PYQs
Practise questions grouped by chapter and source year.
Practice questions are organised using the years and labels in our source collection. Work through the solutions with your teacher; these are not a complete official examination paper.
Practice question 1
Source year: 20253 marksWhat is the functional group in: (a) CH₃COOH (b) CH₃CHO (c) CH₃OH? Name each compound. [CBSE 2025]
Practice question 2
Source year: 20243 marksExplain the formation of scum when hard water is treated with soap. Write the chemical equation. [CBSE 2024]
Practice question 3
Source year: 20233 marksWhat is homologous series? Write three characteristics of a homologous series with example. [CBSE 2023]
Practice question 4
Source year: 20223 marksDraw the structure of: (a) Ethanoic acid (b) Butanone (c) Propanol. Write their molecular formulas. [CBSE 2022]
Practice question 5
Source year: 20213 marksWhat is meant by: (a) Saturated hydrocarbons (b) Unsaturated hydrocarbons? Give one example of each with structure. [CBSE 2021]
Formulae
Revisit important relationships and quick revision formulae.
Alkanes (CₙH₂ₙ₊₂)
Methane: CH₄ Ethane: C₂H₆ Propane: C₃H₈ Butane: C₄H₁₀ Single bonds (saturated)
Alkenes (CₙH₂ₙ)
Ethene: C₂H₄ Propene: C₃H₆ Double bond C=C (unsaturated)
Alkynes (CₙH₂ₙ₋₂)
Ethyne: C₂H₂ Propyne: C₃H₄ Triple bond C≡C (unsaturated)
Functional Groups
Alcohol: -OH Aldehyde: -CHO Ketone: >C=O Carboxylic acid: -COOH Ester: -COO-
Important Reactions
Combustion: CH₄ + 2O₂ → CO₂ + 2H₂O Substitution: CH₄ + Cl₂ → CH₃Cl + HCl Addition: C₂H₄ + H₂ → C₂H₆ Esterification: CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ + H₂O
Derivations
Work through the reasoning behind key concepts.
Catenation
Ability of carbon to form bonds with other carbon atoms Reasons:
- Small size of carbon atom
- High bond energy (C-C bond = 348 kJ/mol)
- Tetravalency (4 valence electrons)
This allows carbon to form long chains, branches, rings
Soap and Detergents
Soap: Sodium or potassium salts of long chain fatty acids Example: C₁₇H₃₅COONa (Sodium stearate)
Structure: Hydrophilic head (ionic) + Hydrophobic tail (hydrocarbon)
Cleansing action:
- Tail attaches to dirt/grease
- Head attaches to water
- Forms micelles, removes dirt
Ethanol Properties
C₂H₅OH (Ethanol/Ethyl alcohol)
Preparation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ (Glucose) (Fermentation)
Properties:
- Neutral to litmus
- Reacts with Na: 2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂
- Burns with blue flame: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O
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