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 16 of 23

1. Q301 CBSE 2020
   For question ​numbers ​13 and 14, two statements are given – one labelled Assertion ​(A) and the ​other labelled ​Reason (R). Select the ​correct answer to these questions from the codes (a), ​(b), (c) and (d) as given below ​:

   Assertion (A): Esterification is a process in which a sweet smelling substance is produced.

   Reason (R): When esters react with sodium hydroxide an alcohol and sodium salt of carboxylic acid are obtained.

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

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

   Step-by-step solution →
2. Q302 CBSE 2020
   For question ​numbers 13 and 14, ​two statements are ​given – one ​labelled Assertion (A) and the other ​labelled Reason (R). Select the ​correct answer to these questions from the ​codes (a), (b), (c) and (d) as given below.

   Assertion (A): In a homologous series of alcohols, the formula for the second member is ${\text{C}}_2{\text{H}}_5\text{OH}$ and the third member is ${\text{C}}_3{\text{H}}_7\text{OH}$.

   Reason (R): The difference between the molecular masses of the two consecutive members of a homologous series is 144.

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

   (c) A is true but R is false.

   Step-by-step solution →
3. Q303 CBSE 2020
   For question numbers 13 and 14, two statements are given – one labelled as Assertion ​(A) ​and the other labelled as Reason (R). Select the correct ​answer to these questions from the codes ​(a), (b), (c) ​and (d) as given below ​:

   Assertion (A): Ethanoic acid is also known as glacial acetic acid.

   Reason (R): The melting point of pure ethanoic acid is 290 K and hence it often freezes during winters in cold climates.

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

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

   Step-by-step solution →
4. Q304 CBSE 2020
   Note : For question numbers 13 ​and 14, two statements are given-one labelled Assertion (A) and the ​other ​labelled Reason (R). Select the correct ​answer to these questions from the codes ​(a), (b), (c) and ​(d) ​as given below :

   Assertion (A): Following are the members of a homologous series : ${\text{CH}}_3\text{OH}$, ${\text{CH}}_3{\text{CH}}_2\text{OH}$, ${\text{CH}}_3{\text{CH}}_2{\text{CH}}_2\text{OH}$

   Reason (R): A series of compounds with same functional group but differing by $-{\text{CH}}_2-$ unit is called a homologous series.

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

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

   Step-by-step solution →
5. Q305 CBSE 2020
   For question numbers 13 ​and 14, two statements are given ​– one ​labelled ​Assertion (A) and the other labelled Reason (R). ​Select the ​correct answer to these questions from the ​codes (a), (b), ​(c) and (d) as given below.

   Assertion (A): Carbon has a strong tendency to either lose or gain electrons to attain noble gas configuration.

   Reason (R): Carbon has four electrons in its outermost shell and has the tendency to share electrons with carbon or other elements.

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

   (d) (A) is false, but (R) is true.

   Step-by-step solution →
6. Q306 CBSE 2020
   3 ​mL of ethanol is taken in a test tube and warmed gently in a water bath. A 5% ​solution of alkaline potassium permanganate ​is added first drop by drop ​to this solution, then in excess.

   1. (i)How ​is 5% solution of ${\text{KMnO}}_4$ ​prepared?
   2. (ii)State the role of alkaline potassium permanganate in this ​reaction. What happens on adding it in excess?
   3. (iii)Write chemical equation of this reaction.
   Show answer

   A 5% solution has 5 g of ${\text{KMnO}}_4$ in 100 mL; it oxidises ethanol to ethanoic acid, and in excess its purple colour persists.

   (i) 5 g of potassium permanganate (${\text{KMnO}}_4$) is dissolved in water and the volume is made up to 100 mL, that is, 5 g of ${\text{KMnO}}_4$ in about 100 mL of water. (ii) Alkaline potassium permanganate acts as an oxidising agent: it supplies oxygen that oxidises ethanol to ethanoic acid, and its purple colour disappears as it is used up. When it is added in excess, the purple colour persists, because no ethanol is left to be oxidised. (iii) ${\text{CH}}_3{\text{CH}}_2\text{OH}+2[\text{O}]\stackrel{{\text{alkaline KMnO}}_4,\text{heat}}{\to }{\text{CH}}_3\text{COOH}+{\text{H}}_2\text{O}$ (ethanol to ethanoic acid).

   Step-by-step solution →
7. Q307 CBSE 2020
   (a) Draw the structures for ​

   1. (i)ethanol,
   2. (ii)ethanoic ​acid. (b) Why ​is the conversion of ethanol to ethanoic acid considered an oxidation reaction? ​Write ​the oxidising ​agent used ​in the reaction ​involved.
   Show answer

   Ethanol gains oxygen to become ethanoic acid, so it is an oxidation, done with alkaline ${\text{KMnO}}_4$ or acidified ${\text{K}}_2{\text{Cr}}_2{\text{O}}_7$.

   (a) (i) Ethanol, ${\text{CH}}_3{\text{CH}}_2\text{OH}$: $$\begin{array}{ccccccc}& & \text{H}& & \text{H}& & \\ & & |& & |& & \\ \text{H}& -& \text{C}& -& \text{C}& -& \text{O}-\text{H}\\ & & |& & |& & \\ & & \text{H}& & \text{H}& & \end{array}$$ (ii) Ethanoic acid, ${\text{CH}}_3\text{COOH}$: $$\begin{array}{ccccccc}& & \text{H}& & \text{O}& & \\ & & |& & \Vert & & \\ \text{H}& -& \text{C}& -& \text{C}& -& \text{O}-\text{H}\\ & & |& & & & \\ & & \text{H}& & & & \end{array}$$ (b) When ethanol changes into ethanoic acid, oxygen is added to it (and two hydrogen atoms are removed), so the conversion is an oxidation. The oxidising agent used is alkaline potassium permanganate, ${\text{KMnO}}_4$ (or acidified potassium dichromate, ${\text{K}}_2{\text{Cr}}_2{\text{O}}_7$).

   Step-by-step solution →
8. Q308 CBSE 2020
   Carbon, a member ​of group 14, ​forms a large number of carbon ​compounds estimated to be about ​three million. ​Why is this property not ​exhibited by ​other elements of this group ? Explain.
   Show answer

   Carbon forms millions of compounds by catenation and tetravalency; other group 14 elements have bigger atoms and weaker bonds.

   Carbon forms about three million compounds because of catenation (its atoms bond to one another in long chains, branched chains and rings) and tetravalency (each atom forms four covalent bonds, with carbon or with other elements). The other members of group 14 do not show this property. The explanation: (1) Carbon, the first member of the group, has the smallest atom, and the force of attraction between its atoms is the highest. (2) Carbon has four valence electrons and needs four more to attain a stable configuration, which it gets by sharing, forming four covalent bonds. Silicon, germanium, tin and lead also have four valence electrons, so this alone does not set carbon apart; its small size and strong bonds do, as (1), (3) and (4) show. (3) Because of its small size, the nucleus of carbon holds the shared pairs of electrons strongly, so its bonds are strong and its compounds stable. (4) The other elements of the group have bigger atoms, so the bonds they form are much weaker; silicon, for example, forms chains of only up to seven or eight atoms, and these are very reactive.

   Step-by-step solution →
9. Q309 CBSE 2020
   1. (a)​How is a ​soap ​different from a ​detergent ​in composition ?
   2. (b)Design an activity to show ​that a detergent works well with all types of water while a soap does not.
   Show answer

   Soap is a carboxylate salt, detergent a sulphonate or ammonium salt; detergent lathers in hard water as well as soft, soap does not.

   (a) A soap is the sodium or potassium salt of a long-chain carboxylic acid, with a carboxylate end ($-{\text{COO}}^{-}{\text{Na}}^{+}$), e.g. sodium stearate. A detergent is an ammonium or sulphonate salt with a long hydrocarbon chain, e.g. the sodium salt of a long-chain sulphonic acid ($-{\text{SO}}_3^{-}{\text{Na}}^{+}$ end); it has no carboxylate group. (b) Take about 10 mL of distilled (soft) water in test tubes A and B and 10 mL of hard water in test tubes C and D. Add five drops of soap solution to A and C and five drops of detergent solution to B and D, and shake all four for the same time. Soap forms plenty of lather in soft water but little lather and a white curdy scum in hard water; detergent forms plenty of lather in both. Hence a detergent works well with all types of water, while a soap does not.

   Step-by-step solution →
10. Q310 CBSE 2020
    Consider ​the molecular formula of the carbon compounds (a) and ​(b) ​given below :

    1. (a)${\text{C}}_3{\text{H}}_8\text{O}$
    2. (b)${\text{C}}_3{\text{H}}_6{\text{O}}_2$ (i) Identify the functional groups in (a) and (b) and write their structures. (ii) Are (a) and (b) isomers ? Give reason. (iii) What happens when alkaline ${\text{KMnO}}_4$ is ​added, drop by drop, into ​a test tube containing warm propanol ​? Write the ​chemical equation ​for the reaction and state the role of alkaline ${\text{KMnO}}_4$ in this reaction.
    Show answer

    Propanol has $-\text{OH}$ and propanoic acid has $-\text{COOH}$; they are not isomers; alkaline ${\text{KMnO}}_4$ oxidises propanol, acting as an oxidising agent.

    (i) (a) ${\text{C}}_3{\text{H}}_8\text{O}$ is propanol (propan-1-ol), an alcohol: functional group $-\text{OH}$; structure ${\text{CH}}_3-{\text{CH}}_2-{\text{CH}}_2-\text{OH}$. (b) ${\text{C}}_3{\text{H}}_6{\text{O}}_2$ is propanoic acid, a carboxylic acid: functional group $-\text{COOH}$; structure ${\text{CH}}_3-{\text{CH}}_2-\text{COOH}$. (ii) No. Isomers have the same molecular formula, but (a) and (b) have different molecular formulae. (iii) The purple colour of alkaline ${\text{KMnO}}_4$ disappears as it oxidises propanol to propanoic acid (once all the propanol is used up, excess ${\text{KMnO}}_4$ stays purple): ${\text{CH}}_3{\text{CH}}_2{\text{CH}}_2\text{OH}+2[\text{O}]\stackrel{{\text{alkaline KMnO}}_4,\text{heat}}{\to }{\text{CH}}_3{\text{CH}}_2\text{COOH}+{\text{H}}_2\text{O}$. Alkaline ${\text{KMnO}}_4$ acts as an oxidising agent.

    Step-by-step solution →
11. Q311 CBSE 2020
    A compound ‘A’ (molecular ​formula ${\text{C}}_3{\text{H}}_6{\text{O}}_2$) reacts with ​sodium metal to form compound ‘B’ and evolves a gas ​which burns with a pop sound. ​The compound ‘A’ on treatment ​with alcohol ‘C’, found in beer, in presence ​of concentrated sulphuric acid, ​forms a sweet smelling compound ‘D’ (molecular formula ${\text{C}}_5{\text{H}}_{10}{\text{O}}_2$). On addition of $\text{NaOH}$ to ‘A’ it also gives ‘B’ and water. ‘D’ on treatment with $\text{NaOH}$ gives back ‘B’ and ‘C’. Identify ‘A’, ‘B’, ‘C’ and ‘D’ and write down the chemical equations of ​the reactions involved.
    Show answer

    'A' is propanoic acid, 'B' sodium propanoate, 'C' ethanol and 'D' ethyl propanoate.

    A: propanoic acid, ${\text{CH}}_3{\text{CH}}_2\text{COOH}$; B: sodium propanoate, ${\text{CH}}_3{\text{CH}}_2\text{COONa}$; C: ethanol, ${\text{C}}_2{\text{H}}_5\text{OH}$; D: ethyl propanoate, ${\text{CH}}_3{\text{CH}}_2{\text{COOC}}_2{\text{H}}_5$ (an ester). With sodium: $2{\text{CH}}_3{\text{CH}}_2\text{COOH}+2\text{Na}⟶2{\text{CH}}_3{\text{CH}}_2\text{COONa}+{\text{H}}_2\uparrow$ Esterification: ${\text{CH}}_3{\text{CH}}_2\text{COOH}+{\text{C}}_2{\text{H}}_5\text{OH}\stackrel{{\text{conc. H}}_2{\text{SO}}_4,\text{warm}}{\to }{\text{CH}}_3{\text{CH}}_2{\text{COOC}}_2{\text{H}}_5+{\text{H}}_2\text{O}$ With sodium hydroxide: ${\text{CH}}_3{\text{CH}}_2\text{COOH}+\text{NaOH}⟶{\text{CH}}_3{\text{CH}}_2\text{COONa}+{\text{H}}_2\text{O}$ Saponification: ${\text{CH}}_3{\text{CH}}_2{\text{COOC}}_2{\text{H}}_5+\text{NaOH}\stackrel{\text{heat}}{\to }{\text{CH}}_3{\text{CH}}_2\text{COONa}+{\text{C}}_2{\text{H}}_5\text{OH}$

    Step-by-step solution →
12. Q312 CBSE 2020
    (a) Write ​the names and ​structures of

    1. (i)an alcohol, ​and
    2. (ii)an aldehyde ​with four carbon atoms ​in their molecules. (b) List two differences between saturated and unsaturated ​hydrocarbons.
    Show answer

    Butanol and butanal are the four-carbon alcohol and aldehyde; saturated hydrocarbons have single bonds and undergo substitution, unsaturated ones undergo addition.

    (a) (i) Alcohol: butanol (butan-1-ol), ${\text{C}}_4{\text{H}}_9\text{OH}$, with the structure ${\text{CH}}_3-{\text{CH}}_2-{\text{CH}}_2-{\text{CH}}_2-\text{OH}$. (ii) Aldehyde: butanal, ${\text{C}}_3{\text{H}}_7\text{CHO}$, with the structure ${\text{CH}}_3-{\text{CH}}_2-{\text{CH}}_2-\text{CHO}$, the end carbon being double-bonded to oxygen and bonded to one hydrogen. The full structural formulas are drawn in the figure. (b) (1) Saturated hydrocarbons have only single bonds between carbon atoms (general formula ${\text{C}}_n{\text{H}}_{2n+2}$); unsaturated hydrocarbons have at least one double or triple bond between carbon atoms (${\text{C}}_n{\text{H}}_{2n}$ or ${\text{C}}_n{\text{H}}_{2n-2}$). (2) Saturated hydrocarbons are less reactive and undergo substitution reactions; unsaturated hydrocarbons are more reactive and undergo addition reactions. They also differ in how they burn: saturated hydrocarbons generally give a clean flame, unsaturated ones a yellow, sooty flame.

    Step-by-step solution →
13. Q313 CBSE 2020
    1. (a)​Why does ​carbon show catenation to maximum extent ? List two reasons.
    2. (b)Draw electron dot structures of (i) ​ethane, and (ii) ethene. (c) An organic compound ‘A’ (molecular formula ${\text{C}}_2{\text{H}}_4{\text{O}}_2$) is used ​for preserving ​pickles and gives ​hydrogen gas with sodium metal. (i) ​Identify ‘A’, and (ii) Write its structural ​formulae.
    Show answer

    Small size and tetravalency give carbon catenation; ethane has a $\text{C}-\text{C}$ single bond and ethene a $\text{C}=\text{C}$ double bond; A is ethanoic acid.

    (a) Carbon shows catenation to the maximum extent because (1) the carbon atom is very small, so its nucleus holds the shared electron pairs strongly and the carbon–carbon bond is very strong and stable; and (2) carbon has a valency of four (tetravalency), so a carbon atom can bond with other carbon atoms and still have bonds left for more carbon atoms or other atoms, forming long chains, branched chains and rings. (b) (i) Ethane, ${\text{C}}_2{\text{H}}_6$: the two carbon atoms share one pair of electrons (a C–C single bond), and each carbon shares one pair with each of three hydrogen atoms, $7$ shared pairs in all. (ii) Ethene, ${\text{C}}_2{\text{H}}_4$: the two carbon atoms share two pairs of electrons (a $\text{C}=\text{C}$ double bond), and each carbon shares one pair with each of two hydrogen atoms, $6$ shared pairs in all. The electron dot structures are drawn in steps 3 and 4. (c) (i) ‘A’ is ethanoic acid (acetic acid), ${\text{CH}}_3\text{COOH}$: vinegar, a 5–8% solution of it in water, preserves pickles, and it reacts with sodium to give hydrogen gas, $2{\text{CH}}_3\text{COOH}+2\text{Na}\to 2{\text{CH}}_3\text{COONa}+{\text{H}}_2$. (ii) Its structural formula is $\text{H}-\underset{\underset{\text{H}}{|}}{\stackrel{\stackrel{\text{H}}{|}}{C}}-\stackrel{\stackrel{\text{O}}{\Vert }}{C}-\text{O}-\text{H}$.

    Step-by-step solution →
14. Q314 CBSE 2020
    1. (a)A compound ‘X’ undergoes addition reaction with ${\text{H}}_2$ to form a compound ‘Y’ having molecular mass $30{\text{g mol}}^{-1}$. ‘X’ decolorises bromine water ​and burns with ​a smoky flame. Identify ​‘X’ and ‘Y’ and write chemical equations of the reactions involved.
    2. (b)Write the structural formulae of (i) Butanone, and (ii) ​Pentanoic ​acid. (c) ​Would you be able to ​check ​if water is hard by using a detergent ? Give reason to justify your answer.
    Show answer

    X is ethene and Y is ethane; a detergent cannot test water hardness because it lathers well in both hard and soft water.

    (a) X is ethene, ${\text{CH}}_2={\text{CH}}_2$ (${\text{C}}_2{\text{H}}_4$), and Y is ethane, ${\text{CH}}_3-{\text{CH}}_3$ (${\text{C}}_2{\text{H}}_6$, molecular mass $2(12)+6(1)=30{\text{g mol}}^{-1}$). Addition of hydrogen: ${\text{CH}}_2={\text{CH}}_2+{\text{H}}_2\stackrel{\text{Ni or Pd catalyst}}{\to }{\text{CH}}_3-{\text{CH}}_3$ Decolorising bromine water: ${\text{CH}}_2={\text{CH}}_2+{\text{Br}}_2⟶{\text{CH}}_2\text{Br}-{\text{CH}}_2\text{Br}$ Burning: ${\text{C}}_2{\text{H}}_4+3{\text{O}}_2⟶2{\text{CO}}_2+2{\text{H}}_2\text{O}+\text{heat and light}$; the flame is smoky because part of the carbon is left unburnt. (b) (i) Butanone, ${\text{CH}}_3-\text{CO}-{\text{CH}}_2-{\text{CH}}_3$: $$\begin{array}{ccccccccccc}& & \text{H}& & \text{O}& & \text{H}& & \text{H}& & \\ & & |& & \Vert & & |& & |& & \\ \text{H}& -& \text{C}& -& \text{C}& -& \text{C}& -& \text{C}& -& \text{H}\\ & & |& & & & |& & |& & \\ & & \text{H}& & & & \text{H}& & \text{H}& & \end{array}$$ (ii) Pentanoic acid, ${\text{CH}}_3-{\text{CH}}_2-{\text{CH}}_2-{\text{CH}}_2-\text{COOH}$: $$\begin{array}{ccccccccccccccc}& & \text{H}& & \text{H}& & \text{H}& & \text{H}& & \text{O}& & & & \\ & & |& & |& & |& & |& & \Vert & & & & \\ \text{H}& -& \text{C}& -& \text{C}& -& \text{C}& -& \text{C}& -& \text{C}& -& \text{O}& -& \text{H}\\ & & |& & |& & |& & |& & & & & & \\ & & \text{H}& & \text{H}& & \text{H}& & \text{H}& & & & & & \end{array}$$ (c) No. A detergent lathers well in both hard and soft water, because the charged ends of detergent molecules do not form insoluble precipitates (scum) with the calcium and magnesium ions of hard water; so hard and soft water behave alike with it. Soap, which forms scum and gives little lather in hard water, is used to check hardness.

    Step-by-step solution →
15. Q315 CBSE 2020
    (a) State any two reasons for carbon ​forming a large number of compounds. Why does carbon form ​compounds

    1. (i)mainly by covalent bonding ?
    2. (ii)having low melting ​and boiling points ? (b) With the help of balanced chemical equations, ​explain what ​happens when (i) ​a piece of sodium ​is added ​to ethanol ? (ii) ethanol burns in the presence of oxygen ?
    Show answer

    Catenation and tetravalency give many carbon compounds, mainly covalent with low melting points; ethanol reacts with sodium (hydrogen evolved) and burns.

    (a) Two reasons: catenation, the ability of carbon atoms to link with one another into long chains, branched chains and rings; and tetravalency, a valency of four, so each carbon atom can bond with four atoms of carbon or of other elements such as hydrogen, oxygen, nitrogen, sulphur and chlorine. (i) Carbon has four valence electrons (configuration $2,4$); gaining four to form ${\text{C}}^{4-}$ or losing four to form ${\text{C}}^{4+}$ is very difficult, so it shares its electrons and forms covalent bonds. (ii) Carbon compounds are made of molecules held together by weak forces of attraction between the molecules, so little energy is needed to separate them, and their melting and boiling points are low. (b) (i) Sodium reacts with ethanol, giving bubbles of hydrogen gas and sodium ethoxide: $2\text{Na}+2{\text{CH}}_3{\text{CH}}_2\text{OH}⟶2{\text{CH}}_3{\text{CH}}_2\text{ONa}+{\text{H}}_2$. (ii) Ethanol burns with a clean blue flame, forming carbon dioxide and water and releasing heat and light: ${\text{CH}}_3{\text{CH}}_2\text{OH}+3{\text{O}}_2⟶2{\text{CO}}_2+3{\text{H}}_2\text{O}+\text{heat and light}$.

    Step-by-step solution →
16. Q316 CBSE 2020
    (a) ​Complete the ​following reactions :

    1. (i)${\text{CH}}_4+{\text{Cl}}_2\stackrel{\text{Sunlight}}{\to }?$
    2. (ii)$\text{R}-\underset{\underset{\text{R}}{|}}{C}=\underset{\underset{\text{R}}{|}}{C}-\text{R}+{\text{H}}_2\underset{\text{heat}}{\overset{\text{Ni}}{\to }}?$ (b) What is an oxidising agent ? What happens when an oxidising agent ​is added to propanol ? ​Explain with ​the ​help of chemical equation.
    Show answer

    Methane undergoes substitution to give chloromethane; the alkene adds hydrogen; an oxidising agent adds oxygen, turning propanol into propanoic acid.

    (a) (i) ${\text{CH}}_4+{\text{Cl}}_2\stackrel{\text{Sunlight}}{\to }{\text{CH}}_3\text{Cl}+\text{HCl}$. Chloromethane and hydrogen chloride are formed: one hydrogen atom of methane is replaced by chlorine, a substitution reaction. (ii) $\text{R}-\underset{\underset{\text{R}}{|}}{C}=\underset{\underset{\text{R}}{|}}{C}-\text{R}+{\text{H}}_2\underset{\text{heat}}{\overset{\text{Ni}}{\to }}\text{R}-\underset{\underset{\text{R}}{|}}{\stackrel{\stackrel{\text{H}}{|}}{C}}-\underset{\underset{\text{R}}{|}}{\stackrel{\stackrel{\text{H}}{|}}{C}}-\text{R}$, that is, ${\text{R}}_2\text{C}={\text{CR}}_2+{\text{H}}_2\to {\text{R}}_2\text{CH}-{\text{CHR}}_2$. Hydrogen adds across the double bond, one hydrogen atom to each carbon, giving a saturated compound: an addition reaction (hydrogenation). (b) An oxidising agent is a substance that adds oxygen to another substance, that is, it brings about oxidation. When an oxidising agent such as alkaline potassium permanganate (or acidified potassium dichromate) is added to propanol and heated, propanol is oxidised to propanoic acid: ${\text{CH}}_3{\text{CH}}_2{\text{CH}}_2\text{OH}+2[\text{O}]\to {\text{CH}}_3{\text{CH}}_2\text{COOH}+{\text{H}}_2\text{O}$. The purple colour of the permanganate disappears as it is used up.

    Step-by-step solution →
17. Q317 CBSE 2020
    1. (a)What ​is ​a homologous series ​? Explain with an example.
    2. (b)Define ​the ​following terms giving one ​example of ​each. (i) Esterification (ii) ​Addition reaction
    Show answer

    Homologous series members share a functional group and differ by $-{\text{CH}}_2-$; esterification gives an ester; addition adds atoms across a multiple bond.

    (a) A homologous series is a series of carbon compounds that have the same functional group (and hence similar chemical properties) and the same general formula, in which successive members differ by a $-{\text{CH}}_2-$ unit (14 u in molecular mass); their physical properties change gradually along the series. Example: the alcohols ${\text{CH}}_3\text{OH}$ (methanol), ${\text{C}}_2{\text{H}}_5\text{OH}$ (ethanol), ${\text{C}}_3{\text{H}}_7\text{OH}$ (propanol) and ${\text{C}}_4{\text{H}}_9\text{OH}$ (butanol) all have the functional group $-\text{OH}$ and the general formula ${\text{C}}_n{\text{H}}_{2n+1}\text{OH}$, and each differs from the next by $-{\text{CH}}_2-$. (b) (i) Esterification: the reaction of a carboxylic acid with an alcohol in the presence of an acid catalyst (concentrated sulphuric acid) to form a sweet-smelling ester and water. Example: ${\text{CH}}_3\text{COOH}+{\text{C}}_2{\text{H}}_5\text{OH}\stackrel{{\text{conc. H}}_2{\text{SO}}_4}{\to }{\text{CH}}_3{\text{COOC}}_2{\text{H}}_5+{\text{H}}_2\text{O}$ (ethyl ethanoate and water). (ii) Addition reaction: a reaction in which atoms, such as hydrogen, add across a double or triple bond of an unsaturated compound, in the presence of a catalyst such as nickel or palladium. Example: ${\text{CH}}_2={\text{CH}}_2+{\text{H}}_2\stackrel{\text{Ni}}{\to }{\text{CH}}_3-{\text{CH}}_3$ (unsaturated ethene gives saturated ethane).

    Step-by-step solution →
18. Q318 CBSE 2020
    1. (a)Compare soaps and detergents on the basis of their composition and ​cleansing action ​in hard ​water.
    2. (b)​What happens when ethanol is treated with sodium metal ? State the behaviour of ethanol ​in this reaction.
    3. (c)​Draw the structure of cyclohexane.
    4. (d)​Name the following ​compound.

    Show answer

    Soaps form scum in hard water but detergents do not; ethanol reacts with sodium releasing hydrogen, acting as an acid; the compound is ethanal.

    (a) Composition: soaps are sodium or potassium salts of long-chain carboxylic (fatty) acids, whereas detergents are generally ammonium or sulphonate salts that also have a long hydrocarbon chain (sodium salts of long-chain sulphonic acids, or ammonium salts with chloride or bromide ions): their charged end is a sulphonate or ammonium group instead of the carboxylate group of a soap. Cleansing action in hard water: soaps react with the calcium and magnesium ions of hard water and form an insoluble scum, so they do not clean well; detergents do not form any scum and clean well even in hard water. (b) Sodium reacts with ethanol, evolving hydrogen gas and forming sodium ethoxide: $2\text{Na}+2{\text{CH}}_3{\text{CH}}_2\text{OH}⟶2{\text{CH}}_3{\text{CH}}_2{\text{O}}^{-}{\text{Na}}^{+}+{\text{H}}_2$. Ethanol behaves like an acid in this reaction. (c) Cyclohexane, ${\text{C}}_6{\text{H}}_{12}$: six carbon atoms joined by single bonds in a ring, each carbon bonded to two hydrogen atoms (structure drawn in the solution). (d) Ethanal (acetaldehyde), ${\text{CH}}_3\text{CHO}$.

    Step-by-step solution →
19. Q319 CBSE 2020
    (a) Carry out following conversions :

    1. (i)​Ethanol to ethene
    2. (ii)Ethanol ​to Ethanoic acid (b) Differentiate between addition ​reaction ​and ​substitution reaction. ​Give ​one ​example of each.
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    Ethanol gives ethene by dehydration and ethanoic acid by oxidation; addition occurs at multiple bonds and gives one product, substitution replaces an atom.

    (a) (i) Ethanol heated at 443 K with excess concentrated sulphuric acid loses water (dehydration): ${\text{CH}}_3{\text{CH}}_2\text{OH}\underset{443\text{K}}{\overset{{\text{hot conc. H}}_2{\text{SO}}_4}{\to }}{\text{CH}}_2={\text{CH}}_2+{\text{H}}_2\text{O}$ (ii) Ethanol heated with alkaline potassium permanganate (or acidified potassium dichromate) is oxidised: ${\text{CH}}_3{\text{CH}}_2\text{OH}+2[\text{O}]\stackrel{{\text{alkaline KMnO}}_4+\text{heat}}{\to }{\text{CH}}_3\text{COOH}+{\text{H}}_2\text{O}$ (b) Addition reaction: an unsaturated compound adds atoms across its double or triple bond, giving a single product; for example, unsaturated hydrocarbons add hydrogen in the presence of a nickel or palladium catalyst to give saturated hydrocarbons: ${\text{CH}}_2={\text{CH}}_2+{\text{H}}_2\stackrel{\text{Ni catalyst}}{\to }{\text{CH}}_3-{\text{CH}}_3$ Substitution reaction: one type of atom or group of atoms in a compound takes the place of another, giving two products; for example, in sunlight chlorine replaces a hydrogen atom of methane: ${\text{CH}}_4+{\text{Cl}}_2\stackrel{\text{sunlight}}{\to }{\text{CH}}_3\text{Cl}+\text{HCl}$ (Any other correct example earns credit.)

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20. Q320 CBSE 2020
    1. (a)Define ​isomerism. ​Draw all possible isomers of butane.
    2. (b)“A compound ‘X’ on combustion gives a ​yellow flame ​with lots of smoke.” What inference would ​you draw from ​this statement ?
    3. (c)​State the role of alkaline ${\text{KMnO}}_4$ in the reaction involving conversion of an alcohol to corresponding ​carboxylic acid.
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    Butane has two isomers, n-butane and isobutane; X is unsaturated; alkaline ${\text{KMnO}}_4$ acts as an oxidising agent.

    (a) Compounds that have the same molecular formula but different structural formulae are called isomers, and this phenomenon is called isomerism. Butane, ${\text{C}}_4{\text{H}}_{10}$, has two isomers (structures as drawn): butane (n-butane), ${\text{CH}}_3-{\text{CH}}_2-{\text{CH}}_2-{\text{CH}}_3$, a straight chain, and isobutane (2-methylpropane), ${\text{CH}}_3-\text{CH}({\text{CH}}_3)-{\text{CH}}_3$, a branched chain. (b) X is an unsaturated carbon compound. (c) Alkaline ${\text{KMnO}}_4$ acts as an oxidising agent: it supplies the oxygen that converts the alcohol into the carboxylic acid.

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