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 18 of 23

1. Q341 CBSE 2019
   What ​are ​structural ​isomers ? List any ​four characteristics ​of ​isomers. Draw the possible structures of butane.
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   Structural isomers have the same molecular formula but different structures; butane has two, the straight-chain n-butane and the branched isobutane.

   Structural isomers: compounds that have the same molecular formula but different structures are called structural isomers. Characteristics of isomers: 1. They have the same molecular formula. 2. They have the same molecular mass and the same number of each kind of atom. 3. They have different structures. 4. They have different physical and chemical properties (for example, butane boils at about $-0.5{}^{\circ }\text{C}$ and isobutane at about $-11.7{}^{\circ }\text{C}$). Possible structures of butane, ${\text{C}}_4{\text{H}}_{10}$: (i) butane (n-butane), a straight chain of four carbon atoms, ${\text{CH}}_3-{\text{CH}}_2-{\text{CH}}_2-{\text{CH}}_3$; (ii) isobutane (2-methylpropane), a chain of three carbon atoms with the fourth attached to the middle carbon, ${\text{CH}}_3-\text{CH}({\text{CH}}_3)-{\text{CH}}_3$.

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2. Q342 CBSE 2019
   In three ​test tubes A, B, ​and C, three different liquids namely, distilled water, underground water and distilled water in which a pinch of calcium sulphate is ​dissolved, respectively are taken. Equal amount of ​soap ​solution is added to each test tube and the ​contents are shaken. In which test tube will the length ​of the foam (lather) be longest ? Justify your answer.
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   Test tube A has the longest foam, because distilled water is soft water and the other two are hard.

   The foam (lather) is longest in test tube A, which contains distilled water. Justification: distilled water contains no dissolved calcium or magnesium salts (it is soft water), so all the soap forms lather. Underground water (B) and distilled water with calcium sulphate (C) are hard water: their calcium (and magnesium) ions react with the soap to form an insoluble scum, so much of the soap is wasted and little lather forms.

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3. Q343 CBSE 2019
   What is observed ​when ​a pinch of sodium hydrogen carbonate is ​added to 2 mL of acetic ​acid taken in a test tube ? Write ​chemical equation for ​the reaction involved ​in this case.
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   A brisk effervescence of carbon dioxide is seen, which turns lime water milky; sodium ethanoate and water also form.

   Observation: a brisk effervescence is seen - bubbles of a colourless, odourless gas, carbon dioxide, are given off (the gas turns lime water milky). ${\text{CH}}_3\text{COOH}+{\text{NaHCO}}_3⟶{\text{CH}}_3\text{COONa}+{\text{H}}_2\text{O}+{\text{CO}}_2$ (Ethanoic acid + sodium hydrogencarbonate gives sodium ethanoate + water + carbon dioxide.)

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4. Q344 CBSE 2019
   List the ​conclusions you will draw ​while studying the ​following ​properties ​of ​ethanoic acid :

   1. (a)Odour
   2. (b)Solubility in water
   3. (c)Effect on litmus ​paper
   4. (d)Reaction with sodium hydrogen carbonate
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   Ethanoic acid smells of vinegar, dissolves in water, is acidic (turns blue litmus red) and gives carbon dioxide with sodium hydrogen carbonate.

   (a) Odour: ethanoic acid has a pungent smell, like that of vinegar. (b) Solubility in water: it dissolves completely in water (mixes in all proportions), giving one clear layer. (c) Effect on litmus paper: it turns blue litmus red and has no effect on red litmus, so it is acidic in nature. (d) Reaction with sodium hydrogen carbonate: brisk effervescence is seen as carbon dioxide is given off, which turns lime water milky: ${\text{CH}}_3\text{COOH}+{\text{NaHCO}}_3⟶{\text{CH}}_3\text{COONa}+{\text{H}}_2\text{O}+{\text{CO}}_2$

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5. Q345 CBSE 2019
   A student is performing ​an ​experiment to study ​the properties of acetic ​acid. Answer the following questions :

   1. (i)Name the substance he ​must add to acetic acid to produce carbon dioxide.
   2. (ii)Give ​the relevant chemical equation for the reaction.
   3. (iii)How would ​he test ${\text{CO}}_2$ ​gas in the laboratory ?
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   Add sodium hydrogen carbonate to give carbon dioxide; pass the gas through lime water, which turns milky.

   (i) Sodium hydrogen carbonate (baking soda), ${\text{NaHCO}}_3$; sodium carbonate, ${\text{Na}}_2{\text{CO}}_3$, also gives carbon dioxide. (ii) ${\text{CH}}_3\text{COOH}+{\text{NaHCO}}_3\to {\text{CH}}_3\text{COONa}+{\text{H}}_2\text{O}+{\text{CO}}_2$ (with sodium carbonate: $2{\text{CH}}_3\text{COOH}+{\text{Na}}_2{\text{CO}}_3\to 2{\text{CH}}_3\text{COONa}+{\text{H}}_2\text{O}+{\text{CO}}_2$) (iii) Pass the gas through lime water (calcium hydroxide solution) with a delivery tube dipping into it: the lime water turns milky, which shows the gas is carbon dioxide. ${\text{Ca(OH)}}_2+{\text{CO}}_2\to {\text{CaCO}}_3+{\text{H}}_2\text{O}$

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6. Q346 CBSE 2018
   A compound ‘X’ on heating with excess conc. ​sulphuric acid at 443 K gives ​an unsaturated ​compound ‘Y’. ‘X’ also reacts with sodium ​metal to ​evolve a colourless gas ​‘Z’. Identify ‘X’, ‘Y’ and ‘Z’. Write the equation of the chemical reaction of formation of ‘Y’ and also write the role ​of sulphuric acid in the reaction.
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   X is ethanol, Y is ethene and Z is hydrogen; concentrated sulphuric acid acts as a dehydrating agent.

   X: ethanol, ${\text{C}}_2{\text{H}}_5\text{OH}$ Y: ethene, ${\text{C}}_2{\text{H}}_4$ (${\text{CH}}_2={\text{CH}}_2$) Z: hydrogen, ${\text{H}}_2$, given off as $2{\text{CH}}_3{\text{CH}}_2\text{OH}+2\text{Na}\to 2{\text{CH}}_3{\text{CH}}_2\text{ONa}+{\text{H}}_2$ Formation of Y: ${\text{CH}}_3{\text{-CH}}_2\text{OH}\underset{443\text{K}}{\overset{{\text{hot conc. H}}_2{\text{SO}}_4}{\to }}{\text{CH}}_2={\text{CH}}_2+{\text{H}}_2\text{O}$ Role of sulphuric acid: concentrated sulphuric acid acts as a dehydrating agent; it removes water from ethanol.

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7. Q347 CBSE 2018
   Carbon has ​four electrons ​in its valence shell. Which type of compounds can ​be formed by carbon ​atom and why ? Give any one ​example ​of ​such compounds.
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   Carbon forms covalent compounds, because it shares its four valence electrons rather than gain or lose four; example, methane.

   Carbon forms covalent compounds. Reason: to reach the stable electron arrangement of a noble gas by forming an ion, carbon would have to gain $4$ electrons, becoming ${\text{C}}^{4-}$ with an octet like neon, or lose $4$, becoming ${\text{C}}^{4+}$ with a duplet like helium. Gaining four is difficult, because a nucleus of $6$ protons cannot hold on to $10$ electrons, and losing four needs a very large amount of energy. So carbon shares its $4$ valence electrons with other atoms (of carbon or of other elements), forming covalent bonds. Example: methane, ${\text{CH}}_4$ (any other covalent compound of carbon, such as ethane or carbon dioxide, is also correct).

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8. Q348 CBSE 2018
   Which ​compounds ​are called

   1. (i)alkanes, ​
   2. (ii)alkenes ​and ​
   3. (iii)alkynes ? ​Which ​of them is ${\text{C}}_4{\text{H}}_{10}$ ​?
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   Alkanes have only single bonds, alkenes a double bond and alkynes a triple bond; ${\text{C}}_4{\text{H}}_{10}$ is an alkane.

   (i) Alkanes are saturated hydrocarbons, whose 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, ${\text{C}}_2{\text{H}}_2$). ${\text{C}}_4{\text{H}}_{10}$ is an alkane, butane: with $n=4$, $2n+2=10$.

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9. Q349 CBSE 2018
   What ​is a homologous ​series of carbon ​compounds ? Write its two ​characteristics. ​Giving reason select two compounds ​from ​the following which belong to the same homologous ​series : ${\text{C}}_2{\text{H}}_2$, ${\text{C}}_2{\text{H}}_4$, ${\text{C}}_2{\text{H}}_6$, ${\text{C}}_3{\text{H}}_4$, ${\text{C}}_4{\text{H}}_5$, ${\text{C}}_6{\text{H}}_6$
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   A homologous series has the same functional group, general formula and similar chemical properties; ${\text{C}}_2{\text{H}}_2$ and ${\text{C}}_3{\text{H}}_4$ belong to one series, the alkynes.

   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. Characteristics (any two): 1. All members are represented by the same general formula. 2. Successive members differ by a $-{\text{CH}}_2-$ unit, that is by $14$ u in molecular mass. 3. All members have similar chemical properties. 4. Physical properties such as melting and boiling points change gradually as the molecular mass increases. Compounds: ${\text{C}}_2{\text{H}}_2$ and ${\text{C}}_3{\text{H}}_4$, because both are alkynes with the general formula ${\text{C}}_n{\text{H}}_{2n-2}$ ($n=2$ and $n=3$), and they differ by one ${\text{CH}}_2$ unit ($26$ u and $40$ u).

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10. Q350 CBSE 2018
    Distinguish between ethanol ​and ethanoic acid on the basis of

    1. (i)litmus test and
    2. (ii)​reaction with ​sodium ​hydrogen ​carbonate. Write the name ​and formula of the oxidizing ​agent used in ​the conversion of ethanol to ethanoic acid.
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    Ethanoic acid turns blue litmus red and fizzes with sodium hydrogen carbonate; ethanol does neither; the oxidising agent is alkaline ${\text{KMnO}}_4$.

    (i) Litmus test: ethanoic acid turns blue litmus red, as it is acidic; ethanol has no effect on litmus (blue litmus stays blue), as it is neutral. (ii) Reaction with sodium hydrogen carbonate: ethanoic acid reacts with brisk effervescence, giving carbon dioxide gas, ${\text{CH}}_3\text{COOH}+{\text{NaHCO}}_3\to {\text{CH}}_3\text{COONa}+{\text{H}}_2\text{O}+{\text{CO}}_2$; ethanol does not react, so there is no effervescence. Oxidising agent: alkaline potassium permanganate, ${\text{KMnO}}_4$ (acidified potassium dichromate, ${\text{K}}_2{\text{Cr}}_2{\text{O}}_7$, is also accepted).

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11. Q351 CBSE 2018
    1. (a)​Why are most carbon compounds poor conductors of ​electricity ?
    2. (b)Write the ​name and structure of a saturated compound in which the carbon atoms are ​arranged in a ring. Give ​the number of single bonds present ​in this ​compound.
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    Carbon compounds are covalent and form no ions; cyclohexane, ${\text{C}}_6{\text{H}}_{12}$, has $18$ single bonds.

    (a) Most carbon compounds are formed by covalent bonds (sharing of electrons), so they do not dissociate into ions. With no charged particles to carry a current, most carbon compounds are poor conductors of electricity. (b) Name: cyclohexane, ${\text{C}}_6{\text{H}}_{12}$. Structure: six carbon atoms joined in a ring by single bonds, each carbon atom also bonded to two hydrogen atoms (see the figure). Number of single bonds: $6$ carbon-carbon + $12$ carbon-hydrogen $=18$. Any other cycloalkane is also correct with its own count, for example cyclopentane, ${\text{C}}_5{\text{H}}_{10}$, with $15$ single bonds.

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12. Q352 CBSE 2018
    What happens when hydrogen is added ​to a vegetable oil ​in the ​presence ​of ​nickel ? Name the reaction and write one difference between the physical ​property of the ​vegetable oil and the product obtained in this reaction. Write the ​role of nickel in this reaction.
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    Hydrogen adds across the double bonds of the oil (hydrogenation), turning liquid oil into solid vegetable ghee; nickel is the catalyst.

    When hydrogen is added to a vegetable oil in the presence of nickel, the hydrogen adds to the carbon-carbon double bonds of the unsaturated oil, and the oil changes into a saturated fat, vegetable ghee (vanaspati): ${\text{R}}_2{\text{C=CR}}_2+{\text{H}}_2\stackrel{\text{Ni}}{\to }{\text{R}}_2{\text{CH-CHR}}_2$. Name of the reaction: hydrogenation (an addition reaction). Difference: the vegetable oil is a liquid at room temperature, whereas the product, vegetable ghee, is a solid at room temperature. Role of nickel: it is a catalyst; it speeds up the addition of hydrogen without itself being used up in the reaction.

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13. Q353 CBSE 2018
    In the ​laboratory of a school, the sample of ​hard water is not available “to study ​the ​comparative cleaning capacity of a sample of soap in soft and hard ​water”. Which salt from the laboratory can be added to tap water ​to make it hard ? In the experiment how is cleaning ​capacity of soap compared ​?
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    Dissolve calcium chloride in tap water to make it hard; the longer the foam column, the greater the soap's cleaning capacity.

    Salt: calcium chloride (or magnesium chloride or magnesium sulphate); a soluble calcium or magnesium salt dissolved in tap water makes it hard. Comparison: take equal volumes of soft (distilled) water and of the hard water in two identical test tubes, add the same number of drops of the same soap solution to each, and shake both equally. Compare the length of the foam column in the two tubes: the longer the foam, the greater the cleaning capacity. Soft water gives a long foam column; hard water gives very little foam and a white curdy scum, so the soap cleans better in soft water.

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14. Q354 CBSE 2018
    In ​a ​school ​laboratory ​the students are studying the properties of ethanoic acid ​through ​certain experiments. How can they test its ​acidic nature ? Give ​two tests.
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    Ethanoic acid turns blue litmus red and gives brisk effervescence of carbon dioxide with sodium hydrogencarbonate, showing it is acidic.

    Test 1 (litmus test): put a drop of ethanoic acid on blue litmus paper. The blue litmus turns red, showing that ethanoic acid is acidic. Test 2 (sodium hydrogencarbonate test): add a pinch of sodium hydrogencarbonate to about 2 mL of ethanoic acid in a test tube. Brisk effervescence is seen as a colourless, odourless gas, carbon dioxide, is given off; it turns lime water milky. ${\text{CH}}_3\text{COOH}+{\text{NaHCO}}_3\to {\text{CH}}_3\text{COONa}+{\text{H}}_2\text{O}+{\text{CO}}_2\uparrow$

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15. Q355 CBSE 2018
    What ​happens when you ​add few drops ​of acetic acid to a test tube containing powder of ​sodium hydrogen ​carbonate ? List two observations. Write ​the name of the gas ​evolved and the method of its testing.
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    Brisk effervescence occurs; the colourless gas turns lime water milky, so it is carbon dioxide.

    Acetic acid reacts with sodium hydrogencarbonate and carbon dioxide gas is given off: ${\text{CH}}_3\text{COOH}+{\text{NaHCO}}_3\to {\text{CH}}_3\text{COONa}+{\text{H}}_2\text{O}+{\text{CO}}_2$ Observations: (i) brisk effervescence (fizzing) takes place; (ii) a colourless, odourless gas is evolved. Gas evolved: carbon dioxide (${\text{CO}}_2$). Test: pass the gas through lime water; the lime water turns milky, because white, insoluble calcium carbonate is formed: ${\text{Ca(OH)}}_2+{\text{CO}}_2\to {\text{CaCO}}_3+{\text{H}}_2\text{O}$.

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16. Q356 CBSE 2018
    You have two samples of ​water marked ​A and ​B. How would you distinguish ​between ​the ​two if ​one sample is of soft water and the other is of hard water ​?
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    Soap lathers easily in soft water; in hard water it forms a white curdy scum with very little lather.

    Take equal volumes of samples A and B in two test tubes. Add the same number of drops of the same soap solution to each and shake both tubes equally. The sample that forms a lot of lather easily is soft water. The sample that forms very little lather and a white, curdy precipitate (scum) is hard water, because the calcium and magnesium salts in hard water react with soap to form insoluble scum.

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17. Q357 CBSE 2017
    Write the ​name ​and formula of ​a ​carbon ​compound having $-\text{OH}$ functional group.
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    Ethanol, ${\text{C}}_2{\text{H}}_5\text{OH}$, is a carbon compound with the $-\text{OH}$ group.

    Ethanol, ${\text{C}}_2{\text{H}}_5\text{OH}$ (written in full as ${\text{CH}}_3{\text{CH}}_2\text{OH}$). It is an alcohol, and its functional group is $-\text{OH}$. (Methanol, ${\text{CH}}_3\text{OH}$, or propanol, ${\text{C}}_3{\text{H}}_7\text{OH}$, answers the question equally well.)

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18. Q358 CBSE 2017
    Draw ​the ​structure of ethane molecule ​and write ​the number ​of covalent bonds ​in ​it.
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    Ethane, ${\text{H}}_3\text{C}-{\text{CH}}_3$, has 7 covalent bonds: six C-H and one C-C.

    Structure: in ethane (${\text{C}}_2{\text{H}}_6$) the two carbon atoms are joined by a single covalent bond and each carbon is bonded to three hydrogen atoms, ${\text{H}}_3\text{C}-{\text{CH}}_3$ (the structural formula is drawn in the figure). Number of covalent bonds: $7$ (six C–H bonds and one C–C bond, all single bonds).

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19. Q359 CBSE 2017
    Write ​the ​name and formula ​of ​the second member of homologous series having general ​formula ${\text{C}}_n{\text{H}}_{2n+1}\text{OH}$.
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    The second member is ethanol, ${\text{C}}_2{\text{H}}_5\text{OH}$.

    The second member of the series is ethanol, ${\text{C}}_2{\text{H}}_5\text{OH}$ (written also as ${\text{CH}}_3{\text{CH}}_2\text{OH}$). It follows methanol, ${\text{CH}}_3\text{OH}$, the first member ($n=1$), by one ${\text{CH}}_2$ unit.

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20. Q360 CBSE 2017
    Write ​chemical name of ​the ​compound ${\text{CH}}_3-{\text{CH}}_2-{\text{CH}}_2-\text{Br}$.
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    The compound is 1-bromopropane (bromopropane).

    The compound is 1-bromopropane (NCERT names it simply bromopropane), ${\text{C}}_3{\text{H}}_7\text{Br}$.

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