CHEMICAL EFFECTS OF ELECTRIC CURRENT 8

Practice Paper

Subject  Physics

Class VIII          ELECTRIC CURRENT AND ITS CHEMICAL EFFECT   

                      

I. Fill in the blanks: 

a. When electric current passed through copper Sulphate, copper gets deposited on the plate connected to the __________ terminal of the battery.

b. The process of depositing a thin layer of any desired metal on another metal by means of electricity is called as __________

c. During electrolysis of water _______ and _________ are produce at the cathode and anode.

d. The process of obtaining pure metal from the impure one is called __________.

e. When the relative motion of the coil is stopped, the flow of current ___________.

f. Carbonic acid is a ___________

g. Most liquids that conduct electricity are solution of _________,_______ and __________.

h. The passage of an electric current through a solution causes _____ effects.

II. Very short answer type questions: Each of 2 marks. 
                                                     

1. What do you mean by electric effect of current?

2. Define  (a) Electrolyte & non electrolyte. (b) Electrolysis. (c) Conductor &Insulator (d) Volt meter (e) Ammeter (f) Volta meter (g) Cell (h) Electrolytic refining of metals? [1x8=8]

3. Explain the cause of conductivity of liquid.

4. What is electroplating?

5. Define an electrode.

6. Define (a) cathode and anode (b) cation and anion.

7. What is current?

8. Name two sources of electric current.

9. What is a battery?

10. What happens when a steady current is passed through water?

11. By which process, we can easily obtain gold ornaments at cheaper costs?

12. What happens when an electric current is passed through the copper Sulphate solution?

13. Which type of energy is converted into electrical energy in an electric cell?

14. What is LED?

15. What is CFL?

16. What will you do to make distilled water conducting?

17. Why do fruits and vegetables conduct electricity?

18. Is air an insulator or conductor of electricity?

19. Name one nonmetal which is good conductor of electricity.

20. Does pure water conduct electricity?

21. Apart from chemical effect, which other effect electric current produce?

22. Write the name of a device that converts magnetic energy into electric energy.

23. Write the name of two strong electrolytes and weak electrolytes.

III. Short answer type questions: 
                                                    

1. State four applications of electrolysis.

2. Name two products obtained by electrolysis of brine (common salt) .

3. Why is an acid or an ionic salt or sodium hydroxide added to water before electrolysis of water?

4. Write the metals which can be obtained by the electrolysis of their molten chlorides, hydroxides or oxides.

5. What are conductor and insulator? Give two examples.

6. Solid sodium chloride does not conduct electricity while molten sodium chloride conducts. Explain why?

7. When tap water is used as a conducting liquid in the closed electric circuit, the bulb glows. Why?

8. Write the name of four metals which are used for electroplating.

9. How will you identify that a particular substance is a conductor or insulator?

10.Which effect of electric current is utilized in electroplating?

11. Is it safe for the electrician to carry out electrical repairs outdoors during heavy thunderstorm?

12. Explain the term chemical effects of an electric current.

13. Name three liquids which when tested in the manner may cause the magnetic needle to deflect.

14. Does pure water conduct electricity? If not, what can do to make it conducting?

15. Why are kitchen gas burns coated with Chromium?

16. Why do we coat an iron article with Chromium?

17. In case of a fire, before the firemen use the water house, they shut off the main electric supply for the area. Explain why they do this.

18. What is the disadvantage of electroplating done in the factories?

19. A tester is used to check the conduction of electricity through two liquids, levelled 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 conclude that:
a. Liquid is a better conductor than liquid B.
b. Liquid B is a better conductor than liquid A.
c. Both liquids are equally conducting.
d. Conducting properties of liquid cannot be compared in this manner.

20. Choose an appropriate word from the following.
Fill in the blanks given below:
Electroplate, ions, cathode, anode, electrolyte, nickel, electrolytic cell.
To ______an article with Nickel, requires an________ which must be a solution containing ________. The article, to be plated, is taken as the _______of the ______ in which the plating is carried out. The ________ of cell is made from pure ________.

IV. Long answer type questions: 
                                                     

1. How are steel spoons plated with silver? Explain with the help of diagram.  

2. Write some points that should be remember while electroplating or write the process of electroplating. 

3. Write some uses of electroplating. 

4. Write chemical reactions describing the electroplating of copper.
5. Why direct current is is used in electroplating?

6. Give one term for (i) the electrode through which current enters the electrolyte.(ii) the electrode connected to the negative terminal of the battery.(iii) Purifying metals by using electrolysis.

7. Give some applications of the chemical effect of current.

8. State some applications of magnetic effect of electric current.

9. State some applications of heating effect of electric current.

10. How will you make a tester?

11. If the bulb of the tester does not glow on touching it to a substance, does it always means that the substance is an insulator?

12. How could you say that chemical reaction takes place during electroplating?

13. During a process 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 brought to be transferred to the thin copper plate. Which electrode should be attached to the positive terminal of battery and why?

14. Alternate current cannot be used in electrolysis. Why? 

15. For the electroplating of silver over Steel spoon, name the substance used as cathode, anode, and electrolyte. Mention the ions formed during the process.

16. Solid calcium chloride does not conduct electricity while sodium chloride solution conduct. Explain why? Or Copper Sulphate powder does not conduct electricity but its Solution does. Why?

17. To carry out electrolysis of water a few drops of sulphuric acid are added to the water. Explain why.

18. Distinguish between strong and weak electrolyte. Give two examples of each.

19. When the free ends of a tester are dipped in a solution, the magnetic needle shows deflection points can you explain the reason?.

20. When an electric current is passed through a cut potato for a considerable time, a colored sport is formed around one of the electrodes.
(a) What is the color of the spot?
(b) Around which electrode the colored spot is formed?

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