Carbon and its Compounds · Class 10 Science: 88 flashcards
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1. What is carbon's electronic configuration, and why can't it form ions?
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2,4 — four outer electrons. Losing four would need enormous energy (unstable C⁴⁺); gaining four would overload the small atom (C⁴⁻). So carbon only SHARES electrons.
2. Define a covalent bond.
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A bond formed when two atoms share a pair of electrons, with both atoms counting the shared pair toward their stable (octet/duet) configuration.
3. How many shared pairs are in H₂, O₂ and N₂?
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H₂: one (single bond). O₂: two (double bond). N₂: three (triple bond).
4. Describe the bonding in methane.
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Carbon shares one electron pair with each of four hydrogen atoms — four single covalent bonds; carbon completes its octet and each hydrogen its duet.
5. Why do covalent compounds have low melting and boiling points?
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Because the forces BETWEEN their molecules are weak — melting/boiling only separates molecules and doesn't break the strong bonds within them.
6. Why are covalent compounds generally poor conductors of electricity?
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They consist of neutral molecules — no ions and no free electrons to carry charge.
7. Define catenation.
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The self-linking property of carbon — its ability to form strong bonds with other carbon atoms, building long chains, branched chains and rings.
8. Define tetravalency of carbon.
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Carbon's valency of four — each carbon atom forms four covalent bonds, with carbon or with elements like H, O, N, S and halogens.
9. State the two properties responsible for the huge number of carbon compounds.
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Catenation (self-linking into chains and rings) and tetravalency (four bonds per atom) — together generating millions of possible structures.
10. Why are carbon-carbon bonds so strong?
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Carbon's small atomic size keeps the shared electron pairs close to both nuclei, making the bonds short and strong — hence stable long chains.
11. Why doesn't silicon form long chains like carbon?
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Silicon's larger atoms make Si-Si bonds longer and weaker; its chains reach only about 7-8 atoms and are reactive, unlike carbon's chains of thousands.
12. What are allotropes? Name carbon's three.
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Different structural forms of the same element with different properties. Carbon's allotropes: diamond, graphite and fullerenes.
13. Describe diamond's structure and two resulting properties.
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Each carbon bonds covalently to FOUR others in a rigid three-dimensional network — making diamond the hardest natural substance, with a very high melting point, and a non-conductor (all electrons locked in bonds).
14. Describe graphite's structure and two resulting properties.
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Each carbon bonds to THREE others, forming flat hexagonal sheets; the fourth electron is free. The sheets slide (soft, slippery — pencil, lubricant) and the free electrons conduct electricity (electrodes).
15. What is C-60?
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Buckminsterfullerene — a fullerene allotrope where 60 carbon atoms form a closed football-shaped cage of hexagons and pentagons.
16. Why is N₂ gas so unreactive?
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Its atoms are joined by a triple bond (three shared pairs) — one of the strongest bonds known, needing great energy to break.
17. How many lone pairs does oxygen carry in a water molecule?
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Two — oxygen shares two of its six outer electrons (one pair with each H) and keeps two unshared lone pairs.
18. Is sugar solution a conductor? Why?
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No — sugar is a covalent compound; it dissolves as whole neutral molecules, giving no ions to carry current.
19. Give four everyday things made of covalent carbon compounds.
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Cooking gas (LPG/methane-propane-butane), petrol/wax, sugar and alcohol, plastics like polythene (also medicines, fabrics, food).
20. Which allotrope of carbon is used in electrodes, and why?
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Graphite — its free (fourth) electrons make it a good conductor, and it resists chemical attack.
21. Contrast melting: salt vs wax. What does it reveal?
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Salt (ionic) melts at ~801 °C; wax (covalent) melts in warm hands. The contrast reveals the strong ionic lattice vs the weak intermolecular forces of covalent molecules.
22. What holds the different sheets of graphite together?
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Only weak forces — which is why the sheets slide over each other easily, making graphite soft and an excellent dry lubricant.
23. What is a hydrocarbon?
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A compound containing carbon and hydrogen only — classified into alkanes, alkenes and alkynes.
24. Write the general formula and first member of alkanes.
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CₙH₂ₙ₊₂; first member methane, CH₄.
25. Write the general formula and first member of alkenes.
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CₙH₂ₙ (one C=C double bond); first member ethene, C₂H₄.
26. Write the general formula and first member of alkynes.
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CₙH₂ₙ₋₂ (one C≡C triple bond); first member ethyne (acetylene), C₂H₂.
27. Differentiate saturated and unsaturated hydrocarbons.
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Saturated (alkanes) have only single C-C bonds — maximum hydrogen held. Unsaturated (alkenes, alkynes) contain a double or triple bond and can add more hydrogen; they are more reactive.
28. Why is there no one-carbon alkene or alkyne?
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A double or triple bond must join two carbon atoms; with only one carbon there is no partner — so both series start at C₂ (ethene, ethyne).
29. What are structural isomers? Give the classic example.
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Compounds with the same molecular formula but different structures. Classic: C₄H₁₀ as n-butane (straight chain) and isobutane (branched chain).
30. From which alkane does structural isomerism begin?
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Butane (C₄H₁₀) — methane, ethane and propane each have only one possible arrangement.
31. Define a homologous series.
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A series of carbon compounds having the same general formula and functional group, in which each successive member differs from the previous by a CH₂ unit (14 mass units).
32. State three characteristics of a homologous series.
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(1) All members fit one general formula and share the same functional group; (2) they show similar chemical properties; (3) physical properties (like boiling point) change gradually as chain length increases — with a constant CH₂/14 u step between members.
33. What mass difference separates consecutive homologues?
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14 u — the mass of one CH₂ unit (12 + 2).
34. What is a functional group?
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An atom or group of atoms (replacing hydrogen in a chain) that determines the characteristic chemical properties of the compound — the same group gives the same chemistry at any chain length.
35. Name the functional groups: −OH, −COOH, −CHO, >C=O.
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−OH: alcohol. −COOH: carboxylic acid. −CHO: aldehyde. >C=O (within the chain): ketone.
36. Which suffixes correspond to alcohol, aldehyde, ketone and carboxylic acid?
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Alcohol: -ol. Aldehyde: -al. Ketone: -one. Carboxylic acid: -oic acid.
37. Give the IUPAC roots for 1-5 carbon atoms.
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1: meth-, 2: eth-, 3: prop-, 4: but-, 5: pent-.
38. Name: CH₃OH, C₂H₅OH, HCOOH, CH₃COOH.
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Methanol, ethanol, methanoic acid, ethanoic acid.
39. Write the formulas of ethene, propane and propyne.
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Ethene: C₂H₄. Propane: C₃H₈. Propyne: C₃H₄.
40. Write the next homologue after (a) C₂H₆, (b) C₃H₆ (alkene).
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(a) C₃H₈ (propane). (b) C₄H₈ (butene) — always add CH₂.
41. What is the common name of ethyne?
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Acetylene — the welding-torch gas.
42. Which gas do ripening fruits release, and which family is it from?
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Ethene (C₂H₄) — the first alkene; it acts as a natural ripening hormone.
43. Identify the functional group and family: CH₃CH₂CHO.
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−CHO, an aldehyde — the compound is propanal (3 carbons).
44. Why do all alcohols react similarly regardless of chain length?
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Because their chemistry is controlled by the common functional group (−OH); the CH₂ units of the chain are chemically inert spectators.
45. Write the combustion equation of methane.
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CH₄ + 2O₂ → CO₂ + 2H₂O + heat + light.
46. What are the products when any carbon compound burns completely?
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Carbon dioxide and water, with the release of heat and light.
47. Which hydrocarbons burn with a clean blue flame, and when?
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Saturated hydrocarbons (alkanes) — when supplied with sufficient air for complete combustion.
48. Why do unsaturated hydrocarbons burn with a sooty yellow flame?
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Their higher carbon content burns incompletely in air — unburnt carbon particles glow yellow and deposit as soot.
49. Why do cooking vessels blacken when a gas stove's air holes are blocked?
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Limited oxygen makes even the saturated LPG burn incompletely — soot (unburnt carbon) deposits on the vessels. The remedy is clearing the air inlets.
50. Which polluting gases come from burning coal and petroleum?
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Oxides of sulphur (SO₂) and oxides of nitrogen — the gases responsible for acid rain.
51. How is ethanol converted to ethanoic acid? Write the change.
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By warming with an oxidising agent — alkaline potassium permanganate (or acidified potassium dichromate): CH₃CH₂OH → CH₃COOH.
52. What are oxidising agents? Give two examples.
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Substances that supply oxygen to others (causing oxidation) — alkaline KMnO₄ and acidified K₂Cr₂O₇.
53. What is observed when alkaline KMnO₄ is added drop-wise to warm ethanol?
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The purple colour of KMnO₄ disappears initially (the alcohol consumes the oxidant); once all the ethanol is oxidised, further drops retain their purple colour.
54. Is KMnO₄ a catalyst in this reaction? Explain.
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No — it is the oxidising agent, actually consumed while donating oxygen (hence its colour loss). A catalyst would remain unconsumed.
55. What is an addition reaction? Which compounds undergo it?
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A reaction in which atoms ADD across a double or triple bond, converting an unsaturated compound to a saturated one — only unsaturated compounds (alkenes/alkynes) undergo it.
56. What is hydrogenation? Name its catalyst.
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The addition of hydrogen across the C=C bonds of an unsaturated compound, using a nickel (or palladium) catalyst.
57. State the industrial application of hydrogenation.
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Converting liquid vegetable oils (unsaturated) into solid fats — vanaspati ghee — by bubbling H₂ through hot oil over a nickel catalyst.
58. Which is considered healthier for cooking — saturated fats or unsaturated oils?
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Unsaturated oils — excess saturated (hydrogenated) fats are associated with harmful health effects.
59. What is a substitution reaction? Which compounds show it?
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A reaction in which an atom (like chlorine) REPLACES a hydrogen atom of a compound — shown by saturated hydrocarbons, which cannot add.
60. Write the reaction of methane with chlorine, with its condition.
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CH₄ + Cl₂ --sunlight--> CH₃Cl + HCl — a substitution reaction requiring sunlight.
61. Why is sunlight necessary for the methane-chlorine reaction?
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Light energy breaks chlorine molecules apart to begin the substitution; without it, the mixture does not react.
62. Can the substitution of methane go further than CH₃Cl?
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Yes — successive hydrogens are replaced: CH₂Cl₂, CHCl₃ (chloroform) and finally CCl₄.
63. How can addition be used as a TEST for unsaturation?
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Unsaturated compounds readily undergo addition (e.g., decolourising bromine water or adding H₂), while saturated ones do not — a positive addition marks the multiple bond.
64. Contrast the conditions for addition vs substitution of hydrocarbons.
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Addition (unsaturated + H₂): needs a nickel/palladium CATALYST. Substitution (saturated + Cl₂): needs SUNLIGHT. Different compounds, different switches.
65. Why are carbon compounds our major fuels?
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They burn readily in oxygen releasing large amounts of heat (and light) — from methane and LPG to petrol, diesel and wax, combustion energy powers kitchens, vehicles and industry.
66. A liquid decolourises bromine water instantly. What does this indicate?
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The liquid is UNSATURATED — its double/triple bonds add the bromine (an addition reaction), removing the colour. Saturated compounds leave bromine water orange.
67. State two physical properties and two uses of ethanol.
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Properties: colourless liquid; miscible with water in all proportions (also neutral to litmus). Uses: solvent in medicines like tincture iodine and cough syrups; in sanitisers/alcoholic drinks (also industrial solvent).
68. Write the reaction of ethanol with sodium and the gas test.
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2Na + 2CH₃CH₂OH → 2CH₃CH₂ONa (sodium ethoxide) + H₂↑. The hydrogen burns with a pop near a flame.
69. What happens when ethanol is heated with excess concentrated sulphuric acid at 443 K?
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Dehydration — a water molecule is removed, forming ethene: CH₃CH₂OH → CH₂=CH₂ + H₂O. Conc. H₂SO₄ acts as the dehydrating agent.
70. What role does concentrated H₂SO₄ play in ethanol's dehydration?
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It is a dehydrating agent — it removes the elements of water from the ethanol molecule.
71. Is ethanol acidic, basic or neutral? How does it still give H₂ with sodium?
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Neutral to litmus. The -OH group's hydrogen is nevertheless replaceable by sodium — a special property of alcohols, not litmus-acidity.
72. What is vinegar?
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A 5-8% solution of ethanoic (acetic) acid in water — used as a preservative and flavouring.
73. Why is pure ethanoic acid called glacial acetic acid?
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Because it freezes at 290 K (16.6 °C) — in cold climates the pure acid solidifies into ice-like crystals.
74. Is ethanoic acid strong or weak? Compare with HCl.
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Weak — it ionises only partially in water, so at equal concentration it gives far fewer H₃O⁺ ions than the fully-ionised strong acid HCl.
75. Write the reaction of ethanoic acid with sodium hydrogencarbonate, with observation.
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CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂↑ — brisk effervescence; the gas turns limewater milky.
76. Write the neutralisation of ethanoic acid with NaOH.
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CH₃COOH + NaOH → CH₃COONa (sodium ethanoate/acetate) + H₂O.
77. What is esterification? Write the equation.
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The reaction of a carboxylic acid with an alcohol, in the presence of concentrated H₂SO₄, forming a sweet-smelling ester: CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ + H₂O.
78. How is the ester detected, and where are esters used?
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Pouring the warm mixture into water releases a sweet, fruity smell. Esters are used in perfumes and as flavouring agents.
79. What is saponification?
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The alkaline hydrolysis of an ester: ester + NaOH → alcohol + sodium salt of the carboxylic acid. With fats (long-chain esters), the salt formed is soap — hence the name.
80. What is soap chemically?
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The sodium or potassium salt of a long-chain carboxylic (fatty) acid.
81. Describe the two parts of a soap molecule.
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A long hydrocarbon TAIL that is hydrophobic (dissolves in oil/grease) and an ionic HEAD (-COO⁻Na⁺) that is hydrophilic (dissolves in water).
82. What is a micelle?
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A spherical cluster of soap molecules in water — hydrophobic tails pointing inward (holding oily dirt) and hydrophilic heads outward (facing the water) — the unit that lifts grease off surfaces.
83. Explain the cleansing action of soap in brief.
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Soap tails embed into the oily dirt while heads stay in water; the molecules surround the grease as micelles; agitation frees the micelles from the cloth, and rinsing washes them — dirt inside — away with the water.
84. What makes water 'hard', and what happens when soap meets it?
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Dissolved calcium and magnesium salts (Ca²⁺, Mg²⁺ ions). They react with soap forming an insoluble precipitate — scum — so lather fails and soap is wasted.
85. Why do detergents work in hard water?
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Their heads (e.g., sulphonate groups) form calcium and magnesium salts that remain SOLUBLE — no scum forms, so lathering and cleaning continue.
86. Give one advantage of soap over detergents, and one of detergents over soap.
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Soap: fully biodegradable — environment-friendly. Detergent: works even in hard water (and often stronger cleansing) — though some are non-biodegradable pollutants.
87. Why can't soap clean effectively in a pure oil medium like kerosene?
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Micelle formation needs water for the hydrophilic heads to face. In pure oil there is no aqueous side — micelles cannot form and the cleansing mechanism fails.
88. Why is industrial alcohol denatured?
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To prevent its misuse for drinking — it is deliberately made poisonous by adding methanol (and coloured with dye as a warning). Consuming it causes blindness and death.
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