Important Questions for Class 8 Chapter 14 - Chemical Effects of Electric Current

Important questions based on NCERT syllabus for Chapter 14 - Chemical Effects of Electric Current:

Question-1: Describe an activity to check the conductivity of different solutions formed by adding the following substances to distilled water.
i) Lemon juice
ii)Caustic soda
iii)Sugar

Solution: Take three clean plastic or rubber caps of bottles. Pour about two teaspoons of distilled water in each of them. Add a few drops of lemon juice to distilled water in one cap. Now in the second cap containing distilled water, add a few drops of caustic soda. Add a little sugar to the distilled water in the third cap and dissolve it. Test which solutions conduct electricity using a tester. This way we can know the conductivity of given substances.

Question-2: What are the major problems that the electroplating factories are faced with? Name the industries that aggravate this problem?

Solution: Electroplating industry consumes and discharges large volumes of wastewater. consisting of rinsed water, spray losses , conducting solution dumping and leakages. These effluents are supposed to be most hazardous as it contains heavy metallic ions such as nickel, chromium, zinc, lead, silver, cadmium, mercury etc. as well as cyanides, hydrogen sulphides, ammonia, chloramines.One can see that a lot of valuable metals like zinc silver, and cyanide are lost in wastewater. There are methods to obtain these from the polluting waste, however , the government has issued a set of specific disposal guidelines to protect the environment.

Typical Industries that aggravate this problem are,

Electroplating shops
Automotive suppliers, trucks, motorcycles etc
Jewellery mfg
Machine tool mfg.
Wire forming - nails, screws etc
Electronics – gold and silver plating of electrical connectors etc.

In the electroplating factories the disposal of the used conducting solution is a major concern. It is a polluting waste and there are specific disposal guidelines to protect the environment.

Question-3: What is the full form of LED ? Why are LED bulbs considered energy efficient? Now explain why LED bulbs are preferred over filament bulbs.

Solution: LED stands for Light Emitting Diode.
LEDs are “directional” light sources, which means they emit light in a specific direction, unlike incandescent and compact fluorescent bulbs, which emit light and heat in all directions. For this reason, LED lighting is able to use light and energy more efficiently in many applications.

LED bulbs are increasingly preferred over filament bulbs because they switch on instantly, heat emitted is low, and are not made of any hazardous materials, besides needs to be replaced only on an average of 400 hours only. This is unlike filament bulbs, which are , fragile, and heat emitted is high , in addition to requiring frequent replacement.