NCERT Solutions for Class 8 Science Chapter 4 Materials Metals and Non-Metals
Q.1 Which of the following can be beaten into thin sheets?
Answer is (a) zinc
Q.2 Which of the following statements are correct?
- All metals are ductile
- All non- metals are ductile
- Generally metals are ductile
- Some non-metals are ductile
Answer is (c) Generally metals are ductile
Q.3 Fill in the blanks.
- Phosphorus is a very reactive non-metal.
- Metals are Good conductors of heat and electricity.
- Iron is more reactive than copper.
- Metals react with acids to produce hydrogen gas.
Q.4 Mark ‘T’ if the statement is true and ‘F’ if it is false.
- Generally, non-metals react with acids.()
- Sodium is a very reactive metal.()
- Copper displaces zinc from zinc sulphate solution.()
- Coal can be drawn into wires.()
Q.5 Some properties are listed in the following table. Distinguish between metals and non-metals on the basis of these properties.
|Condition of electricity|
|Appearance||Lustrous ( shiny)||Non-lustrous (not shiny)|
|Malleability||Can be beaten into thin sheets (malleable)||Cannot be beaten into thin sheets (non-malleable)|
|Ductility||Can be drawn into wires ( ductile)||Cannot be drawn into wires ( non-ductile)|
|Heat conduction||Good conductor of heat||Poor conductor of heat|
|Conduction of electricity||Good conductor of electricity||Poor conductor of electricity|
Q.6 Give reasons for the following.
- Aluminium foils are used to wrap food items.
Solution:- It is a highly malleable cheap metal that does not react with food items therefore, aluminium foils are used to wrap food items.
- Immersion rods for heating liquids are made up of metallic substances.
Solution:- Because metals are good conductors of heat and electricity, that’s why immersion rods are used for heating liquids because they are made up of metallic substances.
- Copper cannot displace zinc from its salt solution.
Solution:- A less reactive metal cannot replace a more reactive metal from a Salt solution. Since zinc is more reactive than copper, therefore, copper cannot replace zinc in its salt solution.
- Sodium and potassium are stored in kerosene.
Solution:- Sodium and potassium are very reactive metals. They react vigorously with oxygen and water, because of their reaction with oxygen and water a lot of heat is generated. If they are kept in an open area they will react with oxygen and moisture present in the air and will catch fire immediately. Therefore, sodium and potassium are stored in kerosene.
Q.7 Can you store lemon pickle in an aluminium utensil? Explain.
Solution:- We cannot store lemon pickle in an aluminium utensil, because lemon pickle contains acid which will react with aluminium (metal) and liberate hydrogen gas. The librated hydrogen gas can spoil lemon pickle. That’s why we can’t keep lemon pickle in an aluminium utensil.
Q.8 Match the substances given in column A with their uses given in column B.
|II) Iron||Electric wire|
|III) Aluminium||Wrapping Food|
|I) Gold||d) Jewellery|
|II) Iron||e) Machinery|
|III) Aluminium||c) Wrapping Food|
|IV) Carbon||f) Fuel|
|V) Copper||b) Electric wire|
Q.9 What happens when.
(Write word equation of the reactions involved.)
- Dilute sulphuric acid is poured on a copper plate?
Solution:- No reaction will be there because copper is a very less reactive metal. However, when dilute sulphuric acid is poured on a copper plate, hydrogen gas evolves along and we can see copper sulphate crystals that are blue in colour.
- Iron nails are placed in copper sulphate solution?
Solution:-In this, iron is more reactive than copper therefore, iron will displace copper from its copper sulphate solution to form iron sulphate.
= Fe+Cuso4 → Feso4 + cu
(Iron)+(Copper sulphate)→(Iron sulphate)+(Copper)
Q.10 Saloni took a piece of burning charcoal and collected the gas evolved in a test tube.
- How will she find the nature of a gas?
Solution:-To find the nature of the gas, add a small amount of water into the test tube in which gas evolved in the test tube is collected. Then quickly cover the test tube and shake it very well. Now test the solution with a red and blue litmus paper, you will observe that blue litmus paper will turn into Red while in red litmus paper we can observe no change. This tells us that the gas that is evolved during the burning of charcoal is acidic nature.
b) Write down word equations of all the reactions taking place in this process.
Solution:- Name of the product formed in this reaction of charcoal with oxygen is carbon dioxide.
(Carbon ( from charcoal)+(oxygen)→carbon dioxide
When carbon dioxide is dissolved in water carbonic acid will form, the carbonic acid turns blue litmus paper to Red., Generally oxides of non-metals or acidic in nature.
Co2 +H2o →H2co3
(Carbon dioxide)+(Water)→(Carbonic acid)
Q.11 One day Rita went to a jewellers shop with her mother. Her mother gave an old gold jewellery to the Goldsmith to polish. Next day when they brought the jewellery back, they found that there was a slight loss and its weight . Can you suggest a reason for the loss in weight?
Solution:- To polish Gold jewellery it is dipped in a mixture of acids called Aqua regia this is a mixture of hydrochloric acid and nitric acid. The outer layer of Gold jewellery dissolves in the acid mixture and all the dust on it comes out and the inner shiny layer appears. Due to this dissolution of the upper layer of gold, it’s weight gets reduced.