Extra 20 long answer questions with answers from Chapter: 3 Metals and Non-Metals of Class 10 CBSE Science:

 

Chapter 3, "Metals and Non-metals," is arguably one of the most important chapters in the Chemistry section. It provides a detailed comparison of the physical and chemical properties of these two major categories of elements and introduces the fundamental concept of ionic bonding and the applied science of metallurgy.

 

Weightage in the Board Exam (Approximate)

"Metals and Non-metals" is a core part of Unit I: Chemical Substances – Nature and Behaviour, which accounts for approximately 25 marks in the 80-mark theory paper.

Individual Weightage: Chapter 3 is considered one of the highest-weightage chapters in the entire Science syllabus, typically carrying around 7 to 10 marks in the board exam.

 

Explain the physical properties of metals and non-metals with examples.

 

Ans:

Metals:

 

Malleability

: Can be hammered into sheets (e.g., Gold, Aluminium).

Ductility

: Can be drawn into wires (e.g., Copper, Silver).

Lustrous

: Have a shiny surface (e.g., Gold, Silver).

Good conductors of heat & electricity

(e.g., Copper, Silver).

High melting & boiling points

(e.g., Iron, Tungsten).

Non-Metals:

 

Brittle

: Breaks easily (e.g., Sulphur, Phosphorus).

Poor conductors of heat & electricity

(e.g., Carbon except Graphite).

Dull appearance

(e.g., Iodine is an exception).

Low melting & boiling points

(except Diamond).

 

What happens when metals react with acids, bases, water, and oxygen? Give examples.

 

Ans:

With Acids:

Forms

salt and hydrogen gas

 

Zn+2HCl→ZnCl2​+H2​

With Bases:

Forms

salt and hydrogen gas

(only some metals)

 

Zn+NaOH→Na2​ZnO2​+H2​

With Water:

 

Highly reactive metals

(e.g., Na, K) react violently.

 

2Na+2H2​O→2NaOH+H2​

Less reactive metals

(e.g., Fe) react slowly.

 

Fe+H2​O→Fe3​O4​+H2​

With Oxygen:

Forms

metal oxides

 

4Al+3O2​→2Al2​O3​

 

What is corrosion? Explain rusting of iron and how it can be prevented.

 

Ans:

Corrosion

is the gradual deterioration of metals due to environmental factors like moisture and air.

Rusting of Iron:

Iron reacts with

water and oxygen

to form

hydrated iron oxide (

Fe₂O

₃·

xH₂O

)

, which is rust.

 

4Fe+3O2​+6H2​O→4

Fe(

OH)3​

Prevention of Rusting:

 

Painting and Oiling

(Prevents air and moisture contact).

Galvanization

(Coating iron with zinc).

Alloying

(Stainless steel).

 

Explain the process of electrolytic refining of metals.

 

Ans:

Used for purifying metals like

Copper, Zinc, Aluminium

.

Process:

 

Anode

: Impure metal

Cathode

: Pure metal sheet

Electrolyte

: Metal salt solution (e.g.,

CuSO

₄ for copper).

Reaction at anode

:

 

Cu→Cu2++2e−

Reaction at cathode

:

 

Cu2++2e−→Cu

Impurities settle as anode mud.

 

Describe the uses of alloys and give examples.

 

Ans:

Alloys

are mixtures of metals to improve strength, corrosion resistance, and conductivity.

Examples:

 

Brass (Cu + Zn)

: Used in electrical fittings.

Bronze (Cu + Sn)

: Used in statues and medals.

Stainless Steel (Fe + Cr + Ni)

: Used in utensils.

 

Differentiate between roasting and calcination with examples.

 

Ans:

Roasting

: Heating

sulphide ores

in the presence of

oxygen

.

 

ZnS+O2​→ZnO+SO2​

Calcination

: Heating

carbonate ores

in the absence of oxygen.

 

CaCO3​→CaO+CO2​

 

What are the different methods of metal extraction?

 

Ans:

Hydraulic Washing

: Uses water to remove impurities.

Froth Flotation

: Used for sulphide ores (e.g., ZnS).

Magnetic Separation

: Removes magnetic impurities.

Roasting & Calcination

: Converts ores to oxides.

Electrolysis

: Used for highly reactive metals (e.g., Na, Al).

 

Explain how metals are arranged in the reactivity series and its significance.

 

Ans:

Metals are arranged in order of decreasing reactivity:

 

K > Na > Ca > Mg > Al > Zn > Fe > Pb > Cu > Ag > Au

Significance:

 

More reactive metals

displace less reactive metals from compounds.

Determines metal extraction process.

 

What is an amphoteric oxide? Give examples and reactions.

 

Ans:

Oxides that react with both

acids and bases

.

Examples:

 

Al₂O

₃,

ZnO

 

Al2​O3​+6HCl→2AlCl3​+3H2​O

 

Al2​O3​+2NaOH→2NaAlO2​+H2​O

 

Why are sodium and potassium stored in kerosene?

 

Ans:

Sodium and potassium react violently with

air and water

, producing heat and catching fire.

Storing in kerosene prevents these reactions.

 

11. Explain the process of obtaining pure metal from its ore.

Ans: The extraction of metals from ores involves three main steps:

Concentration of Ore:

Hydraulic Washing

– Uses water to remove impurities.

Froth Flotation

– Used for sulphide ores like ZnS.

Magnetic Separation

– Separates magnetic ore from impurities.

Extraction of Metal:

Roasting (For Sulphide Ores)

– Heating in the presence of oxygen (e.g., ZnS →

ZnO

).

Calcination (For Carbonate Ores)

– Heating in the absence of oxygen (e.g.,

CaCO

₃ →

CaO

+ CO₂).

Electrolysis

– Used for highly reactive metals like Al and Na.

Refining of Metal:

Electrolytic Refining

– Used for Cu, Al, Zn, etc.

Distillation & Liquation

– Used for metals with different boiling/melting points.

 

12. How does iron react with steam, dilute acids, and moist air?

Ans:

With Steam:

Iron forms iron oxide and hydrogen gas.

 

3Fe+4H2​O→Fe3​O4​+4H2​

With Dilute Acids:

Iron reacts with dilute acids to form iron salts and hydrogen gas.

 

Fe+2HCl→FeCl2​+H2​

With Moist Air (Rusting):

Iron reacts with oxygen and water to form rust.

 

4Fe+3O2​+6H2​O→4

Fe(

OH)3​

 

13. Why is aluminium used for making aircraft and electrical cables?

Ans:

For Aircraft:

Aluminium is

lightweight

(low density).

It has

high tensile strength

.

It is

resistant to corrosion

due to an oxide layer.

For Electrical Cables:

Aluminium is a

good conductor of electricity

.

It is

cheaper than copper

.

It is

ductile

, making it easy to draw into wires.

 

14. Why does silver turn black and copper turn green? Explain the chemical reactions.

Ans:

Silver Turns Black:

Silver reacts with

hydrogen sulphide (H₂S)

in the air, forming

silver sulphide (

Ag₂S

)

.

 

2Ag+H2​S→Ag2​S+H2​

Copper Turns Green:

Copper reacts with

carbon dioxide, oxygen, and water

to form

copper carbonate (

CuCO

₃) and copper hydroxide (

Cu(

OH)₂)

.

 

2Cu+O2​+H2​O+CO2​→CuCO3​

⋅

Cu(OH)2​

 

15. Describe the process of galvanization and its importance.

Ans:

Galvanization

is the process of

coating iron with zinc

to prevent rusting.

Importance:

Zinc forms a

protective layer

that prevents iron from reacting with moisture and oxygen.

If the layer is scratched, zinc undergoes

sacrificial protection

, preventing iron from rusting.

Reaction:

Zinc forms

zinc oxide

when exposed to air:

 

2Zn+O2​→2ZnO

Uses:

Galvanized iron is used in

railings, pipes, and automobile parts

.

 

16. Differentiate between metals and non-metals based on chemical properties.

Ans:

Property	Metals	Non-Metals
Reaction with Oxygen	Forms basic oxides (e.g., Na₂O)	Forms acidic oxides (e.g., CO₂)
Reaction with Water	Produces metal hydroxide and hydrogen (e.g., NaOH)	Generally does not react
Reaction with Acids	Produces salt and hydrogen gas (e.g., Zn + HCl)	No reaction
Electrical Conductivity	Good conductors (e.g., Cu, Al)	Poor conductors (except graphite)
Malleability	Malleable and ductile	Brittle

 

17. How does carbon help in metal extraction? Explain with an example.

Ans:

Carbon is used as a

reducing agent

to extract metals from their oxides.

Example:

Extraction of iron in a blast furnace:

Iron ore (

Fe₂O

₃) is reduced by carbon monoxide (CO):

 

Fe2​O3​+3CO→2Fe+3CO2​

Coke (C) also reduces

Fe₂O

₃:

 

Fe2​O3​+3C→2Fe+3CO

Carbon is used in extracting metals like

Iron, Zinc, and Lead

from their oxides.

 

18. Explain why graphite is used in lubricants and electrical conductors.

Ans:

Graphite as a Lubricant:

Weak van der Waals forces

between layers allow easy sliding.

Used in

machine parts and locks

.

Graphite as an Electrical Conductor:

Contains

free electrons

that allow electricity to flow.

Used in

electrodes of batteries and arc lamps

.

 

19. Describe how the activity series of metals is useful in displacement reactions.

Ans:

The

reactivity series

of metals arranges metals in order of decreasing reactivity:

 

K > Na > Ca > Mg > Al > Zn > Fe > Pb > Cu > Ag > Au

Significance in Displacement Reactions:

A

more reactive metal

can displace a

less reactive metal

from its salt solution.

Example:

 

Zinc displaces Copper from

CuSO

₄ solution:

 

Zn+CuSO4​→ZnSO4​+Cu

Iron displaces Copper from

CuSO

₄ solution:

 

Fe+CuSO4​→FeSO4​+Cu

 

20. How does chlorine help in water purification? Explain with a chemical reaction.

Ans:

Chlorine is a

strong oxidizing agent

that kills

bacteria, viruses, and germs

in water.

It reacts with water to form

hypochlorous acid (

HOCl

)

, which destroys pathogens.

 

Cl2​+H2​

O→HOCl+HCl

Uses:

Disinfecting

drinking water

.

Used in

swimming pools

to prevent bacterial growth.