NCERT Solutions for Class 8th: Ch 4 Materials : Metals and Non-Metals Science

NCERT Solutions for Class 8th: Ch 4 Materials : Metals and Non-Metals Science

Page No: 53

Excercise

1. Which of the following can be beaten into thin sheets?
(a) Zinc
(b) Phosphorus
(c) Sulphur 
(d) Oxygen
► (a) Zinc

2. Which of the following statements is correct?
(a) All metals are ductile.
(b) All non-metals are ductile.
(c) Generally, metals are ductile.
(d) Some non-metals are ductile.
► (c) Generally, metals are ductile.

Page No: 54

3. Fill in the blanks:
(a) Phosphorus is a very _________non-metal.
(b) Metals are ________ conductors of heat and _________.
(c) Iron is ________reactive than copper.
(d) Metals react with acids to produce _________gas.

Answer

(a) Phosphorus is a very reactive non-metal.

(b) Metals are good conductors of heat and electricity.

(c) Iron is more reactive than copper.

(d) Metals react with acids to produce hydrogen gas.

4. Mark 'T' if the statement is true and 'F' if it is false.

(a) Generally, non-metals react with acids. ( )
► False

(b) Sodium is a very reactive metal. ( )
► True 

(c) Copper displaces zinc from zinc sulphate solution. ( )
► False

(d) Coal can be drawn into wires. ( )
► False

5. Some properties are listed in the following Table. Distinguish between metals and non-metals on the basis of these properties.


Properties
Metals
Non-metals
1. Appearance
2. Hardness
3. Malleability
4. Ductility
5. Heat Conduction
6. Conduction of Electricity

Answer

Properties
Metals Non-metals
1. Appearance
2. Hardness
3. Malleability
4. Ductility
5. Heat conduction
6. Conduction of electricity
Lustrous
Hard
Can be beaten into thin sheets
Can be drawn into wires
Good conductors of heat
Good conductors of electricity
Dull
Soft
Cannot be beaten into thin sheets
Cannot be drawn into wires
Poor conductors of heat
Poor conductors of electricity

6. Give reasons for the following.
(a) Aluminium foils are used to wrap food items.
(b) Immersion rods for heating liquids are made up of metallic substances.
(c) Copper cannot displace zinc from its salt solution.
(d) Sodium and potassium are stored in kerosene.

Answer

(a) Aluminium foils are used to wrap food items because aluminium metal is malleable. Therefore, it can be beaten into thin foils.

(b) Metals are good conductors of heat and electricity. Therefore, immersion rods for heating liquids are made of metallic substances.

(c) A metal can displace a less reactive metal from its salt in an aqueous solution. But zinc is more reactive than copper. Therefore, copper cannot displace zinc from its salt solution.
Cu(s)+ ZnSO4 (aq) → No reaction

(d) Sodium and potassium are stored in kerosene because they are highly reactive elements. They can easily catch fire even when in contact with air.

7. Can you store lemon pickle in an aluminium utensil? Explain.

Answer

Lemon pickle cannot be stored in aluminium utensils because lemon pickle contains acids, which can react with aluminium (metal) liberating hydrogen gas. This can lead to the spoiling of the pickle.

8. Match the substances given in Column A with their uses given in Column B.
A
B
(i) Gold (a) Thermometers
(ii) Iron (b) Electric wire
(iii) Aluminium (c) Wrapping food
(iv) Carbon (d) Jewellery
(v) Copper (e) Machinery
(vi) Mercury (f) Fuel

Answer

A
B
(i) Gold (d) Jewellery
(ii) Iron (e) Machinery
(iii) Aluminium (c) Wrapping food
(iv) Carbon (f) Fuel
(v) Copper (b) Electric wire
(vi) Mercury (a) Thermometers

Page No: 55

9. What happens when
(a) Dilute sulphuric acid is poured on a copper plate?
(b) Iron nails are placed in copper sulphate solution?
Write word equations of the reactions involved.

Answer

(a) When dilute sulphuric acid is poured on a copper plate, there will be no reaction between copper and dilute sulphuric acid as copper is less reactive and hence no products will be formed.

(b) Iron being more reactive displaces copper from copper sulphate solution. In this reaction, the blue colour of copper sulphate fades and there is deposition of copper on the iron nail.
Iron (Fe) + Copper Sulphate (CuSO4) → Iron Sulphate (FeSO4) + Copper (Cu)

10. Saloni took a piece of burning charcoal and collected the gas evolved in a test tube.
(a) How will she find the nature of the gas?
(b) Write down word equations of all the reactions taking place in this process.

Answer

(a) Add a few drops of water in the test tube containing gas. Now, cover the test tube and shake it well. After shaking, test the solution with blue litmus and red litmus. It will turn blue litmus red. Thus, the gas is acidic in nature.

(b) Charcoal reacts with oxygen to form carbon dioxide gas.
C + O2 → CO2
(Carbon from Charcoal) + Oxygen → Carbon Dioxide

Carbon dioxide reacts with water to form carbonic acid, which turns blue litmus paper red.
CO2 + H2O → H2CO3
(Carbon Doixide) + Water → (Carbonic Acid - turns blue litmus red)

11. One day Reeta went to a jeweller's 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 in its weight. Can you suggest a reason for the loss in weight?

Answer

To polish a gold ornament, it is dipped in a liquid called aqua regia (a mixture of hydrochloric acid and nitric acid). On getting the environment of aqua regia, the outer layer of gold dissolves and the inner shiny layer appears. The dissolving of the layer causes a reduction in the weight of the jewellery.


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