CARBON AND ITS COMPOUNDS

 

VERY SHORT ANSWER TYPE QUESTION [1 Mark]

1.     Give the names of the following functional groups: (i) —OH (ii) —COOH

Ansswer. (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?

Answer. —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. Answer.

 

4.     What is meant by a sturated hydrocarbon?

Answer. Those hydrocarbons in w hich valency of carbon is satisfied by single bonds only are called sturated hydrocarbons.

5.     Name the compound formed when ethanol is warmed with ethanoic acid in the presence of a few drops of cone.H₂S₀₄ Answer.

 

6.     Draw the structure of CH₃COOH molecule. Answer.

 

7.     Draw the structure of ethanol molecule. Answer.

 

8.     What happens when a small piece of sodium is dropped into ethanol?  

Answer.  

 

9.     Carbon has four electrons in its valence shell. How does carbon attain stable electronic configuration.

Answers. 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.

Answer. (i) Catenation (ii) Tetravalency of carbon

11.  Write the structural formula of chloroethane. Answer.

 

12.  How many covalent bonds are there in a molecule of ethane (C₂H₆)?

Answer. There are 7 covalent bonds in a molecule of ethane.

13.  Write the electron dot structure of ethene molecule (C₂H₄). Answer.

 

14.  Write the electron dot structure of ethane molecule (C₂H₆). Answer.

 

15.  Draw the structure of butanone molecule, CH₃COC₂H₅. Answer.

 

16.  Draw the structure of the hexanal molecule, C₅H₁₁CHO.

Answer.

 

17.  Name the following compound:

 

Answer. 1-Hexyne is IUPAC name of the compound.

18.  Butanone is a four carbon per molecule compound. Name the functional group present in it. Answer. Ketone  

19.  Name the functional group present in each of the following organic compounds:

(i)    C₂H₅CI (ii) C₂H₅OH Answer.

(i)    (—Cl) Halogen (Chloro)

(ii)  (—OH) Alcohol

20.  Name the functional group present in each of the following compounds:

(i)    HCOOH (ii) C₂H₅CHO Answer.

(i)    —COOH (Carboxylic acid)

(ii)  —CHO (Aldehyde)

21.  Name the functional group present in each of the following organic compounds:

(i)CH₃COCH₃ (ii) C₂H₅COOH Answer.

 

22.  Write the name and formula of the second member of the carbon compounds having functional group —OH. Answer.

 

23.  Write the name and formula of the first member of the carbon compounds having functional group —CHO. Answer.

 

24.  Write the name and formula of the first member of the carbon compounds having functional group —COOH. Answer.

 

25.  Write the name and formula of the 2nd member of the series of carbon compounds whose general formula is C_nH_2n+1OH

Answer. Ethanol, C₂H₅OH or CH₃CH₂OH

26.  Write the name and formula of the 2nd member of the series of carbon compounds whose general formula is CnH_2n.

Answer.

C₃H_6, H₂C=CH—CH₃

Propene is second member of series whose general formula is C_nH_2n.

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? Answer.

 

28.  (a) Why are covalent compounds generally poor conductors of electricity?

(b)  Name the following compound:

 

(c)   Name the gas evolved when ethanoic acid is added to sodium carbonate. How would you prove the presence of this gas? Answer.

 

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 r cone.H₂S_04. Answer.

 

30.  Explain why carbon generally forms compounds by covalent bonds.

Answer. 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 r group suffixed as ‘-oic acid’. With the help of a balanced chemical equation and explain what happens when any one of them reacts with sodium hydroxide.

Answer.

 

32.  What is the IUPAC name of (i) CH₃—CH₂—CH=CH₂ (ii) CH₃CHO?

Answer. (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.

Answer.

(i) Nitrogen. 

(ii)

 

(iii) Covalent bond.

34.  Write IUPAC names of (i) CH₃COCH₂CH₃ 

(ii) 

 

(iii) HCOOH (iv) CH₃COOCH₃

Answer. (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?  

CH3 ,C2H6, C2H6O, C2H6O2,CH4O       

Answer. Homologous series is a series of organic compounds which have same functional group and similar chemical properties. Each member of this series is differ by —CH₂— in its molecular formula and 14 u in its molecular mass.

C₂H₆O (C₂H₅OH) and CH₄O (CH₃OH) belong to 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) CH₃CH₂OH

(ii) CH₃COOH

(b) State one point of difference between soap and synthetic detergent.

Answer.

(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.

Answer.

(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. Answer.

 

39.  An ester has the molecular formula C₄H₈O₂. 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? Answer.

 

40.  Out of HCI and CH₃COOH, which one is a weak acid and why? Describe an activity to support your answer.

Answer. Acetic acid ( CH₃COOH) is a weaker acid because it does not dissociate completely into its ions in aqueous solution. .

Activity: Add zinc metal in HCI and CH₃COOH respectively. The hydrogen gas will be evolved faster in HCI and slowly in CH₃COOH. It shows acetic acid is a weak acid.

Alternative Method:

If we use pH paper, the colour of pH paper will be dark red in HCI and light red in CH₃COOH which shows HCI is a strong acid and CH₃COOH is a weak acid.

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. Answer.

 

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. Vegetable oils are hydrogenated to form vegetable ghee. Plants are natural sources of vegetable oils which can be hydrogenated.

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. Answer.

 

43.  What is ethanol? State its two properties. What happens when it is heated with excess of cone. H₂SO₄ at 443 K? What role does cone. H₂SO₄ play in this reaction? Write chemical equation of the reaction involved and the structural formula of the main product formed. Answer.

 

44.  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.  

Answer.

 

45.  What is an ‘esterification’ reaction? Describe an activity to show esterification.

Answer. When carboxylic acid reacts with alcohol in presence of conc. H2SO4, pleasant fruity smelling compound is formed.

 

Activity: Take 1 ml of ethanol in a test tube. Add 1 ml of acetic acid in this test tube.

Add few drops of conc. H2SO4 in the mixture.

Heat the content on water bath for 5 minutes. Smell the resulting mixture formed.

 

Result: Pleasant fruity smelling ester is formed.

46.  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 Answer.

 

 

47.  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. Answer.

 

48.  Describe two examples of different oxidations of ethanol. Name the products obtained in each case. Answer.

 

49.  What are isomers? Draw the structures of two isomers of butane, C₄H₁₀. Why can’t we have isomers of first three members of alkane series?

Answer. Those compounds, which have same molecular formula but different structural formulae are called isomers.

 

In first three members of alkane series, branching is not possible. Therefore, we cannot have isomers.

50.  Define homologous series of organic compounds. List its two characteristics. Write the name and formula of the first member of the series of alkenes.

Answer. The series of organic compounds having same functional group and similar chemical properties is called homologous series.

Each member differs from successive member by —CH₂— group. The difference in molecular weight between two successive members is 14 u. Characteristics:

(i)    It has same general formula, from which, all members can be derived.

(ii)  They have similar chemical properties.

C₂H₄, CH₂=CH₂, Ethene is first member of alkene series.

51.  Complete the following equations:

(i)    CH₄ + O₂ 

(ii)  C₂H₅OH Hot Conc. H SO_{2            4}                           

(iii)                    CH₃COOH + NaOH  Answer.

(i)     CH₄ + O₂  CO₂(g) + 2H₂O(l)

(ii)   C2H5OH Hot Conc. H SO2        4                  CH2=CH2 + H2O

(iii) CH₃COOH + NaOH CH₃COONa + H₂O

 

52.  Why homologous series of carbon compounds are so called? Write chemical formula of two consecutive members of a homologous series and state the part of these compounds that determines their

(i)    physical properties, and (ii) chemical properties.

Answer. The series consists of members of same family with similar physical and chemical properties, therefore, called homologous series

(i) CH₃OH, and (ii) CH₃CH₂OH are two consecutive members of homologous series.

Alkyl group —CH₃ and —CH₃CH₂ part determines physical properties. Functional group —OH determines chemical properties of the compounds.

53.  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.

Answer. Alkaline potassium permanganate or Acidified potassium dichromate.

(i)Ethanol will not affect litmus paper. Ethanoic acid will turn blue litmus ‘ paper red. (ii) Ethanol will not react with sodium hydrogen carbonate. Ethanoic acid will give brisk effervescence due to colourless, odourless carbon dioxide gas.

54.  What are esters? How are they prepared? List two uses of esters.

Answer. Esters are organic compounds (R—COO—R′) formed by a reaction between an alcohol (R′—OH) and an organic acid (R—COOH), i.e. carboxylic acid and usually some catalyst with water as a by-product. Esters are used to make perfumes and soap. They are also used to produce pharmaceutical products, cosmetics, plasticizers and detergents. 

55.  Out of HCl and CH₃COOH, which one is a weak acid and why? Describe an activity to support your answer.

Answer. Acetic acid (CH₃COOH) is a weaker acid because it does not dissociate completely into aqueous solution.

Activity: Add zinc metal in HCl and CH₃COOH respectively. The hydrogen gas will be evolved faster in HCl and slowly in CH₃COOH. It shows acetic acid is a weak acid. 

Alternative Method: If we use pH paper, the colour of pH paper will be dark red in HCl and light red in CH₃COOH which shows HCl is strong acid and CH₃COOH is a weak acid. 

56.  Describe two examples of different oxidations of ethanol. Name the products obtained in each case.

Answer. 

(i)    When ethanol is heated with copper at 573K, ethanal is formed.

 

 

 

(ii)  When ethanol is oxidised with alkaline potassium permanganate solution, ethanoic acid is formed. 

 

57.  (a) Give chemical tests to detect the presence of (i) Ethanol (ii) Ethanoic acid (b) Why ethanoic acid is called glacial acetic acid?

Answer. (a) Add sodium hydrogen carbonate. Ethanol will not react. Ethanoic acid will give brisk effervescence due to carbon dioxide.

(b) Pure ethanoic acid exist as solid like glaciers at 291 K, therefore, called glacial acetic acid. 

58.  List two tests for experimentally distinguishing between an alcohol and a carboxylic acid and describe how these tests are performed.

Answer. (i) NaHCO₃ test: Add sodium hydrogen carbonate to alcohol and a carboxylic acid separately. Alcohol will not react, whereas carboxylic acid will give brisk effervescence. Pass the gas through lime water. It will turn milky.

(ii) Blue litmus test: Add few drops of alcohol and solution of carboxylic acid on blue litmus paper separately. Blue litmus will remain as it is in case of alcohol, whereas it will turn red in carboxylic acid. 

59.  Distinguish between esterification and saponification reactions of organic compounds with the help of the chemical equation for each. What is the use of (i) esters and (ii) saponification process? Answer.

 

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?

Answer.

(a)  (i)-Catenation (ii) Tetravalency

(b)  It is because large number of molecular ions of soaps get aggregated and form colloidal solution. Soap has hydrophobic tail (hydrocarbon) which dissolves in hydrocarbon part and hydrophilic part dissolves in water. Ethanol is non-polar solvent therefore micelles are not formed because hydrocarbon part gets attracted towards ethanol and ionic end will not dissolve in alcohol.

61.  (a) In tabular form, differentiate between ethanol and ethanoic acid under the following heads:

(i)     Physical state (ii) Taste

(iii) NaHCO₃ test (iV) Ester test

(b) Write a chemical reaction to show the dehydration of ethanol.

Answer.  

 

62.  Explain isomerism. State any four characteristics of isomers. Draw the structures of possible isomers of butane, C₄H₁₀

Answer. Isomerism is a phenomenon due to which some compounds have same molecular formula but different structural formulae.

Characteristics:

(i)     They differ in structural formula.

(ii)   They differ in melting point. (iii) They differ in boiling point.

(iv) They differ in solubility in same solvent.

 

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 bums with a sooty flame.

(v)Kerosene does not decolourise bromine water while cooking oils do.

Answer.

(i)     It is because carbon has four valence electrons, it cannot gain or lose four electrons because high energy is needed. It can only share four electrons.

(ii)   It is due to strong covalent bonds and compact structure of diamond.

(iii) It is due to presence of free electrons in graphite because each carbon is linked to three more carbon atoms.

(iv)  It is due to high percentage of carbon, it burns with sooty or smoky flame.

(v)    Kerosene oil is mixture of saturated hydrocarbons therefore does not decolourise bromine water.

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?

Answer. Soaps are sodium or potassium salts of fatty acids having — COONa group. Detergents are sodium or potassium salts of sulphonic acids having — SO₃Na and — SO₄Na group. Cleansing action of soap: Soap molecules consist of a large hydrocarbon tail which is hydrophobic (water-hating or water repelling) with a negatively charged head which is hydrophilic (water-loving) as shown in figure.

 

 

When a soap is dissolved in water, the molecules associate together as clusters called micelles in which water molecules, being polar in nature, surround the ions and the hydrocarbon part of the molecule attracts grease, oil and dirt.

The tails stick inwards and the heads outwards. In cleaning, the hydrocarbon tail attaches itself to oily dirt. When water is agiated (shaken vigorously), the oily dirt tends to lift off from the dirty surface and dissociate into fragments.

This gives opportunity to other tails to stick to oil. The solution now contains small globules of oil surrounded by soap molecules.

The negatively charged and form aggregates. Thus, the oily dirst is removed. Hard water has Ca²⁺ and Mg²⁺ ions. When it reacts with soap, it forms insoluble compound and the soap goes waste.

65.  List in tabular form three physical and two chemical properties on the basis of which ethanol and ethanoic acid can be differentiated Answer.

 

 

 

66.  What are the hydrocorbons write the name and general formula of (i) sturated hydrocarbons, (ii) unsaturated hydrocarbons, and draw the structure of one hydrocarbon of each type. How can an unsaturated hydrocarbon be made saturated? Answer.

 

 

67.  What are detergents chemically? List two merits and two demerits of using detergents for cleansing. State the reason for the suitability of detergents for washing, even in the case of water having calcium and magnesium ions.

Answer. Detergents chemically are sodium or potassium salts of sulphonic acid of benzene or alkene.

Merits:

(i)    They work well with hard water.

(ii)  They are more effective than soaps.

Demerits:

(i)  They are expensive.

(ii)  Some of them having branching are non-biodegradable, therefore create water pollution. Detergents are suitable for hard water having  Mg²⁺ and Ca²⁺ ions because they do not form insoluble salts with Mg²⁺ and Ca²⁺ ions.

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? State briefly how the formation of micelles help to clean the clothes having oily spots.

Answer. Micelles: When molecular ions in soaps and detergents aggregate, they form micelles. It is formed because soap has hydrophobic part. Water can attract hydrophilic part but not hydrophobic part.

No, micelle will not be formed in ethanol, as soap will dissolve in ethanol. Micelles trap (attract) dirt, grease, oily spot, etc. which is washed away by water.

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. Answer. (a) Soap is sodium or potassium salt of higher fatty acids such as oleic acid

(C₁₇H₃₃COOH), stearic acid (C₁₇H₃₅COOH), palimitic acid (C₁₅H₃₁COOH), etc.

A soap is a sodium or potassium salt of long chain fatty acids. Hard water contains salts of calcium and magnesium. On adding soap to water, calcium and magnesium ions present in water displace sodium or potassium ions from the soap molecules forming an insoluble substance called scum. Scum results in wastage of soap.

(b) Cleansing action of soaps: 

The oily spot present on clothes is organic in nature and insoluble in water. Therefore, it cannot be removed by only washing with water. When soap is dissolved in water, its hydrophobic ends attach themselves to the oily spot and remove it from the cloth. Then, the molecules of soap arrange themselves in the form of micelle and trap the dirt at the centre of the cluster. These micelles remain suspended in the water. Hence, the oily spots are easily rinsed away by water.

70.  A carbon compound X turns blue litmus to red and has a molecular formula C₂H₄O₂. 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. H₂SO₄  (b) sodium carbonate.

Answer. ‘X’ is ethanoic acid.