Chapter: Carbon and its Compounds

Class X Science

Very Short Answer Type Questions [1 Mark]

1. Give the names of the following functional groups: (i) —OH (ii) —COOH
   Ans: (i) Alcohol group (ii) Carboxylic acid group
2. What is the difference in the molecular formula of any two consecutive members of a homologous series of organic compounds?
   Ans: —CH₂— is the difference in the molecular formula of any two consecutive members of a homologous series of organic compounds.
3. Name the carbon compound which on heating with excess of concentrated sulphuric acid at 443 K gives ethene.
   Ans: Ethanol (\(CH_3CH_2OH\)).,
4. What is meant by a saturated hydrocarbon?
   Ans: Those hydrocarbons in which the valency of carbon is satisfied by single bonds only are called saturated hydrocarbons.
5. Name the compound formed when ethanol is warmed with ethanoic acid in the presence of a few drops of conc. \(H_2SO_4\).
   Ans: Ethyl ethanoate is formed.
6. Draw the structure of \(CH_3COOH\) molecule.
   
   

   [DIAGRAM: Structure of Ethanoic acid showing Carbon double bonded to Oxygen and single bonded to -OH group]

7. Draw the structure of ethanol molecule.
   
   

   [DIAGRAM: Structure of Ethanol (\(C_2H_5OH\))]

   ,
8. What happens when a small piece of sodium is dropped into ethanol?
   Ans: Hydrogen gas will be evolved.
   Equation: \(2C_2H_5OH(l) + 2Na(s) \rightarrow 2C_2H_5ONa(l) + H_2(g)\)
9. Carbon has four electrons in its valence shell. How does carbon attain stable electronic configuration?
   Ans: By sharing four electrons with other atoms.
10. State two characteristic features of carbon which when put together give rise to large number of carbon compounds.
    Ans: (i) Catenation (ii) Tetravalency of carbon.
11. Write the structural formula of chloroethane.
    Ans: \(CH_3CH_2Cl\) or structure showing two carbons with 5 hydrogens and 1 chlorine.
12. How many covalent bonds are there in a molecule of ethane (\(C_2H_6\))?
    Ans: There are 7 covalent bonds in a molecule of ethane.
13. Write the electron dot structure of ethene molecule (\(C_2H_4\)).
    

    [DIAGRAM: Electron dot structure showing double bond between two carbons and single bonds with hydrogens]

14. Write the electron dot structure of ethane molecule (\(C_2H_6\)).
    

    [DIAGRAM: Electron dot structure showing single bond between two carbons and single bonds with hydrogens]

15. Draw the structure of butanone molecule, \(CH_3COC_2H_5\).
    

    [DIAGRAM: Structure of Butanone showing ketone group on the second carbon]

16. Draw the structure of the hexanal molecule, \(C_5H_{11}CHO\).
    

    [DIAGRAM: Structure of Hexanal showing 6 carbon chain with aldehyde group at the end]

17. Name the following compound: \(H-C \equiv C-C_4H_9\)
    Ans: 1-Hexyne is the IUPAC name of the compound.
18. Butanone is a four carbon per molecule compound. Name the functional group present in it.
    Ans: Ketone.
19. Name the functional group present in each of the following organic compounds: (i) \(C_2H_5Cl\) (ii) \(C_2H_5OH\)
    Ans: (i) (—Cl) Halogen (Chloro) (ii) (—OH) Alcohol.
20. Name the functional group present in each of the following compounds: (i) HCOOH (ii) \(C_2H_5CHO\)
    Ans: (i) —COOH (Carboxylic acid) (ii) —CHO (Aldehyde).
21. Write the name and formula of the 2nd member of the series of carbon compounds whose general formula is \(C_nH_{2n+1}OH\).
    Ans: Ethanol, \(C_2H_5OH\) or \(CH_3CH_2OH\).
22. Write the name and formula of the 2nd member of the series of carbon compounds whose general formula is \(C_nH_{2n}\).
    Ans: \(C_3H_6\), \(H_2C=CH—CH_3\). Propene is the second member of series whose general formula is \(C_nH_{2n}\) (Note: Ethene is the first).

Short Answer Type Questions [I] [2 Marks]

27. (a) Give a chemical test to distinguish between saturated and unsaturated hydrocarbons. (b) (i) Name the products formed when ethanol burns in air. (ii) What two forms of energy are liberated on burning alcohol? (c) Why is the reaction between methane and chlorine considered a substitution reaction?
    Ans: (a) Add bromine water. Saturated hydrocarbons do not react whereas unsaturated hydrocarbon will decolourise bromine water.
    (b) (i) \(CO_2\) and \(H_2O\) are formed. Equation: \(C_2H_5OH(l) + 3O_2(g) \rightarrow 2CO_2(g) + 3H_2O(l) + Heat + Light\). (ii) Heat energy and light energy.
    (c) It is because ‘Cl’ atom substitutes ‘H’ atom of methane to form chloromethane and hydrogen chloride. Equation: \(CH_4(g) + Cl_2(g) \xrightarrow{Sunlight} CH_3Cl(g) + HCl(g)\).
28. (a) Why are covalent compounds generally poor conductors of electricity? (b) Name the compound: \(CH_3COCH_3\). (c) Name the gas evolved when ethanoic acid is added to sodium carbonate. How would you prove the presence of this gas?
    Ans: (a) It is because they do not form ions.
    (b) Propanone.
    (c) Carbon dioxide gas. It turns lime water milky.
    Equation: \(2CH_3COOH(l) + Na_2CO_3(aq) \rightarrow 2CH_3COONa(aq) + H_2O(l) + CO_2(g)\).
29. Write the name and molecular formula of an organic compound having its name suffixed with ‘-ol’ and having two carbon atoms in the molecule. With the help of a balanced chemical equation indicate what happens when it is heated with excess of conc. \(H_2SO_4\).
    Ans: It is ethanol, its molecular formula is \(C_2H_6O\) (\(C_2H_5OH\)). Ethanol forms ethene, when heated with conc. \(H_2SO_4\).
    Equation: \(CH_3CH_2OH \xrightarrow[heat]{Conc. H_2SO_4} CH_2=CH_2 + H_2O\).
30. Explain why carbon generally forms compounds by covalent bonds.
    Ans: Carbon cannot lose four electrons easily because very high energy is required. It cannot gain four electrons easily because six protons cannot hold 10 electrons. It can easily share four electrons forming covalent bonds.
31. Write the names and molecular formula of two organic compounds having functional group suffixed as ‘-oic acid’. With the help of a balanced chemical equation explain what happens when any one of them reacts with sodium hydroxide.
    Ans: Methanoic acid (\(CH_2O_2\)) and Ethanoic acid (\(C_2H_4O_2\)). When acid reacts with sodium hydroxide, its sodium salt and water is formed.
    Equation: \(CH_3COOH + NaOH \rightarrow CH_3COONa + H_2O\) (Sodium ethanoate + Water).
32. What is the IUPAC name of (i) \(CH_3—CH_2—CH=CH_2\) (ii) \(CH_3CHO\)?
    Ans: (i) But-1-ene (ii) Ethanal.
33. Atom of an element contains five electrons in its valence shell. This element is major component of air. It exists as a diatomic molecule. (i) Identify the element. (ii) Show the bond formed between two atoms of this element. (iii) Write the nature of the bond between the two atoms.
    Ans: (i) Nitrogen. (ii) Diagram showing triple bond (:N≡N:). (iii) Covalent bond.
34. Write IUPAC names of (i) \(CH_3COCH_2CH_3\) (ii) \(CH_3-CH(OH)-CH_3\) (iii) HCOOH (iv) \(CH_3COOCH_3\).
    Ans: (i) Butanone (ii) 2-Propanol (iii) Methanoic acid (iv) Methyl ethanoate.
35. What is a homologous series? Which two of the following organic compounds belong to the same homologous? \(CH_3\), \(C_2H_6\), \(C_2H_6O\), \(C_2H_6O_2\), \(CH_4O\).
    Ans: Homologous series is a series of organic compounds which have same functional group and similar chemical properties. Each member of this series differs by —CH₂— in its molecular formula and 14 u in its molecular mass. \(C_2H_6O\) (\(C_2H_5OH\)) and \(CH_4O\) (\(CH_3OH\)) belong to the same homologous series.

Short Answer Type Questions [II] [3 Marks]

36. What is meant by a functional group in an organic compound? Name the functional group present in (i) \(CH_3CH_2OH\) (ii) \(CH_3COOH\) (b) State one point of difference between soap and synthetic detergent.
    Ans: (a) Functional group is an atom or group of atoms or reactive part of compound, which determines chemical properties of compounds. (i) —OH (Alcohol) (ii) —COOH (Carboxylic acid). (b) Soaps do not work well with hard water, detergents work well with hard water.
37. Give reasons for the following observations: (a) The element carbon forms a very large number of compounds. (b) Air holes of a gas burner have to be adjusted when the heated vessels get blackened by the flame. (c) Use of synthetic detergents causes pollution of water.
    Ans: (a) Carbon forms large number of compounds since carbon is small in size and can form stable covalent bonds (catenation) and it shows tetravalency. (b) Air holes of gas burner are made open (adjusted) so that air can pass through, which is needed for complete combustion, so that heated vessels do not get blackened. (c) Some synthetic detergents are non-biodegradable, therefore, cause pollution of water.
38. What is ethanoic acid? Write the formula of the functional group present in this acid. What special name is given to its 5 – 8% solution in water? How does ethanoic acid react with sodium carbonate? Write a chemical equation of the reaction and common name of the salt produced.
    Ans: \(CH_3COOH\) is ethanoic acid. —COOH is the formula of the functional group. Its 5 to 8% solution in water is called vinegar. Sodium ethanoate and brisk effervescence due to carbon dioxide gas are formed on reaction of ethanoic acid with sodium carbonate.
    Equation: \(2CH_3COOH(l) + Na_2CO_3(aq) \rightarrow 2CH_3COONa(aq) + CO_2(g) + H_2O(l)\).
    The salt produced has common name sodium acetate.
39. An ester has the molecular formula \(C_4H_8O_2\). Write its structural formula. What happens when this ester is heated in the presence of sodium hydroxide solution? Write the balanced chemical equation for the reaction and name the products. What is a saponification reaction?
    Ans: Structural formulae can be \(CH_3COOC_2H_5\) (Ethyl ethanoate). Saponification is the process in which an ester is treated with sodium hydroxide to form sodium salt of acid and alcohol.
    Equation: \(CH_3COOC_2H_5 + NaOH \rightarrow CH_3COONa + C_2H_5OH\). Products: Sodium ethanoate and Ethanol.
40. Out of HCl and \(CH_3COOH\), which one is a weak acid and why? Describe an activity to support your answer.
    Ans: Acetic acid (\(CH_3COOH\)) is a weaker acid because it does not dissociate completely into its ions in aqueous solution.
    Activity: Add zinc metal in HCl and \(CH_3COOH\) respectively. The hydrogen gas will be evolved faster in HCl and slowly in \(CH_3COOH\). It shows acetic acid is a weak acid. Or use pH paper; HCl turns it dark red, \(CH_3COOH\) turns it light red.
41. Name the functional group of organic compounds that can be hydrogenated. With the help of suitable example explain the process of hydrogenation mentioning the conditions of the reaction and any one change in physical property with the formation of the product. Name any one natural source of organic compounds that are hydrogenated.
    Ans: Double bond (=) and Triple bond (≡) are functional groups which can be hydrogenated. When unsaturated hydrocarbons are heated with hydrogen in the presence of nickel as catalyst, saturated hydrocarbons are formed. If the starting unsaturated hydrocarbons are liquids, they will change into solids (e.g., Vegetable oils are hydrogenated to form vegetable ghee). Plants are natural sources.
42. An organic compound ‘A’ is an essential constituent of wine and beer. Oxidation of ‘A’ yields an organic acid ‘B’ which is present in vinegar. Name the compounds ‘A’ and ‘B’ and write their structural formula. What happens when ‘A’ and ‘B’ react in the presence of an acid catalyst? Write the chemical equation for the reaction.
    Ans: ‘A’ is ethanol (\(C_2H_5OH\)) and ‘B’ is acetic acid (\(CH_3COOH\)). When ‘A’ and ‘B’ react in the presence of an acid catalyst, ethyl ethanoate (ester) is formed.
    Equation: \(CH_3COOH(l) + C_2H_5OH(l) \xrightarrow{conc. H_2SO_4} CH_3COOC_2H_5(l) + H_2O(l)\).
43. With the help of balanced chemical equations explain what happens when ethanol is heated with (i) alkaline solution of potassium permanganate, (ii) excess concentrated sulphuric acid at 443 K. Mention any two uses of ethanol.
    Ans: (i) Oxidation: \(CH_3CH_2OH + 2[O] \xrightarrow{Alkaline KMnO_4} CH_3COOH + H_2O\) (ii) Dehydration: \(CH_3CH_2OH \xrightarrow[443K]{Conc. H_2SO_4} CH_2=CH_2 + H_2O\) Uses: Tonics/cough syrups, fuel, solvent, wine/beer.
44. What is an ‘esterification’ reaction? Describe an activity to show esterification.
    Ans: When carboxylic acid reacts with alcohol in presence of conc. \(H_2SO_4\), a pleasant fruity smelling compound is formed. Activity: Take 1 ml of ethanol and 1 ml of acetic acid in a test tube. Add few drops of conc. \(H_2SO_4\). Heat on water bath for 5 minutes. Smell the mixture. Result: Pleasant fruity smell.
45. Write a chemical equation in each case to represent the following types of chemical reactions of organic compounds: (i) Oxidation reactions (ii) Addition reactions (iii) Substitution reactions
    Ans: (i) Oxidation: \(CH_3CH_2OH \xrightarrow{Alkaline KMnO_4} CH_3COOH\) (ii) Addition: \(CH_2=CH_2 + H_2 \xrightarrow{Ni} CH_3-CH_3\) (iii) Substitution: \(CH_4 + Cl_2 \xrightarrow{Sunlight} CH_3Cl + HCl\)
46. Write chemical equations for what happens when (i) sodium metal is added to ethanoic acid. (ii) solid sodium carbonate is added to ethanoic acid. (iii) ethanoic acid reacts with a dilute solution of sodium hydroxide.
    Ans: (i) \(2CH_3COOH + 2Na \rightarrow 2CH_3COONa + H_2\) (ii) \(2CH_3COOH + Na_2CO_3 \rightarrow 2CH_3COONa + CO_2 + H_2O\) (iii) \(CH_3COOH + NaOH(dil.) \rightarrow CH_3COONa + H_2O\)
47. What are isomers? Draw the structures of two isomers of butane, \(C_4H_{10}\). Why can’t we have isomers of first three members of alkane series?
    Ans: Compounds with the same molecular formula but different structural formulae are called isomers. Structures: n-Butane and 2-Methylpropane (Isobutane). In the first three members of alkane series, branching is not possible, so no isomers.,
48. Define homologous series of organic compounds. List its two characteristics. Write the name and formula of the first member of the series of alkenes.
    Ans: Series of organic compounds having same functional group and similar chemical properties. Characteristics: (i) Same general formula (ii) Similar chemical properties. First member of alkenes: Ethene (\(C_2H_4\)).,
49. Complete the following equations: (i) \(CH_4 + O_2 \rightarrow\) (ii) \(C_2H_5OH \xrightarrow{Hot Conc. H_2SO_4}\) (iii) \(CH_3COOH + NaOH \rightarrow\)
    Ans: (i) \(CO_2 + 2H_2O\) (ii) \(CH_2=CH_2 + H_2O\) (iii) \(CH_3COONa + H_2O\)
50. Name the oxidising agent used for the conversion of ethanol to ethanoic acid. Distinguish between ethanol and ethanoic acid on the basis of (i) litmus test, (ii) reaction with sodium hydrogencarbonate.
    Ans: Alkaline Potassium Permanganate or Acidified Potassium Dichromate. (i) Ethanol: No change; Ethanoic acid: Turns blue litmus red. (ii) Ethanol: No reaction; Ethanoic acid: Brisk effervescence (\(CO_2\)).
51. What are esters? How are they prepared? List two uses of esters.
    Ans: Esters are organic compounds (R—COO—R′) formed by reaction between alcohol and organic acid. Prepared via Esterification (Acid + Alcohol + catalyst). Uses: Perfumes, soap, flavouring agents.
52. Describe two examples of different oxidations of ethanol. Name the products obtained in each case.
    Ans: (i) Heated with copper at 573K: Forms Ethanal. (ii) Oxidised with alkaline \(KMnO_4\): Forms Ethanoic acid.
53. List two tests for experimentally distinguishing between an alcohol and a carboxylic acid.
    Ans: (i) \(NaHCO_3\) test: Carboxylic acid gives brisk effervescence; Alcohol does not. (ii) Blue litmus test: Carboxylic acid turns it red; Alcohol does not.

Long Answer Type Questions [5 Marks]

60. (a) State two properties of carbon which lead to a very large number of carbon compounds. (b) Why does micelle formation take place when soap is added to water? Why are micelles not formed when soap is added to ethanol?
    Ans: (a) (i) Catenation (ii) Tetravalency. (b) Micelles form because soap has a hydrophobic tail (hydrocarbon) and a hydrophilic head (ionic). In water, the hydrocarbon tail repels water and clusters together, while the ionic head interacts with water. Ethanol is a non-polar solvent; the hydrocarbon part gets attracted to ethanol and the ionic end does not dissolve in the same way, preventing micelle formation.
61. (a) In tabular form, differentiate between ethanol and ethanoic acid under the following heads: (i) Physical state (ii) Taste (iii) \(NaHCO_3\) test (iv) Ester test. (b) Write a chemical reaction to show the dehydration of ethanol.
    Ans: (a)

    Properties	Ethanol	Ethanoic acid
    Physical state	Liquid, specific smell	Liquid, vinegar smell
    Taste	Burning taste	Sour taste
    \(NaHCO_3\) test	No reaction	Brisk effervescence (\(CO_2\))
    Ester test	Forms ester w/ acid	Forms ester w/ alcohol

    (b) \(CH_3CH_2OH \xrightarrow{conc. H_2SO_4} CH_2=CH_2 + H_2O\).
62. Explain isomerism. State any four characteristics of isomers. Draw the structures of possible isomers of butane, \(C_4H_{10}\).
    Ans: Isomerism is the phenomenon where compounds have the same molecular formula but different structural formulae. Characteristics: Differ in structural formula, melting point, boiling point, and solubility. Structures: n-Butane and Isobutane.
63. Give reasons for the following: (i) Element carbon forms compounds mainly by covalent bonding. (ii) Diamond has a high melting point. (iii) Graphite is a good conductor of electricity. (iv) Acetylene burns with a sooty flame. (v) Kerosene does not decolourise bromine water while cooking oils do.
    Ans: (i) Carbon cannot gain/lose 4 electrons due to energy constraints; shares instead. (ii) Strong covalent bonds/compact structure. (iii) Free electrons. (iv) High percentage of carbon. (v) Kerosene is saturated; cooking oils are unsaturated.
64. What is the difference between the chemical composition of soaps and detergents? State in brief the action of soaps in removing an oily spot from a shirt. Why are soaps not considered suitable for washing where water is hard?
    Ans: Soaps are sodium/potassium salts of fatty acids (—COONa). Detergents are salts of sulphonic acids (—\(SO_3Na\)). Cleansing action: Soap molecules have a hydrophobic tail (attracts oil) and hydrophilic head (attracts water). They form micelles around the oil droplet, trapping it. When water is agitated, the oil is lifted off. Hard water contains \(Ca^{2+}\) and \(Mg^{2+}\) ions which react with soap to form insoluble scum (wastage).,
65. List in tabular form three physical and two chemical properties on the basis of which ethanol and ethanoic acid can be differentiated.
    Ans: Physical: Smell, taste, freezing point. Chemical: Reaction with \(NaHCO_3\), reaction with litmus.
66. What are the hydrocarbons? Write the name and general formula of (i) saturated hydrocarbons, (ii) unsaturated hydrocarbons, and draw the structure of one hydrocarbon of each type. How can an unsaturated hydrocarbon be made saturated?
    Ans: (i) Alkanes (\(C_nH_{2n+2}\)), e.g., Methane. (ii) Alkenes (\(C_nH_{2n}\)) and Alkynes (\(C_nH_{2n-2}\)), e.g., Ethene, Ethyne. Unsaturated hydrocarbons are made saturated by hydrogenation (heating with \(H_2\) in presence of Ni catalyst).
67. What are detergents chemically? List two merits and two demerits of using detergents for cleansing.
    Ans: Detergents are sodium salts of sulphonic acid of benzene or alkene. Merits: Work well with hard water, more effective. Demerits: Expensive, some are non-biodegradable (pollution).
68. What are micelles? Why does it form when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?
    Ans: Micelles are aggregates of molecular ions of soap. Formed because soap has a hydrophobic part (repelled by water) and hydrophilic part. No, micelles do not form in ethanol as soap dissolves in it.
69. (a) What is a soap? Why are soaps not suitable for washing clothes when the water is hard? (b) Explain the action of soap in removing an oily spot from a piece of cloth.
    Ans: (a) Sodium/potassium salt of long chain fatty acids. Hard water causes scum formation due to Ca/Mg ions displacing Na/K. (b) Hydrophobic ends attach to oil, hydrophilic ends to water. Micelles form, trapping dirt, which is rinsed away.
70. A carbon compound X turns blue litmus to red and has a molecular formula \(C_2H_4O_2\). Identify X and draw its structure. Write chemical equation for the reaction and name of the product formed in each case when X reacts with (a) ethanol in the presence of conc. \(H_2SO_4\) (b) sodium carbonate.
    Ans: X is Ethanoic acid. (a) Forms Ethyl ethanoate (Ester). (b) Forms Sodium ethanoate, \(CO_2\), and water.