Class 8 Science NCERT Solutions for Chapter – 4 Materials: Metals and Non-Metals

Materials: Metals and Non-Metals

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

Answer:
(a) Zinc

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.

Question 3.
Fill in the blanks :

(a) Phosphorus is a very _______ non metal.
Answer:
Reactive

(b) Metals are _________ conductor of heat and __________.
Answer:

1. Good
2. Electricity

(c) Iron is __________ reactive than copper.
Answer:
More

(d) Metals react with acids to produce _______ gas.
Answer:
Hydrogen

Question 4.
Mark ‘T’ if the statement is true and ‘F’ if it is false.

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

(b) Sodium is a very reactive metal.
Answer:
True

(c) Copper displaces zinc from zinc sulphate solution.
Answer:
False

(d) Coal can be drawn into wires.
Answer:
False

Question 5.
Some properties are listed in the following table. Distinguish between metals and non-metals on the basis of their properties.

Properties	Metals	Non-metals
Appearance
Hardness
Malleability
Ductility
Heat conduction
Conduction of Electricity

Answer:

Properties	Metals	Non-metals
Appearance	Shiny	Dull
Hardness	Very hard and hard	Hard and soft
Malleability	Malleable	Not malleable
Ductility	Ductile	Not ductile
Heat conduction	Conductor of heat	Non-conductor of heat
Conduction of Electricity	Conductor of electricity	Non-conductor of electricity

Question 6.
Give reasons for the following.

(a) Aluminium foils are used to wrap food items.

Answer:
It maintains the temperature of food item intact as it is a good conductor of heat.

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

Answer:
Metals are good conductors of electricity. That is why immersion rods are made up of metals.

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

Answer:
It is because copper is less reactive than zinc.

(d) Sodium and potassium are stored in kerosene.

Answer:
It is because sodium and potassium react vigorously when coming in contact with air or water.

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

Answer:
Aluminium is a metal. Metals are more reactive to acids. That is why acidic foodstuffs like lemon pickle must not be stored in aluminium utensils.

Question 8.
Match the substances given in column A with their uses given in column B.

A	B
Gold	Thermometers
Iron	Electric wire
Aluminium	Wrapping food
Carbon	Jewellery
Copper	Machinery
Mercury	Fuel

Answer:

A	B
Gold	Jewellery
Iron	Machinery
Aluminium	Wrapping food
Carbon	Fuel
Copper	Electric wire
Mercury	Thermometers

Question 9.
What happens when :

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

Answer:
When sulphuric acid is poured on a copper plate, copper sulphate is made and hydrogen gas is evolved as per the following chemical equation :

(b) Iron nails are placed in a copper sulphate solution? Write word equations of the reactions involved.

Answer:
When iron nails are placed in copper sulphate solution, Cu is displaced by iron. The Chemical equation that takes place is as follows :
Iron + Copper sulphate solution → Iron sulphate + Copper

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 gas?

Answer:
When charcoal is burnt, gas is evolved. Collect the gas in a test tube and pour water to it. Thus, The solution of gas is prepared. Now take a blue litmus paper and dip it in the solution, it changes to red. Thus, revealing The acidic nature of the solution.

(b) Write down word equations of all the reactions taking place in this process.

Answer:

1. Carbon + Oxygen Carbon dioxide (charcoal) (air) (gas)
2. Carbon dioxide + Water Carbonic acid (gas) (acidic nature)

Question 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?

Answer:
In polishing, the jeweller put the gold jewellery in a mild acidic solution, which on reaction with acid goes into the solution. So, in this process, a certain amount of gold is lost to the acidic solution.

InText Questions and Answers

Question 1.
You are familiar with a number of materials like iron, aluminium, copper, etc. Some materials have been given in Table 4.1 (Textbook, P. 44). Complete the table.

Answer:

Object/ Material	Appearance (Shiny/Dull)	Hardness (Very hard/ Not very hard)
Iron	Shiny	Very hard
Coal	Dull	Not very hard
Sulphur	Dull	Soft
Aluminium	Shiny	Hard
Copper	Shiny	Very hard
Phosphorus	Dull	Not hard (in fact soft)

Question 2.
Can you name The materials which are metals in the table given in the previous question?

Answer:
Yes.

• Iron
• Aluminium
• Copper are metals.

4.1 Physical Properties of Metals and Non-metals

Question 3.
Have you ever seen a blacksmith beating an iron piece or an article made up of iron, like a spade, a shovel, an axe, etc. ? Do you find a change in the shape of these articles on beating? Would you expect a similar change if we try to beat a wood log?

Answer:
Yes, I have seen a blacksmith beating the iron piece/article made up of iron. Yes, their shapes changed on beating. However, if a piece of wood is beaten, it will not change its shape, rather, it would break down into several pieces.

Activity 4.1

Question 1.
Record your observations in Table 4.2 (Textbook, P. 44).

Answer:

Object Material	Change in Shape (Flattens/Breaks into pieces)
Iron nail	Flattens
Coal piece	Breaks into pieces
Aluminium wire	Flattens
Pencil lead	Breaks into pieces

Question 4.
Can we call coal piece and pencil lead as materials?

Answer:
No, because these are not malleable.

Question 5.
Can you hold a hot metallic pan which is without plastic or a wooden handle and not get hurt? Perhaps not! Why?

Answer:
Yes, I will get hurt (with bum) if I hold a hot metallic pan which is without plastic or wooden handle. Plastic and wood are non-conductor of heat. Without the handle, heat from the hot pan will get conducted up to the handle, which in turn will become hot. And that can burn hand of pan holder.

Question 6.
Try to list some other experiences in which a wooden or plastic handle protects you from being hurt while handling hot things. On the basis of these experiences, what can you say about the conduction of heat by wood and plastics. ?

Answer:
Wooden plastic handles are bad conductors of heat. They do not conduct electricity through it.

Question 7.
You must have seen an electrician using his screwdriver. What kind of handle does it have? Why?

Answer:
An Electrician has plastic handle screwdriver. It is because the plastic handle is non-conductor, which does not allow current to pass through his body.

Activity 4.2

Question 1.
Observe and group these materials into good conductors and poor conductors.
Answer:

S.No.	Materials	Good conductor! Poor conductor
1.	Iron rod/nail	Good conductor
2.	Sulphur	Poor conductor
3.	Goal piece	Poor conductor
4.	Copper wire	Good conductor

Question 8.
Where do you find the use of aluminium and copper wire?

Answer:
In the electrical wires of the house¬hold electrification, we can see aluminium and copper wires.

Question 9.
Have you ever noticed the difference in sound on dropping an iron sheet/plate, a metal coin, and a piece of coal on the floor? If not, you can try it now. Do you note any difference in the- sound produced?

Answer:
Yes, the iron sheet/plate and a metal coin when dropped on the floor, produce sharp metallic sound. But, a coal piece, when dropped on the ground, does not produce any metallic sound.

Question 10.
Have you seen wooden bells in temples? Can you give the reason?

Answer:
No, because the wooden bell cannot produce metallic sound (ringing sound) as it is not a metal.

Question 11.
Suppose you have two boxes similar in appearance, one made of wood and the other of metal. Can you tell which box is made of metal by striking both the boxes?

Answer:
On striking the boxes, the box that produces ringing sound is made of metal and others which does not produce such ringing sound is made of wood.

4.2 Chemical Properties of Metals and Non-metals

Question 12.
Recall the reaction by which rust is formed.

Answer:
Rusting takes place on iron when Iron comes in contact with oxygen in presence of water vapour in the atmosphere. Reaction :
3Fe + O₂ + 2H₂O → Fe3O4 + 2H₂ Fe3O4 is rust formed on iron.

Question 13.
Complete the following reactions of iron and magnesium with oxygen. Iron (Fe) + Oxygen (O₂) + Water (H₂O) → ? Magnesium (Mg) + Oxygen (O₂) → ?

Answer:
3Fe + O₂ + 2H₂0 → Fe3O4 + 2H₂
2Mg + O₂ → 2MgO .

Activity 4.3

Question 1.
What do you observe? Is the solution acidic or basic?

Answer:
The red litmus turns blue in this solution, which confirms that the solution is basic in nature.

Question 14.
Does copper also get rusted? I have seen a greenish deposit on the surface of copper vessels.

Answer:
Yes, copper to get rusted. When copper is exposed to moist air for long, it acquires a dull green coating. The green material is a mixture of copper hydroxide [Cu(OH)₂] and copper carbonate (CuCO3).
Reaction :

Question 15.
The ash obtained on burning magnesium ribbon is dissolved in water and tested for its acidic/basic nature. Is . the solution acidic or basic? How do you ascertain this?

Answer:
The solution is basic. This is ascertained by putting red litmus paper in the solution, which turns blue which is the test of the basic nature of the solution.

Activity 4.4

Question 1.
Specify what is formed as the end product What does litmus test reveals, when tested for this aqueous solution?

(1) When sulphur is heated in the air?

Answer:
When sulphur is heated in air sulphur dioxide is formed.
S + O₂ → SO₂

(2) When gas obtained from burning sulphur is dissolved in water?

Answer:
When gas obtained from burning sulphur is dissolved in water, sulphurous acid is formed.
SO₂ + H₂O → H₂SO3
Blue litmus turns red, signifying acidic nature of sulphurous acid (aq).

Question 16.
Recall the name of some of the laboratory acids and bases you have read in Class VII. Note down their names in Table 4.4 (Textbook P. 48). Identify the metal or non-metal present in them which forms oxides with oxygen.

Answer:

S.No.	Name of the base	Metal	Name of the acid	Non­ metal
1.	Calcium Hydroxide	Calcium	Sulphuric acid	Sulphur
2.	Magnesium Hydroxide	Magne­sium	Hydrobromic acid	Hydrobromic acid
3.	Ferric oxide	Iron	Hydrochloric acid	Chlorine
4.	Zinc Hydroxide	Zinc	Nitric acid	Nitrogen
5.	Sodium hydroxide	Sodium	Phosphoric acid	Phosphorus

Activity 4.5

Question 1.
When sodium is made to react with water, what happens to the beaker in which the reaction takes place. Also, verify that the solution is acidic or basic.

Answer:
The beaker becomes very hot because sodium reacts vigorously with water. The solution thus obtained is basic in nature, as it turns red litmus blue.

Question 2.
Why is phosphorus stored in the water?

Answer:
Phosphorus is a very reactive non¬metal. It catches fire if exposed to air. To prevent the contact of phosphorus with atmospheric oxygen, it is stored in water. Generally, non-metals do not react with water though they may be very reactive in air.

Activity 4.6

Question 1.
Record your observations in Table 4.5.

Answer:

Question 17.
Is there a difference in the way metal and non-metal react with acid? What could the ‘pop’ sound in some cases be due to when a burning match stick is brought near the mouth of the test tubes?

Answer:
Yes. Non-metals generally do not react with acids, but metals react with acids and produce hydrogen gas that bums with a ‘pop’ sound on bringing a burning matchstick near the mouth of the test tube.

Question 18.
What could the ‘pop’ sound in some cases be due to when a burning matchstick is brought near the mouth of the test tubes?

Answer:
The Pop sound is produced when a burning matchstick is brought near the mouth of the test tube indicating the presence of hydrogen gas It is the hydrogen gas which burns with the ‘pop’ sound.

Activity 4.8

Question 1.
Record your observations in Table 4.7.

Answer:

Beaker Label
S.no.	Observa­tions	A	B	C	D	E
1.	Colour of solution	Blue colour dis­ appears	Green colour	No change	No change	No change
2.	Appearance of metal	Copper	Copper	Copper	Copper	Iron

Question 19.
Can you guess the sequence of metals from more reactive to less reactive among zinc, iron and copper?

Answer:
Zn > Fe > Cu

Question 20.
What is the basic rule of displacement in a chemical reaction?

Answer:
The rule is :
A non-reactive metal can replace a less reactive metal, but a less reactive one cannot replace a more reactive metal. 4.3 Uses of Metals and Non-metals

Question 21.
Here are some interesting non-metals. We are sure that you will guess them right :

(a) Non-metal essential for our life, which all living beings inhale during breathing,

Answer:
Oxygen

(b) Non-metals used in fertilizers to enhance the growth of plants,

Answer:

• Phosphorus
• Nitrogen

(c) Non-metal used in the water purification process,

Answer:
Chlorine

(d) Non-metal used in the purple coloured solution which is applied on wounds as an antiseptic,

Answer:
Lodine

(e) Non-metals used.in crackers.

Answer:

• Sulphur
• Phosphorus, etc.

Question 22.
I heard that magnesium is found in plants. In what form is it found in them?
Answer:
Magnesium is found in fruits and vegetable of the plants.

Question 23.
The doctor reported an iron deficiency in my body. Where is iron in my body?.
Answer:
In our red blood corpuscles.