Chapter 4 Materials : Metals and Non Metals

Class 8 | Science | Ch 4 |
Materials : Metals and Non Metals | NCERT Solutions

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

Answer: (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.

Answer: (c) Generally, metals are ductile.

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. ( )
(b) Sodium is a very reactive metal. ( )
(c) Copper displaces zinc from zinc sulphate solution. ( )
(d) Coal can be drawn into wires. ( )

Answer:

(a) Generally, non-metals react with acids. (F)
(b) Sodium is a very reactive metal. (T)
(c) Copper displaces zinc from zinc sulphate solution. (F)
(d) Coal can be drawn into wires. (F)

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:

	Metal	Non-metal
Appearance	Lustrous	Dull
Hardness	Hard	Soft
Malleability	Malleable	Non-mellable
Ductility	Ductile	Non-ductile
Heat conduction	Good conductors	Poor conductors
Conduction of electricity	Good conductors	Poor conductors

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 i.e. it can be beaten into thin sheets.It does not react with food items.

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

c) In reactivity series a metal of higher reactivity can displace a metal of lower reactivity from its salt solution. 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 highly reactive metals. They can catch fire even when they come in contact with air. So, they have to be kept in kerosene.

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 liberating hydrogen gas.This can lead to spoiling of pickle.

8. Match the substances given in Column A with their uses given in
Column B.
Column A                  Column 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:

Column A                  Column 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

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) There will be no reaction between copper and dilute sulphuric acid as copper is less reactive and hence no product will be formed.

b) In reactivity series , iron is more reactive than copper. Therefore , iron will displace copper from copper sulphate solution.

Iron(Fe) + Copper Sulphate(CuSO₄) ——–> Iron Sulphate(FeSO₄) + Copper(Cu)

In this reaction the blue colour of copper sulphate fades and there is deposition of copper on iron nail.

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 some water in the test tube in which gas is collected. Now, cover the test tube. Shake it well. Test the solution with blue litmus and red litmus. Blue litmus turns red. Thus, the nature of gas is acidic.

(b) Charcoal when reacts with oxygen forms carbon dioxide gas

C + O₂ ——> CO₂

Charcoal+ Oxygen ———> Carbondioxide

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 aqua regia (a mixture of hydrochloric acid and nitric acid). The outer layer of gold dissolves in the acid and the inner shiny layer is visible. Because of loss of upper layer of jewellery, its weight is reduced.