Science NCERT Grade 8, Chapter 4, Materials: Metals and Non-Metals lay emphasis on fundamentals of metals and non-metals. The chapter starts with a discussion on appearances and hardness of different materials used commonly. The first part of the chapter, Materials: Metals and Non -metals discusses the physical properties of metals and non-metals in a detailed manner. The following properties of metals and non-metals are covered:

  • Ductility

  • Malleability

  • Lustre

  • Electrical conductivity

Each property is explained using activities and suitable examples.

In the second part of the chapter, Materials: Metals and Non-metals, the chemical properties of metals and non-metals are explained under the following labels:

  • Reaction with oxygen

  • Reaction with water

  • Reaction with acids

  • Reaction with bases

  • Displacement reactions

Discussion on each of the above mentioned reactions with metals and non-metals respectively is supplemented with activities, examples and chemical equations wherever required to make the concept clearer. The last section of the chapter, Materials: Metals and Non-metals focus on the uses of metals and non-metals in daily life.

The chapter, Materials: Metals and Non-metals cover the following topics:

  1. Physical Properties of Metals and Non-metals
  2. Chemical Properties of Metals and Non-metals
  3. Uses of Metals and Non-metals

Page No 53:

Question 1:

Which of the following can be beaten into thin sheets?

(a) Zinc (b) Phosphorus (c) Sulphur (d) Oxygen

Answer:

(a) Zinc

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Question 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

However, mercury metal− a liquid at room temperature − cannot be drawn into wires and is not ductile.



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Question 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.

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Question 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:

(i) Generally, non-metals react with acids. (F)

(ii) Sodium is a very reactive metal. (T)

(iii) Copper displaces zinc from zinc sulphate solution. (F)

(iv) Coal can be drawn into wires. (F)

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Question 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

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Question 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.

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Question 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.

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Question 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:

Question 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 evolution of hydrogen gas along with the formation of blue color crystals of coppersulphate.

CuSO4 + H2SO4   CuSO4  + H2

 

(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.

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Question 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.

Carbon dioxide reacts with water to form carbonic acid, which turns blue litmus paper red.

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Question 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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