Carbon and its compounds is the Class 10 chemistry chapter with the most reactions to write and the clearest pattern of questions: a nomenclature or functional-group question, a reaction with its conditions, a test, and the soap-and-micelle explanation turn up almost every year. These 30 questions, from one-mark MCQs and assertion-reason to five-mark reaction sets, cover the current CBSE syllabus for the chapter, with every answer written the way the marking scheme awards it: balanced, with the condition on the arrow, and the reason stated.
Part A: ten one-mark questions
1. The number of covalent bonds in a molecule of ethane (C₂H₆) is
A. 5 · B. 6 · C. 7 · D. 8
2. Which of the following is not an allotrope of carbon?
A. graphite · B. diamond · C. fullerene · D. carborundum
3. The functional group –CHO belongs to
A. alcohols · B. aldehydes · C. ketones · D. carboxylic acids
4. The successive members of a homologous series differ by
A. CH₂ and 14 u · B. CH₃ and 15 u · C. CH₂ and 12 u · D. C₂H₄ and 28 u
5. The IUPAC name of CH₃–CH₂–CH₂–OH is
A. propanol · B. propan-1-ol · C. propan-2-ol · D. propanal
6. The gas evolved when ethanoic acid reacts with sodium carbonate is
A. hydrogen · B. oxygen · C. carbon dioxide · D. carbon monoxide
7. Which reagent is used to oxidise ethanol to ethanoic acid?
A. alkaline KMnO₄ · B. sodium metal · C. concentrated H₂SO₄ · D. nickel
8. Butanone is a four-carbon compound with the functional group
A. carboxylic acid · B. aldehyde · C. ketone · D. alcohol
9. Assertion (A): Carbon forms a very large number of compounds. Reason (R): Carbon shows catenation and tetravalency.
A. both A and R are true and R explains A · B. both true but R does not explain A · C. A true, R false · D. A false, R true
10. Assertion (A): Soap does not lather well in hard water. Reason (R): Soap forms insoluble calcium and magnesium salts (scum) with the salts in hard water.
A. both true and R explains A · B. both true but R does not explain A · C. A true, R false · D. A false, R true
Part B: eight two-mark questions
11. Why does carbon form covalent bonds rather than ionic bonds?
12. What is catenation? Why does carbon show it more than any other element?
13. Draw the electron-dot structure of methane and of ethene.
14. Define a homologous series and give two characteristics.
15. Give the IUPAC names of: (a) CH₃–CH₂–CHO (b) CH₃–CO–CH₃ (c) CH₃–CH₂–COOH (d) CH₃–CH₂–CH₂–CH₂–Br.
16. Why does ethanol dissolve in water but hexane does not?
17. Why do diamond and graphite have such different properties when both are pure carbon?
18. What happens when ethanol is heated with concentrated sulphuric acid at 443 K? Give the equation.
Part C: seven three-mark questions
19. Describe two tests to distinguish a saturated hydrocarbon from an unsaturated one.
20. Explain the substitution reaction of methane with chlorine, with the equation and the condition.
21. What is hydrogenation? Give the equation and its industrial use.
22. Write the reactions of ethanoic acid with (a) sodium hydroxide (b) sodium carbonate (c) ethanol, with conditions.
23. Why is the conversion of ethanol to ethanoic acid called an oxidation reaction? Give the equation and the reagent.
24. What is a micelle? Explain with a diagram how soap removes an oily stain.
25. What is the difference between soaps and detergents? Why are detergents preferred in hard-water areas but a problem for the environment?
Part D: five five-mark questions
26. An organic compound A of molecular formula C₂H₆O reacts with sodium to give a gas B and with alkaline KMnO₄ to give compound C of formula C₂H₄O₂. A and C react in the presence of concentrated sulphuric acid to give a sweet-smelling compound D. Identify A, B, C and D and write all the reactions.
27. (a) Why is carbon dioxide a gas but silicon dioxide a solid, from the bonding? (b) Why are covalent compounds generally poor conductors with low melting points? (c) Name the three allotropes of carbon and one use of each.
28. Write the structures of the first five alkanes and the first three members of the alcohol series. State the general formula of alkanes, alkenes and alkynes.
29. Explain the cleansing action of soap in five steps, and why the same soap fails in hard water. Draw the structure of a soap molecule with its two parts labelled.
30. Give the physical properties and two uses each of ethanol and ethanoic acid, and the reaction of each with sodium.
Answers, written to the marking scheme
| No. | Answer |
|---|---|
| 1 | C, 7 (one C–C and six C–H). |
| 2 | D, carborundum (silicon carbide). |
| 3 | B, aldehydes. |
| 4 | A, CH₂ and 14 u. |
| 5 | B, propan-1-ol. |
| 6 | C, carbon dioxide (brisk effervescence; turns lime water milky). |
| 7 | A, alkaline KMnO₄ (or acidified K₂Cr₂O₇). |
| 8 | C, ketone (CH₃–CO–CH₂–CH₃). |
| 9 | A: carbon forms millions of compounds because it bonds with itself in long chains, branches and rings (catenation) and forms four bonds (tetravalency); R explains A. |
| 10 | A: the Ca²⁺ and Mg²⁺ ions in hard water react with soap to form insoluble scum, so soap is used up before it lathers; R explains A. |
| 11 | Carbon has four electrons in its outer shell. Gaining four electrons (C⁴⁻) or losing four (C⁴⁺) would need too much energy and give an unstable ion. Sharing four electrons with other atoms completes its octet without charge, so carbon forms covalent bonds. |
| 12 | Catenation is the ability of an element to form bonds with other atoms of the same element, giving chains, branched chains and rings. Carbon's small size makes the C–C bond strong and stable, so it shows catenation far more than silicon or any other element. |
| 13 | Methane: a C in the centre with four H around it, each C–H a shared pair (eight electrons around C). Ethene: two C atoms sharing two pairs (a double bond), each C with two H sharing one pair. |
| 14 | A series of compounds with the same functional group and similar chemical properties, in which successive members differ by a –CH₂– unit (14 u). Characteristics: a general formula (alkanes CₙH₂ₙ₊₂); physical properties such as melting and boiling point change gradually along the series; chemical properties are the same because the functional group is the same. |
| 15 | (a) propanal (b) propanone (c) propanoic acid (d) 1-bromobutane. |
| 16 | Ethanol has a polar –OH group that forms hydrogen bonds with water, so it dissolves; hexane has only non-polar C–H and C–C bonds and cannot bond with water, so it does not. |
| 17 | In diamond each carbon is bonded to four others in a rigid three-dimensional network, so it is the hardest known substance and does not conduct. In graphite each carbon is bonded to three others in flat hexagonal layers with one free electron per atom; the layers slide over each other (soft, slippery) and the free electrons conduct electricity. |
| 18 | Dehydration: ethanol loses a water molecule to form ethene. CH₃CH₂OH → (conc. H₂SO₄, 443 K) → CH₂=CH₂ + H₂O. Concentrated sulphuric acid is the dehydrating agent. |
| 19 | (i) Bromine water: an unsaturated hydrocarbon decolourises the brown bromine water (addition across the double bond); a saturated one does not. (ii) Flame: a saturated hydrocarbon burns with a clean blue flame; an unsaturated one burns with a sooty yellow flame, because of the higher carbon percentage and incomplete combustion. |
| 20 | In the presence of sunlight, chlorine replaces the hydrogen atoms of methane one at a time. CH₄ + Cl₂ → (sunlight) → CH₃Cl + HCl; the reaction continues to CH₂Cl₂, CHCl₃ and CCl₄. It is a substitution reaction because one atom is replaced by another; the condition, sunlight, must be written. |
| 21 | Addition of hydrogen to an unsaturated hydrocarbon to make it saturated, in the presence of a nickel or palladium catalyst. CH₂=CH₂ + H₂ → (Ni) → CH₃–CH₃. Industrial use: hydrogenation of vegetable oils (unsaturated) to make solid vegetable ghee (saturated fat). |
| 22 | (a) CH₃COOH + NaOH → CH₃COONa + H₂O (neutralisation; sodium ethanoate). (b) 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂ (effervescence of CO₂). (c) CH₃COOH + CH₃CH₂OH → (conc. H₂SO₄, warm) → CH₃COOCH₂CH₃ + H₂O (esterification; ethyl ethanoate, sweet smelling). |
| 23 | Because oxygen is added to the molecule (and hydrogen removed): the –CH₂OH group becomes –COOH. CH₃CH₂OH + 2[O] → (alkaline KMnO₄, heat) → CH₃COOH + H₂O. Alkaline potassium permanganate (or acidified potassium dichromate) supplies the oxygen; it is called an oxidising agent. |
| 24 | A soap molecule has a long hydrocarbon tail (hydrophobic, dissolves in oil) and an ionic head (hydrophilic, dissolves in water). In water, soap molecules cluster with the tails inward around an oil droplet and the heads outward, forming a micelle. The oil is trapped in the centre; the micelle stays suspended in water (the heads repel each other, so micelles do not settle), and rinsing washes it away. Diagram: a circle of tails pointing in, heads out, oil in the middle. |
| 25 | Soaps: sodium or potassium salts of long-chain carboxylic (fatty) acids, from oils and fats; form insoluble scum with Ca²⁺ and Mg²⁺ in hard water. Detergents: sodium salts of long-chain sulphonic acids or ammonium salts with chloride or bromide, from petroleum; their Ca and Mg salts are soluble, so they lather in hard water. Many detergents are not easily biodegradable, so they pollute water bodies. |
| 26 | A: ethanol, CH₃CH₂OH. B: hydrogen. C: ethanoic acid, CH₃COOH. D: ethyl ethanoate (an ester), CH₃COOCH₂CH₃. Reactions: 2CH₃CH₂OH + 2Na → 2CH₃CH₂ONa + H₂; CH₃CH₂OH + 2[O] → (alk. KMnO₄) → CH₃COOH + H₂O; CH₃COOH + CH₃CH₂OH → (conc. H₂SO₄) → CH₃COOCH₂CH₃ + H₂O. |
| 27 | (a) CO₂ is a small molecule with two C=O double bonds and weak forces between molecules, so it is a gas; SiO₂ forms a giant three-dimensional network of Si–O single bonds, so it is a hard, high-melting solid. (b) Covalent molecules have strong bonds within the molecule but weak forces between molecules, so they melt and boil at low temperatures, and they have no free electrons or ions, so they do not conduct. (c) Diamond: cutting glass, jewellery. Graphite: pencil leads, lubricant, electrodes. Fullerene (C₆₀): research, as a carrier for drugs and in lubricants. |
| 28 | Alkanes: methane CH₄, ethane C₂H₆, propane C₃H₈, butane C₄H₁₀, pentane C₅H₁₂ (draw each as a chain of C with H around). Alcohols: methanol CH₃OH, ethanol CH₃CH₂OH, propanol CH₃CH₂CH₂OH. General formulas: alkanes CₙH₂ₙ₊₂, alkenes CₙH₂ₙ, alkynes CₙH₂ₙ₋₂. |
| 29 | (1) The hydrocarbon tails of soap dissolve in the oily dirt. (2) The ionic heads stay in the water. (3) Soap molecules surround the oil droplet to form a micelle with tails in and heads out. (4) The micelles stay suspended as an emulsion because the charged heads repel. (5) Rinsing carries the micelles and the dirt away. In hard water the Ca²⁺ and Mg²⁺ ions react with the soap first to form insoluble scum, so no micelles form until all the hardness is used up. Structure: a long zig-zag hydrocarbon chain (tail) ending in –COO⁻ Na⁺ (head). |
| 30 | Ethanol: colourless liquid, boiling point 351 K, miscible with water, a good solvent; uses: in medicines (tincture of iodine, cough syrups), as a fuel additive and solvent. Reaction with sodium: 2CH₃CH₂OH + 2Na → 2CH₃CH₂ONa + H₂ (sodium ethoxide and hydrogen). Ethanoic acid: colourless liquid with a pungent smell, freezes at 290 K (glacial acetic acid), miscible with water, a weak acid; uses: vinegar (5 to 8 per cent solution) as a preservative, in making esters and plastics. With sodium: 2CH₃COOH + 2Na → 2CH₃COONa + H₂. |
The pattern behind the paper
Three things the marking scheme rewards every year: the condition on the arrow (sunlight, Ni, conc. H₂SO₄ at 443 K, alkaline KMnO₄; a reaction without its condition is half marks), the name and the structure together (propan-2-ol and the drawn chain, not one or the other), and the reason in any "why" question (not "because carbon is special" but "because gaining or losing four electrons needs too much energy"). The chapter is small enough that these 30 questions, done from blank paper twice, cover it; the reactions from all the Class 10 chemistry chapters, with conditions, are in important chemical reactions for Class 10, and the method for the equations is in how to balance chemical equations.
How we teach Class 10 chemistry
Sixty-minute 1-on-1 classes on a shared whiteboard, in the NCERT order, with the reactions written by the student and the conditions tested from blank paper at the start of the next class, and the sample-paper pattern from the first term. Our tutors are a team of 20+ women educators with master's degrees in chemistry and the sciences, teaching online since 2018, in English, Hindi or Punjabi, to students in India, the Gulf, the UK and the US. The first 30-minute class is free; details on the CBSE Class 9 and 10 science page.
Questions parents ask
1Which questions from carbon and its compounds come most often in the Class 10 board exam?
2What are the chemical properties of carbon compounds asked in Class 10?
3What is the difference between soap and detergent for the exam?
4Is this the rationalised syllabus?
5How do I write the reactions for full marks?
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