Q.Describe two methods of preparation of ethane. Give any three reactions of ethane.

Showing the 12 most recent of 14 on this concept.

1. CBSE 2026Set ANNUAL1 markMCQ
   Q.The reaction used for preparation of higher alkanes from alkyl halides is

   (a) Wurtz reaction

   (b) Kolbe's reaction

   (c) β-elimination

   (d) Friedel-Crafts acylation

   ›Reveal solutionSolution

   The Wurtz reaction converts alkyl halides into higher (longer-chain) alkanes by coupling two alkyl groups using sodium metal in dry ether.

   The Wurtz reaction: 2 R-X + 2 Na --(dry ether)--> R-R + 2 NaX

   Here, two molecules of an alkyl halide (R-X) react with sodium metal in dry ether. The sodium removes the halogen atoms and couples the two alkyl (R) groups together, forming a new C-C bond and producing a symmetrical alkane with twice the number of carbons as the starting alkyl halide (plus sodium halide as a by-product).

   For example: 2 CH3-Br + 2 Na --(dry ether)--> CH3-CH3 (ethane) + 2 NaBr.

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2. CBSE 2026Set ANNUAL1 mark
   Q.Identify [A] in the reaction: CH3Br + 2Na + BrCH3 --(dry ether)--> [A] + 2NaBr

   ›Reveal solutionSolution

   This is a Wurtz reaction; [A] = ethane (CH3-CH3).

   The Wurtz reaction couples two molecules of an alkyl halide using sodium metal in dry ether, joining the two alkyl groups by a new C-C bond and eliminating two sodium halide units: 2R-X + 2Na, in dry ether, gives R-R + 2NaX.

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3. CBSE 2026Set ANNUAL1 mark
   Q.Write chemical equation for the preparation of butane by Wurtz reaction.

   ›Reveal solutionSolution

   Two molecules of ethyl bromide couple via sodium metal in dry ether to give butane (a symmetrical alkane) plus sodium bromide.

   The Wurtz reaction couples two molecules of an alkyl halide using sodium metal in dry ether, forming a new C–C bond and a symmetrical alkane with double the carbon count of the starting halide. To get butane ($C_4H_{10}$, 4 carbons), the alkyl halide used must have 2 carbons, i.e. ethyl bromide ($CH_3CH_2Br$):

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4. CBSE 2025Set ANNUAL1 markMCQ
   Q.The reaction used for obtaining of higher alkanes from alkyl halides is

   (a) Wurtz reaction

   (b) Kolbe's reaction

   (c) beta-elimination

   (d) Friedel-Crafts acylation

   ›Reveal solutionSolution

   The Wurtz reaction couples two molecules of an alkyl halide using sodium metal in dry ether, joining their carbon chains to build a longer (higher) alkane with twice as many carbons.

   The Wurtz reaction is written as:

   2 R-X + 2 Na --(dry ether)--> R-R + 2 NaX

   where R-X is an alkyl halide (e.g. CH3Br) and R-R is the resulting symmetrical higher alkane (e.g. 2 CH3Br + 2Na -> CH3-CH3 (ethane) + 2NaBr).

   Mechanistically, sodium metal donates electrons to generate alkyl radicals (or organosodium intermediates) from two molecules of the alkyl halide, and these two alkyl fragments then couple together to form a new C-C bond, joining the two chains into one longer molecule — this is exactly how 'higher alkanes' (alkanes with more carbons than the starting alkyl halide) are synthesised in the lab from smaller alkyl halides.

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5. CBSE 2025Set ANNUAL1 mark
   Q.Write the chemical equation for Wurtz reaction.

   ›Reveal solutionSolution

   Wurtz reaction: 2R−X + 2Na (dry ether) → R−R + 2NaX.

   The Wurtz reaction couples two alkyl halide molecules using sodium metal in dry ethereal solution, forming a symmetrical higher alkane with double the number of carbons of the starting halide, along with sodium halide:

   $2R\text{-}X + 2Na \xrightarrow{\text{dry ether}} R\text{-}R + 2NaX$

   For example, with methyl bromide:

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6. CBSE 2024Set ANNUAL1 mark
   Q.What is Wurtz Reaction?

   ›Reveal solutionSolution

   Sodium couples two alkyl halide molecules together (via a free-radical mechanism) to build a longer, symmetrical alkane.

   In the Wurtz reaction, an alkyl halide reacts with sodium metal in dry ether solvent. Two molecules of the alkyl halide are 'coupled' together (via a free-radical mechanism, with sodium donating electrons), forming a new C-C bond between them and releasing sodium halide:

   2R-X + 2Na --(dry ether)--> R-R + 2NaX

   …

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7. CBSE 2024Set ANNUAL1 mark
   Q.Alkyl halides react with sodium in dry ether to form symmetrical alkanes containing double the number of carbon atoms present in the halides. Name the reaction.

   ›Reveal solutionSolution

   Sodium metal in dry ether couples two alkyl halide molecules together into one longer symmetrical alkane — this coupling reaction is named the Wurtz reaction.

   When an alkyl halide is treated with sodium metal in dry ether, two molecules of the halide couple together (via a free-radical or organosodium intermediate) to form a single, symmetrical alkane containing double the number of carbon atoms of the original halide, with sodium halide as the by-product:

   $2R-X + 2Na \xrightarrow{dry\ ether} R-R + 2NaX$

   For example, $2CH_3Br + 2Na \rightarrow CH_3-CH_3 + 2NaBr$ (ethane from methyl bromide).

   …

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8. CBSE 2024Set ANNUAL1 markMCQ
   Q.The reaction used for preparation of higher alkanes from alkyl halide is

   (a) Wurtz reaction

   (b) Kolbe's reaction

   (c) beta-elimination

   (d) Friedel-Crafts acylation

   ›Reveal solutionSolution

   The Wurtz reaction uses sodium metal in dry ether to couple two molecules of an alkyl halide, joining their carbon chains to build a higher (usually symmetrical) alkane.

   Wurtz reaction: 2 R-X + 2 Na --dry ether--> R-R + 2 NaX

   Two alkyl halide molecules react with sodium metal, which removes the halogen atoms and couples the two alkyl groups together, forming a new C-C bond and producing an alkane with double the carbon count of the starting alkyl halide (plus sodium halide as a by-product).

   …

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9. CBSE 2022Set TERM21 markMCQ
   Q.Alkyl halides react with sodium in dry either to give hydrocarbons containing double number of Carbon atoms present in the halides. The rex is known as:

   (a) Wurtz rex

   (b) Wurtz-Fittig rex

   (c) Swarts rex

   (d) None of these

   ›Reveal solutionSolution

   Alkyl halides couple with sodium metal in dry ether to double the carbon chain — this is the Wurtz reaction.

   When an alkyl halide is treated with sodium metal in dry ether, two alkyl groups couple together (Wurtz coupling), eliminating NaX and forming a higher (symmetrical) alkane with double the number of carbon atoms:

   $2R\text{-}X + 2Na \xrightarrow{\text{dry ether}} R\text{-}R + 2NaX$

   …

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10. CBSE 2022Set ANNUAL1 markMCQ
    Q.Isopropyl bromide gives on Wurtz's reaction

    (a) Hexane

    (b) Propane

    (c) 2,3-dimethyl butane

    (d) Neohexane

    ›Reveal solutionSolution

    Wurtz reaction of isopropyl bromide gives 2,3-dimethylbutane — option (c).

    From NCERT Class 11 Chemistry (Hydrocarbons): in the Wurtz reaction, 2R–X + 2Na → R–R + 2NaX.

    Here R = isopropyl, (CH₃)₂CH–. Coupling two isopropyl units: …

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11. CBSE 2019Set ANNUAL1 markMCQ
    Q.CH3Br + 2Na + CH3Br --Dry ether--> CH3-CH3 + 2NaBr. The reaction is

    (a) Friedel-Crafts reaction

    (b) Wurtz reaction

    (c) Fittig reaction

    (d) none of these.

    ›Reveal solutionSolution

    Treating an alkyl halide with sodium metal in dry ether to couple two alkyl groups into a symmetrical alkane is the Wurtz reaction.

    2CH3Br + 2Na --dry ether--> CH3-CH3 + 2NaBr

    Sodium first forms a very reactive alkylsodium intermediate, which then displaces bromide from a second molecule of CH3Br in an SN2-like coupling, joining the two methyl groups to give ethane (CH3-CH3) and releasing NaBr. This coupling of two alkyl halide molecules using sodium in dry ether is named the Wurtz reaction (distinct from the Fittig reaction, which is t …

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12. CBSE 2019Set ANNUAL1 markMCQ
    Q.Which of the following organic compounds are formed by Wurtz reaction?

    (a) Alcohols

    (b) Hydrocarbons

    (c) Haloalkanes

    (d) Haloarenes

    ›Reveal solutionSolution

    Wurtz reaction: 2 R–X + 2Na → R–R + 2NaX (dry ether), giving a higher alkane — a hydrocarbon.

    The Wurtz reaction is the treatment of an alkyl halide with sodium metal in dry ether:

    $2R\text{–}X + 2Na \xrightarrow{\text{dry ether}} R\text{–}R + 2NaX$

    …

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