Fresh HOTS-level problems on carbon compounds beyond the standard exercise. See the standard-level Solutions first if you haven’t already.
Extra Questions (HOTS Level): Carbon and its Compounds (Class 10 Science Chapter 4)
Q1. An organic compound X with molecular formula C₂H₆O turns blue litmus red only when a catalyst oxidises it further to Y. Identify X and Y and write the oxidation equation.
X = ethanol (C₂H₄OH) — itself neutral to litmus. On oxidation (e.g. with alkaline KMnO₄/acidified K₂Cr₂O₉), it forms Y = ethanoic acid (CH₃COOH), which is acidic and turns blue litmus red.
Equation: CH₃CH₂OH + 2[O] → CH₃COOH + H₂O.
Q2. Assertion-Reason: Assertion (A): Diamond and graphite are both allotropes of carbon but have very different physical properties. Reason (R): The atoms in diamond and graphite are arranged differently, giving different bonding structures. Choose: (i) Both true, R explains A (ii) Both true, R doesn’t explain A (iii) A true, R false (iv) A false, R true.
Diamond has a rigid 3D tetrahedral network (each C bonded to 4 others) making it extremely hard, while graphite has layers of hexagonal rings (each C bonded to 3 others) that slide over each other, making it soft and a good lubricant/conductor. The different atomic arrangement directly explains the different properties.
Answer: (i).
Q3. Two test tubes contain hexane and hexene respectively. Bromine water is added to both and shaken. Predict the observation in each and explain.
Hexene (unsaturated, has a C=C double bond) decolourises the bromine water instantly via an addition reaction.
Hexane (saturated alkane) shows no immediate decolourisation under normal conditions, since it has no double/triple bond for bromine to add across.
Q4. A compound has the molecular formula C₄H₁₀O and reacts with sodium metal to liberate hydrogen gas but does not react with sodium carbonate. Identify the functional group present and justify.
Both alcohols and carboxylic acids react with sodium to liberate H₂ gas, but only carboxylic acids react with sodium carbonate (releasing CO₂). Since this compound reacts with Na but NOT with Na₂CO₃, it must contain an –OH (alcohol) functional group, not a carboxylic acid group.
Q5. Write the structural formula and name of the first three members of the alkyne homologous series, and state their general formula.
General formula: CₙH₂ₙ−₂.
Ethyne (C₂H₂): H–C≡C–H.
Propyne (C₃H₄): CH₃–C≡C–H.
Butyne (C₄H₆): CH₃–CH₂–C≡C–H.
Related: Solutions | Extra Questions | Revision Notes | Formulas Handbook | Class 10 Science Book
