Carbon Compounds
Key Concepts
| # | Concept | Explanation |
|---|---|---|
| 1 | Catenation | Carbon’s unique ability to form long chains/rings by bonding with itself; reason for ~10 million organic compounds. |
| 2 | Tetravalency | Carbon has 4 valence electrons → forms 4 covalent bonds; gives 3-D stability to molecules. |
| 3 | Functional Group | Atom/group that decides chemical behaviour; e.g. –OH (alcohol), –COOH (acid), –CHO (aldehyde). |
| 4 | Homologous Series | Sequence of compounds with same functional group & successive –CH₂– difference; shows gradation in physical properties. |
| 5 | Hydrocarbons | Only C & H; divided into saturated (alkanes, CₙH₂ₙ₊₂) & unsaturated (alkenes CₙH₂ₙ, alkynes CₙH₂ₙ₋₂). |
| 6 | Isomerism | Same molecular formula but different arrangement/structure; e.g. C₄H₁₀ → n-butane & isobutane. |
| 7 | Combustion | Oxidation with O₂ → CO₂ + H₂O + heat; saturated hydrocarbons burn cleaner (blue flame) than unsaturated (yellow, sooty). |
| 8 | Nomenclature (IUPAC) | Longest C-chain + suffix for family (ane/ene/yne/ol/al/oic acid) + position number of substituent/double bond. |
15 Practice MCQs
- The property by which carbon forms straight, branched & cyclic chains is called
A. Tetravalency
B. Catenation
C. Polymerisation
D. Allotropy
Answer: B. Catenation
Solution: Self-linking ability of carbon atoms.
Shortcut: CATenation → CAT-chains.
Tag: Basic property
- General formula of alkenes is
A. CₙH₂ₙ₊₂
B. CₙH₂ₙ
C. CₙH₂ₙ₋₂
D. CₙHₙ
Answer: B. CₙH₂ₙ
Solution: One double bond removes 2 H atoms from alkane formula.
Shortcut: “ENE = Even H (2n)”.
Tag: Hydrocarbons
- Which is NOT a saturated hydrocarbon?
A. Propane
B. Butane
C. Cyclohexane
D. Ethene
Answer: D. Ethene (C₂H₄)
Solution: Contains C=C double bond → unsaturated.
Shortcut: Ending “ENE” = double bond.
Tag: Saturated vs Unsaturated
- Functional group present in acetic acid is
A. –CHO
B. –COOH
C. –OH
D. –CO–
Answer: B. –COOH
Solution: “oic acid” suffix → carboxylic acid group.
Shortcut: ACID has COOH.
Tag: Functional group
- Number of covalent bonds in ethane molecule (C₂H₆) is
A. 6
B. 7
C. 8
D. 9
Answer: B. 7
Solution: 1 C–C + 6 C–H bonds.
Shortcut: Alkane bonds = (3n+1); n=2 → 7.
Tag: Bond counting
- Which shows isomerism with n-butane?
A. Propane
B. Isobutane
C. Ethane
D. Pentane
Answer: B. Isobutane
Solution: Same C₄H₁₀, branched chain.
Shortcut: “ISO” = isomer.
Tag: Isomerism
- Product of complete combustion of ethanol is
A. CO + H₂O
B. CO₂ + H₂
C. CO₂ + H₂O
D. C + H₂O
Answer: C. CO₂ + H₂O
Solution: Complete oxidation.
Shortcut: Burn organics → “CO₂ & Water”.
Tag: Combustion
- Dehydration of ethanol with conc. H₂SO₄ at 443 K gives
A. Ethane
B. Ethene
C. Ethyne
D. Ethanoic acid
Answer: B. Ethene
Solution: –H & –OH removed → double bond.
Shortcut: De-hydration → Remove H₂O → make “ENE”.
Tag: Reaction
- Which compound will give a positive test with litmus?
A. CH₃OH
B. CH₃COOH
C. CH₃CHO
D. CH₄
Answer: B. CH₃COOH
Solution: Acid turns blue litmus red.
Shortcut: Acid → COOH → litmus RED.
Tag: Properties
- IUPAC name of CH₃–CH₂–CH₂–OH is
A. Propanal
B. Propanone
C. Propanol
D. Propanoic acid
Answer: C. Propanol
Solution: 3 C atoms, –OH on first C → “ol” suffix.
Shortcut: Count C → prop; –OH → “ol”.
Tag: Nomenclature
- Which has a triple bond?
A. Ethane
B. Ethene
C. Ethyne
D. Benzene
Answer: C. Ethyne
Solution: C₂H₂; “yne” suffix.
Shortcut: YNE = three letters → triple bond.
Tag: Unsaturated
- When vegetable oil is hydrogenated, the product is
A. Alkanes
B. Fats
C. Soap
D. Proteins
Answer: B. Fats
Solution: Addition of H to double bonds of oil → solid fat.
Shortcut: H₂ + oil = hard fat.
Tag: Application
- Which is the first member of the alkyne series?
A. Methyne
B. Ethyne
C. Propyne
D. Butyne
Answer: B. Ethyne
Solution: C₂H₂; no stable “C₁” alkyne.
Shortcut: Alkyne starts at 2 carbons.
Tag: Homologous series
- Substance that gives brisk effervescence with NaHCO₃?
A. Ethanol
B. Ethanoic acid
C. Ethene
D. Ethane
Answer: B. Ethanoic acid
Solution: Acid + NaHCO₃ → CO₂ gas bubbles.
Shortcut: COOH + Bicarb = Fizz.
Tag: Test
- Vinegar contains mainly
A. 5 % ethanoic acid
B. 50 % methanol
C. 95 % ethanol
D. 30 % propanone
Answer: A. 5 % ethanoic acid
Solution: Fermented juice oxidised to vinegar.
Shortcut: Vinegar = “5 % Acid”.
Tag: Everyday chemistry
Speed Tricks
| Situation | Shortcut | Example |
|---|---|---|
| Identify saturated vs unsaturated | Check suffix: ane = saturated; ene/yne = unsaturated | Butane (ane) vs Butene (ene) |
| Count covalent bonds in alkane | 3n + 1 | Hexane (n=6) → 19 bonds |
| Functional group from suffix | “ol”=alcohol; “al”=aldehyde; “oic acid”=carboxylic | Propanol vs Propanal |
| Isomer possibility | Alkanes ≥ 4 C can show chain isomerism | C₄ → 2 isomers; C₅ → 3 |
| Combustion oxygen balance | CₓHᵧ + (x + y/4)O₂ → xCO₂ + y/2 H₂O | C₂H₆ needs 3.5 O₂ → 7/2 |
Quick Revision
| Point | Detail |
|---|---|
| 1 | Carbon = 6C, 2,4 config → 4 valence e⁻ → 4 covalent bonds. |
| 2 | Catenation & tetravalency → millions of stable organic compounds. |
| 3 | Alkanes: single bonds; alkenes: C=C; alkynes: C≡C. |
| 4 | Functional group decides properties, not molecular size. |
| 5 | Homologous series difference = –CH₂–; gradual b.p. rise. |
| 6 | IUPAC: longest chain → number from nearer multiple bond/substituent. |
| 7 | Ethanol → ethene (443 K, H₂SO₄) → ethanoic acid (alk. KMnO₄). |
| 8 | NaHCO₃ test → brisk CO₂ bubbles → carboxylic acid present. |
| 9 | Hydrogenation of oils → fats (Ni catalyst) → margarine. |
| 10 | Combustion: saturated → clean blue flame; unsaturated → yellow sooty flame. |
BETA
