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

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

These NCERT Solutions for Class 8 Science Chapter 4 Materials: Metals and Non-Metals Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

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

Class 8 Science Chapter 4 Materials: Metals and Non-Metals Textbook Exercise Questions and Answers

Page 53-55

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.
b. Metals are …………….. conductors of heat and ……………..
c. Iron is …………….. reactive than copper.
d. Metals react with acids to produce …………….. gas.
Answer:
a. reactive,
b. good, electricity,
c. more,
d. hydrogen

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:
a. False
b. True
c. False
d. False

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 N Electricity

Answer:

Properties	Metals	Non-metals
1. Appearance	Lustrous	Dull
2. Hardness	Hard	Soft
3. Malleability	Can be beaten into thin sheets have property of Malleability	Cannot be beaten into thin sheets
4. Ductility	Can be drawn into wires	Cannot be drawn into wires
5. Heat Conduction	Good conductors of heat	Poor conductors of heat
6. Conduction of Electricity	Good conductors of electricity	Poor conductors of electricity

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 reacts with air to make a coating of aluminium oxide on it. This layer prevents aluminium from further reactions with any substance. Due to this, aluminium foils are used to wrap food items because it does not react with food.

b. Metals are good conductors of heat and have a high melting point. Immersion rods need to heat up quickly and should not melt at high temperatures. Hence, immersion rods for heating liquids are made up of metallic substances.

c. Copper is less reactive than zinc. Hence, copper cannot displace zinc from its salt solution.

d. Sodium and potassium are highly reactive and react vigorously with water even at room temperature. The reaction is highly exothermic and the reaction mixture instantly catches fire. Sodium and potassium are stored in kerosene to prevent this reaction and to prevent accidental fire.

Question 7.
Can you store lemon pickle in an aluminium utensil? Explain.
Answer:
No, it is not possible to store lemon pickle in an aluminium utensil because lemon pickle is acidic and can react with aluminium (metal) liberating hydrogen gas. This may spoil the pickle.

Question 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:
(i) → d,
(ii) → e,
(iii) → c,
(iv) → f,
(v) → b,
(vi) → a

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. Copper does not react with dilute sulphuric acid. So, no reaction takes place when dilute sulphuric acid is poured on a copper plate. However, when concentrated sulphuric acid is poured on copper plate, hydrogen gas evolves along with the formation of blue coloured copper sulphate crystals.
Cu + H₂SO₄ (conc.) → CuSO₄ + H₂O
Copper + Dilute sulphuric acid → No reaction

b. When iron nails are placed in copper sulphate solution, the blue colour of copper sulphate solution is replaced by a light green colour. This happens because, iron being more reactive than copper, displaces copper from copper sulphate and makes iron sulphate solution.
Copper sulphate (blue) + Iron → Iron sulphate (light green) + Copper
Fe + CuSO₄ → FeSO₄ + Cu

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. Saloni should bring a wet blue litmus paper near the evolved gas. If litmus paper turns to red, it indicates that the evolved gas is acidic in nature.

b. Carbon (in charcoal) reacts with oxygen to produce carbon dioxide gas.
C + O₂ → CO₂
Carbon dioxide reacts with water to form carbonic acid.
CO₂ + H₂O → H₂CO₃ (acidic)

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:
Jewellers use aqua regia to clean the jewellery. Gold is an inert metal which does not react with acids. But aqua regia is a mixture of hydrochloric acid and nitric acid in 3 : 1 ratio. It is so potent that it even dissolves gold and silver. Some of the gold is thus lost during the cleaning of jewellery. This explains the weight loss in jewellery.

NCERT Extended Learning Activities and Projects

Question 1.
Prepare Index Cards for any four metals and four non-metals. The card should have information like name of metal/non-metal; its physical properties, chemical properties and its uses.
Hint:
Uses of Metals

• Iron metal is used for making cooking vessels, water boilers, stoves, tools, wires, nails, bolts, electromagnets, etc.
• Aluminium is a very light metal so it is used in making the aircraft bodies,
• Copper is most widely used for making electric wires and all things related to electricity because it is a good conductor of electricity,
• Silver is widely used for making jewellery.

Uses of Non-metals

• Phosphorous is used in matchbox industry and in fertilisers,
• Iodine is used as an antiseptic,
• Oxygen is essential for all living beings.
• Sulphur is used for making firecrackers, gun powder and sulphuric acid.

Question 2.
Visit a blacksmith and observe how metals are moulded.
Hint:
Do it yourself.

Question 3.
Suggest an experiment to compare the conductivity of electricity by iron, copper, aluminium and zinc. Perform the experiment and prepare a short report on the results.
Hint:
Let us make a simple circuit by connecting one end of the torch bulb to a cell and another end of torch bulb to an aluminium metal strip or wire and back to the cell (as shown in figure).
Repeat the same activity with different metal strips like iron, copper and zinc.

In the case of copper, we will observe that the bulb glows the fastest and more brightly than others, while in case of iron, the bulb glows the slowest and less brightly than the others.
Hence, the sequential order of their decreasing electrical conductivity is: copper → aluminium → zinc → iron.

Question 4.
Find out the locations of the deposits of iron, aluminium and zinc in India. Mark these in an outline map of India. In which form are the deposits found? Discuss in the class.
Hint:
Iron is found as haematite ore, aluminium as bauxite and zinc as zinc blende or zinc carbonate.

Question 5.
Discuss with your parents/ neighbours/goldsmiths why gold is preferred for making jewellery.
Hint:
Gold is the most ductile and least reactive metal with large amount of lustre.

Activity 1

Objective: To show that the oxides of non¬metals (e.g., sulphur) are acidic in nature.
Materials Required: Powdered sulphur, deflagrating spoon, gas jar, glass cover, water, litmus solution.
Procedure:

• Take a small amount of powdered sulphur in a deflagrating spoon.
• Heat it over a flame.
• As soon as the sulphur starts burning, introduce the spoon into a gas jar.
• Cover the gas jar with a glass cover.
• When the reaction is over, remove the spoon and add 5 mL of water into the jar and replace the glass cover.
• Shake the jar and add about 1 mL blue litmus solution in it.
• Shake it and observe the colour change.

Observation: When the solution of sulphur is mixed with blue litmus, it turns red.
Conclusion: Sulphur is a non-metal and its oxide is acidic in nature.

ii. Reaction with Water:
Metals: When a metal reacts with water, a metal hydroxide and hydrogen gas are formed. Different metals react with water at different temperatures. Some metals react vigorously with water, while some others do not react with water at all.
Metal + Water → Metal hydroxide + Hydrogen

Example: Sodium is a highly reactive metal and reacts vigorously with water. This is a highly exothermic reaction. During this reaction, sodium catches fire because of too much heat being evolved. Due to this, sodium is stored in kerosene to prevent accidental fires.

Non-metals: Generally, non-metals do not react with water though they may be very reactive in air. Some non-metals, such as phosphorus, react with air vigorously. It catches fire if exposed to air. Hence, phosphorus is stored in water.

iii. Reaction with Acids:
Metals: Metals give hydrogen gas every time they react with a dilute acid.
Metal + Acid → Metal salt + Hydrogen
Example: Zinc gives hydrogen gas along with zinc chloride when it reacts with hydrochloric acid.

Similarly, zinc also gives hydrogen gas when it reacts with sulphuric acid.
Also, metals like copper do not react with dilute sulphuric acid even on heating but it reacts with concentrated sulphuric acid.

Non-metals: Non-metals do not react with acids.

Activity 2

Objective: To show the reaction of metals and non-metals with dilute hydrochloric acid and dilute sulphuric acid.
Materials Required: Test tube, metals and non-metals (magnesium ribbon, aluminum foil, iron filings, charcoal and sulphur powder), hydrochloric acid, sulphuric acid and matchbox.
Procedure:

• Take a samples of metals and non-metals in separate test tubes and label them as A, B, C, D and E.
• With the help of a dropper, add 5 mL of dilute hydrochloric acid to each test tube one by one.
• Observe the reaction carefully. If no reaction occurs in the cold solution, warm the test tube gently.
• Bring a burning match stick near the mouth of each test tube.
• Repeat the same activity using dilute sulphuric acid in place of dilute hydrochloric acid.

Observations:

Conclusion: Metals usually displace hydrogen from dilute acids and liberate hydrogen gas while non-metals do not react with dilute acids and no hydrogen gas is evolved.

iv. Reaction with Bases:
Metals: Metals give hydrogen gas when they react with a base. This gas produces a pop sound when a burning matchstick is put above the mouth of the beaker containing reaction mixture.
Example: Aluminium metal reacts with sodium hydroxide to fonn hydrogen gas and sodium aluminate.

Non-metals: Reactions of bases with non-metals are complex.
Aqua regia: It is a freshly-prepared solution of concentrated HCl and concentrated HNO₃ in the ratio of 3 : 1 respectively. It can dissolve even gold and platinum.

Displacement reaction: When a more reactive metal displaces a less reactive metal from its salt solution, it is called a displacement reaction.
Metal A + Salt solution of metal B → Salt solution of metal A + Metal B
In the above equation, metal A is more reactive than metal B, so B will be displaced.

Example 1: When aluminium metal is dipped in the solution of copper sulphate, it forms aluminium sulphate and copper.

Example 2: When iron reacts with solution of copper sulphate, it gives iron sulphate and copper.

In the above two reactions, aluminium and iron are more reactive than copper, that is why they displaced copper from the copper sulphate solution.

Activity 3

Objective: To show displacement reaction with the help of an activity.
Materials Required: Five beakers (100 mL), water, zinc sulphate, iron sulphate, copper sulphate, zinc granules, iron nails and copper turnings
Procedure:

• Take five 100 mL beakers and label them as A, B, C, D and E.
• Take about 50 mL of water in each beaker.
• Dissolve in beakers A and B, a teaspoonful of copper sulphate (CuSO₄), in beakers C, D and E zinc sulphate (ZnSO₄), iron sulphate (FeSO₄) and zinc sulphate (ZnSO₄), respectively.
• Put zinc granules, iron nail, copper turnings, copper turnings and iron nail in beakers A, B, C, D and E, respectively.
• Observe the changes.

Reactions:
A : CuSO₄ + Zn → ZnSO₄ + Cu
B : CuSO₄ + Fe → FeSO₄ + Cu
C : ZnSO₄ + Cu → No change
D : FeSO₄ + Cu → No change
E : ZnSO₄ + Fe → No change

Observation: We see that in beakers A and B, colour is changed while in C, D and E, there is no change of colour. Beakers A and B show displacement reactions.

Conclusion: We have seen that only a more reactive metal displaces a less reactive metal from its salt solution but a less reactive metal does not do so.

Uses of Metals:
i. Metals are used in making wires and sheets, which are used for various purposes. For example, copper and aluminium wires are used for the conduction of electricity, in electrical equipments, etc. Iron wires are used for fencing and various other purposes. Iron sheets are often used for making roof sheds.
ii. Metals are used in making machinery, automobiles, utensils, industrial gadgets, water boilers, etc.
iii. Some metals like iron, sodium and calcium are essential parts of our body.
iv. Alloys: An alloy is a solid mixture of two or more metals or a metal and a non¬metal.
a. Alloys of metals are used in making coins, satellites, stainless steel, wooden ships sheathing and casting. For example, Muntz is an alloy of 60% Cu and 40% Zn. Similarly, brass is an alloy of copper and zinc.
b. Alloys like duralumin, have great strength. It is used in aircrafts, pressure cookers, automobiles, etc. Naval brass is used for marine and engineering castings.

Uses of Non-metals:

• The number of non-metals is very less in comparison to metals, but non-metals are very useful for us. So far, only about 22 non-metals have been discovered.
• Non-metals, such as oxygen, are essential for our life which all living being inhale during breathing.
• Sodium chloride (common salt) cannot be formed without chlorine (a non¬metal) which is a necessary ingredient of our food.
• Non-metals are used in fertilisers to enhance the growth of plants. For example, NPK fertilisers.
• They are also used in water-purification process. Chlorine, a non-metal, is used as a disinfectant in water treatment plants.

Class 8 Science Chapter 4 Materials: Metals and Non-Metals Additional Important Questions and Answers

Very Short Answer Type Questions

Question 1.
Define metal.
Answer:
Metal is usually a hard substance which is lustrous, sonorous, ductile and is a good conductor of heat and electricity.

Question 2.
Define non-metal.
Answer:
Non-metal is a substance which is usually soft, non-lustrous, non-sonorous, non-ductile and is a bad conductor of heat and electricity.

Question 3.
What is lustre?
Answer:
The typical shine of a metal is called lustre.

Question 4.
Name two metals which can be cut with a knife?
Answer:
Sodium and potassium.

Question 5.
Name a non-metal which is a good conductor of electricity.
Answer:
Graphite.

Question 6.
An element forms an oxide which is acidic in nature. Is the element a metal or a non-metal?
Answer:
Non-metal.

Question 7.
Give the chemical equation representing the reaction of iron with oxygen.
Answer:
2Fe + O₂ + H₂O → Fe₂O₃.xH₂O

Question 8.
What is the chemical formula of magnesium oxide?
Answer:
MgO.

Question 9.
Do metals also react with bases?
Answer:
Metals also react with bases like sodium hydroxide and produce hydrogen gas.

Question 10.
What is the chemical formula of copper hydroxide?
Answer:
Cu(OH)₂.

Question 11.
What are metalloids?
Answer:
The elements which show the properties of both metals and non-metals e.g., silicon and arsenic, are called metalloids.

Question 12.
What is a displacement reaction?
Answer:
It is a reaction in which a more reactive metal displaces a less reactive metal from its salt solution.

Question 13.
Give an example of a displacement reaction.
Answer:
CuSO₄ (copper sulphate) + Zn (Zinc) → ZnSO₄ (Zinc sulphate) + Cu (Copper).

Question 14.
Give the name of one metal and one non-metal which exist in liquid state.
Answer:
Mercury (liquid metal) and bromine (liquid non-metal).

Short Answer Type Questions

Question 1.
Copper coins develop greenish patches when kept unused for a long time. Why?
Answer:
When copper is exposed to moist air for a long time, it acquires a greenish coating. The green coat is a mixture of copper hydroxide and copper carbonate which is formed as a result of reaction of copper with moist air.
2Cu + H₂O + CO₂ + O₂ → Cu(OH)₂ + CuCO₃
Due to this, copper coins develop greenish patches when kept unused for a long time.

Question 2.
What happens when a magnesium ribbon is heated in the presence of air?
Answer:
Magnesium bums with a bright dazzling light in the presence of oxygen and forms a white powder of magnesium oxide.
2Mg(s) + O₂(g) → 2MgO(s)

Question 3.
How does a base react with metals and non-metals?
Answer:
Reaction of base with metals and non-metals is as follows:
a. Metals react with bases to produce metal salt and hydrogen gas.
For example: Aluminium + Sodium hydroxide → Sodium aluminate + Hydrogen gas
b. Reaction of non-metals with bases is much complex.

Question 4.
What happens when zinc granules are kept in copper sulphate solution?
Answer:
When zinc granules are kept in copper sulphate solution, the blue colour of copper sulphate disappears and the solution becomes colourless. Zinc is more reactive than copper and hence displaces copper from copper sulphate solution and forms zinc sulphate solution which is colourless.
CuSO₄ (Blue) + Zn → ZnSO₄ (Colourless) + Cu

Question 5.
What happens when copper turnings are kept in zinc sulphate solution?
Answer:
Copper is less reactive than zinc. Hence, copper cannot displace zinc from its salt solution. Hence, no reaction takes place when copper turnings are kept in zinc sulphate solution.

Question 6.
Explain an activity to test the nature of rust.
Answer:
Collect some quantity of rust after a reaction between iron, oxygen and water. Dissolve it in a very little amount of water. Shake the mixture of rust and water well. Test the solution with red and blue litmus papers. It will be observed that the red litmus paper turns blue. It shows that the nature of rust is basic.

Question 7.
Metals are good conductor of electricity. Explain this with the help of an activity.
Answer:
Make an electric circuit as shown in the given figure. The circuit is used to test whether electricity can pass through a given material or not. Repeat this activity with different materials as shown in the table. Observe whether the bulb glows or not in each case and identify whether they are good or bad conductors of electricity.

Materials	Good Conductor/ Poor Conductor
Iron rod/nail	Good Conductor
Sulphur	Poor Conductor
Coal piece	Poor Conductor
Copper wire	Good Conductor

It will be observed that iron rod/nail and copper wire are good conductors while rolled sulphur piece and coal piece are bad conductors.

Question 8.
Explain the reaction of sodium with water with the help of an activity.
Answer:
Take a 250 mL beaker/glass tumbler. Fill half of it with water. Now carefully cut a small piece of sodium metal. Dry it using filter paper and wrap it in small pieces of cotton. Put the sodium piece wrapped in cotton into the beaker. Observe carefully. During observation, keep yourself away from the beaker. When reaction stops, touch the beaker. Now test the solution with red and blue litmus papers. The solution turns red litmus into blue.

This activity indicates that sodium is highly reactive and it reacts vigorously with water. A lot of heat is generated in the reaction to form basic solution of sodium hydroxide.
Sodium + Water → Sodium hydroxide + Heat

Question 9.
Have you ever seen a blacksmith beating an iron piece? Find a change in the shape of these pieces on beating. Would you expect a similar change in a wood log on beating?
Answer:
Yes, we have seen blacksmith beating the iron pieces. We have seen the changes in the shape on beating. It increases in size and it does not break. A similar change in a wood log cannot be expected at all. A wood log will break into pieces if beaten.

Question 10.
State three reasons (of which at least one must be chemical) for believing that sulphur is a non-metal.
Answer:

1. Sulphur is neither malleable nor ductile. It cannot be hammered into sheets or drawn into wires. Sulphur is brittle and breaks into pieces when hammered.
2. Sulphur does not conduct electricity.
3. Sulphur forms an acidic oxide, i.e., sulphur dioxide, hence it is a non-metal.

Question 11.
Concentrated sodium hydroxide solution cannot be stored in aluminum containers. Give reasons.
Answer:
Aluminium metal will react will NaOH base and liberate highly inflammable hydrogen gas.
2Al + 2NaOH + 2H₂O → 2NaAlO₂ + 3H₂
Hence, sodium hydroxide solution cannot be kept in aluminium containers.

Question 12.
What happens when metals react with dilute acids? Write equations of the reactions of magnesium and zinc metals with dilute hydrochloric acid.
Answer:
Metals form their respective salts when they react with dilute acids and liberate hydrogen gas.
Metal + dilute acid → Metal salt + Hydrogen

a. Reaction of magnesium metal with dilute hydrochloric acid:
Magnesium chloride and hydrogen gas are formed when magnesium reacts with dilute hydrochloric acid.
Mg + 2HCl → MgCl₂ + H₂

b. Reaction of aluminium with dilute hydrochloric acid: Aluminium chloride and hydrogen gas are formed.
2Al + 6HCl → 2AlCl₃ + 3H₂

Question 13.
A solution of copper sulphate was kept in an iron pot. After a few days, the iron pot was found to have a number of holes in it. Write the reaction that took place. Explain this reaction.
Answer:
Iron is more reactive than copper. Iron displaces copper from copper sulphate solution and forms iron sulphate. Hence, holes appear on the pot as iron gets dissolved in the solution.
Fe + CuSO₄ (aq) → FeSO₄ (aq) + Cu

Question 14.
Why are aluminium and zinc known as self protecting metals?
Answer:
Aluminium and zinc are self protecting metals because when they come in contact with air, they form their respective oxides that form an impermeable layer on their surface which prevents further attack of air on the metal.

Long Answer Type Questions

Question 1.
What is the difference between the chemical properties of metals and non-metals?
Answer:

Metals	Non-metals
1. Metals react with oxygen and form oxides which are basic in nature.	1. Non-metals react with oxygen to form oxides which are acidic in nature.
2. Metals react with water to form oxides and hydroxides.	2. They generally do not react with water.
3. Metals react with acids to produce hydrogen gas.	3. Non-metals generally do not react with acids.
4. More reactive metals can displace less reactive metals from their salt solutions.	4. They cannot displace less reactive metals from their salt solutions.

Question 2.
State five uses each of metals and non-metals.
Answer:
Uses of metals:

• Lead metal is used in making car batteries.
• Zinc is used for galvanizing iron to protect it from rusting.
• Iron, copper and aluminium are used to make utensils.
• Copper and aluminium metals are used to make electrical wires.
• Aluminium is used to make aluminium foil for packing food materials.

Uses of non-metals:

• Hydrogen is used in the hydrogenation of vegetable oils.
• Carbon is used to make electrodes of electrolytic cells and dry cells.
• Nitrogen is used in the manufacture of ammonia, nitric acid and fertilisers.
• Sulphur is used for producing sulphuric acid.
• Liquid hydrogen is used as rocket fuel.

Question 3.
You are given samples of three metals-sodium, magnesium and copper. Suggest any two activities to arrange them in order of their decreasing reactivities.
Answer:
a. Activity 1: When sodium, magnesium and copper are left in air, sodium reacts vigorously with oxygen to form sodium oxide, magnesium reacts with oxygen to form magnesium oxide only on heating, whereas copper does not bum in air even on strong heating. It reacts only on prolonged heating. This shows that sodium is most reactive, then magnesium and copper is the least reactive among the three.

b. Activity 2: Sodium reacts vigorously with cold water to form sodium hydroxide and hydrogen, magnesium does not react with cold water but reacts with hot water to form magnesium hydroxide and hydrogen but copper does not react even with steam. This shows that sodium is highly reactive, magnesium is less reactive than sodium and copper is the least reactive among the three.

Picture-Based Questions

Question 1.
Observe the given diagram and answer the following questions:

a. Which property of metals is shown by this diagram?
b. Name two metals, other than iron, which have this property.
c. Name a non-metal which has this property.
Answer:
a. The given diagram shows the property of electrical conductivity of metals.
b. Copper and silver.
c. Graphite.

Question 2.
Observe the given figure and answer the following questions:

a. Which property of metals is shown in the figure?
b. Names the articles shown in the figure.
c. Name two metals which show this property.
d. Name two metals which lack this property.
Answer:
a. In the given figure, the property of malleability of a metal is shown.
b. Hammer and iron nails.
c. Gold and silver.
d. Sodium and potassium.

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