Extra 20 long-answer questions with answers from Chapter:4 Carbon and its Compounds for Class 10 CBSE Science:
Explain the versatile nature of carbon. Why does carbon form covalent bonds?
Ans:
Carbon exhibits
catenation
(forms long chains).
It has
4 valence electrons
and cannot easily lose/gain electrons, so it shares electrons forming
covalent bonds
.
Forms
single, double, and triple bonds
(e.g., alkanes, alkenes, alkynes).
Can form
straight, branched, or ring structures
, leading to diversity in compounds.
Differentiate between saturated and unsaturated hydrocarbons. Give examples.
Ans:
|
Property |
Saturated Hydrocarbons |
Unsaturated Hydrocarbons |
|---|---|---|
|
Bonding |
Single bonds only |
Double or triple bonds present |
|
Type |
Alkanes (CnH2n+2) |
Alkenes (CnH2n) & Alkynes (CnH2n-2) |
|
Example |
Methane (CH4), Ethane (C2H6) |
Ethene (C2H4), Ethyne (C2H2) |
|
Reactivity |
Less reactive |
More reactive |
|
Addition Reaction |
Not possible |
Possible |
What are the different allotropes of carbon? Explain their structures and properties.
Ans:
Diamond:
Hard, transparent, non-conductor, used in
jewelry
and cutting tools.
Graphite:
Soft, black, conductor, used in pencils and lubricants.
Fullerenes:
Spherical molecules (e.g., C60), used in nanotechnology.
Explain the concept of a homologous series with an example.
Ans:
A
homologous series
is a group of organic compounds having the same
functional group
and a general formula.
Members differ by
CH2
unit.
Example:
Alkanes
(CnH2n+2)
Methane (CH4)
Ethane (C2H6)
Propane (C3H8)
What are functional groups? Explain with examples.
Ans:
Functional groups are
specific groups of atoms
that define the properties of organic compounds.
Examples:
Alcohol (-OH):
Ethanol (C2H5OH)
Carboxyl (-COOH):
Ethanoic acid (CH3COOH)
Aldehyde (-CHO):
Methanol
(HCHO)
What is ethanol? Write its properties and two reactions.
Ans:
Formula:
C2H5OH
Properties:
Liquid,
colourless
, soluble in water, burns with a blue flame.
Reactions:
With Sodium:
2C2H5OH+2Na→2C2H5ONa+H22C2H5OH + 2Na → 2C2H5ONa + H22C2H5OH+2Na→2C2H5ONa+H2
Combustion:
C2H5OH+O2→CO2+H2O+HeatC2H5OH + O2 → CO2 + H2O + HeatC2H5OH+O2→CO2+H2O+Heat
Describe the hydrogenation of vegetable oils.
Ans:
Unsaturated fats are
converted into saturated fats
by adding hydrogen in the presence of a
nickel catalyst
.
Example:
C2H4+H2→C2H6C2H4 + H2 → C2H6C2H4+H2→C2H6
What is esterification? Explain with an equation.
Ans:
Esterification is the reaction between an
alcohol
and a
carboxylic acid
to form an
ester
.
Example:
CH3COOH+C2H5OH→CH3COOC2H5+H2OCH3COOH + C2H5OH → CH3COOC2H5 + H2OCH3COOH+C2H5OH→CH3COOC2H5+H2O
Write a short note on soaps and detergents. How do they work?
Ans:
Soap:
Made from
fats and oils
, works poorly in hard water.
Detergent:
Made from
petroleum products
, works in hard and soft water.
Mechanism:
Forms
micelles
, trapping dirt inside hydrophobic tails.
10. Explain the versatility of carbon. Why does it form covalent bonds?
Ans:
Carbon is a unique element that forms millions of compounds due to:
Catenation
– Carbon can form long chains, branched chains, and ring structures by bonding with itself (e.g., alkanes, alkenes, alkynes).
Tetravalency
– Carbon has
4 valence electrons
and forms
four covalent bonds
(C–C, C–H, etc.), leading to stable structures.
Ability to form multiple bonds
– Carbon can form
single, double, and triple bonds
(e.g., ethane C2H6, ethene C2H4, ethyne C2H2).
Covalent bonding
– Carbon cannot donate or accept 4 electrons, so it
shares electrons
, forming
stable covalent bonds
.
11. Differentiate between alkanes, alkenes, and alkynes. Explain with examples.
Answer:
|
Type |
General Formula |
Bond Type |
Example |
Structure |
|---|---|---|---|---|
|
Alkanes |
CnH2n+2 |
Single Bonds |
Methane (CH4), Ethane (C2H6) |
H–C–H |
|
Alkenes |
CnH2n |
One Double Bond |
Ethene (C2H4), Propene (C3H6) |
H2C=CH2 |
|
Alkynes |
CnH2n-2 |
One Triple Bond |
Ethyne (C2H2), Propyne (C3H4) |
HC≡CH |
Alkanes are saturated hydrocarbons, while alkenes and alkynes are unsaturated hydrocarbons.
12. What are isomers? Explain with examples of butane and isobutane.
Answer:
Isomers
are compounds that have the
same molecular formula
but
different structures and properties
.
Example: Butane (C4H10) has two isomers:
n-Butane:
Straight-chain structure.
Iso-butane:
Branched structure.
Significance:
Isomerism leads to a variety of compounds with different properties, even though their molecular formulas are the same.
13. Explain the concept of a homologous series with examples.
Answer:
Homologous series
refers to a group of compounds with:
Same functional group
Same general formula
Similar chemical properties
Differ by CH2 unit
Example:
Alcohols (–OH functional group)
Methanol: CH3OH
Ethanol: C2H5OH
Propanol: C3H7OH
Butanol: C4H9OH
14. What happens when ethanol reacts with sodium? Give the equation and explain.
Answer:
When ethanol reacts with sodium, hydrogen gas is liberated, and sodium ethoxide is formed.
2C2H5OH+2Na→2C2H5ONa+H22C2H5OH + 2Na → 2C2H5ONa + H22C2H5OH+2Na→2C2H5ONa+H2
Sodium reacts with ethanol, replacing hydrogen and forming
sodium ethoxide
.
This reaction proves that
alcohols are weak acids
.
15. What is esterification? Write the reaction and explain its significance.
Answer:
Esterification
is the reaction between
an alcohol and a carboxylic acid
to form an
ester and water
.
CH3COOH+C2H5OH→CH3COOC2H5+H2OCH3COOH + C2H5OH → CH3COOC2H5 + H2OCH3COOH+C2H5OH→CH3COOC2H5+H2O
Ester formation
gives a
sweet fruity smell
, and esters are used in perfumes,
flavours
, and cosmetics.
16. Explain the oxidation of ethanol and ethanoic acid.
Answer:
Ethanol (C2H5OH) is oxidized to Ethanoic acid (CH3COOH)
when heated with an oxidizing agent like acidified potassium dichromate (K2Cr2O7).
C2H5OH+O2→CH3COOH+H2OC2H5OH + O2 → CH3COOH + H2OC2H5OH+O2→CH3COOH+H2O
Significance:
This oxidation reaction is used in
vinegar production
and the
alcohol industry
.
17. What are soaps and detergents? How do they work?
Answer:
|
Soaps |
Detergents |
|---|---|
|
Made from natural fats/oils |
Made from synthetic chemicals |
|
Form scum in hard water |
Work well in hard and soft water |
|
Biodegradable |
Some are non-biodegradable |
Mechanism of Cleaning:
Soap molecules form
micelles
in water, where the
hydrophobic tail
dissolves grease and dirt, while the
hydrophilic head
interacts with water, allowing dirt to be washed away.
18. What happens when ethanoic acid reacts with sodium carbonate? Write an equation.
Answer:
Reaction:
CH3COOH+Na2CO3→CH3COONa+CO2+H2OCH3COOH + Na2CO3 → CH3COONa + CO2 + H2OCH3COOH+Na2CO3→CH3COONa+CO2+H2O
Observation:
CO2 gas bubbles are formed.
Significance:
This reaction is used in the
baking industry
to produce CO2 gas, which makes dough rise.
19. Describe the process of saponification. Why is it important?
Answer:
Saponification:
The reaction of
fats (or oils) with NaOH (sodium hydroxide) to produce soap and glycerol
.
Fat+NaOH→Soap+GlycerolFat + NaOH → Soap + GlycerolFat+NaOH→Soap+Glycerol
Importance:
Soaps are used in cleaning and the
cosmetic industry
.
20. Why are detergents preferred over soaps in hard water?
Answer:
Hard water contains
Ca²⁺ and Mg²⁺ ions
, which react with soap to form
scum
.
Detergents do not form scum and work better in
both soft and hard water
.
