A. Lemon juice makes the water more conducting as it conducts electricity. But when the lemon juice is not added to it, the conductivity will be low.

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1 Chapter 14-Chemical Effects of Electric Current Topicwise Assignment Chemical Effects of Electric Current Do Liquids Conduct Electricity? A. 1. Yes 2. Yes 3. Lemon juice is a good conductor. 4. The ends are not connected to each other but they are connecting to a conductor, which is lemon juice and hence the bulb glows. 5. No, the bulb will not glow if the distilled water is taken instead of the lemon juice as the distilled water is pure and salts do not dissolve in it. Therefore, it will not conduct electricity. C. Current does not flow in the circuit because the circuit is incomplete. Air is a poor conductor of electricity. In some situations like lightning and thunderstorm, air acts as a conductor and conducts electricity. Chemical Effects of Electric Current A. Lemon juice makes the water more conducting as it conducts electricity. But when the lemon juice is not added to it, the conductivity will be low. B. 1. Circuit A shows the correct observation. 2. The spot observed is useful in identifying the positive terminal of a cell or a battery. Electroplating A. Electroplating is defined as the process of depositing a layer of any desired metal on another material by using electricity. B. Yes, copper will be deposited on the carbon rod. This is because when an electric current is passed through the circuit, copper from its solution gets deposited on the carbon rod and copper from the copper plate transfers into solution. C. (i) In the process of purification of copper, pure copper gets deposited on plate A. (ii) The impure copper gets deposited on plate B. (iii) The solution used in the process of purification of copper is copper sulphate solution. By the process of electroplating copper from impure copper plate is shifted to the pure copper plate. Exercises A. 1. Good conductors of electricity are those which conduct electricity easily. 2. Bad conductors of electricity are those which conduct electricity in some situations like air conducts electricity during thunderstorm.

2 3. (i) Lemon juice (ll) Aluminium 4. (l) Plastic (ll) Rubber 5. The cells of the battery will drain very quickly. 6. Heating effect of electric current 8. No, sugar solution does not conduct electricity. 9. The compass needle will show deflection. 10. Magnetic effect of electric current. 11. Pure water does not conduct electricity. To make pure water conducting, we can add some salts or acids to it. Salt and acid produce free ions that conduct electric current in liquid. 12. (i) Chemical effect (ii) Magnetic effect (iii) Heating effect 13. The solutions of acids, bases and salts conduct electricity. 14. Terminals through which an electric current enters or leaves an electrolytic cell or other medium are called electrodes. 15. The reaction depends on the solution and electrodes that are used in the reaction process. 16. Due to the process of electroplating. 17. The boy will observe the coating of copper on the carbon rod. B. 1. It is dangerous to touch an electrical appliance with wet hands because water conducts electricity due to the mineral salts present in it naturally and a person might get an electric shock. 2. As the both the ends of the wire are connected to the plastic covering of a screwdriver which acts as an insulator so there is no conduction of electricity. 3. The bulb attached to the circuit will help in identifying that the given conduction tester is working or not. If the bulb glows, then the conduction tester is working and if the bulb does not glow, the conduction tester is not working. 4. The reasons behind not glowing the bulb are as follows:. Bulb is fused.. The circuit is incomplete or the connection is loose.. Cells are used up. 5. When the electric current passes through the bulb due to the heating effect of current, the filament of the bulb gets heated to a high temperature and it starts glowing.

3 6. We can make another tester by replacing bulb with an LED as it glows even when a weak current is passed through it. 7. The solution is a conductor, which conducts the electric current. When the free ends of the tester are dipped into a solution, the circuit becomes complete and the electric current flows showing the deflection in magnetic needle. 8. Insulators are those which never conduct electricity. But in some situations, nonconducting air also conducts electricity. Hence the substances which can conduct in some situations are classified as bad conductors instead of insulators. Similarly, when temperature rises, the conductivity of conductors reduces. 9. Distilled water does not conduct electricity because it does not have salts or ions dissolved in it, Tap water containing salts or ions, is impure and conducts electricity. Hence we should not touch electrical appliances with wet hands as it may give shock to us. 10. By using electrodes, we can detect the occurrence of chemical reaction in the liquid through which the electric current is passed. 11. When the electric current passed through copper sulphate solution, the copper sulphate solution dissociates into copper and sulphate ions. 12. The disposal of the used conducting solution is a major concern as it is a polluting waste and no proper disposal methods are available to protect the environment from the pollution. 13. Iron gets easily corroded and rusted when it comes in contact with the atmospheric air and moisture. To prevent it from corrosion and rusting, zinc is coated over iron. 14. The current passed through solution by one cell was not sufficient to dissociate it into ions and conduct electricity. With two cells, more current was passed and solution conducted electricity. 15. Liquid A was a good conductor, while liquid B was a poor conductor. When she replaced liquid A by liquid B, then a weak current is produced which is detected by an LED not by a bulb. 16. Water from the natural sources contains the dissolved mineral salts in it. This makes the water a good conductor of electricity. 17. Seawater contains more amount of salt dissolved in it as compared to drinking water. Hence on passing the electric current through it, the compass needle shows more deflection. 18. No it is not safe as water is a good conductor of electricity and the electrician may get an electric shock.

4 19. Distilled water does not have any salts or impurities in it but rainwater may have some impurities or salts due to its reaction with pollutants in air. These help to conduct electricity and show a deflection in the compass needle. 20. Chromium plating is done on car parts, bath taps, kitchen gas burners, bicycle handlebars, wheel rims and many other objects. The following are the properties of chromium: Chromium has shiny appearance. It does not corrode. It resists scratches. 21. Iron is more reactive than tin and tin is electroplated on the iron so that the food that comes into contact with it. Is protected from getting spoilt. 22. The plate of pure copper is connected to negative terminal of battery and that of impure copper is connected to positive terminal of battery as copper from impure copper rod dissociates and gets deposited on the electrode connected to negative terminal of the battery. Be a Genius 1. The following may be the possible reasons: Cells may be discharged to produce any electric current. Solution used may be distilled water free of any type of impurity (non-conductor of electricity). Problem in connection in circuit, i.e. broken circuit etc. 2. Firemen shut off the main electrical supply for the area because water is a good conductor of electricity due to dissolved salts in it and the firemen can get electrocuted when water from the hosepipe com in the contact with electric wires or appliances carrying current. 3. William Nicholson, had shown that if the electrodes were immersed in water and a current was passed through it, the bubbles of oxygen and hydrogen were produced. Oxygen bubbles formed on the electrode connected to the positive terminal of the battery and hydrogen bubbles formed on the other electrode. 4. Electroplating is the process of depositing a layer of any desired metal on another material by using electricity. Activity: Take 250 ml. of copper sulphate solution and copper plates. Dip the copper plates in the solution and connect the plates to the terminals of a battery. Allow the current to pass for about 15 minutes. Now remove the electrodes from the solution and look at them. You will observe that one plate is copper plated.

5 5. When electricity is passed through copper sulphate solution then it will dissociate into copper and sulphate ions. CuSO Cu 2+ + SO Some of the electroplated objects are: cooking utensils, handles of doors, tin cans, rims of vehicles, handle bars of cycles and motor cycles, ornaments, decorative items, pots of metals and bath taps. 7. When electric current is passed through a conducting solution, then these observations are possible: Bulb will glow. Bulb will not glow. Electroplating 8. Take the tray of matchbox and place a compass needle inside it. Wrap an electric wire on the tray. Now connect one free end of the wire to the terminal of a battery and leave the other and free. Take another piece of wire and connect it to the other terminal of the battery. Join the free ends of two wires. The compass needle shows deflection. Now, the tester with free ends is ready, 9. We can show that liquids which conduct electricity are solutions of acids, bases and salts by doing following activity: Take three clean plastic caps and pour two tea spoonful of distilled water in each of them. Add few drops of acid in cap A, few drops of caustic soda in cap B and salt in cap 3. Use conduction tester to check whether these solutions conduct or not. On dipping the wire ends of the conduction tester the bulb glows in each case which shows that all these 3 caps will conduct electricity. Hence it proves that the liquids of acid, bases and salts conduct electricity. 10. The spoon should be connected to the negative terminal of the battery. The other electrode is made up of silver. This is because, she wants to do electroplating of silver. When current starts flowing, silver from the electrode will dissolve in the solution and the solution of silver nitrate will dissociate into silver and nitrate ions. Silver ions from the solution will deposit on the iron spoon. 11. The effluents discharged after electroplating have heavy metals like zinc, copper, nickel, lead etc. These can cause severe diseases like cancer, respiratory tract infection, baldness etc. To resolve these problems, alternatives of chromium are being searched. Care should be taken that industrial effluents should not be discharged in water bodies. 12. Uses of LED bulbs: lighting at homes and offices, cabinet lights, traffic lights etc. CFLs are preferred over LEDs because they have low costs. 13. [Answers of students may vary] Substances electroplated-utensils, jewellery, pipes etc.

6 Purpose-Prevent corrosion and provide shine or attractive look. Unfortunately, most of the effluents such as nickel, zinc and lead in our country are released in water bodies or open grounds. 14. (a) Current flows through the circuit. (b) Current is weak and is not enough to light up a bulb. (c) The deflection of needle will increase. (d) The deflection of needle will increase. (e) Salt solution, lemon juice and orange juice.