You may have been warned by adults not to touch electrical appliances with wet hands. This caution stems from the fact that water can conduct electricity, increasing the risk of electric shock, especially when the body is also wet and provides a path for current to flow.

We previously learned that materials that allow electric current to pass through them are called good conductors of electricity (e.g., metals like copper, aluminium). Materials that do not easily allow electric current to pass are called poor conductors or insulators (e.g., rubber, plastic, wood).

Simple testers can be used to check if a solid material conducts electricity, typically by completing a circuit and observing if a bulb glows or a magnetic needle deflects.

So far, we have tested solid materials. But what about liquids? Can liquids conduct electricity?

Do Liquids Conduct Electricity?

To determine if a liquid conducts electricity, we can use a tester similar to the one used for solids. A simple tester consists of a battery (or cell), a bulb, and connecting wires. The free ends of the wires are dipped into the liquid being tested. If the liquid conducts electricity, the circuit is completed, and the bulb glows.

To test liquids, it's often useful to replace the simple cell with a battery (multiple cells) to provide a slightly stronger potential difference. Before testing liquids, ensure the tester is working by briefly joining the free ends; the bulb should light up. If not, check for loose connections, a fused bulb, or drained cells.

When testing liquids like lemon juice or vinegar using a tester with a bulb, if the bulb glows, it indicates that the liquid conducts electricity, classifying it as a conductor. If the bulb doesn't glow, the liquid might be a poor conductor or an insulator.

However, sometimes, even if a liquid conducts electricity, the bulb in the tester might not glow brightly, or at all. This happens if the electric current passing through the circuit is too weak. A standard bulb's filament requires sufficient heating effect to glow, and a weak current may not provide enough heat.

A weak current can occur if the liquid, although conducting, does not conduct electricity as easily as a metal. In such cases, while the circuit is complete, the current magnitude is low.

To detect weak currents, we can use a tester that relies on the magnetic effect of electric current. Even a small current can cause a noticeable deflection in a compass needle placed near a wire carrying the current.

A tester using the magnetic effect can be made by wrapping a wire around a compass and connecting the wire ends to a battery terminals via free probes. When the probes are dipped into a liquid, if the liquid conducts even a weak current, the compass needle will deflect.

An alternative for detecting weak currents is to use a Light Emitting Diode (LED) instead of a bulb. LEDs glow even when a weak current flows through them. LEDs have two leads; the longer lead is connected to the positive terminal of the battery, and the shorter one to the negative terminal.

Using a magnetic compass tester or an LED tester, we can test various liquids like tap water, vegetable oil, milk, and honey to see if they conduct electricity. It's important to clean and dry the tester ends after testing each liquid to avoid contamination.

Testing tap water reveals that it conducts electricity (compass needle deflects). However, testing distilled water shows that it does not conduct electricity, or conducts very poorly. But if a pinch of common salt is dissolved in distilled water, the resulting salt solution conducts electricity, and the compass needle deflects.

This indicates that pure water (distilled water) is a poor conductor of electricity, whereas water containing dissolved salts is a good conductor. Natural sources of water (taps, wells, ponds) contain dissolved mineral salts, making them good conductors. These mineral salts are beneficial for health but also make the water conductive, which is why handling electrical appliances with wet hands or on a wet floor is dangerous.

Generally, most liquids that conduct electricity are solutions of acids, bases, and salts in water. Dissolving small amounts of acids (like lemon juice or dilute hydrochloric acid), bases (like caustic soda), or salts in distilled water makes it a conducting solution. Sugar solution, however, does not conduct electricity.

Under specific conditions, even materials typically classified as poor conductors (like air during lightning) can allow electric current to pass. Therefore, it is more accurate to classify materials as good conductors and poor conductors rather than simply conductors and insulators.

Chemical Effects Of Electric Current

When an electric current flows through a conducting solution, it can cause chemical reactions within the solution. These changes are known as the chemical effects of electric current.

The nature of the chemical effects depends on the type of solution and the materials used as electrodes (the objects immersed in the solution to connect to the circuit). Common effects include:

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

An experiment involving passing electric current through water with dissolved salt or lemon juice (to make it conducting) using carbon rods (electrodes) from old cells demonstrates this. Gas bubbles can be observed near the electrodes, indicating a chemical reaction (like the decomposition of water into hydrogen and oxygen gases).

In 1800, British chemist William Nicholson showed that passing current through water using electrodes caused the formation of oxygen bubbles at the electrode connected to the positive terminal of the battery and hydrogen bubbles at the electrode connected to the negative terminal. This process, breaking down water using electricity, is called electrolysis.

A curious observation occurred when testing a potato with a tester: a greenish-blue spot formed around the wire connected to the positive terminal. This colour change is a chemical effect of the current on substances in the potato. Such unexpected observations can sometimes lead to useful discoveries, like identifying the positive terminal of a battery.

Electroplating

Have you noticed how new shiny objects like bicycle handlebars or inexpensive jewellery lose their shine over time, revealing a different material beneath? This is often due to the wearing off of a thin coating of one metal over another material. The process of depositing a layer of any desired metal onto another material using electricity is called electroplating.

Electroplating is a significant application of the chemical effects of electric current and is widely used in various industries.

A simple demonstration of electroplating copper onto another object can be done using a solution of copper sulphate and copper plates as electrodes.

When electric current is passed through the copper sulphate solution, the copper sulphate breaks down into copper ions and sulphate ions. The positively charged copper ions move towards the electrode connected to the negative terminal of the battery (the cathode) and get deposited as a layer of copper metal on that electrode.

To maintain the concentration of copper ions in the solution, an equal amount of copper is typically dissolved from the electrode connected to the positive terminal (the anode), if it is made of copper. This process continuously transfers copper from the anode to the cathode.

Electroplating is used to coat objects made of cheaper metals with a thin layer of a more desirable metal that possesses specific properties lacking in the base metal, such as:

• Chromium plating: Applied to car parts, bath taps, kitchen gas burners, bicycle parts, etc., because chromium has a shiny appearance, resists corrosion, and is scratch-resistant. The object is made of a cheaper metal, and only the outer layer is chromium due to chromium's high cost.
• Gold and Silver plating: Jewellery makers use electroplating to deposit a layer of gold or silver on less expensive metals, creating ornaments that look valuable but are more affordable.
• Tin plating: Food cans are made by electroplating tin onto iron. Tin is less reactive than iron, protecting the food inside from reacting with the iron and getting spoilt.
• Zinc plating (Galvanization): A coating of zinc is deposited on iron used in structures like bridges and automobiles. Zinc is more reactive than iron and corrodes preferentially, protecting the underlying iron from rusting.

The disposal of chemical waste solutions from large-scale electroplating facilities is an environmental concern, and specific guidelines must be followed to prevent pollution.

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