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

 

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+H2Zn + 2HCl →

ZnCl

₂ + H₂Zn+2HCl→ZnCl2​+H2​

With Bases:

Forms

salt and hydrogen gas

(only some metals)

 

Zn+NaOH→Na2ZnO2+H2Zn + NaOH →

Na₂ZnO

₂ + H₂Zn+NaOH→Na2​ZnO2​+H2​

With Water:

 

Highly reactive metals

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

 

2Na+2H2O→2NaOH+H22Na + 2H₂O → 2NaOH + H₂2Na+2H2​O→2NaOH+H2​

Less reactive metals

(e.g., Fe) react slowly.

 

Fe+H2O→Fe3O4+H2Fe + H₂O →

Fe₃O

₄ + H₂Fe+H2​O→Fe3​O4​+H2​

With Oxygen:

Forms

metal oxides

 

4Al+3O2→2Al2O34Al + 3O₂ → 2Al₂O₃4Al+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+6H2O→4

Fe(

OH)34Fe + 3O₂ + 6H₂O → 4Fe(OH)₃4Fe+3O2​+6H2​O→4Fe(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−Cu → Cu²⁺ + 2e⁻Cu→Cu2++2e−

Reaction at cathode

:

 

Cu2++2e−→CuCu²⁺ + 2e⁻ → CuCu2++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+SO2ZnS + O₂ →

ZnO

+ SO₂ZnS+O2​→ZnO+SO2​

Calcination

: Heating

carbonate ores

in the absence of oxygen.

 

CaCO3→CaO+CO2CaCO₃ →

CaO

+ CO₂CaCO3​→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

 

Al2O3+6HCl→2AlCl3+3H2OAl₂O₃ + 6HCl → 2AlCl₃ + 3H₂OAl2​O3​+6HCl→2AlCl3​+3H2​O

 

Al2O3+2NaOH→2NaAlO2+H2OAl₂O₃ + 2NaOH → 2NaAlO₂ + H₂OAl2​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+4H2O→Fe3O4+4H23Fe + 4H₂O →

Fe₃O

₄ + 4H₂3Fe+4H2​O→Fe3​O4​+4H2​

With Dilute Acids:

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

 

Fe+2HCl→FeCl2+H2Fe + 2HCl →

FeCl

₂ + H₂Fe+2HCl→FeCl2​+H2​

With Moist Air (Rusting):

Iron reacts with oxygen and water to form rust.

 

4Fe+3O2+6H2O→4

Fe(

OH)34Fe + 3O₂ + 6H₂O → 4Fe(OH)₃4Fe+3O2​+6H2​O→4Fe(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+H2S→Ag2S+H22Ag + H₂S →

Ag₂S

+ H₂2Ag+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+H2O+CO2→CuCO3

⋅

Cu(OH)22Cu + O₂ + H₂O + CO₂ →

CuCO

₃·Cu(OH)₂2Cu+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→2ZnO2Zn + O₂ → 2ZnO2Zn+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):

 

Fe2O3+3CO→2Fe+3CO2Fe₂O₃ + 3CO → 2Fe + 3CO₂Fe2​O3​+3CO→2Fe+3CO2​

Coke (C) also reduces

Fe₂O

₃:

 

Fe2O3+3C→2Fe+3COFe₂O₃ + 3C → 2Fe + 3COFe2​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+CuZn +

CuSO

₄ →

ZnSO

₄ + CuZn+CuSO4​→ZnSO4​+Cu

Iron displaces Copper from

CuSO

₄ solution:

 

Fe+CuSO4→FeSO4+CuFe +

CuSO

₄ →

FeSO

₄ + CuFe+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+H2O→HOCl+HClCl₂ + H₂O →

HOCl

+ HClCl2​+H2​

O→HOCl+HCl

Uses:

Disinfecting

drinking water

.

Used in

swimming pools

to prevent bacterial growth.