CBSE Class 8 Science Chemical Effect of Current Chapter Notes. Learning the important concepts is very important for every student to get better marks in examinations. The concepts should be clear which will help in faster learning. The attached concepts made as per NCERT and CBSE pattern will help the student to understand the chapter and score better marks in the examinations.
CHEMICAL EFFECT OF CURRENT
Your parents and teachers always warn you not to touch the electrical switches with wet hands, as you are likely to get a severe electric shock. It is just possible that a drop of water may trickle inside the electric switch and make contact with electric wire. The water on our hands always contains small amount of salt dissolved in it. This makes the water good conductor of electricity. Thus, the electric current from the switch flows through the water and enters your body. The flow of electric current in your body gives an electric shock.
CAUTION : Do not touch the electric switch with wet hands, just for the fun or to check the above statement. It can be highly dangerous.
Let us perform the following activities to find out which of liquids conduct electricity and which of them do not conduct electricity.
To find out whether distilled water conducts electricity or not.
Materials required :
* A dry cell. *Three insulated copper wires A, Band C with bare ends* a 1 volt bulb fixed in a bulb holder * a beaker * distilled water * cellotape.
Method : Half fill the beaker with distilled water. Connect the bare ends of the copper wires A, B and C through a bulb with the help of cellotape. Touch the bare ends of the wires B and C with one another. We will observe that bulb glows, thereby showing that all the parts of circuit are conducting electricity.
Dip the bare ends of the wires B and C in the distilled water. We will observe that the bulb does not glow. Thus, the activity clearly proves that distilled water does not conduct electricity
To show that the addition of salts, acids or alkalis, make the distilled water a conductor of electricity.
MATERIALS REQUIRED : All materials as in activity 1 and * common salt * sulphuric acid * sodium hydroxide.*a glass rod and a dropper.
METHOD: Proceed as in Activity 1 and confirm that distilled water does not conduct electricity. Now take a spoonful of common salt and add it into distilled water. Dissolve the common salt by stirring it with a glass rod. Dip the bare ends of the wires B and C in the above solution. You will observe that bulb lights up. Thus, the activity proves that addition of common salt in water makes it a conductor of electricity. Pour off the common salt solution and rinse the beaker with distilled water. Half fill the beaker with distilled water and add to it about 10 drops of sulphuric acid. On dipping the bare ends of wire B and C in the above solution you will observe that bulb lights up. This proves that acids on dissolving in distilled water make it a conductor of electricity.
Similarly, if we repeat the activity by adding 10 drops of sodium hydroxide solution in distilled water, the bulb will light up, thereby proving that alkalis on dissolving in distilled water make it conductor of electricity.
To find electrically conducting liquids and non-conducting liquids.
Materials required : *A dry cell * three insulated copper wire A, Band C with bare ends. *cellotape * 1 volt bulb fixed in a bulb holder. *100 cc beaker containing distilled water.*tap water *common salt solution. *vinegar solution *lemon juice solution. *alcohol petrol.*kerosene oil *mustard oil and dilute hydrochloric acid solution.
Method : Set up the apparatus as in Activity 1 or 2. Dip the bare ends of the wires Band C in the above mentioned solutions one by one, and record in which solutions the bulb lights up and in which solutions the bulb does not light up. We will observe that bulb lights up in case of tap water, common salt solution, vinegar solution, lemon juice solution and dilute hydrochloric acid solution. Thus, these liquids conduct electricity. We will also observe that bulb does not light up in case of distilled water, alcohol, petrol, kerosene oil and mustard oil. Thus, these liquids do not conduct electricity.
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