Class VIII Science - Chemical Effects of Electric Current Notes PDF

BIRLA PUBLIC SCHOOL – DOHA, QATAR Class VIII – Science Ch-14 Chemical Effects of electric current ​ Electric Current It can be defined as the flow of electrons. An electric current can produce chemical, heating and magnetic effects. Electric cur...

BIRLA PUBLIC SCHOOL – DOHA, QATAR Class VIII – Science Ch-14 Chemical Effects of electric current ​ Electric Current It can be defined as the flow of electrons. An electric current can produce chemical, heating and magnetic effects. Electric current cannot flow on the conductor on its own. An electric circuit, which is a closed-loop path made up of electric components like wire, battery, switch, bulb etc. is needed for current to flow in a wire or conductor. Electrical conductivity The ability of a material to conduct electricity is called its electrical conductivity. Based on these substances are divided into conductors, semi-conductors and poor conductors. Electrical conductivity of solids Some solids are good conductors of electricity. E.g.- copper, steel, iron, aluminium etc. ∙ Some solids are poor conductors of electricity. E.g.- wood, plastic, rubber, glass etc. Electrical conductivity of liquids: Some liquids are good conductors of electricity E.g.- tap water, salt solution, hydrochloric acid, sodium hydroxide etc. Solutions of acids, bases and salts are conductors of electricity. Some liquids are poor conductors of electricity. E.g.- distilled water, sugar solution, kerosene, spirit etc. Conduction tester : A conduction tester is a device used to determine whether a substance is a good or poor conductor of electricity. Conduction tester using a torch bulb : A simple conduction tester has an electric cell and a torch bulb. One terminal of the cell is connected to one terminal of the bulb by a wire. The other terminal of the cell and bulb has wires which can be brought in contact with materials to test whether they are good or poor conductors of electricity. If the material is a good conductor, the bulb glows and if it is a poor conductor the bulb does not glow. Conduction tester using LED: Sometimes the current flowing through the circuit may be too weak and the filament of the bulb may not get sufficiently heated to make it glow. Then instead of a torch bulb an LED can be used in the circuit. LED glows even when weak current flows in the circuit. Conduction tester using a magnetic compass : If a magnetic compass is kept near a wire and current flows through the wire, the magnetic needle gets deflected. So, we can use a magnetic compass instead of a torch bulb or LED in the circuit. The magnetic needle gets deflected even if a weak current flows in the circuit. Terms related to Electrolysis 1.​ Electrodes: The metal rods of plates through which current leaves or enters an electrolyte are called electrodes. There are two electrodes: Cathode and Anode. ​ Cathode: The electrode is connected to the negative terminal of a cell or a battery. They are negatively charged. ​ Anode: The electrode is connected to the positive terminal of a cell or a battery. They are positively charged. 2.​ Electrolyte The aqueous solution of a compound which conducts electricity and undergoes a chemical change at the same time is called an electrolyte. Eg: Copper Sulphate, Tap Water etc 3.​ Ions When electricity is passed, the particles get electrically charged; they are called ions and the process is ionization. ​ Cations: The positively charged ions are called Cations. During electrolysis, cations move to the cathode and get deposited. ​ Anions: The negatively charged ions are called Anions. During electrolysis, anions move to anode and get deposited. Electrolysis of water : When electric current is passed through water, it splits up into hydrogen and oxygen. This is called electrolysis of water. When electric current is passed through water then oxygen gas bubbles are produced at the electrode connected to the positive terminal of the battery and hydrogen gas bubbles are produced at the electrode connected to the negative terminal of the battery. Electroplating: The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating. E.g.- For electroplating of copper on an object, the object is dipped in acidified copper sulphate solution and connected to the negative terminal of a battery. A copper strip is dipped in the solution and connected to the positive terminal of the battery. When electric current is passed through the solution, copper from the copper strip is deposited on the object. Electroplating is a very useful process and widely used in industry. Electroplating is a technique for depositing a layer of metal with desired properties on another metal that is utilized in various industries. The main reason is as follows ​ To protect the metal object by coating different metal on the metal object. ​ Cost-efficient for example since chromium is a costly metal, the objects are made of a cheaper metal and a chromium coating is applied for a shiny appearance. ​ Prevent metal from corrosion Applications of electroplating: 1.​ Electroplating is used in industry for coating metal objects with a thin layer of a desired metal. 2.​ Chromium has a shiny appearance and it does not corrode. Chromium plating is done on objects like bicycle parts, car parts, taps, gas burners, wheel rims etc. 3.​ Jewelry makers electroplate gold and silver on less expensive metals to give an appearance of gold or silver. 4.​ Tin cans used for storing food are electroplated with tin over iron because tin is less reactive than iron and protects iron from corrosion. 5.​ Medical equipment is made up of nickel which is harmful to the human body hence to avoid it from coming in contact with the body a coating of platinum or gold is applied on the surface of the nickel. 6.​ Iron objects are coated with zinc to protect it from corrosion. ------------------------------------------------------------------------