NOTES PREPARED BY
ASHAQ HUSSAIN BHAT
TEACHER SCHOOL
EDUCATION DEPARTMENT
JAMMU AND KASHMIR
CHAPTER 8
Chemical effects of Electric Current
KEYWORDS
Conductor: Which conduct electric current easily.
Insulator: Which cannot conduct electric current.
Salt solution: Salt dissolved in distilled water.
Chemical effect: Chemical reactions caused by passage of electric current.
Electroplating: Process of depositing a layer of any desired metal on another metallic object.
TEXT BOOK EXERCISE
Fill in the blanks:-
(a) Most liquids that conduct electricity are solutions of.........and............
(b) The passage of an electric current through a solution causes chemical............
(c) Copper gets deposited on the plate connected to.............terminal of battery.
(d) The process of depositing a layer of any desired metal on another metallic object, by means of electricity, is called..............
Ans. (a) - acids, bases, salts;
(b) - reaction;
(c) - negative;
(d) -electroplating
Q.2. When the free ends of a tester are dipped into a solution, the magnetic compass needle shows deflection. Can you explain the reason?
Ans. The compass needle kept nearby gets deflected because the solution conducts the electricity. Even if the current is small, the deflection of the magnetic needle can be seen.
Q.3. Name three liquids, which when poured in the beaker shown in figure, may cause the magnetic compass needle to deflect.
Ans. Water, lemon juice solution, vinegar solution, hydrochloric acid solutions etc
Q.4. The bulb does not glow in the setup shown in figure. List the possible reasons. Explain your answer.
Ans. The possible reasons may be :
(i) The connections of the circuit may be loose.
(ii) Bulb may be fused.
(iii) Cells may be used up.
(iv) The liquid may be poor conductor.
Q.5. A tester is used to check the conduction of electricity through two liquids, labelled A and B. It is found that the bulb of the tester glows, brightly, for liquid A while it glows very dimly for liquid B. You would conlude that:
(i) liquid A is a better conductor than liquid B.
(ii) liquid B is a better conductor than liquid A.
(iii) both liquids are equally conducting.
(iv) conducting properties of liquid cannot be compared in this manner.
Ans. We conclude that option (i) liquid A is a better conductor than liquid B.
Q.6.Does pure water conduct electricity? If not what can we do to make it conducting?
Ans. No, pure water does not conduct electricity. To make the pure water conducting, we have to dissolve some acid, base or salt in it, which are good conductors of electricity.
Q.7. In case of any fire, before the firemen use the water hoses, shut off the main electrical supply for the area. Explain the reason why they do this.
Ans. As water used by fireman is collected from the sources, like; wells, ponds, which is not pure but a solution having few amounts of mineral salts and conductor of electricity. So, to prevent the electrocution, the fireman shut off the main electricity supply.
Q.8. A child staying in the coastal region tests the drinking water and also the seawater with his tester. He finds that the compass needle deflects more in case of seawater. Can you explain the reason?
Ans. In seawater, amount of mineral salts is more than the drinking water. So, the seawater can conduct the electricity more easily than drinking water that is why the compass needle deflects more in case of seawater.
Q.9. Is it safe for the wireman to carry out electrical repairs during heavy downpour? Explain.
Ans. No, during heavy downpour, there a risk of electrocution because impure water is good conductor of electricity.
Q10. Paheli had heard that rainwater is as pure as distilled water. So she collected some rainwater in a clean glass tumbler and tested it using a tester. To her surprise she found that the compass needle showed deflection. What could be the reasons?
Ans. Rain water is, like; distilled water, but some impurities are mixed in from the atmosphere. These impurities make the rain water conducting. This could be the reason for the deflection of compass needle.
Q.11. Prepare a list of objects around you that are electroplated.
Ans. Electroplated objects.
(i) Handle bar of cycle.
(ii) Wheel rims.
(iii) Artificial ornaments.
(iv) Bath taps.
(v) Kitchens gas burners.
Q.12. The the cess that you saw in activity 8.7 is used for purification of copper. A thin plate of pure copper and a thick rod of impure copper are used as electrodes. Copper from impure rod is sought to be transfer to the thin copper plate. Which electrode should be attached to be positive terminal of thebattery and why?
Ans. Thick rod of impure copper is to be attached to positive terminals of battery as pure copper moves to electrode connected negative terminal of the battery. As copper deposited on thin copper plate, battery. so, thick copper plate will be attached to the positive terminal of
ADDITIONAL SHORT ANSWER TYPE
Q.1. What do you mean electric current ?
Ans. The continuous and directional flow of charges (electrons) is called electric current. It is denoted by I and its unit is ampere.
Q.2. Discuss few chemical effects of the electric current.
Ans. The passage of an electric current through a conducting solution causes chemical reactions. As a result, bubbles of gas are formed, deposits of metal on electrodes may be seen and changes of colour of solution may occur, depending on what solutions and electrodes are used. These are some of the chemical effects of the electric current.
Q.3. What is electrolysis ?
Ans. Electrolysis: Breaking up of chemical compounds under the action of electric current is called electrolysis. When we pass electric current through water (acidulated), it breaks up into its constituents: hydrogen and oxygen. Hydrogen goes to cathode and oxygen is liberated at the anode.
Q.4. Define electroplating.
Ans. The process of depositing a layer of any desired metal on another metallic object by means of electricity is called electroplating. It is one of the common applications of chemical effects of electric current.
Q.5. Why iron is electroplated by zinc ?
Ans. Iron is used in bridges and automobiles to provide strength. However, iron tends to corrode and rust, so zinc is plated on to protect it from corrosion and the formation of rust.
Q.6. Distinguish between conductor and electrolyte.
Ans. Liquid which allow the current to pass through them but do not dissociate into ions are called good conductors. For example, mercury.Liquid which allow the current to pass through them and also dissociate into ions are called electrolyte. For example, the solution of salt
Q. 7 What is tester?
Ans. The instrument which is used to check the flow of electric current is called tester. It is attached to the terminals of the electric current. If the bulb of tester flows, it confirms that current is flowing through the circuit.
Q . 8 Give a brief account of LED
Ans. It is light emitting diode. It glows even when the current is very small. It consists a bulb with two legs called leads. One leg is longer and other leg is shorter. Longer leg is attached to +ive terminal of battery and shorter leg is attached to -ive terminal.
Q.9. What do you mean by magnetic effect of electricity?
Ans. When electric current is passed through a coil or wire, then it behaves, like; a magnet. This is called magnetic effect of current. The strength of magnetic field depends on the amount of current passing through a coil or wire. The coil or wire shows magnetism till current is passed.
Q.10. How can you show that liquid allows electric current to pass?
Ans. To test whether a liquid allows electric current to pass through it or not, we can use a tester which contains a bulb and a battery. When the liquid between the two ends of the tester allows the electric current to pass, the circuit of the tester becomes complete. The current flows in the circuit and the bulb glows. When the liquid does not allow the electric current to pass, the circuit of the tester is not complete and the bulb does not glow.
ADDITIONAL LONG ANSWER TYPE QUESTIONS
Q.11. What are the two methods of testing an insulator or a conductor ?
Ans. These two methods are used to test the conduction.
 |
| Method of testing insulator And conductor |
(1) We use an electric lamp to test conductivity. An electric lamp is attached in the electric circuit. It the substance allows the current to pass through it, the bulb will start glowing. Otherwise the bulb will not glow. This method does not work when current is very small. In such cases magnetic compass is used.
(ii) A magnetic tester is used to test conductivity when current is allowed to pass through it, it creates a magnetic field and the compass shows deflection. The deflection of compass shows that the current is passing through circuit.
Q.12. What is electroplating? How does is
Ans. Electroplating is the process of coating a desired metal on an undesired metal surface using
 |
| A simple circuit showing electroplating |
electric current. Metallic plate and the substance requiring coating are dipped in conducting solution with conducting wires. The object to be c coated is attached to the negative terminal. When electric current is passed through the solution, the compounds of the conducting solution start breaking and free metallic particles get deposited on the object at negative terminal of battery. In this way, we can get a coating of desired metal on any object by preparing suitable conducting solution and using suitable electrodes.
Q.13. What are the advantages of electroplating?V V Imp.
Or
What are the uses of electroplating?
Ans. Advantages of Electroplating:
(i) It is used to coat metal surfaces with desired metal coating.
(ii) It saves metal surfaces from rusting.
(iii) It saves corrosion of surfaces of metals.
(iv) Coating of chromium on metals give luster to objects.
(v) Cheap metals, like; iron, aluminium etc., can be coated with costly metals like silver, gold etc., to give them rich look as in case of artificial jewellary.
(vi) It can make reactive metals, like; iron etc., less reactive and they can be used for storing food items etc.
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