Do Liquids Conduct Electricity?

We already know that materials are classified as good conductors or poor conductors of electricity based on whether they allow electric current to pass through them easily or not. Metals like copper and aluminium are good conductors (conduct electricity), while materials like rubber, plastic, and wood are poor conductors (do not conduct electricity easily, also called insulators).

We can use a tester, often consisting of a battery and a bulb connected by wires, to determine if a material conducts electricity. If the material completes the circuit, allowing current to flow, the bulb glows. However, this method is typically used for solid materials.

Liquids can also conduct electricity. To test this, we can use a similar tester, potentially using a battery instead of a single cell for higher voltage, and perhaps a more sensitive indicator like an LED or a compass needle deflection, especially for detecting weak currents. An LED glows even with weak currents, and a compass needle deflects due to the magnetic effect of even a small current flowing nearby.

When the free ends of a tester are dipped into a liquid, if the liquid conducts electricity, it completes the circuit, and the indicator (bulb glows, LED glows, or compass needle deflects). If the liquid does not conduct, the circuit remains open, and there is no indication of current flow.

Some liquids, like lemon juice or vinegar, conduct electricity, causing a tester's bulb to glow or a compass needle to deflect. These are considered good conductors of electricity.

In some cases, even if a liquid is conducting, the current might be too weak to heat the filament of a standard bulb enough to make it glow. Using a more sensitive indicator like an LED or a compass needle deflection is helpful for detecting weak currents.

Tap water conducts electricity because it contains dissolved salts and minerals, which make it a good conductor. Distilled water, which is pure and lacks these dissolved salts, is a poor conductor. Adding a small amount of common salt to distilled water makes it a conducting solution.

Most liquids that conduct electricity are solutions of acids, bases, or salts dissolved in water. Pure water itself is a very poor conductor.

The presence of dissolved mineral salts in water, even in small amounts, makes it a good conductor, which is why it is dangerous to handle electrical appliances with wet hands or while standing on a wet floor.

Under certain conditions, even materials usually classified as poor conductors (like air) can allow electricity to pass, such as during lightning.

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Chemical Effects Of Electric Current

When an electric current passes through a conducting solution (an electrolyte), it can cause chemical reactions. These resulting effects are known as the chemical effects of electric current.

One of the notable chemical effects is the decomposition of the conducting solution. For example, when an electric current passes through water containing dissolved salt or acid (to make it more conductive), bubbles of gases may form at the electrodes. In 1800, William Nicholson showed that passing current through water produces oxygen bubbles at the electrode connected to the positive terminal of a battery and hydrogen bubbles at the electrode connected to the negative terminal.

Other chemical effects can include:

• Formation of gas bubbles on the electrodes.
• Deposition of a metal on the electrodes.
• Changes in the colour of the solution.

The specific reactions and effects observed depend on the composition of the conducting solution and the material of the electrodes used.

Sometimes, unexpected chemical effects can be observed. For example, inserting a tester's copper wires into a potato and passing current caused a greenish-blue spot to form around the wire connected to the positive terminal. This colour change indicates a chemical reaction taking place in the potato tissue due to the current.

Electroplating

One of the most important applications of the chemical effects of electric current is a process called electroplating.

Electroplating is the process of depositing a thin layer of a desired metal onto another material using electricity. This is done to give the object a specific property (like shiny appearance, resistance to corrosion, or durability) that the base material lacks or to make it look like a more expensive metal.

A simple electroplating setup involves a conducting solution containing salts of the metal to be deposited, and two electrodes connected to a battery:

• The object to be electroplated is placed at the negative terminal of the battery.
• The metal to be deposited (or an inert material) is placed at the positive terminal of the battery.
• The conducting solution (electrolyte) contains ions of the metal to be deposited.

When electric current passes through the solution, the metal ions in the solution are attracted to the negatively charged electrode (the object being plated) and get deposited as a thin metallic layer on its surface. To maintain the concentration of metal ions in the solution, the positive electrode is often made of the same metal being deposited, which dissolves into the solution as plating proceeds.

Electroplating is widely used in industry for various purposes:

• Chromium Plating: Applied to objects like car parts, bath taps, kitchen gas burners, and bicycle parts. Chromium is shiny, corrosion-resistant, and hard (resists scratches), but expensive. So, a thin layer is electroplated onto cheaper metals.
• Gold and Silver Plating: Jewellery makers electroplate less expensive metals with layers of gold or silver to create affordable ornaments that look like precious metals.
• Tin Plating: Used for tin cans that store food. Tin is electroplated onto iron. Tin is less reactive than iron, preventing the food from reacting with the iron and spoiling.
• Zinc Plating (Galvanisation): A coating of zinc is deposited on iron structures like bridges and automobile parts to protect them from rusting and corrosion.

While electroplating is very useful, the waste solutions containing chemicals used in the process can be polluting and require proper disposal according to environmental guidelines.

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