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Living Science Solutions for Class 8 Science Chapter 4 - Metals And Non Metals

Living Science Solutions for Class 8 Science Chapter 4 Metals And Non Metals are provided here with simple step-by-step explanations. These solutions for Metals And Non Metals are extremely popular among class 8 students for Science Metals And Non Metals Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Living Science Book of class 8 Science Chapter 4 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Living Science Solutions. All Living Science Solutions for class 8 Science are prepared by experts and are 100% accurate.

Page No 60:

Question 1:

Which of the following is true for all metals?
(a) They are hard solids.
(b) They have high melting and boiling points.
(c) They have 1−3 valence electrons.
(d) They are malleable and ductile.

Answer:

(c) They have 1-3 valence electrons.
All the metals have 1-3 electrons in their valence shell and they lose their valence electrons to form positive ions. However, other properties like hardness, high melting and boiling points, malleability and ductility are not shown by all metals. Even though sodium and potassium are solids, they are soft, non-malleable and non-ductile metals. Further, they have low melting and boiling points. Similarly, mercury is found in liquid state at room temperature.

Page No 60:

Question 2:

Gold normally occurs in nature
(a) in free state.
(b) as carbonate ore.
(c) as sulphate ore.
(d) as sulphide ore.

Answer:

(a) in free state
Gold is an inert metal and doesn't react easily, therefore, it occurs in free state in nature.

Page No 60:

Question 3:

Which of these is the most reactive metal?
(a) magnesium
(b) gold
(c) platinum
(d) sodium

Answer:

(d) Sodium
Sodium reacts vigorously with oxygen and water at room temperature by catching fire. It is considered highly reactive and placed at the top in the reactivity series. It is stored under kerosene to prevent reaction.

Page No 60:

Question 4:

Which of these metals cannot displace hydrogen from a dilute acid?
(a) iron
(b) zinc
(c) silver
(d) calcium

Answer:

(c) silver

Silver cannot displace hydrogen from a dilute acid because it is a less reactive noble metal and does not react with acids.

Page No 60:

Question 5:

Which one of the following alloys is light and strong?
(a) brass
(b) stainless steel
(c) duralium
(d) bronze

Answer:

(c) duralumin

Duralumin contains aluminium, copper, magnesium and manganese. These constituents make this alloy light and strong. Therefore, it is used in the construction of airplane and vehicle bodies. 



Page No 61:

Question 6:

Which metal is higher up in the reactivity series − sodium or silver?

Answer:

Sodium, being highly reactive metal, is placed high in the reactivity series, whereas silver, being very less reactive metal, is placed low in the reactivity series.

Page No 61:

Question 7:

Any rock containing metallic mineral is called an ore. True or false?

Answer:

False. Any rock containing metallic mineral is not an ore as it depends on the quantity of metal in the rock. If the quantity of metal in the rock is less, it cannot be extracted profitably. Thus, rocks containing metallic minerals in adequate quantity, from which metals can be extracted profitably, are called ores.

Page No 61:

Question 8:

__________ is the most abundant element in the universe, whereas __________ is the most abundant element in the earth's crust.

Answer:


Hydrogen is the most abundant element in the universe, whereas oxygen is the most abundant element in the earth's crust.

Page No 61:

Question 9:

Sand contains the non-metals __________ and __________

Answer:

Sand contains the non-metals silicon and oxygen.

Page No 61:

Question 10:

Which non-metal has very high melting and boiling points?

Answer:

Graphite is a non-metal, which has very high melting and boiling points.

Page No 61:

Question 1:

Name a metal which is liquid at room temperature.

Answer:

Mercury (Hg) is liquid at room temperature.

Page No 61:

Question 2:

Metals generally have a low specific gravity. True or false?

Answer:

False.
Metals generally have a very high specific gravity. Metals like iron, lead, mercury, gold etc. have specific gravity values greater than 7.5. However, sodium and potassium are the only metals with a specific gravity value below 1. 

Page No 61:

Question 3:

If a material can be drawn into thin wires, it is said to be __________

Answer:


If a material can be drawn into thin wires, it is said to be ductile.

Page No 61:

Question 4:

Aluminium does not react with water. True or false?

Answer:

False.
Aluminium reacts with water to form a thin layer of aluminium oxide on it. This thin coating of aluminium oxide on aluminium acts as a barrier and stops further reactions.

Page No 61:

Question 5:

Zn + CuSO4 → ZnSO4 + Cu is an example of a __________ reaction.

Answer:

Zn + CuSO4 → ZnSO4 + Cu is an example of a displacement reaction.

Page No 61:

Question 11:

Metal food containers have a coating of __________

Answer:

Metal food containers have a coating of tin (Sn).

Page No 61:

Question 12:

Name a soft metal.

Answer:

Sodium is a soft metal, which can be cut easily with the help of a knife.

Page No 61:

Question 13:

What is the black material inside a pencil?

Answer:

The black material inside a pencil is graphite, an allotrope of carbon (non-metal).

Page No 61:

Question 14:

Metals react with oxygen to produce __________ oxides, and non-metals react with oxygen to produce __________ oxides.

Answer:

Most metals react with oxygen to produce basic oxides and non-metals react with oxygen to produce acidic oxides.

Page No 61:

Question 15:

Do non-metals react with water?

Answer:

No, non-metals do not react with water. Hence, highly reactive non-metals such as phosphorous, which catch fire when exposed to air, are stored under water.

Page No 61:

Question 16:

A metal X can replace another metal Y from its metal salt. Is X above or below Y in the reactivity series?

Answer:

X is above Y in the reactivity series. A more reactive metal can displace a less reactive metal from its salt solution. More reactive metals are placed at the top of the reactivity series and can displace other metals below them in the reactivity series.

Page No 61:

Question 17:

The presence of air and __________ are necessary for iron to rust.

Answer:

The presence of air and moisture are necessary for iron to rust.

Page No 61:

Question 18:

Galvanized iron starts rusting if there is a scratch on the zinc layer. True or false?

Answer:

False.
Galvanised iron does not rust even if there is a scratch on the zinc layer. Even if there is a scratch, zinc reacts with atmosphere and forms sacrificial layer of zinc carbonate, which provides protection against corrosion.

Page No 61:

Question 19:

Copper corrodes in the presence of __________ and water.

Answer:

Copper corrodes in the presence of carbon dioxide and water.

Page No 61:

Question 20:

Name a metal that does not corrode in air.

Answer:

Gold does not corrode in air. It is the least reactive metal. Hence, gold jewellery glitters even after many years.



Page No 62:

Question 1:

What do you mean by malleability and ductility? How are these properties different in metals and non-metals?

Answer:

The property of a substance to be hammered into thin sheets is called malleability. The property of a substance to be stretched into thin wires is called ductility. The property of malleability and ductility differs in metals and non-metals. Most of the metals have high degree of malleability and ductility; for example, aluminium, copper, gold, etc. However, non-metals are highly brittle and do not exhibit these properties; for example, coal and graphite (both contain carbon).

Page No 62:

Question 2:

Give three examples of reactions between metals and water, to show that different metals have different reactivities.

Answer:

Metals react with water to form oxides or hydroxides with release of hydrogen gas.

1. Sodium and potassium react vigorously even with cold water producing hydroxides with release of enormous heat.
 
   2 NaSodium + 2 H2OWater  2 NaOHSodium hydroxide + H2Hydrogen2 KPotassium + 2 H2OWater  2 KOHPotassium hydroxide + H2Hydrogen      
                       
2. Magnesium does not react with cold water, but reacts with hot water or steam to form magnesium oxide.
     
 
2 MgMagnesium + 2 H2OWater  2 MgOMagnesium oxide + 2 H2Hydrogen
                                       
3.
Aluminium reacts with water to form a thin layer of aluminium oxide on it. This thin coating of aluminium oxide on aluminium acts as a barrier and stops further reactions.

2 AlAluminium + 3 H2OWater  Al2O3Aluminium oxide + 3H2Hydrogen

From the above examples, we can say that sodium and potassium are highly reactive, magnesium is less reactive and aluminium is least reactive. This shows that different metals have different reactivities with water.

Page No 62:

Question 3:

Give the important uses of copper.

Answer:

Important uses of copper are:
i. Copper is commonly used in electric cables and wires. It is also used as coil in many electrical appliances.
ii. It is used to prepare utensils, calorimeters and car radiators.
iii. It is also used to form alloys such as brass, bronze, which are hard and corrosion resistant with many uses.

Page No 62:

Question 4:

Aluminium protects itself against corrosion. Discuss why it is necessary to anodize aluminium to make it corrosion resistant.

Answer:

Aluminium reacts with air and forms a thin layer of aluminium oxide on it. This layer of oxide prevents further reactions and protects the metal from corrosion. This is how aluminium protects itself against corrosion. 
4 Al + 3 O2  2 Al2O3
But this oxide layer is not uniform and may lead to corrosion over a period of time. If it is more uniform, the metal below the layer would be well-protected. This can be made with the help of a process called anodising. In this process, electric current is passed through sulphuric acid, utilising aluminium as anode. Oxygen, which is liberated at anode, reacts with aluminium and forms a uniform oxide layer of aluminium, which protects the metal from corrosion. This is why anodising of aluminium is essential.

Page No 62:

Question 5:

List three important uses of hydrogen.

Answer:

Three important uses of hydrogen are:
i. Hydrogen is mainly used in the manufacture of ammonia, which is further used to prepare fertilisers like urea, ammonium sulphate etc.
ii. It is used in the extraction of metals such as copper, lead, tungsten, tin; for example, hydrogen is used as a reducing agent in the reduction of tungsten oxide to purify tungsten during extraction.
iii. It is used in cutting and welding of metals in industries. When hydrogen is burnt in oxygen, an oxy-hydrogen flame is obtained by which cutting and welding of metal is performed. 

Page No 62:

Question 6:

List three uses of silicon.

Answer:

Three uses of silicon are:
i. Silicon is widely used in electronic and computer industries for the manufacturing of transistors, integrated chips and solar cells.
ii. Silicones, a compound of silicon, is used in the manufacturing of grease, polish and water-proof materials. They are also used as insulating materials in electrical equipments.
iii. Silicon carbide, a component of silicon, is used as an abrasive material.

Page No 62:

Question 7:

Can alloying be used to lower the melting point? Give an example.

Answer:

Yes, alloying can be used to lower the melting point. Solder, an alloy of tin and lead, has a low melting point than that of tin and lead. Thus, this property of solder is helpful for copper wires to be used as a fuse in an electrical circuit. Hence, alloying helps to change the properties of a metal.

Page No 62:

Question 8:

How is anodizing of aluminium carried out?

Answer:

Aluminium reacts with air and forms a thin layer of aluminium oxide on it. This layer of oxide prevents further reactions and protects the metal from corrosion. If this oxide layer formation is more uniform, the metal below the layer would be well-protected. This can be formed with the help of a process called anodising. In this process, electric current is passed through sulphuric acid, utilising aluminium as anode. Oxygen is liberated at anode and it reacts with aluminium and forms a uniform oxide layer of aluminium, which protects the metal from corrosion. This is how anodising of aluminium is done.



Page No 63:

Question 4:

It has been noticed that silverware becomes black faster today than it did fifty years ago. What can be the reason for this?

Answer:

Silverwares become black due to the formation of a thin layer of silver sulphide on them by reacting with hydrogen sulphide present in the air.
2 Ag + H2S  Ag2S + H2
Fifty years ago, the presence of hydrogen sulphide in the air was very less due to pollution free environment. Thus, silver objects did not become black faster. Now a days, industrial revolution and excessive usage of automobiles have increased the percentage of sulphur in air. This has further increased the percentage of hydrogen sulphide leading to fading or blackening of silver objects faster.

Page No 63:

Question 5:

Aluminium is above iron in the reactivity series. However, its reactions with oxygen and water seem to indicate that it is less reactive than iron. Explain.

Answer:

Aluminium is above iron in the reactivity series. However, its reactions with oxygen and water seem to indicate that it is less reactive than iron due to the following reason:

Aluminium reacts with air and forms a thin layer of aluminium oxide on it. 
 
4 Al Aluminium+ 3 O2Oxygen  2 Al2O3Aluminium oxide2 Al Aluminium+ 3 H2OWater  Al2O3Aluminium oxide + 3 H2Hydrogen

This layer of oxide prevents further reactions, making aluminium less reactive. This layer also protects the metal from corrosion. This is how aluminium protects itself against corrosion.

Page No 63:

Question 6:

If you are an engineer constructing a multi-storey building. Which alloy would you be extensively using and why?

Answer:

The alloy that is used extensively during the construction of buildings is steel, which is an alloy of iron and carbon. Steel is very strong and its usage makes the building strong and sturdy.

Page No 63:

Question 7:

A doctor diagnosed a patient with iron deficiency, and gave him tablets containing iron. But the tablets were not hard and did not look like iron at all. What do you think the tablets contained?

Answer:

The tablets do contain iron but the iron is in the ionic form (Fe2+ as soluble ferrous ion). Such an iron in ionic form is easily absorbed by our body. It does not retain the property of hardness, which a metallic iron has. Therefore, iron tablets are not hard or look like metallic iron.



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