Class 8 Science Solution : Chemical Effect of Electric Current : part 2

 Chemical effect of electric current: part 2

25. Sugar solution does or does not conduct electricity.
Answer: sugar solution does not conduct electricity.

26. A torch bulb cannot be used to detect weak electric current flowing through a liquid in a circuit .............why?
Answer: the current in the circuit may be weak if the the electrical conductivity of the liquid we are testing is very low. So, if we test a liquid hav*ZzzZing very low electrical conductivityz by using a torch bulb in the circuit , then the bulb may not glow at all. Because too week current flowing through it. Show a torch bulb cannot be used to detect with electric current flowing through a liquid in a circuit.

27. How do we detect electric current flowing through liquids?
Answer: the with electric current flowing through liquids having low electrical conductivity can be detected in two ways:
i) by using a LED
ii) by using a compass.

28. Write the full form of "LED".
Answer: light emitting diode.

29. How do we connect LED to the circuit?
Answer: while connecting LED in the circuit the longer lead is always connected to the positive terminal of the battery and the shorter lead is connected to the negative terminal of the battery.

30. Even if a weak electric current flows through the liquid in the circuit, the magnetic needle of compuss will show deflection .....why?
Answer: this is because even a weak electric current flowing through a wire produces a magnetic field around it. And this magnetic field of electric current acts on the magnetic needle of the compass  and deflects it from its usual north-south position.

31. Most of the liquids that conduct electricity are solutions of acids bases and salts .........why?
Answer: this is because the solutions of acids bases and salts contain charged particles (called ions) which conduct electricity through this solutions.

32. Distilled water does not conduct electricity.......why?
Answer: distilled water does not contain any dissolved salts in it which can provide it ions to conduct electricity. Thus, distilled water is pure water and it does not conduct electricity.

33. How do we make distilled water to conduct electricity?
Answer: i) by adding some salt like common salt
ii) by adding some acid like dilute sulphuric acid , lemon juice or vinegar
iii) by adding some bases like Sodium Hydroxide or potassium hydroxide.

34. Tap water is a conductor of electricity .......why?
Answer: tap water is a conductor of electricity because it contains small amounts of various salt dissolved in it.

35. We should never operate an electric switch or touch any working electrical appliance with wet hands ....... why?
Answer: it is dangerous to operate an electric switch or touch a working electrical appliance with wet hands because the tap water present on wet hands is a conductor of electricity due to which it may conduct electric current from the electric switch to our hand and give us an electric shock.

36. We should never handle an electrical appliance while standing barefooted on a wet floor. ....... why?
Answer: because the tap water present on  a wet floor  is a conductor of electricity due to which it may conduct electric current from the electrical appliances to our body and give us an electric shock.

37. In case of a fire, before the firemen use big water hoses to throw water on a burning house, they usually cut of the electricity supply of that area............why?
Answer: the Electric Supply is cut off to prevent electroelectrocution of Fireman who are busy in fire fighting operations. Ordinary water is a conductor of electricity, so if the electricity supply is not cut off and Fireman come in contact with with electric switches, electric wires and other electrical appliances, they may get electrocuted.

38. The electrical conductivity of sea water is much more than that of drinking water..........why?
Answer:  the electrical conductivity of sea water is much more than that of drinking water because drinking water contain small amounts of dissolved salts in it but sea water contains a large amount of dissolved salts in it.

39. Which is good conductor of electricity (drinking water/ sea water)
Answer: Sea water.
40. Rain water is pure water but it conduct electricity ........... why?
Answer: ring water is said to be pure water. But when rain water falls to the earth through the atmosphere, it dissolves an acidic gas carbon dioxide from the air and forms a weak acid called carbonic acid. The rain water may also dissolve other acidic gases such as sulphur dioxide and nitrogen oxides to form small amounts of other acids such as sulphuric acid and nitric acid. Due to the presence of small amounts of acids in it, rain water becomes a conductor of electricity.

41. It is not safe for an electrician to carry out electrical repairs in the outdoor area during heavy downpour or heavy rain ........ why?
Answer: since the rain water being a conductor of electricity may cause electrocution of the electrician.

42. Write the application of the chemical effect of electric current.
Answer: the chemical effect of electric current is used in industries for factories for the following purposes:
i) electroplating metals
ii) purification of metals
iii) production of certain metals from the ore
iv) production of chemical compounds
v) decomposing chemical compounds.

43. Write the meaning of electroplating?
Answer: In the term "electroplating", the word 'electro' stands for electric current and 'plating' means the act of covering a metal object with a theme layer for coating of a different metal.

44. What is electroplating?
Answer:  the process of depositing a thin layer of a desired metal over a 'metal object' with the help of electric current is called electroplating.

45. Write two uses of electroplating.
Answer: the purpose of electroplating is to protect the metal objects from corrosion or rusting and to make the metal objects look more attractive.

46. Name some metals which are used as electroplating substances.
Answer: the metal objects which are usually electroplated with chromium 3 Nickel silver gold or copper metals.

47.define chromium plating.
Answer: when a metal object is electroplated with chromium, it is called chromium plating or chrome plating.

48. Define tin plating.
Answer: when a metal object is electroplated with tin is called tin plating.

49. Define Nickel plating.
Answer: when a metal object is electroplated with Nickel is called Nickel plating


50. Write the conditions we should follow while electroplating a metal.
Answer: i) the 'metal object on which electroplating' is to be done is made the negative electrode or cathode.
ii) the 'metal whose layer is to be deposited' is made the positive electrode or anode
iii) a water soluble salt of the 'metal to be deposited' is taken as the electrolyte.