Chapter 11: Chemical Effects of Electric Current
Do Liquids Conduct Electricity?
Some materials allow electric current to pass through them, while others do not.
- Good Conductors: Materials which allow electric current to pass through them easily. Most metals like copper and aluminum are good conductors.
- Poor Conductors (Insulators): Materials which do not allow electric current to pass through them easily. Examples include rubber, plastic, and wood.
Some liquids are good conductors of electricity and some are poor conductors. Liquids that conduct electricity are solutions of acids, bases, and salts. Distilled water is a poor conductor, but water with dissolved salts (like tap water) can conduct electricity.
Chemical Effects of Electric Current
The passage of an electric current through a conducting liquid causes chemical reactions. This is known as the chemical effect of electric current. The process is called electrolysis.
Key components in this process:
- Electrolyte: The conducting solution.
- Electrodes: The two terminals (usually metal rods or plates) dipped in the electrolyte to pass the current. The electrode connected to the positive terminal of the battery is the anode, and the one connected to the negative terminal is the cathode.
Some effects observed during electrolysis:
- Bubbles of gas may be formed on the electrodes.
- Deposits of metal may be seen on electrodes.
- Changes in the colour of the solution may occur.
In 1800, a British chemist, William Nicholson, showed that if electrodes were immersed in water and a current was passed, bubbles of oxygen and hydrogen were produced. Oxygen bubbles formed on the anode, and hydrogen bubbles formed on the cathode.
Electroplating
Electroplating is the process of depositing a layer of any desired metal on another material by means of electricity. It is a very useful application of the chemical effects of electric current.
How Electroplating Works:
To coat an object with another metal:
- The object to be plated is made the cathode (connected to the negative terminal).
- The metal to be plated is made the anode (connected to the positive terminal).
- The electrolyte is a salt solution of the metal that is to be coated (e.g., copper sulphate solution for copper plating).
When electric current passes through the electrolyte, the metal from the anode dissolves into the solution and then gets deposited onto the cathode.
Uses of Electroplating
Electroplating is widely used in industry for coating metal objects with a thin layer of a different metal.
- Appearance: Chromium has a shiny appearance and does not corrode. It is plated on objects like car parts, bath taps, and kitchen gas burners to give them a bright, attractive finish.
- Protection from Corrosion: Iron objects are often coated with a layer of zinc to protect them from corrosion and the formation of rust. This process is called galvanization. Tin cans used for storing food are made by electroplating tin onto iron because tin is less reactive than iron.
- Jewellery: Jewellers electroplate less expensive metals with silver and gold to create jewellery that has the appearance of precious metals but is much less expensive.
Frequently Asked Questions (FAQ)
Why does tap water conduct electricity while distilled water does not?
Tap water contains dissolved salts and minerals, which dissociate into ions that can carry electric charge. Distilled water is pure H₂O and lacks these free ions, making it a poor conductor.
What is electrolysis?
Electrolysis is the process of using electricity to bring about a chemical change. It involves passing an electric current through a liquid (electrolyte), causing it to decompose or undergo a reaction.
In electroplating, why is the object to be coated always made the cathode?
The object is made the cathode (negative electrode) because the metal ions in the electrolyte are positively charged. They are attracted to the negative cathode, where they gain electrons and get deposited as a thin layer of pure metal.
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