These DAV Class 8 Science Notes and DAV Class 8 Science Chapter 16 Notes – Electric Current and Its Chemical Effects act as excellent revision resources, particularly in preparation for board exams.
Electric Current and Its Chemical Effects Class 8 DAV Notes
→ Cause of Conductivity of Liquids: Movement of ions results in conduction of electricity through a liquid. Molecules of salts, acids and bases break up into free ions; when dissolved in water. These free ions allow the passage of electric current through the solution.
→ Electrolyte: A compound which conducts electricity in molten or aqueous state and which simultaneously undergoes decomposition with the passage of electricity through it is called an electrolyte. Electrolytes can be classified into two types:
→ Strong Electrolyte: An electrolyte which completely ionizes in a solution is called a strong electrolyte. In case of a strong electrolyte’s solution, a large number of ions are available to conduct electricity.
→ Conversion of Chemical Energy into Electrical Energy:
An electric cell is a device which converts chemical energy into electrical energy. Alessandro Volta was the first scientist who demonstrated this conversion in 1790; by making voltaic cell.
→ Structure of Voltaic Cell: An electrolytic solution is kept in a container. Two electrodes are dipped in the solution. The electrodes are connected to electric wires and a resistance or an electrical appliance; like a bulb. Car battery is composed of many voltaic cells. A cell in such a battery is usually filled with dilute sulphuric acid. A zinc rod and a copper rod are used as electrodes in it.
→ Chemical Effects Of Electric Current:
When electric current passes through an ionic solution, chemical changes take place in the solution. The effects of these changes are known as chemical effects of electric current.
Michael Faraday was the first scientist who conducted experiments on this in 1834. The process was named as electrolysis; by Michael Faraday.
→ Effect of Electric Current on Water: A British scientist; William Michlsen conducted an experiment to observe the effect of electric current on water. He observed that when a steady current is passed through water, water decomposes into oxygen and hydrogen. The oxygen bubbles are formed on anode and the hydrogen bubbles are formed at the cathode. It is important to note that the anode is connected to the positive terminal and the cathode is connected to the negative terminal of a battery.
→ The chemical reactions taking place in a solution depend on following factors:
Nature of electrodes
Nature and concentration of solution
→ Some effects of electrolysis:
- Metals may get deposited at the electrode surface
- Gaseous bubbles may form near the electrodes
- Change of colour of solution may occur due to dissolving of different ions
→ Applications of Electrolysis:
→ Extraction of metals from ores: Some metals are extracted from their ores by the process of electrolysis, e.g. aluminium, sodium, potassium, calcium, etc.
→ Electrorefining of metals: A pure metal can be obtained from an impure one by the process of electrolysis.
→ Electroplating: The process of depositing a layer of any desired metal on another material by the process of electrolysis is called electroplating.
→ Process of Electroplating:
- The article to be electroplated should be made the cathode of an electrolytic cell.
- The anode is made of that pure metal, which is to be coated on the article.
- A suitable salt solution of the anode metal is taken as electrolyte.
→ Applications of Electroplating:
→ To improve the appearance of an article: Electroplating imparts a shiny luster on an article which improves the appearance of an article.
→ To provide protective/strengthening coating: Iron articles are often electroplated to provide a protective coating. The protective coating prevents the rusting of iron. Rims and handles of bicycle are electroplated with chrome. Bathroom fittings are electroplated with chrome.
→ To minimize the cost: Jewelleries of cheaper metals are coated with gold so that they can look like gold. This helps in reducing the cost of the ornament.
→ Electromagnetic Induction: Electromagnetic induction was discovered by Michael Faraday in 1831. He discovered that a changing magnetic field can generate electricity. This phenomenon is known as electromagnetic induction. Electric generator works on the principle of electromagnetic induction. Faraday made following observations:
Whenever there is a relative motion between a magnet and a coil, an electric current flows through the coil.
When the coil and the magnet are at rest with respect to each other, the flow of current stops. The magnitude of electric current in the coil depends on the speed of relative motion between the coil and the magnet.
The direction of current when magnet is moved away from the coil is opposite to the direction of current when magnet is moved towards the coil.
→ Electrolysis : Chemical changes in an ionic solution; because of passage of electric current; are known as electrolysis.
→ Electrolyte : A solution which allows electric current to pass through it is called an electrolyte.
→ Electric cell : A device which converts chemical energy into electñcal energy.
→ ElectroplatIng : Coating a layer of a metal on an article through the process of electrolysis is called electroplating.
→ Weak Electrolyte: An electrolyte which partially ionizes in a solution is called a weak electrolyte. In case of a weak electrolyte’s solution, a small number of ions are available to conduct electricity.
| Electrolytes | Weak Electrolytes |
| Sea water | Ordinary tap water |
| Nitric acid | Oxalic acid |
| Copper sulphate solution | Carbonic acid |
| Sodium chloride | Ammonium hydroxide |
| Sulphuric acid | Citric acid |