NCERT Solutions for Class 8 Science Chapter 4 Materials Metals And Non Metals

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Written by Team Trustudies
Updated at 2021-03-18


NCERT solutions for class 8 Science Chapter 4 Materials Metals And Non Metals Exercise

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



NCERT Solutions for Class 8 Science Chapter 4 Materials Metals And Non Metals


Answer :

(a) zinc

EXPLANATION :

Metals have different advantageous properties as compared to non-metals, thus making the metals more preferable over non-metals.

Metals show malleability. This means that they can be beaten into thin sheets by hammering or rolling without breaking.

As zinc is a metal, hence it can be beaten into thin sheets. While phosphorus, sulphur and oxygen are non-metals, hence they doesn't show malleability and thus cannot be beaten into thin sheets.

Q.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.



NCERT Solutions for Class 8 Science Chapter 4 Materials Metals And Non Metals


Answer :

(c) Generally, metals are ductile.

EXPLANATION :
Ductility is the property of a solid material in which the material is drawn into wire under the tensile strain by stretching without breaking.

1) Option(a) All metals are ductile
This option is not true because all metals doesn't show the property of ductility. There is an exception for this statement. Mercury is a metal which exist in liquid state at the room temperature and thus cannot be drawn into wires.

2) Option(b) All non-metals are ductile
This option is not true because non-metals doesn't show the property of ductility. They are brittle in nature and thus upon stretching, they come under tensile strain and hence they break.

3) Option(d) Some non-metals are ductile
This option is not true because non-metals doesn't show the property of ductility.

Q.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.



NCERT Solutions for Class 8 Science Chapter 4 Materials Metals And Non Metals


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.

EXPLANATION :

(a) White phosphorus is more reactive than red phosphorus because red phosphorus has polymeric structure while white phosphorus has unstable arrangement which makes the white phosphorus extremely reactive.

(b) Metals are good conductors of heat and electricity because metals have free electrons that allows the flow of electrons, thus conducting electricity.

(c) Iron is more reactive than copper because it has more free electrons than copper. Thus iron has greater tendency to lose electrons and form positive ions as compared to copper.

(d) Metals react with acids to produce hydrogen gas. When metals react with acid, metals oxidize by releasing electrons and these electrons reduce hydrogen ions into H2, thus releasing hydrogen gas.

Q.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. ( )



NCERT Solutions for Class 8 Science Chapter 4 Materials Metals And Non Metals


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 )

EXPLANATION :

a) Generally, non-metals react with acids. This statement is not true because when a substance reacts with acids it provides electrons to the H+ ions produced by the acids. Non-metals are acceptors of electrons and hence, they cannot donate electrons.

b) Sodium is a very reactive metal. This statement is true because sodium is quite reactive with air and its reactivity is a function of the relative humidity or water-vapour content of the air. The corrosion of solid sodium by oxygen is accelerated by the presence of small amounts of impurities in the sodium.

c) Copper displaces zinc from zinc sulphate solution. This statement is not true because copper is less reactive than zinc and hence cannot displace zinc from its solution.

d) Coal can be drawn into wires. This statement is not true because coal is mostly composed of carbon which is ultimately a non-metal. As non-metals doesn't show ductility hence coal cannot be drawn into wires and if stretched, it breaks.

Some properties are listed in the following table. Distinguish between metals and non-metals on the basis of these properties.
Properties
1. Appearance
2. Hardness
3. Malleability
4. Ductility
5. Heat Conduction
6. Conduction of Electricity



NCERT Solutions for Class 8 Science Chapter 4 Materials Metals And Non Metals


Answer :

METALS

1) Metals are lustrous as they can shine.
2) Metals are hard.
3) Metals are malleable as they can be beaten into thin sheets without breaking.
4) Metals are ductile as they can be drawn into thin wires without breaking.
5) Metals can conduct heat as it has free electrons that can carry heat from one point to another.
6) Metals can conduct electricity as it has free electrons that can carry current from one point to another.

NON-METALS

1) Non-metals are non-lustrous as they cannot shine.
2) Non-metals are brittle.
3) Non-metals doesn't show malleability as they cannot be beaten into thin sheets.
4) Non-metals doesn't show ductility as they cannot be drawn into thin wires.
5) Non-metals cannot conduct heat as it has no free electrons that can carry heat from one point to another.
6) Non-metals cannot conduct electricity as it has no free electrons that can carry current from one point to another.

Q.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



NCERT Solutions for Class 8 Science Chapter 4 Materials Metals And Non Metals


Answer :

a) Aluminium is a metal which shows malleability and thus can be drawn into thin sheets. Hence aluminium foils are used to wrap food items.

b) Immersion rods for heating liquids are made up of metallic substances because metals are good conductors of heat and electricity. Metals have free electrons that can carry heat and current from one point to another.

c) Copper cannot displace zinc from its salt solution because copper is less reactive than zinc so it cannot displace zinc.

d) Sodium and potassium are highly reactive metals which reacts immediately with atmospheric oxygen, once it comes in contact with air. To avoid any hazardous situation sodium and potassium are stored in kerosene.

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



NCERT Solutions for Class 8 Science Chapter 4 Materials Metals And Non Metals


Answer :

Pickles are preserved by a combination of some acids, salt, reduced moisture and spices.

Pickles can be prepared either by lactic acid fermentation of vegetables or with the preservation of vegetables in acetic acid (vinegar). Now the lemon pickle has citric acid, which can react with aluminium, thus making the pickle inedible for us.

As pickle consists of acids which can react with aluminium metal of the utensil to produce salt and hydrogen, hence pickle is not stored in aluminium utensil.

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



NCERT Solutions for Class 8 Science Chapter 4 Materials Metals And Non Metals


Answer :

A

(i) Gold
(ii) Iron
(iii) Aluminium
(iv) Carbon
(v) Copper
(vi) Mercury

B

(d) Jewellery
(e) Machinery
(c) Wrapping food
(f) Fuel
(b) Electric wire
(a) Thermometers

EXPLANATION :

1) Gold does not tarnish, rust or corrode upon their usage in daily life. Due to its wonderful properties and its luster, gold is considered as the most important metal in jewellery making.

2) Iron is used to make machines because they are hard, strong and do not show wear and tear so easily. There are many applications of gray iron which include automotive engine blocks, gears, flywheels, brake discs & drums and machine bases. Gray iron serves well in machinery applications because exhibits good fatigue resistance.

3) Aluminium is used for wrapping food items because it is flexible and non-reactive with the food ingredients. Aluminum is a soft and malleable metal. It can be easily beaten into thin sheets to form wrapping foils.

4) Carbon is used as fuel because they burn with a clean flame and thus no smoke is produced. Carbon and their compounds give out a lot of heat, energy and light when they are burnt in air and this is mainly because carbon compounds have greater calorific values.

5) Copper is used to make electric wires because it has low resistivity towards electrical current and thus consumes less power. Hence it is as an excellent conductor of electricity. Copper is also less oxidative than other metals.

6) Mercury is used as liquid in thermometers because it is the only metal that exists in liquid state at room temperature. It has high coefficient of expansion, so that it can note even the slightest change in temperature.

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



NCERT Solutions for Class 8 Science Chapter 4 Materials Metals And Non Metals


Answer :

(a) No reaction takes place when dilute sulphuric acid is poured on a copper plate.

However, when concentrated sulphuric acid is poured on a copper plate, hydrogen gas evolves along with the formation of copper sulphate. When the product is allowed to cool down, there is formation of blue coloured crystals of copper sulphate.

The chemical reaction of concentrated sulphuric acid and copper is:

Cu(s) + H2SO4 (conc.) ---> CuSO4(l) + H2(g)

(b) When iron nails are placed in a copper sulphate solution then iron being more reactive than copper, it displaces copper from its solution.

With the formation of ferrous sulphate, the blue colour of copper sulphate fades and the solution appears white in colour (colour of ferrous sulphate in water).Copper gets deposited on the iron nail.

Fe(s) + CuSO4(l) ---> FeSO4(l) + Cu(s)

Q.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



NCERT Solutions for Class 8 Science Chapter 4 Materials Metals And Non Metals


Answer :

a) The gas collected from charcoal is the carbon gas.

1) Carbon gas was collected in a test tube.
2) A few drops of water was added to the test tube.
3) Then the test tube was covered and was shaken well.
4) Now the solution was tested with blue litmus.

Observation:
It was observed that the blue litmus paper turns blue into red.
This indicates that the product formed during the reaction was acidic in nature.


b) Charcoal reacts with oxygen to form carbon dioxide gas.



where,

C is the carbon gas obtained from charcoal.
O2 is a dioxygen molecule obtained from water.
CO2 is the carbondioxide gas that is formed from the reaction.

Q.11 One day Reeta went to a jeweller’s shop with her mother. Her mother gave 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?



NCERT Solutions for Class 8 Science Chapter 4 Materials Metals And Non Metals


Answer :

Gold ornaments are polished using a liquid called aqua regia .

Aqua regia is a mixture of concentrated nitric acid and hydrochloric acid in the ratio of 1 : 3. It is a highly corrosive liquid.

It is a yellow-orange fuming liquid which can dissolve gold and platinum but not all metals.

When gold is dipped in aqua regia, the outer layer which had become lustreless, dissolves in aqua regia and the inner layer appears, thus making the gold look lustrous.

As the outer layer is dissolved in the aqua regia, hence some portion of gold is lost during this process. Therefore it has a slight loss in its weight.



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