Chemical effects of electric current Worksheet-5

Chemical effects of electric current Worksheet-5

 

  1. Define electroplating

 

  1. Is air a conductor or an insulator?

 

  1. What do you mean by electric current?

 

  1. What is a tester?

 

  1. How can you test liquids conduct or not conduct the electricity?

 

  1. Show that lemon juice and vinegar are good conductor of electricity.

 

  1. Explain the mechanism of glowing of bulb in liquid.

 

  1. Explain why a bulb glows on passing current.

 

  1. What is LED? Why is it most important source of light?

 

  1. What do you mean by magnetic effect of electricity?

 

  1. The ordinary water can conduct electricity while distilled water can not. Explain why.

 

  1. Why do we need magnetic compass to test the conduction of electric current?

 

  1. What is chemical effect of electricity? Give some example of chemical effects.

 

  1. What are the two methods of testing an insulator or a conductor?

 

  1. What do you mean by electroplating? How does it take place?

 

  1. Explain the advantages of electroplating.

 

Answer:

  1. The coating of a layer of desired metal on other metallic surface by passing electric current is called electroplating.

 

  1. Insulator

 

  1. The continuous and directional flow of charges (electrons) is called electric current. It is denoted by I and its unit is ampere.

 

  1. The instrument which is used to check the flow of electric current is called tester. It is attached to the terminals of the electric circuit. If the bulb of tester glows, it shows that current is flowing through the circuit.

 

  1. Some liquids are the good conductor of electricity while some are not. The liquids can be tested for conductor of electricity. The free ends of a tester are dipped in liquid to be tested and then bulb is observed, if it glows, it shows that the liquid is good conductor otherwise it is a poor conductor.

 

  1. An activity can be done to show that lemon juice and vinegar are good conductor of electricity.

Collect a few plastic or rubber caps of bottles.

Pour one tea spoon of lemon juice or vinegar in one cap.

Bring the tester over the cap and let the ends of the tester dip into lemon juice or vinegar.

We will see that bulb has started glowing. It indicates that lemon juice and vinegar are good conductors of electricity.

 

  1. When the liquid between the two ends of tester allows the electric current to pass, the circuit of the tester becomes complete. The current flows in the liquid 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.

 

  1. When the current passes through a bulb, the filament of the bulb gets heated to a high temperature due to the heating effect of current and the bulb starts glowing. Sometimes the current is too weak and filament does not get heated enough so bulb does not glow.

 

  1. The device which is used in the tester in place of bulb is called LED. It is used even when a weak electric current flows through it and it glows even in weak current. There are two wires called leads attached to the LED. One lead is longer than the other. A long wire is connected with positive terminal and shorter lead is connected to the negative terminal of battery.

 

  1. 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 the coil or wire. The coil or wire shows magnetism only till current is passed.

 

  1. The water that we get from various sources like taps, hand pumps, wells and ponds is not pure. It contains several salts dissolved in it. This water is thus good conductor of electricity. Distilled water is free of salts due to which it is poor conductor.

 

  1. Sometimes the bulb does not glow on passing electric current. This is because the electric current flowing through conductor is so small, that the filament of the bulb does not get heated up to the temperature where it starts glowing. So, in case of small current we need magnetic compass to test the conduction.

 

  1. The process in which a chemical reaction or change takes place in a solution on passing electricity.

The passage of an electric current through a conducting solution causes chemical reactions. For example change in colour of solutions and electroplating.

 

  1. (i) We use an electric lamp to test conductivity. An electric lamp is attached in the electric circuit. If 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.

 

  1. The process of coating a desired metal on other metal surface by using electric current is called electroplating.

A metal plate and the substance to be coated are dipped in a current conducting solution with conducting wires.

The object to be coated is attached to the negative terminal. When electric current is passed through the solution, the compounds of the conducting solution start breaking.

The free metallic particles get deposited on the object at negative terminal of the battery.

In this way we can get a coating of desired metal on any object by preparing suitable conducting solution and by using suitable electrodes.

 

  1. The advantages of electroplating:

(i) It is used to apply a coat of a desired metal on other objects.

(ii) It protects the metals from the corrosion and rusting.

(iv) Some cheap and dull metals are coated with costly and shiny metals sometimes to make artificial jewellery

(v) More reactive metals can be made less reactive for specific purposes.

(vi) Coating of chromium on metals give luster to objects.