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 15 of 23

1. Q281 CBSE 2022
   “Two ​different forms of carbon ​– ​diamond and graphite have ​different structures and very different physical properties even though ​their ​chemical properties ​are same.” Explain why.
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   Different bonding of the same carbon atoms gives different physical properties; the atoms are the same, so the chemical properties are the same.

   Diamond and graphite are both made of carbon atoms only (they are allotropes of carbon); they differ only in the way the carbon atoms are bonded to one another. In diamond each carbon atom is bonded to four other carbon atoms, forming a rigid three-dimensional structure, so diamond is extremely hard (the hardest natural substance) and does not conduct electricity. In graphite each carbon atom is bonded to three other carbon atoms in the same plane, giving hexagonal layers placed one above another; the layers are held together only weakly and slide over each other, so graphite is soft, smooth and slippery, and it is a good conductor of electricity. Physical properties depend on this arrangement of the atoms, so the two forms have very different physical properties. Chemical properties depend on the atoms themselves, the same carbon atoms with the same four valence electrons in both, so the two forms react in the same way: for example, both burn in oxygen to give only carbon dioxide, $\text{C}+{\text{O}}_2\to {\text{CO}}_2$.

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2. Q282 CBSE 2022
   State the reasons, ​why carbon cannot

   1. (i)Lose four electrons to ​form ${\text{C}}^{4+}$ cation, ​and
   2. (ii)Gain four electrons to ​form ${\text{C}}^{4-}$ anion. How ​does carbon overcome this problem to form ​compounds ?
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   Losing four electrons needs too much energy and gaining four is difficult, so carbon shares its four valence electrons and forms covalent bonds.

   (i) Carbon (2, 4) would have to lose four electrons to form ${\text{C}}^{4+}$. Removing four electrons would require a large amount of energy, and it would leave a cation with six protons in its nucleus holding on to just two electrons. (ii) To form ${\text{C}}^{4-}$, carbon would have to gain four electrons. It would be difficult for a nucleus with only six protons to hold on to ten electrons, that is, four extra electrons. Carbon overcomes this problem by sharing its four valence electrons with other atoms of carbon or with atoms of other elements, forming covalent bonds. The shared electrons belong to the outer shells of both atoms, so both attain a noble-gas configuration: in methane, ${\text{CH}}_4$, carbon shares one pair with each of four hydrogen atoms and so has eight electrons in its outermost shell, while each hydrogen has two.

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3. Q283 CBSE 2020
   Name ​a ​cyclic unsaturated ​carbon ​compound.
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   Cyclohexene, ${\text{C}}_6{\text{H}}_{10}$, is cyclic (ring) and unsaturated (has a double bond).

   Cyclohexene, ${\text{C}}_6{\text{H}}_{10}$: its six carbon atoms form a ring (cyclic) and the ring contains a carbon–carbon double bond (unsaturated). Cyclopentene, ${\text{C}}_5{\text{H}}_8$, or benzene, ${\text{C}}_6{\text{H}}_6$, is equally correct, and so is any other ring compound of carbon with a double or triple bond.

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4. Q284 CBSE 2020
   Name the functional ​group present ​in ​propanone.
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   The ketone group, $>\text{C}=\text{O}$.

   Ketone group, $>\text{C}=\text{O}$: a carbonyl group joined to two carbon atoms, as in propanone, ${\text{CH}}_3{\text{COCH}}_3$.

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5. Q285 CBSE 2020
   Covalent compounds have ​low ​melting ​and ​boiling point. ​Why ?
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   Covalent compounds have weak intermolecular forces, so little heat energy is needed to separate their molecules.

   Because the forces of attraction between the molecules of a covalent compound (the intermolecular forces) are weak. Melting and boiling only have to separate the molecules from one another, which needs little heat energy, so covalent compounds melt and boil at low temperatures.

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6. Q286 CBSE 2020
   How are covalent bonds formed ?
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   A covalent bond forms when two atoms share a pair (or pairs) of electrons.

   Covalent bonds are formed by the sharing of a pair (or pairs) of electrons between two atoms. The shared pair is attracted by both nuclei and counts towards the outer shell of each atom, so both atoms attain a stable, completely filled outer shell without any electron being transferred.

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7. Q287 CBSE 2020
   Write ​the number ​of valence ​electrons present ​in a nitrogen ​atom $\left({}_7^{14}\text{N}\right)$.
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   A nitrogen atom has 5 valence electrons, since its configuration is $2,5$.

   A nitrogen atom has $5$ valence electrons. Its $7$ electrons are arranged $2,5$, and the outermost ($\text{L}$) shell holds $5$ of them.

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8. Q288 CBSE 2020
   Which ​oils should be chosen for ​cooking to ​remain ​healthy ​?
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   Choose oils with unsaturated fatty acids, such as sunflower, groundnut, mustard or olive oil.

   Oils containing unsaturated fatty acids should be chosen, for example vegetable oils such as sunflower, groundnut, mustard or olive oil. Animal fats, and hydrogenated fats such as vanaspati ghee, contain saturated fatty acids, which are said to be harmful for health. Naming a suitable edible oil also earns the mark.

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9. Q289 CBSE 2020
   Draw ​the ​structure of a carboxylic ​acid containing ​three carbon ​atoms.
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   Propanoic acid, ${\text{CH}}_3-{\text{CH}}_2-\text{COOH}$: three carbon atoms in a chain, the third being the carboxyl carbon.

   Propanoic acid, ${\text{CH}}_3-{\text{CH}}_2-\text{COOH}$ (molecular formula ${\text{C}}_3{\text{H}}_6{\text{O}}_2$). Its structure is a chain of three carbon atoms: the first carbon carries three hydrogen atoms, the second carbon two hydrogen atoms, and the third carbon is the carboxyl carbon, joined to one oxygen atom by a double bond and to an $-\text{OH}$ group by a single bond.

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10. Q290 CBSE 2020
    Covalent ​compounds ​are generally ​poor conductors of electricity. ​Why ​?
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    Covalent compounds have no ions or free electrons to carry charge, so they are poor conductors.

    Because covalent compounds contain no charged particles (ions) to carry the current. Their atoms are bonded by sharing electrons, so no ions are formed and the compound is made of neutral molecules; with no ions (and no free electrons) to move and carry charge, covalent compounds are generally poor conductors of electricity.

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11. Q291 CBSE 2020
    Name ​the type ​of bonds formed ​when one ​carbon atom combines ​with four ​hydrogen atoms to ​form a molecule.
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    Covalent bonds: carbon shares an electron pair with each hydrogen atom in methane, ${\text{CH}}_4$.

    Covalent bonds. The carbon atom shares one pair of electrons with each of the four hydrogen atoms, so the molecule formed, methane (${\text{CH}}_4$), has four single covalent bonds.

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12. Q292 CBSE 2020
    Write ​the ​name and formulae ​of the ​first member of the homologous ​series ​of ​alkenes.
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    The first alkene is ethene, ${\text{C}}_2{\text{H}}_4$.

    Ethene (also called ethylene). Molecular formula ${\text{C}}_2{\text{H}}_4$; structural formula ${\text{H}}_2\text{C}={\text{CH}}_2$.

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13. Q293 CBSE 2020
    A carbon ​compound ​is a constituent of beer, whisky and some cough ​syrups. Identify ​the compound ​and write ​its formula.
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    The compound is ethanol, ${\text{C}}_2{\text{H}}_5\text{OH}$.

    Ethanol (ethyl alcohol); formula ${\text{C}}_2{\text{H}}_5\text{OH}$, that is ${\text{CH}}_3{\text{CH}}_2\text{OH}$.

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14. Q294 CBSE 2020
    How is ​acetic ​acid ​prepared from ethanol ​?
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    Ethanol is oxidised to acetic acid by heating with alkaline potassium permanganate or acidified potassium dichromate.

    By oxidising ethanol: ethanol is heated with alkaline potassium permanganate (or with acidified potassium dichromate), which converts it into acetic (ethanoic) acid. ${\text{CH}}_3{\text{CH}}_2\text{OH}+2[\text{O}]\to {\text{CH}}_3\text{COOH}+{\text{H}}_2\text{O}$, where $[\text{O}]$ is oxygen supplied by the oxidising agent.

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15. Q295 CBSE 2020
    The formula of an ​ester is ${\text{CH}}_3{\text{COOC}}_3{\text{H}}_7$. Write the ​name or the ​formula of ​the parent alcohol and the parent ​carboxylic acid ​from ​which this ​ester is prepared.
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    The parent alcohol is propanol and the parent carboxylic acid is ethanoic acid.

    Parent alcohol: propanol, ${\text{C}}_3{\text{H}}_7\text{OH}$ (${\text{CH}}_3{\text{CH}}_2{\text{CH}}_2\text{OH}$). Parent carboxylic acid: ethanoic acid (acetic acid), ${\text{CH}}_3\text{COOH}$. They form the ester by esterification: ${\text{CH}}_3\text{COOH}+{\text{C}}_3{\text{H}}_7\text{OH}\to {\text{CH}}_3{\text{COOC}}_3{\text{H}}_7+{\text{H}}_2\text{O}$.

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16. Q296 CBSE 2020
    What ​happens ​when ethyl ​ethanoate reacts with ​sodium hydroxide ?
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    Saponification: the ester breaks down into ethanol and sodium ethanoate (sodium acetate).

    It undergoes saponification: the ester is broken down into ethanol and sodium ethanoate (sodium acetate). ${\text{CH}}_3{\text{COOC}}_2{\text{H}}_5+\text{NaOH}\to {\text{CH}}_3\text{COONa}+{\text{C}}_2{\text{H}}_5\text{OH}$.

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17. Q297 CBSE 2020
    When sodium hydrogen ​carbonate is added to ethanoic acid a gas evolves. Consider the following statements about the gas evolved? (A) It turns lime water ​milky. (B) ​It is evolved ​with ​a brisk effervescence. (C) ​It has a smell of burning sulphur. (D) It is also a by-product ​of ​respiration. The correct statements are :

    1. (a)(A) and (B) only
    2. (b)(B) and (D) only
    3. (c)(A), (C) and (D)
    4. (d)(A), (B) and (D)
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    (d) (A), (B) and (D)

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18. Q298 CBSE 2020
    ${\text{CH}}_4+{\text{Cl}}_2\stackrel{\text{Sunlight}}{\to }{\text{CH}}_3\text{Cl}+\text{HCl}$ The ​above reaction ​is an ​example ​of

    1. (a)displacement reaction
    2. (b)addition reaction
    3. (c)substitution reaction
    4. (d)double displacement reaction
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    (c) substitution reaction

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19. Q299 CBSE 2020
    Which one ​of the following ​compounds ​changes ​blue ​litmus to ​red ​?

    1. (a)${\text{C}}_2{\text{H}}_5\text{OH}$
    2. (b)${\text{CH}}_3{\text{COCH}}_3$
    3. (c)${\text{C}}_2{\text{H}}_5\text{CHO}$
    4. (d)${\text{C}}_2{\text{H}}_5\text{COOH}$
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    (d) ${\text{C}}_2{\text{H}}_5\text{COOH}$

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20. Q300 CBSE 2020
    Incomplete ​combustion ​of ​coal and ​petroleum ​: (A) increases air ​pollution. (B) increases efficiency of machines. (C) reduces global warming. (D) produce poisonous gases. The ​correct option is :

    1. (a)(A) and (B)
    2. (b)(A) and (D)
    3. (c)(B) and (C)
    4. (d)(C) and (D)
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    (b) (A) and (D)

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