NCERT Class 8 Science Solutions Chapter 4 Materials metals and non-metals

NCERT Class 8 Science Solutions Chapter 4 Materials metals and non-metals

Question-1

Which of the following can be beaten into thin sheets?

(i) Phosphorus (ii) oxygen (iii) zinc (iv) sulphur

Answer-

(iii) Zinc

Question-2

Which of the following statements is correct?

(i) Generally, metals are ductile

(ii) All metals are ductile

(iii) Some non-metals are ductile

(iv) All non-metals are ductile

Answer-

(i) Generally, metals are ductile.

Mercury is a metal and it is liquid at room temperature, hence it cannot be drawn into sheets and it is not ductile.

Question-3

Fill in the blanks with appropriate words:

(i) Iron is                  reactive than copper.

(ii) Phosphorus is a very                  non-metal.

(iii) To produce                   gas, metal reacts with an acid.

(iv) Metals are                    conductors of heat and

Answer-

(i) Iron is a more reactive than copper.

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

(iii) To produce hydrogen gas, metal reacts with an acid.

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

Question-4

Mark ‘True’ and ‘False’ of the following sentence:

(i) Sodium is a very reactive metal. ( )

(ii) Coal can be drawn into wires. ( )

(iii) Generally, non-metals react with acids. (  )

(iv) Copper displaces zinc from zinc sulphate solution. ( )

Answer-

(i) Sodium is a very reactive metal. (True)

(ii) Coal can be drawn into wires. (False)

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

(iv) Copper displaces zinc from zinc sulphate solutions. (False)

Question-5 

In the table given below distinguish between metals and non-metals according to their properties.

Properties	Metals	Non-metals
i) Appearance ii) Ductility iii) Malleability iv) Hardness v)Conduction of electricity. vi) Heat conduction

Answer-

Properties	Metals	Non-metals
i) Appearance ii) Ductility iii)Malleability iv) Hardness v)Conduction of electricity. vi) Heat conduction	Lustrous Can be drawn into wires Can be beaten into sheets Hard Good conductor Good conductor	Dull Cannot be drawn into wires Cannot be beaten into sheets Soft Bad conductor Bad conductor

Question-6

Give reason for the following:

(i) Copper cannot displace zinc from its salt solution.

(ii) Aluminium foils are used to wrap foods items.

(iii) Sodium and potassium are stored in kerosene.

(iv) Immersion rods for heating liquids are made up of metallic substances.

Answer-

(i) In an aqueous solution, a metal can displace a less reactive metal from its salt. But zinc is more reactive than copper. And because of it, copper cannot displace zinc from its salt solution.

Cu(s) +ZnSO4 (aq)        No reaction

(ii) Aluminium foils are used to wrap foods items because aluminum metal is malleable and it can be beaten into foil.

(iii) Sodium and potassium are stored in kerosene because they are highly reactive elements and can easily catch fire with the contact of air.

(iv) Immersion rods for heating liquids are made up of metallic substances because metals are good conductors of heat and electricity.

Question-7

Do you think it is possible to store lemon pickle in an aluminum utensil?

Answer-

No, it is not possible to store lemon pickle in an aluminum utensil because lemon pickle contains an acid which can react with aluminum (metal) liberating hydrogen gas. This may spoil the pickle.

Question-8

Match the following with column A with column B

A	B
a) Iron	i) Wrapping food
b) Mercury	ii) Jewellery
c) Carbon	iii) Fuel
d) Gold	iv) Thermometer
e)Copper	v) Machinery
f) Aluminum	vi) Electric Wires

Answer-

A	B
a) Iron	v) Machinery
b) Mercury	iv) Thermometer
c) Carbon	iii) Fuel
d) Gold	ii) Jewellery
e)Copper	vi) Electric Wires
f) Aluminum	i) Wrapping food

Question-9

What happen when:

i) Iron nails are placed in copper sulphate solution?

ii) Dilute sulphuric acid is poured on a copper plate?

Write word equations of the reaction involved

Answer-

i) Iron being more reactive displaces copper from copper sulphate In this reaction, the blue color of copper sulphate fades and there is deposition of copper on the iron nail.

Fe + CuSO4        FeSO4 + Cu

ii) when dilute sulphuric acid is poured on a copper plate, there will be evolution of hydrogen gas along with the formation of blue color crystal of copper sulphate.

CuSO4 + H2SO4       CuSO4 + H2

Question-10

Mahima took a piece of burning charcoal and collected the gas evolved in a test tube.

a) How will she find out the nature of gas?

b) Mention the equation of the reaction taking place in this process.

Answer-

a) In a test tube containing gas, add a few drops of water. Now cover the test tube and shake well. After shaking, test the solution with blue litmus and red litmus. It will change from blue to 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

Question-11

Once Meera along with her mother went to the jeweler’s shop. Her mother gave old gold jewelry to the goldsmith to polish. Next day when they brought the jewelry back, they found that there was a slight loss in his weight. Can you suggest a reason for the loss in weight?

Answer-

In order to polish the gold ornament, it is to be dipped into a liquid called aqua regia (a mixture of hydrochloric acid and nitric acid). On getting dissolved in the environment of aqua regia, the outer layer of gold dissolves and an inner shiny layer appears. The dissolving of the layer causes a reduction in the weight of the jewelry.