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 12 of 23

1. Q221 CBSE 2023
   The ​carbon ​compound having the functional group ​shown below ​is ​:

   1. (a)Propanal
   2. (b)Propanone
   3. (c)Propyne
   4. (d)Propanol
   Show answer

   (a) Propanal

   Step-by-step solution →
2. Q222 CBSE 2023
   Which one of the following ​properties of Carbon is not ​responsible ​for its ​formation ​of ​large number ​of compounds ​?

   1. (a)Tetravalency
   2. (b)Isomerism
   3. (c)Allotropy
   4. (d)Catenation
   Show answer

   (c) Allotropy

   Step-by-step solution →
3. Q223 CBSE 2023
   Two statements are given ​— ​one labelled ​as Assertion (A) and ​the other ​labelled ​as Reason (R). Select the correct answer to this question from the codes ​(a), (b), (c) and (d) as given below.

   Assertion (A): Ethyne is widely used for cutting and welding iron and steel.

   Reason (R): Ethyne is an unsaturated hydrocarbon involving carbon-to-carbon triple bond.

   1. (a)Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of the Assertion (A).
   2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
   3. (c)Assertion (A) is true, but Reason (R) is false.
   4. (d)Assertion (A) is false, but Reason (R) is true.
   Show answer

   (b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).

   Step-by-step solution →
4. Q224 CBSE 2023
   These ​consists of ​two statements ​– ​Assertion (A) and Reason (R). Answer this question ​selecting the appropriate option given below ​:

   Assertion (A): Melting point and boiling point of ethanol are lower than that of sodium chloride.

   Reason (R): The forces of attraction between the molecules of ionic compounds are very strong.

   1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of (A).
   2. (b)Both Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of (A).
   3. (c)Assertion (A) is true, but Reason (R) is false.
   4. (d)Assertion (A) is false, but Reason (R) is true.
   Show answer

   (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of (A).

   Step-by-step solution →
5. Q225 CBSE 2023
   An organic compound 'X' when reacts ​with sodium liberates hydrogen. The same compound ​'X' when heated at 443 K in the presence of ​concentrated sulphuric acid gives an unsaturated hydrocarbon.

   1. (i)Identify 'X'.
   2. (ii)Write the ​chemical equations for the ​above mentioned reactions and state the ​role of concentrated sulphuric acid in the second ​reaction.
   Show answer

   X is ethanol; with hot conc. sulphuric acid at 443 K it forms ethene, the acid acting as a dehydrating agent.

   (i) X is ethanol, ${\text{C}}_2{\text{H}}_5\text{OH}$. (ii) With sodium: $2{\text{C}}_2{\text{H}}_5\text{OH}+2\text{Na}\to 2{\text{C}}_2{\text{H}}_5\text{ONa}+{\text{H}}_2$, giving sodium ethoxide and hydrogen gas. On heating at $443$ K with concentrated sulphuric acid: ${\text{C}}_2{\text{H}}_5\text{OH}\to {\text{C}}_2{\text{H}}_4+{\text{H}}_2\text{O}$, giving ethene, an unsaturated hydrocarbon. In the second reaction the concentrated sulphuric acid acts as a dehydrating agent: it removes a molecule of water from ethanol.

   Step-by-step solution →
6. Q226 CBSE 2023
   (i) ​Why are the chemical properties of different members of a homologous series similar ? (ii) What is the difference ​in ​the number of ​carbon and hydrogen atoms between any two ​successive members of a homologous series ? Justify your answer by giving an example from

   1. (i)alkynes,
   2. (ii)alcohols ​and
   3. (iii)​aldehydes.
   Show answer

   Same functional group gives similar chemical properties; successive members differ by ${\text{CH}}_2$, one carbon and two hydrogen atoms.

   (i) All the members of a homologous series have the same functional group, and the chemical properties of a carbon compound are decided by its functional group, so the members show similar chemical properties (their physical properties change gradually with molecular mass). (ii) Any two successive members differ by one carbon atom and two hydrogen atoms, that is by a $-{\text{CH}}_2-$ unit (a difference of $14$ u in molecular mass). Alkynes: ethyne ${\text{C}}_2{\text{H}}_2$ and propyne ${\text{C}}_3{\text{H}}_4$ differ by ${\text{CH}}_2$. Alcohols: methanol ${\text{CH}}_3\text{OH}$ and ethanol ${\text{C}}_2{\text{H}}_5\text{OH}$ differ by ${\text{CH}}_2$. Aldehydes: methanal $\text{HCHO}$ and ethanal ${\text{CH}}_3\text{CHO}$ differ by ${\text{CH}}_2$.

   Step-by-step solution →
7. Q227 CBSE 2023
   1. (i)​Why are carbon ​compounds exceptionally ​stable ?
   2. (ii)Differentiate between saturated ​and unsaturated compounds. ​Give ​structures of both ​the types of ​compounds having three carbon atoms in their molecules.
   Show answer

   Strong bonds from the small carbon atom make its compounds stable; saturated (propane) has only single bonds, unsaturated (propene) has a double bond.

   (i) The carbon atom is very small, so its nucleus holds the shared electron pairs firmly and the covalent bonds it forms, both carbon to carbon and carbon to other elements, are exceptionally strong. A large amount of energy is needed to break such bonds, so carbon compounds are exceptionally stable and generally unreactive. (ii) A saturated compound has only single bonds between its carbon atoms; it is less reactive, gives substitution reactions and burns with a clean blue flame. An unsaturated compound has at least one double or triple bond between carbon atoms; it is more reactive, gives addition reactions and burns with a yellow sooty flame. Three-carbon structures: saturated is propane, ${\text{CH}}_3-{\text{CH}}_2-{\text{CH}}_3$ (${\text{C}}_3{\text{H}}_8$); unsaturated is propene, ${\text{CH}}_2=\text{CH}-{\text{CH}}_3$ (${\text{C}}_3{\text{H}}_6$), or propyne, $\text{CH}\equiv \text{C}-{\text{CH}}_3$ (${\text{C}}_3{\text{H}}_4$).

   Step-by-step solution →
8. Q228 CBSE 2023
   (i) State reasons why

   1. (1)Carbon ​forms strong bonds ​and stable compounds with most other elements.
   2. (2)The melting and boiling ​points of covalent compounds are low. (ii) Draw the electron dot ​structure for the ​molecule of ​Chlorine (Atomic number ​17).
   Show answer

   Carbon's small size gives strong bonds; weak forces between molecules lower melting points; ${\text{Cl}}_2$ has one shared pair and three lone pairs per atom.

   (i) (1) Carbon has a small atom, so its nucleus holds the shared pairs of electrons strongly; the bonds it forms with most other elements are therefore strong, and its compounds are stable. (2) Covalent compounds are made of molecules, and the forces of attraction between the molecules are weak, so little heat energy is needed to separate them; hence their melting and boiling points are low. (ii) Chlorine (atomic number $17$) is $2,8,7$. Two chlorine atoms share one pair of electrons, one electron from each, forming a single covalent bond $\text{Cl}-\text{Cl}$; each atom keeps three lone pairs and so has $8$ electrons in its outer shell (see the electron dot structure).

   Step-by-step solution →
9. Q229 CBSE 2023
   (a) Write the names ​of the following compounds :

   1. (i)${\text{CH}}_3-{\text{CH}}_2\text{COOH}$
   2. (ii)${\text{C}}_6{\text{H}}_6$ (b) What is a ​homologous series of ​carbon ​compounds ? Construct a homologous series of ​alcohols. (c) ​What ​happens when ethanol reacts with ethanoic acid in the presence of an acid ? ​Name the reaction and write its chemical equation.
   Show answer

   Propanoic acid and benzene; methanol, ethanol, propanol and butanol form an alcohol series; ethanol and ethanoic acid give ethyl ethanoate by esterification.

   (a)(i) ${\text{CH}}_3-{\text{CH}}_2\text{COOH}$ is propanoic acid (three carbon atoms in the chain, with a $-\text{COOH}$ group). (a)(ii) ${\text{C}}_6{\text{H}}_6$ is benzene. (b) A homologous series is a series of carbon compounds in which every member has the same functional group and fits one general formula, and each member differs from the next by a $-{\text{CH}}_2-$ unit, that is by $14$ u. The members show similar chemical properties and a gradual change in physical properties. Series of alcohols (general formula ${\text{C}}_n{\text{H}}_{2n+1}\text{OH}$): ${\text{CH}}_3\text{OH}$ methanol ($32$ u), ${\text{C}}_2{\text{H}}_5\text{OH}$ ethanol ($46$ u), ${\text{C}}_3{\text{H}}_7\text{OH}$ propanol ($60$ u), ${\text{C}}_4{\text{H}}_9\text{OH}$ butanol ($74$ u). (c) Warmed with a little concentrated sulphuric acid, ethanol and ethanoic acid give a sweet-smelling ester, ethyl ethanoate, and water. The reaction is called esterification. ${\text{CH}}_3\text{COOH}+{\text{C}}_2{\text{H}}_5\text{OH}\stackrel{{\text{conc. H}}_2{\text{SO}}_4}{\to }{\text{CH}}_3{\text{COOC}}_2{\text{H}}_5+{\text{H}}_2\text{O}$

   Step-by-step solution →
10. Q230 CBSE 2023
    A saturated organic compound 'A' belongs to the homologous series of alcohols. On heating 'A' with concentrated ​sulphuric acid at 443 K, it forms an unsaturated compound 'B' with ​molecular mass 28 u. The compound 'B' on addition of one mole of ​hydrogen in the presence of Nickel, ​changes to a ​saturated hydrocarbon 'C'.

    1. (i)Identify A, B ​and C.
    2. (ii)Write the chemical equations showing the conversion of A into B.
    3. (iii)What happens when compound C undergoes combustion ?
    4. (iv)State one industrial application of hydrogenation reaction.
    5. (v)Name the products formed when compound A ​reacts with sodium.
    Show answer

    A is ethanol, B ethene, C ethane; hydrogenation makes vanaspati ghee; ethanol with sodium gives sodium ethoxide and hydrogen.

    (i) A is ethanol, ${\text{C}}_2{\text{H}}_5\text{OH}$; B is ethene, ${\text{CH}}_2={\text{CH}}_2$; C is ethane, ${\text{CH}}_3{\text{CH}}_3$. (ii) ${\text{C}}_2{\text{H}}_5\text{OH}\underset{443\text{K}}{\overset{\text{conc. }{\text{H}}_2{\text{SO}}_4}{\to }}{\text{CH}}_2={\text{CH}}_2+{\text{H}}_2\text{O}$ (iii) Ethane burns in a sufficient supply of air with a clean blue flame, giving carbon dioxide and water vapour and releasing a large amount of heat and light: $2{\text{C}}_2{\text{H}}_6+7{\text{O}}_2⟶4{\text{CO}}_2+6{\text{H}}_2\text{O}$. (iv) Hydrogenation is used to harden vegetable oils into vanaspati ghee, by passing hydrogen through the oil over a nickel catalyst. (v) Sodium ethoxide, ${\text{C}}_2{\text{H}}_5\text{ONa}$, and hydrogen gas: $2{\text{C}}_2{\text{H}}_5\text{OH}+2\text{Na}⟶2{\text{C}}_2{\text{H}}_5\text{ONa}+{\text{H}}_2$.

    Step-by-step solution →
11. Q231 CBSE 2023
    An acid ‘X’ and an alcohol ‘Y’ react with each other in the presence of an acid catalyst ​to form a sweet smelling ​substance ‘Z’. Identify ‘X’, ‘Y’ and ‘Z’. Write ​the chemical ​equation ​for the reaction involved and name it. The substance ‘Z’ on treatment with sodium ​hydroxide produces back the alcohol ‘Y’ and sodium ethanoate. Write the ​chemical equation for the reaction involved ​and name it, giving justification for the name.
    Show answer

    X is ethanoic acid, Y is ethanol and Z is ethyl ethanoate; the second reaction, alkaline hydrolysis of an ester, is saponification.

    ‘X’ is ethanoic acid, ${\text{CH}}_3\text{COOH}$; ‘Y’ is ethanol, ${\text{C}}_2{\text{H}}_5\text{OH}$; ‘Z’ is ethyl ethanoate, ${\text{CH}}_3{\text{COOC}}_2{\text{H}}_5$. Reaction 1 (esterification): ${\text{CH}}_3\text{COOH}+{\text{C}}_2{\text{H}}_5\text{OH}\stackrel{\text{conc. }{\text{H}}_2{\text{SO}}_4}{\to }{\text{CH}}_3{\text{COOC}}_2{\text{H}}_5+{\text{H}}_2\text{O}$. Reaction 2 (saponification): ${\text{CH}}_3{\text{COOC}}_2{\text{H}}_5+\text{NaOH}⟶{\text{CH}}_3\text{COONa}+{\text{C}}_2{\text{H}}_5\text{OH}$. It is named saponification because the same alkaline hydrolysis carried out on the esters of long chain fatty acids in oils and fats gives their sodium salts, which are soap.

    Step-by-step solution →
12. Q232 CBSE 2023
    (i) Draw the structure ​of the following compounds : (a) Butanoic acid ​(b) ​Chloropentane (ii) ​How are structure

    1. (i)and structure
    2. (ii)given below related to one another ? ​Give reason to justify your answer. Draw ​one more possible structure for above case.
    3. (iii)Differentiate between saturated and unsaturated carbon compounds on the basis ​of their general formula.

    Show answer

    Butanoic acid and 1-chloropentane drawn; the two ${\text{C}}_6{\text{H}}_{14}$ structures are chain isomers (n-hexane is another); alkanes are ${\text{C}}_n{\text{H}}_{2n+2}$, unsaturated compounds ${\text{C}}_n{\text{H}}_{2n}$ or ${\text{C}}_n{\text{H}}_{2n-2}$.

    (i) (a) Butanoic acid: ${\text{CH}}_3-{\text{CH}}_2-{\text{CH}}_2-\text{COOH}$; (b) Chloropentane: ${\text{CH}}_3-{\text{CH}}_2-{\text{CH}}_2-{\text{CH}}_2-{\text{CH}}_2-\text{Cl}$ (1-chloropentane). (ii) Both structures have the same molecular formula ${\text{C}}_6{\text{H}}_{14}$ but different arrangements of their carbon atoms, so they are structural isomers (chain isomers) of each other. One more possible structure is n-hexane, ${\text{CH}}_3-{\text{CH}}_2-{\text{CH}}_2-{\text{CH}}_2-{\text{CH}}_2-{\text{CH}}_3$. (iii) Saturated open-chain carbon compounds (alkanes) have the general formula ${\text{C}}_n{\text{H}}_{2n+2}$, while unsaturated ones have ${\text{C}}_n{\text{H}}_{2n}$ when they contain one double bond and ${\text{C}}_n{\text{H}}_{2n-2}$ when they contain one triple bond.

    Step-by-step solution →
13. Q233 CBSE 2023
    A neutral organic compound 'X' (Molecular formula ${\text{C}}_2{\text{H}}_6\text{O}$) on reacting with ​acidified ${\text{K}}_2{\text{Cr}}_2{\text{O}}_7$ gives an organic compound ​'Y' which ​is acidic in nature. 'X' reacts with 'Y' on warming in the ​presence of conc. ${\text{H}}_2{\text{SO}}_4$ to give a sweet smelling ​compound 'Z'.

    1. (i)Identify 'X', ​'Y' ​and 'Z'.
    2. (ii)Write the chemical equations for the reactions in the conversion of (1) 'X' to 'Y' and (2) 'X' to 'Z'. (iii) State the role of (1) ​acidified ${\text{K}}_2{\text{Cr}}_2{\text{O}}_7$ in the conversion of 'X' to 'Y' and (2) conc. ${\text{H}}_2{\text{SO}}_4$ in the reaction of 'X' and 'Y'. (iv) Name the reaction which occurs when 'Z' reacts with an alkali.
    Show answer

    X is ethanol, Y is ethanoic acid and Z is ethyl ethanoate; acidified dichromate oxidises X to Y; alkali hydrolyses Z in saponification.

    (i) 'X' is ethanol, ${\text{CH}}_3{\text{CH}}_2\text{OH}$; 'Y' is ethanoic acid, ${\text{CH}}_3\text{COOH}$; 'Z' is ethyl ethanoate, ${\text{CH}}_3{\text{COOC}}_2{\text{H}}_5$. (ii)(1) ${\text{CH}}_3{\text{CH}}_2\text{OH}+2[\text{O}]\stackrel{{\text{acidified K}}_2{\text{Cr}}_2{\text{O}}_7}{\to }{\text{CH}}_3\text{COOH}+{\text{H}}_2\text{O}$ (2) ${\text{CH}}_3\text{COOH}+{\text{C}}_2{\text{H}}_5\text{OH}\stackrel{{\text{conc. H}}_2{\text{SO}}_4}{\to }{\text{CH}}_3{\text{COOC}}_2{\text{H}}_5+{\text{H}}_2\text{O}$ (iii)(1) Acidified ${\text{K}}_2{\text{Cr}}_2{\text{O}}_7$ acts as an oxidising agent, supplying the oxygen that turns ethanol into ethanoic acid. (2) Conc. ${\text{H}}_2{\text{SO}}_4$ acts as a dehydrating agent and catalyst, removing the water formed so that the ester is obtained in good yield. (iv) Saponification (the alkaline hydrolysis of an ester).

    Step-by-step solution →
14. Q234 CBSE 2023
    (i) A compound ​'A' with a molecular ​formula of ${\text{C}}_2{\text{H}}_4{\text{O}}_2$ reacts with a base to give salt and water. Identify 'A', state its nature and the name of the functional group it possesses. Write chemical equation ​for the reaction involved. (ii) When the ​above stated compound 'A' reacts ​with another ​compound 'B' having molecular formula ${\text{C}}_2{\text{H}}_6\text{O}$ in the presence of an acid, a sweet smelling compound ​'C' is formed.

    1. (1)Identify 'B' and 'C'.
    2. (2)State the role of acid in this reaction.
    3. (3)Write chemical equation ​for the reaction involved.
    Show answer

    A is ethanoic acid (carboxyl group); B is ethanol and C is ethyl ethanoate, formed with conc. sulphuric acid as catalyst and dehydrating agent.

    (i) 'A' is ethanoic acid, ${\text{CH}}_3\text{COOH}$. It is acidic in nature (a weak carboxylic acid) and its functional group is the carboxyl group, $-\text{COOH}$. With a base: ${\text{CH}}_3\text{COOH}+\text{NaOH}\to {\text{CH}}_3\text{COONa}+{\text{H}}_2\text{O}$. (ii)(1) 'B' is ethanol, ${\text{C}}_2{\text{H}}_5\text{OH}$, and 'C' is ethyl ethanoate, ${\text{CH}}_3{\text{COOC}}_2{\text{H}}_5$ — an ester. (ii)(2) The concentrated sulphuric acid acts as a catalyst and as a dehydrating agent: it removes the water formed and so drives the reaction towards the ester. (ii)(3) ${\text{CH}}_3\text{COOH}+{\text{C}}_2{\text{H}}_5\text{OH}\stackrel{{\text{conc. H}}_2{\text{SO}}_4}{\to }{\text{CH}}_3{\text{COOC}}_2{\text{H}}_5+{\text{H}}_2\text{O}$

    Step-by-step solution →
15. Q235 CBSE 2023
    1. (a)Write the molecular formula of methane and ethane, stating the general formula of the homologous series to which these compounds belong. What is ​the difference in the molecular mass in between the two successive members of a homologous series ?
    2. (b)​Write the name and molecular formula of ​an alcohol ​having two carbon ​atoms in its molecule. Write balanced chemical equation to indicate what happens ​when this compound is ​heated at 443 K with excess conc. ${\text{H}}_2{\text{SO}}_4$. Name the ​main product formed in the reaction stating the function of conc. ${\text{H}}_2{\text{SO}}_4$ in the reaction.
    Show answer

    ${\text{CH}}_4$ and ${\text{C}}_2{\text{H}}_6$ are alkanes (${\text{C}}_n{\text{H}}_{2n+2}$) differing by 14 u; ethanol gives ethene, conc. sulphuric acid being the dehydrating agent.

    (a) Methane is ${\text{CH}}_4$ and ethane is ${\text{C}}_2{\text{H}}_6$; both belong to the alkane homologous series, whose general formula is ${\text{C}}_n{\text{H}}_{2n+2}$. Two successive members differ by one ${\text{CH}}_2$ unit, so the difference in molecular mass is $14$ u. (b) The alcohol with two carbon atoms is ethanol, ${\text{C}}_2{\text{H}}_5\text{OH}$. On heating at $443$ K with excess concentrated sulphuric acid it is dehydrated: ${\text{C}}_2{\text{H}}_5\text{OH}\underset{443\text{K}}{\overset{{\text{conc. H}}_2{\text{SO}}_4}{\to }}{\text{C}}_2{\text{H}}_4+{\text{H}}_2\text{O}$. The main product is ethene, ${\text{C}}_2{\text{H}}_4$, and the concentrated sulphuric acid acts as a dehydrating agent, removing a molecule of water from the ethanol.

    Step-by-step solution →
16. Q236 CBSE 2023
    1. (i)What are isomers? Write the structures ​of two compounds having ​molecular formula ${\text{C}}_3{\text{H}}_6\text{O}$ ​and give their names.
    2. (ii)​What ​are soaps? How are ​they chemically different from ​detergents? Why do soaps not work effectively in hard water?
    Show answer

    Propanal and propanone are isomers; soaps are carboxylate salts, detergents sulphonate or ammonium salts; soap forms scum with hard-water calcium and magnesium ions.

    (i) Isomers are compounds that have the same molecular formula but different structures. Two compounds with the formula ${\text{C}}_3{\text{H}}_6\text{O}$ are propanal, ${\text{CH}}_3-{\text{CH}}_2-\text{CHO}$, an aldehyde, and propanone (acetone), ${\text{CH}}_3-\text{CO}-{\text{CH}}_3$, a ketone; their full structural formulae are drawn in the figure. (ii) Soaps are sodium or potassium salts of long-chain carboxylic acids, such as sodium stearate, ${\text{C}}_{17}{\text{H}}_{35}\text{COONa}$. Detergents are generally sodium salts of sulphonic acids, or ammonium salts with chloride or bromide ions, also with a long hydrocarbon chain; so the ionic end of a soap is a carboxylate group, $-{\text{COO}}^{-}$, while that of a detergent is a sulphonate group, $-{\text{SO}}_3^{-}$, or an ammonium group. Hard water contains calcium and magnesium ions, which react with soap to form an insoluble substance called scum; the soap is used up in forming scum instead of cleaning, so a large amount of soap is wasted. The charged ends of detergents do not form insoluble precipitates with these ions, so detergents work in hard water.

    Step-by-step solution →
17. Q237 CBSE 2023
    1. (i)With the help of diagram, ​show the formation of ​micelles, ​when ​soap is applied on oily dirt.
    2. (ii)Take two test tubes X and Y with 10 mL of hard water in each. In test tube 'X', add few drops of soap solution ​and in test tube 'Y' add a few drops of detergent solution. Shake both the test tubes for the same period. (1) In ​which test tube the formation of foam will be more ? Why ? (2) ​In which test tube is a curdy solid formed ? Why ​?
    Show answer

    Soap forms micelles around oily dirt; in hard water detergent (tube Y) foams more and soap (tube X) gives curdy scum.

    (i) A soap molecule has a long hydrocarbon tail that is water hating and an ionic head that is water loving. When soap is applied to oily dirt in water, the tails of many soap molecules bury themselves in the oil droplet while the ionic heads stay outside in the water. The droplet is then surrounded by a spherical cluster of soap molecules called a micelle, and it is carried away in the water as an emulsion when the cloth is rinsed (see the diagram). (ii) (1) Test tube Y, the detergent, gives more foam, because the calcium and magnesium salts of a detergent are soluble in water, so the detergent is not precipitated and goes on lathering even in hard water. (2) Test tube X gives the curdy solid. Soap reacts with the ${\text{Ca}}^{2+}$ and ${\text{Mg}}^{2+}$ ions of hard water to form insoluble calcium and magnesium salts of the fatty acid, which separate out as a curdy white scum.

    Step-by-step solution →
18. Q238 CBSE 2023
    1. (i)Name the simplest saturated hydrocarbon. Draw ​its electron dot structure. Which type of bonds ​exist in this compound ?
    2. (ii)Name any two ​mixtures of the carbon compound used as a fuel in daily life, of which the above mentioned compound is ​an important component.
    3. (iii)In which homologous series of carbon compounds can this ​compound be placed ? Write the general formula of the series.
    4. (iv)Which type of flame is produced ​on burning it ​?
    Show answer

    Methane, with four single covalent bonds; found in CNG and biogas; an alkane, ${\text{C}}_n{\text{H}}_{2n+2}$; burns with a clean blue flame.

    (i) Methane, ${\text{CH}}_4$. Its electron dot structure has one carbon atom sharing one electron pair with each of four hydrogen atoms (see the figure); the bonds are four single covalent bonds. (ii) Compressed natural gas (CNG) and biogas (gobar gas). (iii) The alkanes (saturated hydrocarbons), general formula ${\text{C}}_n{\text{H}}_{2n+2}$. (iv) A clean blue, non-sooty flame, because methane undergoes complete combustion in a sufficient supply of air.

    Step-by-step solution →
19. Q239 CBSE 2023
    1. (i)What ​happens when a small piece ​of sodium is dropped in ethanol ? Write the equation for this reaction.
    2. (ii)​Why is glacial acetic acid called so ​?
    3. (iii)What happens when ethanol is heated at 443 ​K in the presence of conc. ${\text{H}}_2{\text{SO}}_4$ ? ​Write the role of conc. ${\text{H}}_2{\text{SO}}_4$ in this case.
    4. (iv)Write an ​equation showing saponification.
    Show answer

    Sodium gives sodium ethoxide and hydrogen; glacial acetic acid freezes at 290 K; sulphuric acid dehydrates ethanol to ethene; ester plus alkali is saponification.

    (i) Sodium dissolves with brisk effervescence, giving sodium ethoxide and hydrogen gas: $2{\text{C}}_2{\text{H}}_5\text{OH}+2\text{Na}⟶2{\text{C}}_2{\text{H}}_5\text{ONa}+{\text{H}}_2\uparrow$. (ii) Pure ($100\%$) acetic acid freezes at $290$ K, a little below room temperature, forming an ice-like solid, so it is called glacial acetic acid. (iii) The ethanol is dehydrated to ethene: ${\text{CH}}_3{\text{CH}}_2\text{OH}\underset{443\text{K}}{\overset{\text{conc. }{\text{H}}_2{\text{SO}}_4}{\to }}{\text{CH}}_2={\text{CH}}_2+{\text{H}}_2\text{O}$; the role of conc. ${\text{H}}_2{\text{SO}}_4$ is that of a dehydrating agent, which removes the water formed. (iv) ${\text{CH}}_3{\text{COOC}}_2{\text{H}}_5+\text{NaOH}⟶{\text{CH}}_3\text{COONa}+{\text{C}}_2{\text{H}}_5\text{OH}$ (on a fat or oil the same reaction gives soap and glycerol).

    Step-by-step solution →
20. Q240 CBSE 2023
    Carry out the ​following conversions, ​stating the condition(s) for each :

    1. (i)Ethanol $⟶$ ​Ethene
    2. (ii)Ethene $⟶$ Ethane
    3. (iii)​Ethane $⟶$ Chloroethane
    4. (iv)Ethanol $⟶$ Ethanoic ​acid
    5. (v)​Ethanoic acid $⟶$ Ethyl ​ethanoate
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    Dehydration (conc. sulphuric acid, 443 K), hydrogenation (Ni), substitution (sunlight), oxidation (alkaline KMnO4) and esterification (conc. sulphuric acid).

    (i) ${\text{CH}}_3{\text{CH}}_2\text{OH}\underset{443\text{K}}{\overset{{\text{conc. H}}_2{\text{SO}}_4}{\to }}{\text{CH}}_2={\text{CH}}_2+{\text{H}}_2\text{O}$ (dehydration: hot conc. ${\text{H}}_2{\text{SO}}_4$ at $443$ K). (ii) ${\text{CH}}_2={\text{CH}}_2+{\text{H}}_2\underset{473\text{K}}{\overset{\text{Ni}}{\to }}{\text{CH}}_3{\text{–CH}}_3$ (addition of hydrogen over a nickel catalyst). (iii) ${\text{CH}}_3{\text{–CH}}_3+{\text{Cl}}_2\stackrel{\text{sunlight}}{\to }{\text{CH}}_3{\text{–CH}}_2\text{Cl}+\text{HCl}$ (substitution in the presence of sunlight). (iv) ${\text{CH}}_3{\text{CH}}_2\text{OH}+2[\text{O}]\underset{\Delta }{\overset{{\text{alkaline KMnO}}_4}{\to }}{\text{CH}}_3\text{COOH}+{\text{H}}_2\text{O}$ (oxidation; acidified ${\text{K}}_2{\text{Cr}}_2{\text{O}}_7$ with heat also works). (v) ${\text{CH}}_3\text{COOH}+{\text{C}}_2{\text{H}}_5\text{OH}\stackrel{{\text{conc. H}}_2{\text{SO}}_4}{\to }{\text{CH}}_3{\text{COOC}}_2{\text{H}}_5+{\text{H}}_2\text{O}$ (esterification: warm with ethanol and conc. ${\text{H}}_2{\text{SO}}_4$).

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