Class 10 Science · Chapter 4

Carbon and its Compounds

442 Class 10 Science questions on Carbon and its Compounds from the NCERT textbook, NCERT Exemplar and CBSE board papers 2017–2026, each with its answer and a step-by-step solution.

CBSE Class 10 Science previous year papers, with answers →

Questions · page 17 of 23

1. Q321 CBSE 2019
   Write ​the molecular formula ​of ​ethene ​and draw ​its electron ​dot structure.
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   Ethene is ${\text{C}}_2{\text{H}}_4$, with two shared pairs between the carbons (a double bond) and one shared pair for each C-H bond.

   Molecular formula of ethene: ${\text{C}}_2{\text{H}}_4$. Electron dot structure: the two carbon atoms share two pairs of electrons (a carbon-carbon double bond), and each carbon shares one pair with each of its two hydrogen atoms, so each carbon has an octet and each hydrogen a duplet (dots are carbon electrons, crosses hydrogen electrons): $$\begin{array}{ccc}\text{H}& & \text{H}\\ \bullet \times & & \bullet \times \\ \text{C}& \begin{array}{c}\bullet \bullet \\ \bullet \bullet \end{array}& \text{C}\\ \bullet \times & & \bullet \times \\ \text{H}& & \text{H}\end{array}$$ Structural formula: ${\text{H}}_2{\text{C=CH}}_2$.

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2. Q322 CBSE 2019
   Draw ​electron dot ​structure of carbon dioxide and write ​the ​nature ​of bonding between carbon and oxygen in ​its molecule.
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   Carbon shares two pairs of electrons with each oxygen, so ${\text{CO}}_2$ has two double covalent bonds, $\text{O}=\text{C}=\text{O}$.

   Electron dot structure: carbon ($2,4$) shares two pairs of electrons with each oxygen atom ($2,6$), so two shared pairs lie between carbon and each oxygen and each oxygen keeps two lone pairs: $\underset{\cdot \cdot }{\stackrel{\cdot \cdot }{O}}::\text{C}::\underset{\cdot \cdot }{\stackrel{\cdot \cdot }{O}}$ (see the figure). Every atom now has eight electrons in its outermost shell. Nature of bonding: the bonds are covalent (formed by sharing electrons); each carbon-oxygen bond is a double covalent bond, so the molecule is $\text{O}=\text{C}=\text{O}$.

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3. Q323 CBSE 2019
   List ​two ​properties of ​carbon which lead to the huge number ​of carbon compounds ​we ​see around ​us, giving reason for ​each.
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   Catenation (strong C-C bonds) and tetravalency (four bonds with carbon or other elements) give carbon its huge number of compounds.

   (i) Catenation: carbon atoms can link with other carbon atoms by covalent bonds to form long chains, branched chains and rings. Reason: the carbon-carbon bond is very strong and stable (the carbon atom is small), so these chains are stable. (ii) Tetravalency: carbon has a valency of four, so each carbon atom forms four covalent bonds. Reason: all four valencies can be satisfied by carbon atoms or by atoms of other elements such as hydrogen, oxygen, nitrogen, sulphur and chlorine, so many different compounds are formed.

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4. Q324 CBSE 2019
   What happens when ​5% alkaline potassium ​permanganate solution is added drop by drop to ​warm propyl alcohol (propanol) taken in ​a test ​tube ? Explain with ​the help of a chemical ​equation.
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   The purple colour of alkaline permanganate disappears as propanol is oxidised to propanoic acid, and persists once the propanol is used up.

   The purple colour of the alkaline potassium permanganate disappears as each drop is added, because it is used up in oxidising the propanol; once all the propanol has been oxidised, the purple colour of further drops persists. Alkaline ${\text{KMnO}}_4$ acts as an oxidising agent, and propyl alcohol (propanol) is oxidised to propanoic acid: ${\text{CH}}_3{\text{CH}}_2{\text{CH}}_2\text{OH}\stackrel{{\text{alkaline KMnO}}_4,\text{heat}}{\to }{\text{CH}}_3{\text{CH}}_2\text{COOH}$ or ${\text{CH}}_3{\text{CH}}_2{\text{CH}}_2\text{OH}+2[\text{O}]\to {\text{CH}}_3{\text{CH}}_2\text{COOH}+{\text{H}}_2\text{O}$.

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5. Q325 CBSE 2019
   Write the name and molecular formula of ​a carbon ​compound having its name suffixed with ​“-ol” and having two carbon atoms in its molecule. With ​the ​help of a ​chemical equation indicate what happens when this compound is heated ​with excess conc. ${\text{H}}_2{\text{SO}}_4$.
   Show answer

   Ethanol, ${\text{C}}_2{\text{H}}_5\text{OH}$, loses water on heating with excess concentrated sulphuric acid at 443 K, giving ethene.

   Name: Ethanol (the suffix '-ol' shows an alcohol and 'eth-' shows two carbon atoms). Molecular formula: ${\text{C}}_2{\text{H}}_5\text{OH}$, that is, ${\text{C}}_2{\text{H}}_6\text{O}$. On heating at $443$ K with excess concentrated sulphuric acid, ethanol is dehydrated to ethene: ${\text{CH}}_3{\text{CH}}_2\text{OH}\underset{\text{443 K}}{\overset{{\text{hot conc. H}}_2{\text{SO}}_4}{\to }}{\text{CH}}_2={\text{CH}}_2+{\text{H}}_2\text{O}$ Concentrated sulphuric acid acts as a dehydrating agent: it removes a molecule of water from each molecule of ethanol.

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6. Q326 CBSE 2019
   “Conversion of ethanol to ethanoic acid ​is ​an oxidation reaction.” ​Justify this ​statement giving ​the relevant equation ​for the chemical reaction ​involved.
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   Ethanol gains oxygen and loses hydrogen to become ethanoic acid when heated with an oxidising agent, so it is oxidation.

   Ethanol is converted to ethanoic acid by heating it with alkaline potassium permanganate (or with acidified potassium dichromate), which acts as an oxidising agent: ${\text{CH}}_3{\text{CH}}_2\text{OH}+2[\text{O}]\stackrel{{\text{alkaline KMnO}}_4,\text{heat}}{\to }{\text{CH}}_3\text{COOH}+{\text{H}}_2\text{O}$ Justification: In this change ethanol (${\text{C}}_2{\text{H}}_6\text{O}$) gains an oxygen atom and loses two hydrogen atoms to become ethanoic acid (${\text{C}}_2{\text{H}}_4{\text{O}}_2$); the oxygen is supplied by the oxidising agent. Gain of oxygen (and loss of hydrogen) is oxidation, so the conversion of ethanol to ethanoic acid is an oxidation reaction.

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7. Q327 CBSE 2019
   List ​two ​chemical properties ​on the ​basis of which ethanol ​and ethanoic acid may ​be ​differentiated and ​explain how.
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   Ethanoic acid reacts with sodium hydroxide (and turns blue litmus red) and gives effervescence with sodium hydrogencarbonate; ethanol does neither.

   (i) Reaction with a base (acidic nature): ethanoic acid reacts with sodium hydroxide to give sodium ethanoate and water, ${\text{CH}}_3\text{COOH}+\text{NaOH}\to {\text{CH}}_3\text{COONa}+{\text{H}}_2\text{O}$, and it turns blue litmus red; ethanol does not react with sodium hydroxide and has no effect on litmus. (ii) Reaction with sodium hydrogencarbonate (or sodium carbonate): ethanoic acid gives brisk effervescence of carbon dioxide, which turns lime water milky, ${\text{CH}}_3\text{COOH}+{\text{NaHCO}}_3\to {\text{CH}}_3\text{COONa}+{\text{H}}_2\text{O}+{\text{CO}}_2$; ethanol gives no effervescence.

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8. Q328 CBSE 2019
   Unsaturated hydrocarbons contain ​multiple bonds between two carbon atoms and these compounds show addition reactions. Out of ​saturated ​and unsaturated carbon compounds, ​which compounds ​are more ​reactive ? ​Write a test to distinguish ethane from ethene.
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   Unsaturated compounds are more reactive; ethene decolourises bromine water but ethane does not.

   Unsaturated carbon compounds are more reactive than saturated ones, because their double or triple bond allows addition reactions. Test (bromine water test): bubble each gas through reddish-brown bromine water. Ethene decolourises it at once, because bromine adds across its double bond, ${\text{CH}}_2={\text{CH}}_2+{\text{Br}}_2\to {\text{CH}}_2\text{Br}-{\text{CH}}_2\text{Br}$ (colourless); ethane, being saturated, does not react, so the bromine water stays reddish-brown. (Also accepted: ethene decolourises purple alkaline ${\text{KMnO}}_4$ (Baeyer's reagent) and burns with a yellow, sooty flame, while ethane does neither and burns with a clean flame.)

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9. Q329 CBSE 2019
   What ​is a ​homologous ​series of ​carbon compounds ? Give ​an example and list its ​three characteristics.
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   A homologous series has the same functional group; for example alcohols share ${\text{C}}_n{\text{H}}_{2n+1}\text{OH}$ and differ by ${\text{CH}}_2$ ($14$ u).

   A homologous series is a series of carbon compounds in which the same functional group substitutes for hydrogen in a carbon chain, so that successive members differ by a ${\text{CH}}_2$ unit. Example: the alcohols, ${\text{CH}}_3\text{OH}$, ${\text{C}}_2{\text{H}}_5\text{OH}$, ${\text{C}}_3{\text{H}}_7\text{OH}$, ${\text{C}}_4{\text{H}}_9\text{OH}$ (the alkanes ${\text{CH}}_4$, ${\text{C}}_2{\text{H}}_6$, ${\text{C}}_3{\text{H}}_8$ are another). Characteristics: (i) All members have the same general formula (${\text{C}}_n{\text{H}}_{2n+1}\text{OH}$ for the alcohols). (ii) All members have the same functional group ($-\text{OH}$ for the alcohols). (iii) Successive members differ by a ${\text{CH}}_2$ unit, that is, by $14$ u in molecular mass. They also show similar chemical properties, and their physical properties change gradually; either of these is accepted as a characteristic too.

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10. Q330 CBSE 2019
    Which ​compounds are ​called

    1. (i)alkanes, ​
    2. (ii)alkenes and
    3. (iii)alkynes ? ${\text{C}}_4{\text{H}}_{10}$ ​belongs to which ​of these ? ​Draw two structural ​isomers of this compound.
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    Alkanes have single bonds, alkenes a double bond and alkynes a triple bond; ${\text{C}}_4{\text{H}}_{10}$ is an alkane with isomers n-butane and isobutane.

    (i) Alkanes are saturated hydrocarbons in which the carbon atoms are joined by single bonds only; general formula ${\text{C}}_n{\text{H}}_{2n+2}$ (for example ethane, ${\text{C}}_2{\text{H}}_6$). (ii) Alkenes are unsaturated hydrocarbons containing a carbon-carbon double bond; general formula ${\text{C}}_n{\text{H}}_{2n}$ (for example ethene, ${\text{C}}_2{\text{H}}_4$). (iii) Alkynes are unsaturated hydrocarbons containing a carbon-carbon triple bond; general formula ${\text{C}}_n{\text{H}}_{2n-2}$ (for example ethyne, ${\text{C}}_2{\text{H}}_2$). ${\text{C}}_4{\text{H}}_{10}$ fits ${\text{C}}_n{\text{H}}_{2n+2}$ with $n=4$, so it is an alkane (butane). Its two structural isomers are n-butane, ${\text{CH}}_3-{\text{CH}}_2-{\text{CH}}_2-{\text{CH}}_3$ (straight chain), and isobutane or 2-methylpropane, ${\text{CH}}_3-\text{CH}({\text{CH}}_3)-{\text{CH}}_3$ (branched chain); their full structural formulas are shown in the figure.

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11. Q331 CBSE 2019
    (a) What is ​a hydrocarbon ? Give its ​one ​example. (b) Give the ​structural difference between saturated and unsaturated hydrocarbons ​with two examples ​each. (c) Name the following ​compounds :

    1. (i)${\text{CH}}_3-\text{OH}$
    2. (ii)${\text{CH}}_3-\text{C}\begin{array}{l}╱\text{H}\\ ╲╲\text{O}\end{array}$
    3. (iii)${\text{CH}}_3-\underset{\stackrel{\Vert }{O}}{C}-{\text{CH}}_3$
    4. (iv)${\text{CH}}_3-\stackrel{\underset{\Vert }{O}}{C}-\text{OH}$
    Show answer

    A hydrocarbon has only carbon and hydrogen; unsaturated ones have a double or triple bond; the compounds are methanol, ethanal, propanone and ethanoic acid.

    (a) Hydrocarbons are compounds made up of carbon and hydrogen only. Example: methane, ${\text{CH}}_4$. (b) Saturated hydrocarbons have only single bonds between their carbon atoms, e.g. ethane (${\text{C}}_2{\text{H}}_6$) and propane (${\text{C}}_3{\text{H}}_8$). Unsaturated hydrocarbons have at least one double or triple bond between carbon atoms, e.g. ethene (${\text{C}}_2{\text{H}}_4$, with $\text{C}=\text{C}$) and ethyne (${\text{C}}_2{\text{H}}_2$, with $\text{C}\equiv \text{C}$). (c) (i) Methanol (methyl alcohol); (ii) Ethanal (acetaldehyde); (iii) Propanone (acetone); (iv) Ethanoic acid (acetic acid).

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12. Q332 CBSE 2019
    1. (a)​Distinguish between ​esterification ​and saponification reactions with the help of chemical equations for ​each.
    2. (b)With ​a labelled diagram describe in brief an ​activity to show the ​formation of an ester.
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    Esterification makes an ester from an acid and alcohol; saponification splits an ester with an alkali; a fruity smell shows the ester formed.

    (a) Esterification: a carboxylic acid reacts with an alcohol in the presence of an acid catalyst (a few drops of concentrated sulphuric acid) to form a sweet-smelling ester and water: ${\text{CH}}_3\text{COOH}+{\text{C}}_2{\text{H}}_5\text{OH}\stackrel{{\text{conc. H}}_2{\text{SO}}_4}{\to }{\text{CH}}_3{\text{COOC}}_2{\text{H}}_5+{\text{H}}_2\text{O}$ Saponification: an ester reacts with an alkali such as sodium hydroxide to give back the alcohol and the sodium salt of the carboxylic acid; with fats and oils this reaction makes soap: ${\text{CH}}_3{\text{COOC}}_2{\text{H}}_5+\text{NaOH}⟶{\text{C}}_2{\text{H}}_5\text{OH}+{\text{CH}}_3\text{COONa}$ Thus esterification forms an ester from an acid and an alcohol with an acid catalyst, while saponification breaks an ester with a base into an alcohol and a salt. (b) Take 1 mL ethanol, 1 mL glacial ethanoic acid and a few drops of concentrated sulphuric acid in a test tube. Warm it in a water bath for about five minutes (see the labelled diagram). Pour the mixture into a beaker containing 20 to 50 mL of water and smell it. A sweet, fruity smell shows that an ester, ethyl ethanoate, has been formed.

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13. Q333 CBSE 2019
    (a) ​State the reason why carbon can neither form ${\text{C}}^{4+}$ ​cations nor ${\text{C}}^{4-}$ anions, ​but forms covalent bonds. Also ​state reasons to explain why covalent compounds

    1. (i)are bad ​conductors of electricity.
    2. (ii)have low melting and boiling points. (b) Write ​the ​structural formula of benzene, ${\text{C}}_6{\text{H}}_6$.
    Show answer

    Carbon shares electrons; covalent compounds lack free charges and have weak forces between molecules; benzene is a ring with alternate single and double bonds.

    (a) Carbon (electrons 2, 4) has four valence electrons. It cannot form ${\text{C}}^{4+}$ because removing four electrons would need a very large amount of energy, leaving six protons holding only two electrons. It cannot form ${\text{C}}^{4-}$ because a nucleus with six protons cannot hold on to ten electrons, that is, four extra electrons. So carbon shares its four valence electrons with other atoms and forms covalent bonds. (i) Covalent compounds are bad conductors of electricity because their electrons are shared between atoms and no ions are formed, so there are no free charged particles to carry the current. (ii) They have low melting and boiling points because the forces of attraction between their molecules are weak, so little energy is needed to separate the molecules. (b) Benzene, ${\text{C}}_6{\text{H}}_6$, is a hexagonal ring of six carbon atoms joined by alternate single and double bonds, with one hydrogen atom bonded to each carbon atom, as drawn in the figure.

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14. Q334 CBSE 2019
    What is the difference between soaps and ​detergents ? State ​in brief the cleansing action of soaps ​in ​removing an oily ​spot from a fabric. ​Why are soaps not very effective when a fabric is washed in hard ​water ? How is this problem resolved ​?
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    Soaps are carboxylate salts, detergents sulphonate or ammonium salts; soap tails dissolve in oil, forming micelles; hard water gives scum, solved by using detergents.

    Difference: soaps are sodium or potassium salts of long-chain carboxylic (fatty) acids, while detergents are generally sodium salts of long-chain sulphonic acids (or ammonium salts). Soaps form scum with hard water and do not work well in it; detergents work well in both soft and hard water. Cleansing action: a soap molecule has an ionic end that dissolves in water and a long hydrocarbon tail that dissolves in oil. In soap solution the tails dissolve in the oily spot and the ionic ends face the water, so the molecules form micelles with the oily dirt trapped at the centre. On rubbing, the micelles are pulled off the fabric and, being held in the water by their ionic ends, are washed away with the dirt. Hard water contains calcium and magnesium ions, which react with soap to form an insoluble precipitate called scum, so a large amount of soap is wasted and little lather forms: $2{\text{C}}_{17}{\text{H}}_{35}\text{COONa}+{\text{Ca}}^{2+}⟶({\text{C}}_{17}{\text{H}}_{35}\text{COO}{)}_2\text{Ca}\downarrow +2{\text{Na}}^{+}$ The problem is resolved by using detergents, whose charged ends do not form insoluble precipitates with calcium and magnesium ions; the hardness can also be removed before washing, by boiling (temporary hardness) or with washing soda (permanent hardness).

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15. Q335 CBSE 2019
    1. (a)Define the ​term ‘isomer’.
    2. (b)Two ​compounds ​have same molecular formula ${\text{C}}_3{\text{H}}_6\text{O}$. Write the name of these compounds ​and their structural formula.
    3. (c)How would you bring the ​following conversions : (i) ​Ethanol ​to ethene (ii) Propanol ​to propanoic acid
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    Isomers share a molecular formula but differ in structure; ${\text{C}}_3{\text{H}}_6\text{O}$ is propanal or propanone; dehydration gives ethene, oxidation gives propanoic acid.

    (a) Compounds that have the same molecular formula but different structural formulae (different arrangements of atoms) are called isomers. (b) The two compounds are propanal, an aldehyde, ${\text{CH}}_3-{\text{CH}}_2-\text{CHO}$, and propanone (acetone), a ketone, ${\text{CH}}_3-\text{CO}-{\text{CH}}_3$. In propanal the C=O group is on the end carbon, which also carries a hydrogen atom; in propanone it is on the middle carbon. Their full structural formulae are drawn in the solution. (c)(i) Ethanol is heated at $443$ K with excess concentrated sulphuric acid, which removes water: ${\text{CH}}_3{\text{CH}}_2\text{OH}\stackrel{{\text{hot conc. H}}_2{\text{SO}}_4}{\to }{\text{CH}}_2={\text{CH}}_2+{\text{H}}_2\text{O}$. (ii) Propanol is heated with alkaline potassium permanganate (or acidified potassium dichromate), which oxidises it: ${\text{CH}}_3{\text{CH}}_2{\text{CH}}_2\text{OH}\stackrel{{\text{alkaline KMnO}}_4,\text{heat}}{\to }{\text{CH}}_3{\text{CH}}_2\text{COOH}$.

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16. Q336 CBSE 2019
    1. (a)Distinguish between esterification ​and ​saponification reactions ​with the ​help ​of ​chemical equation for each.
    2. (b)Write an ​activity to show the formation ​of an ester in a school laboratory.
    Show answer

    Esterification makes a sweet-smelling ester from an acid and an alcohol; saponification splits an ester with alkali; the ester is recognised by its smell.

    (a) Esterification: a carboxylic acid reacts with an alcohol, when warmed with a few drops of concentrated sulphuric acid (an acid catalyst), to form a sweet-smelling ester and water: ${\text{CH}}_3\text{COOH}+{\text{C}}_2{\text{H}}_5\text{OH}\stackrel{{\text{conc. H}}_2{\text{SO}}_4}{\to }{\text{CH}}_3{\text{COOC}}_2{\text{H}}_5+{\text{H}}_2\text{O}$ (ethanoic acid + ethanol give ethyl ethanoate + water). Saponification: an ester reacts with an alkali such as sodium hydroxide to give back the alcohol and the sodium salt of the carboxylic acid: ${\text{CH}}_3{\text{COOC}}_2{\text{H}}_5+\text{NaOH}\to {\text{C}}_2{\text{H}}_5\text{OH}+{\text{CH}}_3\text{COONa}$ (ethyl ethanoate + sodium hydroxide give ethanol + sodium ethanoate). So esterification forms an ester from an acid and an alcohol in an acidic medium, while saponification breaks an ester with a base and is used to make soap. (b) Activity: take $1$ mL of ethanol and $1$ mL of glacial ethanoic acid in a test tube and add a few drops of concentrated sulphuric acid; warm the test tube in a water bath for at least $5$ minutes; pour the mixture into a beaker containing $20$ to $50$ mL of water and smell it. A sweet, fruity smell shows that an ester (ethyl ethanoate) has been formed.

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17. Q337 CBSE 2019
    Write the chemical ​formula and name ​of the compound which is the active ingredient of all alcoholic drinks. ​List ​its ​two uses. Write chemical equation and name of the product formed ​when this compound reacts with ​–

    1. (i)sodium metal
    2. (ii)hot concentrated sulphuric acid
    Show answer

    Ethanol, ${\text{C}}_2{\text{H}}_5\text{OH}$, is a solvent and used in medicines; sodium gives sodium ethoxide and hydrogen; hot conc. sulphuric acid gives ethene.

    The compound is ethanol (ethyl alcohol), ${\text{C}}_2{\text{H}}_5\text{OH}$. Two uses: (1) it is a good solvent, used in industry; (2) it is used in medicines such as tincture of iodine, cough syrups and tonics. Other correct uses, such as a fuel mixed with petrol, are also valid. (i) $2{\text{C}}_2{\text{H}}_5\text{OH}+2\text{Na}\to 2{\text{C}}_2{\text{H}}_5\text{ONa}+{\text{H}}_2$; the product is sodium ethoxide (hydrogen gas is given off). (ii) ${\text{C}}_2{\text{H}}_5\text{OH}\underset{443\text{K}}{\overset{{\text{hot conc. H}}_2{\text{SO}}_4}{\to }}{\text{CH}}_2={\text{CH}}_2+{\text{H}}_2\text{O}$; the product is ethene (the acid removes water from ethanol).

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18. Q338 CBSE 2019
    1. (a)Draw electron dot ​structure of ​methane ​molecule.
    2. (b)Identify the functional groups ​present in the following compounds : (i) ${\text{C}}_2{\text{H}}_6\text{O}$ (ii) ${\text{C}}_2{\text{H}}_4\text{O}$ (c) A mixture of oxygen ​and ethyne is burnt ​for welding. ​Why do you think a mixture of ethyne and air is not used for welding ​?
    Show answer

    Methane has four shared pairs; ${\text{C}}_2{\text{H}}_6\text{O}$ has $-\text{OH}$, ${\text{C}}_2{\text{H}}_4\text{O}$ has $-\text{CHO}$; ethyne burns incompletely in air but gives a very hot flame in oxygen.

    (a) In methane, ${\text{CH}}_4$, carbon (configuration $2,4$) shares one pair of electrons with each of four hydrogen atoms: C is in the centre with an H on each of its four sides, and each C–H link is a shared pair made of one electron from carbon and one from hydrogen. Carbon thus has an octet and each hydrogen a duplet, with four single covalent bonds and no lone pairs. (b) (i) ${\text{C}}_2{\text{H}}_6\text{O}$ is ethanol, ${\text{C}}_2{\text{H}}_5\text{OH}$: alcohol group, $-\text{OH}$. (ii) ${\text{C}}_2{\text{H}}_4\text{O}$ is ethanal, ${\text{CH}}_3\text{CHO}$: aldehyde group, $-\text{CHO}$. (c) Air contains only about $21\%$ oxygen, so ethyne burnt in air burns incompletely, with a sooty flame that is not hot enough for welding. In pure oxygen it burns completely and gives a very hot flame (about $3000^{\circ }$C) that melts metals: $2{\text{C}}_2{\text{H}}_2+5{\text{O}}_2\to 4{\text{CO}}_2+2{\text{H}}_2\text{O}+\text{heat}$.

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19. Q339 CBSE 2019
    What is methane? Draw its electron dot structure. ​Name the type of bonds formed in ​this compound. Why are such compounds:

    1. (i)poor conductors of electricity ? and
    2. (ii)have low ​melting and boiling ​points? ​What happens when this compound ​burns in ​oxygen?
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    Methane, ${\text{CH}}_4$, has four covalent bonds; it has no ions and weak intermolecular forces, and burns to carbon dioxide and water.

    Methane, ${\text{CH}}_4$, is the simplest hydrocarbon (the first alkane), a compound of one carbon atom and four hydrogen atoms; it is the main constituent of natural gas, CNG and biogas. Electron dot structure (see the figure): carbon shares one pair of electrons with each of the four hydrogen atoms, so carbon has 8 outer electrons and each hydrogen 2. Type of bonds: covalent bonds (four single covalent bonds between carbon and hydrogen). (i) Such compounds are poor conductors of electricity because their electrons are shared and no ions (charged particles) are formed, so nothing can carry the current. (ii) They have low melting and boiling points because they are covalent compounds whose molecules are held together only by weak forces of attraction, so little energy is needed to separate the molecules. When methane burns in oxygen it forms carbon dioxide and water, with a lot of heat and light: ${\text{CH}}_4+2{\text{O}}_2\to {\text{CO}}_2+2{\text{H}}_2\text{O}$ + heat and light.

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20. Q340 CBSE 2019
    (a) Carry out the following conversions giving complete conditions for ​the reaction ​to take place in each case :

    1. (i)Ethanoic ​acid from ​Ethanol
    2. (ii)Ethane from Ethene
    3. (iii)Ester from Ethanoic ​acid and ethanol Also ​state the names given to all the above ​conversions. (b) Detergents are preferred over soaps. Why ​? (Give one reason)
    Show answer

    Oxidation, hydrogenation and esterification give ethanoic acid, ethane and ethyl ethanoate; detergents form no scum in hard water.

    (a) (i) Ethanol is heated with alkaline potassium permanganate (or acidified potassium dichromate): ${\text{CH}}_3{\text{CH}}_2\text{OH}\stackrel{{\text{alkaline KMnO}}_4+\text{heat}}{\to }{\text{CH}}_3\text{COOH}$. Name: oxidation. (ii) Ethene and hydrogen are passed over a nickel (or palladium) catalyst on heating: ${\text{CH}}_2={\text{CH}}_2+{\text{H}}_2\stackrel{\text{Ni, heat}}{\to }{\text{CH}}_3-{\text{CH}}_3$. Name: hydrogenation (an addition reaction). (iii) Ethanoic acid is warmed with ethanol and a few drops of concentrated sulphuric acid as catalyst: ${\text{CH}}_3\text{COOH}+{\text{CH}}_3{\text{CH}}_2\text{OH}\stackrel{{\text{conc. H}}_2{\text{SO}}_4}{\to }{\text{CH}}_3{\text{COOCH}}_2{\text{CH}}_3+{\text{H}}_2\text{O}$, giving the sweet-smelling ester ethyl ethanoate. Name: esterification. (b) Detergents can be used even in hard water: unlike soaps, they do not form an insoluble scum with the calcium and magnesium ions of hard water, so they still lather and clean.

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