Carbon and its Compounds — Previous Year Questions (Class 10 Science)
Carbon forms the backbone of all organic compounds. Understanding its bonding, structure, and reactions is fundamental to studying chemistry and biology.
TL;DR: Carbon forms the backbone of all organic compounds. Understanding its bonding, structure, and reactions is fundamental to studying chemistry and biolo…
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Carbon forms the backbone of all organic compounds. Understanding its bonding, structure, and reactions is fundamental to studying chemistry and biology.
Carbon and its Compounds — Previous Year Questions with Solutions
Q (2023, 3 marks): Why is carbon versatile in forming compounds? Explain its four main properties that make it unique.
Answer: Carbon is versatile because:
1. Tetravalency: Carbon has 4 valence electrons and forms 4 covalent bonds, allowing it to bond with many elements.
2. Catenation: Carbon can bond with other carbon atoms, forming long chains and rings, creating a wide variety of structures.
3. Small size: Carbon's relatively small atomic radius allows it to form strong bonds with other atoms.
4. Variable oxidation states: Carbon can exhibit oxidation states from -4 to +4, allowing it to participate in diverse chemical reactions.
Q (2022, 2 marks): Distinguish between saturated and unsaturated hydrocarbons with examples.
Answer: Saturated hydrocarbons:
- Contain only single bonds between carbon atoms (C-C)
- General formula: CnH(2n+2)
- Example: Ethane (C2H6), Propane (C3H8)
- Less reactive, mostly used as fuels
Unsaturated hydrocarbons:
- Contain double or triple bonds between carbon atoms (C=C or C≡C)
- General formula: CnH(2n) for alkenes, CnH(2n-2) for alkynes
- Example: Ethene (C2H4), Ethyne (C2H2)
- More reactive, used in synthesis of other compounds
Q (2023, 3 marks): What happens when ethanol is oxidized? Write the chemical equation for the oxidation of ethanol to acetaldehyde.
Answer: Ethanol is oxidized using oxidizing agents like acidified potassium dichromate (K2Cr2O7) or acidified potassium permanganate (KMnO4).
C2H5OH + [O] → CH3CHO + H2O
Or in detailed form:
C2H5OH + K2Cr2O7 + H2SO4 → CH3CHO + Cr2(SO4)3 + K2SO4 + H2O
The orange color of K2Cr2O7 changes to green (Cr3+), indicating oxidation has occurred.
Q (2022, 3 marks): Draw the structural formula of propane and propene. Explain the difference in their properties.
Answer: Propane (C3H8):
H-C-C-C-H
| | |
H H H
Propene (C3H6):
H-C=C-C-H
| | |
H H H
Differences:
Propane: Saturated, single bonds, inert, doesn't react with bromine water, used as fuel.
Propene: Unsaturated, double bond, reactive, decolorizes bromine water rapidly, used in synthesis of other compounds.
Q (2023, 2 marks): Explain the combustion of methane with equation. Is this reaction exothermic or endothermic?
Answer: CH4 + 2O2 → CO2 + 2H2O
This is a complete combustion reaction.
The reaction is exothermic (heat is released). Energy is released when new bonds form in CO2 and H2O, which exceeds the energy needed to break bonds in CH4 and O2.
This is why methane is used as a fuel for heating and cooking.
Q (2021, 3 marks): What is the difference between addition and substitution reactions? Give one example of each for organic compounds.
Answer: Addition reaction:
- Atoms or groups are added across a double or triple bond
- The general formula changes (more atoms in product)
- Example: C2H4 + Br2 → C2H4Br2 (addition of bromine to ethene)
Substitution reaction:
- One atom or group is replaced by another
- The general formula remains the same
- Example: CH4 + Cl2 → CH3Cl + HCl (chlorine substitutes hydrogen in methane, in presence of light)
Frequently Asked Questions
What makes organic compounds distinct from inorganic compounds?
Organic compounds contain carbon bonded to other elements (usually hydrogen, oxygen, nitrogen, sulfur), while most inorganic compounds do not contain carbon. Organic compounds are typically formed by living organisms or synthetic routes, covalent in nature, and generally have lower melting/boiling points than inorganic salts.
Why does ethene react with bromine water but ethane does not?
Ethene contains a C=C double bond, which is a region of high electron density. Bromine is electrophilic and readily attacks this double bond, resulting in an addition reaction that decolorizes bromine water. Ethane contains only C-C single bonds, which are less reactive, and does not readily react with bromine under normal conditions.
More Class 10 Science PYQs
- Chemical Reactions and Equations
- Light (Reflection and Refraction)
- Electricity
- Acids, Bases and Salts
- Metals and Non-metals
- Life Processes
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