Class 8 Chemical Effects-current Very Short Answer

Class 8 Science Home Page

Previous

Very Short Answer Questions:

  1. What is an electric current?

Electric current is a flow of electric charge.

  1. What are conductors and insulators? Give two examples of each.

Materials which allow electric current to pass through them are good conductors of

electricity. Metals like copper, aluminium are few examples of it.

Materials which do not allow electric current to pass through them easily are called as

insulators or poor conductors. Materials such as rubber & plastic are the examples for this.

  1. How can distilled water be made a conductor of electricity?

There are very few ions in water so it does not conduct electricity very well. When table salt

is dissolved in water, the solution conducts electricity well because the solution contains ions.

  1. Will a bulb glow when a circuit is completed in an insulating solution?

No.

  1. What is electroplating?

 It is widely used in various industries for coating metal objects with the thin layer of a different metal.

 6. Vinegar is a sour liquid. State whether vinegar will conduct electricity or not?

Yes, vinegar will conduct electricity.

 7. Which metal is electroplated on iron for making ‘cans’ used for storing food?

 Tin is deposited on iron cans used as food containers to prevent reaction of food with iron.

 Long Answer Questions:

  1. List the advantages of electroplating.

1. Electroplating protects surfaces by covering them with a thin layer of metal that will be more resistant to corrosion than the material of which they are primarily composed.

 2. Gold and silver are excellent conductors of electricity, but they are expensive. Through electroplating techniques, very small amounts of these precious, highly conductive metals can be incorporated into electronic components and integrated circuits. Cell phones, computers and other electronic devices use electroplating techniques in their circuits.

     3. Tin is deposited on iron cans used as food containers to prevent reaction of food with iron

  1. zinc is deposited on the iron to prevent it from rusting. This process of coating of zinc

over the iron article is called galvanization.

 5.Purification of metals:

The chemical effect of electric current is used in the purification of impure metals

which is extracted from their naturally occurring compounds called ores?

 6.Production of metals/ Extraction of metals:

Extraction of metals by the process by of electrolysis is known as electro-metallurgy.

This process is used in case of highly reactive metals such as sodium.

  1. Production of compounds: The chemical effect of electric current (or electrolysis) is used in the production of various chemical compounds.

Decomposition of compounds: The chemical effect of electric current/or electrolysis is used to decompose various chemical compounds into their elements.

 2. A student had heard that rainwater is as good as distilled water.

 So, he collected some rainwater in a clean glass beaker and tested it. To his surprise, he found that the bulb glows. What could be the reason?

Rainwater contains dissolved salts. This makes the rainwater a conducting solution. There is no salt is dissolved in pure water. Hence, rainwater can allow electricity to pass through it while distilled or pure water cannot.

  1. What is the application of chemical effects of electricity in our daily life? Give examples.

The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating. It is one of the most common applications of chemical effects of electric current.

Electroplating is a very useful process. It is widely used in industry for coating metal objects with a thin layer of a different metal. The layer of metal deposited has some desired property, which the metal of the object lacks. For example, chromium plating is done on many objects such as car parts, bath taps, kitchen gas burners, bicycle handlebars, wheel rims and many others.

Chromium has a shiny appearance. It does not corrode. It resists scratches. However, chromium is expensive and it may not be economical to make the whole object out of chromium. So the object is made from a cheaper metal and only a coating of chromium over it is deposited. Jewellery makers electroplate silver and gold on less expensive metals. These ornaments have the appearance of silver or gold but are much less expensive.

  1. Describe the electroplating of copper on an iron spoon.

In the process of electroplating of copper on a metallic spoon, the iron spoon is made the cathode. A thin sheet of pure copper is made the cathode. When electricity is passed through the solution, Cu2+ ion moves towards the cathode and get reduced to copper metal. This copper metal gets electroplated on the object, i.e, metallic spoon.

The sulphate ion moves towards the anode. Here the sulphate ions do not get oxidised. Instead, the copper metal of the anode gets oxidised to Cu2+ ions. These copper ions go into the solution.

Fig.

  1. What do you mean by electrolytes and non-electrolytes? Give some examples.

Electrolytes

The chemical compounds whose molecules ionise into positively and

negatively charged ions in a solution are called electrolytes, e.g., sodium chloride.

 Non-electrolytes – The chemical compounds which do not conduct electricity when

dissolved in water are called non-electrolytes e.g., glucose.


Class 8 Science Home Page

Previous

Next Chapter 15>>