Copper Sulphate (CuSO4) dissociates into Copper ions (Cu++) and Sulphate ions (SO4--).

A battery has a positive terminal (usually marked with +) and a negative terminal (marked with -). Current flows from the positive terminal to the negative terminal through the external circuit.

William Nicholson (1753-1815) was a British chemist who discovered the electrolysis of water. He demonstrated that electricity could decompose water into its constituent gases, hydrogen and oxygen, establishing the link between electricity and chemical reactions.

In the electrolysis of water, the gas evolved at the cathode is hydrogen. It can be identified because it burns with a pop sound when a burning matchstick is brought near it.

In the electrolysis of water, the gas evolved at the anode is oxygen. It supports combustion and can relight a glowing splint, which distinguishes it from hydrogen.

Salt water is a very good conductor of electricity compared to tap water due to the high concentration of sodium and chloride ions. This property increases the risk of short circuits and corrosion in electrical equipment exposed to sea water.

Rainwater is often thought to be pure, but as it falls, it dissolves atmospheric gases like CO2, SO2, and NO2. These form weak acids, turning rainwater into a conducting solution, unlike pure distilled water.

It is unsafe to carry out electrical repairs outdoors during rain because the wet environment creates a conductive path for electricity. This significantly increases the risk of severe electric shocks to the electrician.

Water is never used to extinguish electrical fires because ordinary water conducts electricity. Spraying water on live electrical equipment can electrocute the person fighting the fire. CO2 extinguishers or sand are used instead.

Electrolysis is used to purify metals like copper. Impure copper is used as the anode, and pure copper as the cathode. The pure metal transfers from the anode to the cathode, leaving impurities behind as anode mud.

Reactive metals like sodium, potassium, and aluminium are extracted from their ores using electrolysis. The process separates the metal from its compounds in a molten state.

Anodizing is an electrolytic process used to increase the thickness of the natural oxide layer on the surface of metal parts, especially aluminium. This oxide layer provides better corrosion resistance and allows for dyeing.

Electrotyping is a method of reproducing type or objects by electroplating. A mold is made of the object, and metal is electrodeposited onto the mold to create an exact replica.

Michael Faraday formulated the laws of electrolysis, which relate the amount of substance deposited at an electrode to the quantity of electricity passed through the electrolyte. These laws are fundamental to electrochemical science.

Ionization is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons. In solution, this leads to the formation of ions that can conduct electricity.

A voltaic cell or galvanic cell generates electric current from chemical reactions (chemical energy to electrical energy). In contrast, an electrolytic cell uses electric current to drive chemical reactions (electrical energy to chemical energy).

A cation is a positively charged ion. It is named so because it is attracted to the cathode (negative electrode) during electrolysis. Examples include Na+, K+, Ca++, etc.

An anion is a negatively charged ion. It moves towards the anode (positive electrode) during electrolysis. Examples include Cl-, SO4--, OH-, etc.

When setting up an electric circuit or checking conduction, connections must be tight and clean. Rust or oxide layers on wires can act as insulators, preventing current flow and giving false results.

A solution of sugar in distilled water does not conduct electricity. Sugar (sucrose) is a covalent compound and does not dissociate into ions in water, so there are no charge carriers to conduct the current.

Vinegar is a weak acid (acetic acid). When dissolved in water, it partially dissociates into ions. Therefore, vinegar is a conductor of electricity, but it is a weaker conductor than strong acids like sulphuric acid.

The human body contains a lot of water with dissolved salts and ions. This makes the body a good conductor of electricity. This is why electric shocks can easily pass through us, causing injury or death.