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SCIENCE 8TH

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Published in: Science
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Keen T / Amritsar

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  1. @ KEEN TUTORIALS CBSE Class 08 science Revision Notes Chapter - 14 Chemical Effects of Electric Current Materials through which electric currentcan pass through easily are called conductors of electricity. Electrical conductivity is a measure of the ability of a substance to allow the flow of an electric current. Among solids metals and graphite are good conductors of electricity which have high electrical conductivity. Some liquids are also good conductors. Pure water or distilled water is a poor conductor of electricity. But the presence of even small amount of impurities(salts and minerals) makes water a good conductor as it contains ions through which conduction takes place. Hence water from taps, wells, ponds, rivers, seas, lakes, etc. conduct electricity as they contain impurities. Most liquids that conduct electricity are solutions of acids, bases and salts. When electricity is passed through a conducting solution, the molecules of the solution dissociate into ions. Ions are atoms or group of atoms with a positive or a negative charge. These ions cause electrical conduction through the liquid. A liquid That conducts electricity due to the presence of ions is called an electrolyte. Electrolysis: The process of decomposition of a chemical compound in a solution when an electric current passes through it is called electrolysis. This process is due to the chemical effect of electric current. Two electrodes are inserted in the solution and are connected to the terminals of a battery with a switch in between. This arrangement is called an electrolytic cell. The electrode that is connected to the positive terminal of the battery is called the anode, and the other connected to the negative terminal is called the cathode. Electrolysis is used in refining and extraction of metals from impure samples. This process is called electrorefining. It is also useful in coating one metal with another. This process is called electroplating. The passage of an electric current through a conducting solution causes chemical reactions. This is known as the chemical effect of electric current. Some of the chemical effects of electric current are the following: • Formation of bubbles of a gas on the electrodes • Deposition of metal on electrodes • Change in colour of solutions Electroplating:The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating. ADD:- 42, STAR AVENUE,RAM TIRATH ROAD,AMRITSAR. B/S HARMAN SWEET SHOP.M.9 0 4 1 S 9 8 8 8 9 Copyright 0 2006 KEEN TUTORIALS. All Rights Reserved.
  2. @ KEEN TUTORIALS The object to be electroplated is made the cathode (negative electrode) by connecting it to the negative terminal of the battery. The metal which has to be deposited is made the anode (positive electrode) by connecting it to the positive terminal of the battery. The electrolyte is usually a salt solution of the metal to be coated. Application of Electroplating: (i) Metals that rust are often coated with other metals to prevent rusting. (ii) Chromium plating is found on bath taps, car bumpers, etc. to give a bright attractive appearance and resist scratches and wear. (iii) Silver plating is done on cutlery and jewellery items. (iv) Tin cans, used for storing food, are made by electroplating tin onto iron. Tin is less reactive than iron. Thus, food does not come intwcontact with iron and is protected from getting spoilt. Do Liquids Conduct Electricity? A conductor is any material or substance that allows electricity to flow through it. Electrical conductors materials: silver gold copper sea water An insulator is any substance or material that prevents the flow of electricity through it. Electrical insulator materials: rubber glass oil diamond dry wood The electrons of the conductors can flow freely (they are delocalized) and hence can take electric current through them. Insulators do not allow the flow of charges through them because their electrons are tightly packed with their particles. Some materials can allow a little flow of electricity through them and are called poor conductors of electricity. Some materials can allow the complete flow of electricity through them and are called good conductors of electricity. Water containing salts and minerals dissolved in it always conducts electricity. ADD:- 42, STAR AVENUE,RAM TIRATH ROAD,AMRITSAR. B/S HARMAN SWEET SHOP.M.9 0 4 1 S 9 8 8 8 9 Copyright 0 2006 KEEN TUTORIALS. All Rights Reserved.
  3. @ KEEN TUTORIALS Distilled water that does not contain any salts cannot conduct electricity. An solution of acids or bases can also conduct electrici Material under test Distilled water a water Lemon •uice me ar Cookin Oils Milk Hone Soda com ounds Mercur Fuels Good conductor Poor conductor Poor conductor ood conductor ood conductor Poor conductor ood conductor ood conductor Poor conductor ood conductor ood conductor Poor conductor Set up to detect if a liquid can conduct electricity Lermn J $ LED glows even when a weak electric current flows through it. So we can use LED in place of a torch for detecting weak electric current passing through a liquid. If we take some distilled water in a beaker and pass electricity through it, we will find that there is no deflection in the magnetic needle of the compass but it can become a good conductor of electricity by dissolving a little salt in it. ADD:- 42, STAR AVENUE,RAM TIRATH ROAD,AMRITSAR. B/S HARMAN SWEET SHOP.M.9 0 4 1 S 9 8 8 8 9 Copyright 0 2006 KEEN TUTORIALS. All Rights Reserved.
  4. @ KEEN TUTORIALS When we take liquids like vinegar, lemon juice, tap water, rainwater, and seawater in the circuit, there is a deflection in the magnetic needle. This shows that they are conductors of electricity. The effect in which components of a compound get split due to passing an electric current through it is called electrolysis. canon sot ANION Electrode: An electrode is a conductor of electricity that can carry electric current into non-metals and other poor conductors of electricity. Electrolyte: A solution that breaks into its ions on passing electricity through it is called an electrolyte. Electrolytes are used in the process of electroplating. The positively charged electrode is called an anode and the negatively charged electrode is called the cathode. An anion is a negatively charged ion and a cation is a positively charged ion. Heating effect of an electric current: electric current causes heating of the electrical equipment. For example, the filament of a bulb gets heated up due to electric current and therefore glows. Chemical effect of an electric current: an electric current can lead to the production of chemical energy or chemical reactions. The mechanical effect of an electric current: an electric current can lead to the generation of mechanical energy in appliances. For example, fans and motors work due to this effect. Magnetic effect of an electric current: an electric current can give rise to the magnetic field of a substance. Chemical Effects of Electric Current An electric current passes through the solution it ionizes and breaks down into ions. This is because of chemical reactions that take place when an electric current passes through a solution. Depending on the nature of the solution and the electrodes used, the following effects can be observed in the solution: • metallic deposits on the electrodes • change in the colour of the solution ADD:- 42, STAR AVENUE,RAM TIRATH ROAD,AMRITSAR. B/S HARMAN SWEET SHOP.M.9 0 4 1 S 9 8 8 8 9 Copyright 0 2006 KEEN TUTORIALS. All Rights Reserved.
  5. @ KEEN TUTORIALS • a release of gas or production of bubbles in the solution Electric current can bring about chemical changes, so it is said to have a chemical effect. When electric current is passed through acidified water by using carbon electrodes, then a chemical reaction takes place to form hydrogen gas and oxygen gas. In this reaction, water has been decomposed into two elements hydrogen and oxygen, by the action of electric current. The chemical decomposition produced by passing an electric current through a conducting liquid is called electrolysis. Pure metals are extracted from metal ores through the process of electrolysis. Electricity is passed through the metal ores and they get broken down into an ionic lattice and thus the metal is obtained separately. For example, metals like aluminium, magnesium, potassium, sodium, and calcium are obtained from their ores in this way. Negative Carbon Cathode Positive Carbon Anodes lumina + Cryolite Aluminium out Steel container Purification of metals: The method of electrolysis is also used to purify metal by separating it from the impurities. Theimpure metal is used as an anode which first dissolves in the electrolyte solution and then deposits on the cathode in its pure form. The impurities of the metal remain in the electrolyte solution only. Metals like aluminium, zinc, and copper are purified in this way. Negative Terminal Of Battery Thin Plate of pure copper Positive Terminal of Battery Thick Rod of impure cong copper sulphate solution. Production of compounds: The electrolysis method is used for the production of some compounds. For example, sodium hydrochlorite. ADD:- 42, STAR AVENUE,RAM TIRATH ROAD,AMRITSAR. B/S HARMAN SWEET SHOP.M.9 0 4 1 S 9 8 8 8 9 Copyright 0 2006 KEEN TUTORIALS. All Rights Reserved.
  6. @ KEEN TUTORIALS Decomposition of compounds: The electrolysis method is also used to decompose a compound into its constituents. For example, water can be decomposed using the process of electrolysis to obtain hydrogen and oxygen. Electroplating Electroplating is a process in which a layer of metal is deposited on another material with the help of electricity. Electroplating is used in many industries for depositing a layer of metal with desired characteristics on another metal. Different metals used for electroplating are Nickel, Copper, Gold Silver, Tin, Brass, Zinc, Chromium, and Platinum. The process of depositing a thin layer of desired metal over a metal object with the help of an electric current is called electroplating. Copper Key Uses of Electroplating: It is widely used in industry for coating metal objects with a thin layer of a different metal. It resists corrosion. iii. It gives a shiny appearance to the metal on which it is done. Tin cans used for storing food, are made by electroplating tin onto the iron. Tin is less reactive than iron. Due to electroplating, food does not come into contact with iron and is protected from getting spoilt. Iron is used in bridges and automobiles to provide strength but it tends to corrode and rust. So, a coating of zinc is deposited on iron to protect it from corrosion and the formation of rust. ADD:- 42, STAR AVENUE,RAM TIRATH ROAD,AMRITSAR. B/S HARMAN SWEET SHOP.M.9 0 4 1 S 9 8 8 8 9 Copyright 0 2006 KEEN TUTORIALS. All Rights Reserved.

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