Chapter 4: Carbon and its Compounds

Multiple Choice Questions

1. Carbon exists in the atmosphere in the form of

(a) carbon monoxide only

(b) carbon monoxide in traces and carbon dioxide

(c) carbon dioxide only

(d) coal

Answer : (c) carbon dioxide only

[ Carbon exists in the atmosphere primarily in the form of carbon dioxide (). ]

2. Which of the following statements are usually correct for carbon compounds? These

(i) are good conductors of electricity

(ii) are poor conductors of electricity

(iii) have strong forces of attraction between their molecules

(iv) do not have strong forces of attraction between their molecules

(a) (i) and (iii) (b) (ii) and (iii)

(c) (i) and (iv) (d) (ii) and (iv)

Answer :  (d) (ii) and (iv)

[ Carbon compounds are generally poor conductors of electricity (ii) and do not have strong forces of attraction between their molecules (iv).]

3. A molecule of ammonia () has

(a) only single bonds

(b) only double bonds

(c) only triple bonds

(d) two double bonds and one single bond

Answer : (a) only single bonds .

[ A molecule of ammonia () has only single bonds. ]

4. Buckminsterfullerene is an allotropic form of

(a) phosphorus

(b) sulphur

(c) carbon

(d) tin

Answer :  (c) carbon

[ Buckminsterfullerene is an allotropic form of carbon. ]

5. Which of the following are correct structural isomers of butane?

(a) (i) and (iii) (b) (ii) and (iv)

(c) (i) and (ii) (d) (iii) and (iv)

Answer : (c) (i) and (ii)

6.

In the above given reaction, alkaline   acts as

(a) reducing agent

(b) oxidising agent

(c) catalyst

(d) dehydrating agent

Answer : (b) oxidising agent

[ In the given reaction: 

Alkaline  is acting as an oxidizing agent. ]

7. Oils on treating with hydrogen in the presence of palladium or nickel catalyst form fats. This is an example of

(a) Addition reaction

(b) Substitution reaction

(c) Displacement reaction

(d) Oxidation reaction

Answer : (a) Addition reaction

[ The process described, where oils are treated with hydrogen in the presence of a catalyst (palladium or nickel) to form fats, is an example of an addition reaction. ]                                                                                      

8. In which of the following compounds, — OH is the functional group?

(a) Butanone

(b) Butanol

(c) Butanoic acid

(d) Butanal

Answer : (b) Butanol

[ In the given options, the functional group —OH is present in the compound Butanol.]

9. The soap molecule has a

(a) hydrophilic head and a hydrophobic tail

(b) hydrophobic head and a hydrophilic tail

(c) hydrophobic head and a hydrophobic tail

(d) hydrophilic head and a hydrophilic tail

Answer : (a) hydrophilic head and a hydrophobic tail

[ The soap molecule has a hydrophilic (water-attracting) head and a hydrophobic (water-repelling) tail. ]

10. Which of the following is the correct representation of electron dot structure of nitrogen?

Answer : (d)

11. Structural formula of ethyne is

Answer :  (a) H – C ≡ C – H

12. Identify the unsaturated compounds from the following

(i) Propane

(ii) Propene

(iii) Propyne

(iv) Chloropropane

(a) (i) and (ii) (b) (ii) and (iv)

(c) (iii) and (iv) (d) (ii) and (iii)

Answer :  (d) (ii) and (iii).

[ The unsaturated compounds are (ii) Propene and (iii) Propyne. ]

13. Chlorine reacts with saturated hydrocarbons at room temperature in the

(a) absence of sunlight

(b) presence of sunlight

(c) presence of water

(d) presence of hydrochloric acid

Answer : (b) presence of sunlight.

 [ Chlorine reacts with saturated hydrocarbons at room temperature in the presence of sunlight. The reaction is a substitution reaction known as free radical halogenation. ]

14. In the soap micelles

(a) the ionic end of soap is on the surface of the cluster while the carbon chain is in the interior of the cluster.

(b) ionic end of soap is in the interior of the cluster and the carbon chain is out of the cluster.

(c) both ionic end and carbon chain are in the interior of the cluster

(d) both ionic end and carbon chain are on the exterior of the cluster

Answer : (a) The ionic end of soap is on the surface of the cluster while the carbon chain is in the interior of the cluster.

 [In the formation of micelles, the hydrophobic tails (carbon chain) of soap molecules cluster in the interior, away from water, while the hydrophilic heads (ionic end) remain on the surface, interacting with water. ]

15. Pentane has the molecular formula . It has

(a) 5 covalent bonds

(b) 12 covalent bonds

(c) 16 covalent bonds

(d) 17 covalent bonds

Answer :  (c) 16 covalent bonds.

16. Structural formula of benzene is

Answer : (C)

17. Ethanol reacts with sodium and forms two products. These are

(a) sodium ethanoate and hydrogen

(b) sodium ethanoate and oxygen

(c) sodium ethoxide and hydrogen

(d) sodium ethoxide and oxygen

Answer : (c) sodium ethoxide and hydrogen

[ When ethanol () reacts with sodium (Na), it undergoes a reaction known as alcoholysis. The products of this reaction are sodium ethoxide () and hydrogen gas (). Therefore, the correct option is: (c) sodium ethoxide and hydrogen

18. The correct structural formula of butanoic acid is

Answer : (d)

19. Vinegar is a solution of

(a) 50% – 60% acetic acid in alcohol

(b) 5% – 8% acetic acid in alcohol

(c) 5% – 8% acetic acid in water

(d) 50% – 60% acetic acid in water

Answer : (c) 5% – 8% acetic acid in water

[ Vinegar is a solution of  5% – 8% acetic acid in water. ]

20. Mineral acids are stronger acids than carboxylic acids because

(i) mineral acids are completely ionised

(ii) carboxylic acids are completely ionised

(iii) mineral acids are partially ionised

(iv) carboxylic acids are partially ionised

(a) (i) and (iv) (b) (ii) and (iii)

(c) (i) and (ii) (d) (iii) and (iv)

Answer : (a) (i) and (iv).

[ Mineral acids are stronger acids than carboxylic acids because : (i) Mineral acids are completely ionized. (iv) Carboxylic acids are partially ionized. ]

21. Carbon forms four covalent bonds by sharing its four valence electrons with four univalent atoms, e.g. hydrogen. After the formation of four bonds, carbon attains the electronic configuration of

(a) helium

(b) neon

(c) argon

(d) krypton

Answer : (c) Argon

[ Carbon forms four covalent bonds by sharing its four valence electrons with four univalent atoms, typically hydrogen. After the formation of four bonds, carbon attains the electronic configuration of argon .

22. The correct electron dot structure of a water molecule is

Answer : (c)

23. Which of the following is not a straight chain hydrocarbon?

Answer :  (d)

24. Which among the following are unsaturated hydrocarbons?

(a) (i) and (iii) (b) (ii) and (iii)

(c) (ii) and (iv) (d) (iii) and (iv)

Answer : (c)  (ii)  and (iv)

25. Which of the following does not belong to the same homologous series?

(a) 

(b)

(c) 

(d) 

Answer : (d)  - Butene

[ The homologous series is a group of organic compounds that have the same functional group and share a similar chemical properties and successive members differ by -CH2-.

The reason is that it is an alkene (contains a double bond), while the others are alkanes (contain only single bonds). ]

26. The name of the compound  is

(a) Propanal

(b) Propanone

(c) Ethanol

(d) Ethanal

Answer : (a) Propanal

27. The heteroatoms present in  are

(i) oxygen

(ii) carbon

(iii) hydrogen

(iv) chlorine

(a) (i) and (ii) (b) (ii) and (iii)

(c) (iii) and (iv) (d) (i) and (iv)

Answer : (d) (i) and (iv).

[ The heteroatoms present in the given molecule are: (i) Oxygen (iv) Chlorine ]

28. Which of the following represents saponification reaction?

(a)  

(b)

(c) 

(d)

Answer :  (d)

29. The first member of alkyne homologous series is

(a) ethyne         (b) ethene      (c) propyne       (d) methane

Answer :  (a) ethyne .

Short Answer Questions

30. Draw the electron dot structure of ethyne and also draw its structural formula.

Solution:  The electron dot structure of ethyne :

       

The structural formula of ethyne () :

      

31. Write the names of the following compounds

Answer :  (a) pentanioc Acid

(b) Butyne

(c) Heptanal

(d) Pentanal

32. Identify and name the functional groups present in the following compounds.

Answer : (a) Alcohol :

(b) Carboxylic acid : 

(c) Ketone :

(d) Alkene : (Butene)

33. A compound X is formed by the reaction of a carboxylic acid  and an alcohol in presence of a few drops of  . The alcohol on oxidation with alkaline  followed by acidification

gives the same carboxylic acid as used in this reaction. Give the names and structures of (a) carboxylic acid, (b) alcohol and (c) the compound X. Also write the reaction.

Answer : (a) Carboxylic acid (Original):

Name: Ethanoic acid

Structure: 

(b) Alcohol:

Name: Ethanol

Structure: 

(c) Compound X (Ester):

Name: Ethyl ethanoate

Structure: 

The reaction:

To regenerate the original carboxylic acid (Ethanoic acid) through oxidation of the alcohol (Ethanol):

  

So, the overall process involves the formation of ethyl ethanoate (X) from ethanoic acid and ethanol, and then the oxidation of ethanol back to ethanoic acid

34. Why detergents are better cleansing agents than soaps? Explain.

Answer : Detergents are better cleansing agents than soaps because they can function effectively in both hard and soft water. Unlike soaps, detergents do not form insoluble precipitates with calcium and magnesium ions in hard water, maintaining their cleaning efficiency in various water conditions.

35. Name the functional groups present in the following compounds

(a) 

(b) 

(c) 

(d)

Answer :  (a) : Ketone

(b)  : Carboxylic Acid

(c)  : Aldehyde

(d)  : Alcohol

36. How is ethene prepared from ethanol? Give the reaction involved in it.

Answer : Ethene can be prepared from ethanol by the process of dehydration. The reaction involves removing water from ethanol () to obtain ethene ( ).

 

The dehydration process is often carried out in the presence of a dehydrating agent, such as concentrated sulfuric acid () . The acid helps in the elimination of water from ethanol, leaving behind ethene.

37. Intake of small quantity of methanol can be lethal. Comment.

Solution : Methanol is highly toxic, even in small quantities, as it is metabolised in the body to formaldehyde and formic acid, causing severe damage to the optic nerve and other organs. Ingesting even a small amount can lead to blindness, organ failure, and death.

38. A gas is evolved when ethanol reacts with sodium. Name the gas evolved and also write the balanced chemical equation of the reaction involved.

Answer : The gas evolved when ethanol reacts with sodium is hydrogen gas (). The balanced chemical equation for the reaction is:

 

39. Ethene is formed when ethanol at 443 K is heated with excess of concentrated sulphuric acid. What is the role of sulphuric acid in this reaction? Write the balanced chemical equation of this reaction.

Answer : In the dehydration of ethanol to form ethene, concentrated sulfuric acid serves as a dehydrating agent, removing water from the ethanol molecule. The acid protonates the hydroxyl group in ethanol, leading to the elimination of water and the formation of ethene.

The balanced chemical equation for this reaction is:

 

40. Carbon, Group (14) element in the Periodic Table, is known to form compounds with many elements. Write an example of a compound formed with

(a) chlorine (Group 17 of Periodic Table)

(b) oxgygen (Group 16 of Periodic Table)

Answer : Not in Syllabus

41. In electron dot structure, the valence shell electrons are represented by crosses or dots.

(a) The atomic number of chlorine is 17. Write its electronic configuration

(b) Draw the electron dot structure of chlorine molecule.

Answer :  The atomic number of chlorine is 17.

Electronic configuration of chlorine is 2.8.7 .

         

The electron dot structure of chlorine molecule.

            

42. Catenation is the ability of an atom to form bonds with other atoms of the same element. It is exhibited by both carbon and silicon. Compare the ability of catenation of the two elements. Give reasons.

Answer :  Carbon exhibits a greater ability for catenation than silicon due to its smaller atomic size, which allows for stronger C-C bonds. Additionally, carbon's ability to form stable multiple bonds (double and triple bonds) enhances its catenation properties. Silicon, with its larger atomic size and weaker Si-Si bonds, shows less catenation capability.

43. Unsaturated hydrocarbons contain multiple bonds between the two C-atoms and show addition reactions. Give the test to distinguish ethane from ethene.

Solution: To distinguish ethane from ethene, you can use the bromine water test. Ethene, an unsaturated hydrocarbon with a double bond, will decolorize bromine water, while ethane, a saturated hydrocarbon with only single bonds, will not react and thus will not colourless the bromine water.

Procedure: (i) Take two test tubes, one containing ethane and the other containing ethene.

(ii) Add a few drops of bromine water (which is brownish-red) to each test tube.

(iii) Observe the color change.

Observation: (i) In the test tube with ethene, the bromine water will turn colorless, indicating the presence of a double bond and an addition reaction.

(ii) In the test tube with ethane, the bromine water will remain brownish-red, indicating no reaction.

This test confirms the presence of an unsaturated hydrocarbon (ethene) due to the colourless of bromine water.

44. Match the reactions given in Column (A) with the names given in Column (B).

Answer :  (a)  : (iv) Esterification reaction

(b) : (i) Addition reaction

(c) : (ii) Substitution reaction

(d) : (iii) Neutralization reaction

45. Write the structural formulae of all the isomers of hexane.

Answer : The structural isomers of hexane :

                    Hexane

         2-methyl pentane

    

         3-methyl pentane 

     

        2,2-dimethylbutane

       

              2,3-dimethylbutane

46. What is the role of metal or reagents written on arrows in the given chemical reactions?

Answer: (a) Addition Reaction: Nickel is a catalyst .

(b) Esterification Reaction : Acid is a Catalyst .

(c) Oxidation Reaction : Alkaline Potassium permanganate is a oxidising agent .

Long Answer Questions

47. A salt X is formed and a gas is evolved when ethanoic acid reacts with sodium hydrogencarbonate. Name the salt X and the gas evolved. Describe an activity and draw the diagram of the apparatus to prove that the evolved gas is the one which you have named. Also, write chemical equation of the reaction involved.

Answer :  The salt formed is sodium ethanoate (X), and the gas evolved is carbon dioxide.

Activity: Testing the Evolution of Carbon Dioxide

Apparatus: (i) Test tube , (ii) Delivery tube   (iii) Rubber stopper  (iv) Burette or gas syringe  (v) Sodium hydrogencarbonate ()  (vi) Ethanoic acid ()

Procedure: (i) Add a small amount of sodium hydrogencarbonate () to a test tube.

(ii) Pour a small amount of ethanoic acid () into the test tube containing  .

(iii) Quickly close the test tube with a rubber stopper containing a delivery tube connected to a burette or gas syringe.

(iv) Collect the gas evolved in the burette or gas syringe.

    

Chemical Equations are :

(i) 

 (ii)

The gas collected will displace the water in the burette or push the syringe plunger. The evolved gas can be tested by passing it through lime water (), which will turn milky () , confirming the presence of carbon dioxide ()

48. (a) What are hydrocarbons? Give examples.

(b) Give the structural differences between saturated and unsaturated hydrocarbons with two examples each.

(c) What is a functional group? Give examples of four different functional groups.

Answer : (a) Hydrocarbons are organic compounds consisting exclusively of carbon and hydrogen atoms.

They are categorised into three main types:

Alkanes: Saturated hydrocarbons with single bonds between carbon atoms.

Examples :  Methane ( Ethane ( and Propane (

Alkenes: Unsaturated hydrocarbons with at least one double bond between carbon atoms.

Examples:  Ethene ( and Propene (

Alkynes: Unsaturated hydrocarbons with at least one triple bond between carbon atoms.

Examples :  Ethyne ( and Propyne (

 (b) Structural Differences between Saturated and Unsaturated Hydrocarbons:

(i) Saturated Hydrocarbons (Alkanes):

Structure: Single bonds between carbon atoms.

Examples: Methane (), Ethane ()

Unsaturated Hydrocarbons:

(i) Alkenes (One double bond):

Structure: Contains at least one carbon-carbon double bond.

Examples: Ethene () , Propene ()

(ii) Alkynes (One triple bond):

Structure: Contains at least one carbon-carbon triple bond.

Examples: Ethyne () ,  Propyne () .

(c) Functional Group: A functional group is a specific group of atoms within a molecule that is responsible for its characteristic chemical reactions.

(i) Hydroxyl Group ( ):

Example:  Ethanol ( ).

(ii) Halo-(Chloro/Bromo) Group ( - Cl  / - Br  ):

Example :  Chloroethane ()

(iii) Aldehyde ( ):

 Example: Formaldehyde ()

(iv) Ketone ():

Example: Acetone ()

(v) Carboxyl Group (  ):

Example: Acetic acid ().

49. Name the reaction which is commonly used in the conversion of vegetable oils to fats. Explain the reaction involved in detail.

Answer : The reaction commonly used to convert vegetable oils into fats is hydrogenation. In this process, vegetable oils (which are unsaturated fats) are treated with hydrogen gas in the presence of a catalyst like nickel at high pressure and temperature. This reaction adds hydrogen atoms to the double bonds in the unsaturated fatty acids, converting them into saturated fats and making the oil more solid at room temperature.

50. (a) Write the formula and draw electron dot structure of carbon tetrachloride.

(b) What is saponification? Write the reaction involved in this process.

Answer : (a) Carbon Tetrachloride (CCl₄):

Formula: CCl₄

    

Electron Dot Structure terrachloride:

    

 (b) Saponification:  Saponification is the chemical process of breaking down an ester into an alcohol and a carboxylate salt by treating it with a strong alkali, such as sodium hydroxide. This reaction is particularly important in soap-making, where fats (esters) are hydrolyzed to produce soap (sodium or potassium salts of long-chain carboxylic acids) and glycerol.

The reaction involved in saponification is:

51. Esters are sweet-smelling substances and are used in making perfumes. Suggest some activity and the reaction involved for the preparation of an ester with well labeled diagram.

Answer : To prepare an ester, mix 1 mL ethanol (absolute alcohol) with 1 mL glacial acetic acid in a test tube. Add a few drops of concentrated sulphuric acid as a catalyst. Warm this mixture in a water bath for at least five minutes. After heating, pour the mixture into a beaker containing 20-50 mL of water. The resulting solution will have a sweet- smelling substances, indicating the formation of the ester, ethyl acetate, through the reaction of ethanol and acetic acid.

The chemical Reaction:

52. A compound C (molecular formula,) reacts with Na-metal to form a compound R and evolves a gas which burns with a pop sound. Compound C on treatment with an alcohol A in presence

of an acid forms a sweet smelling compound S (molecular formula, ) . On addition of NaOH to C, it also gives R and water. S on treatment with NaOH solution gives back R and A. Identify C, R, A, S and write down the reactions involved.

Answer : Compound C:  ()

Reaction with Na metal forms a compound R and evolves a gas:

       (evolved gas)

The evolved gas is likely hydrogen (), which burns with a pop sound.

Compound C with alcohol A in the presence of an acid forms a sweet-smelling compound S ():

Adding NaOH to C forms R and water :

 

S with NaOH gives back R and regenerates A :

The compounds are :   ()​ is Acetic Acid or Ethanoic Acid.

R is Sodium Acetate ().

A is Ethanol ().

   is Ethyl Acetate.

S is Sodium Acetate ().

53. Look at Figure 4.1 and answer the following questions

(a) What change would you observe in the calcium hydroxide solution taken in tube B?

(b) Write the reaction involved in test tubes A and B respectively.

(c) If ethanol is given instead of ethanoic acid, would you expect the same change?

(d) How can a solution of lime water be prepared in the laboratory?

Answer : (a) In tube B, which contains lime water (a calcium hydroxide solution), the solution turns milky. This occurs because the carbon dioxide gas produced in test tube A reacts with the calcium hydroxide in tube B, forming calcium carbonate, which is insoluble in water and causes the milky appearance.

(b) In test tube A:
The reaction involves ethanoic acid () reacting with sodium carbonate (). The reaction produces sodium ethanoate (), carbon dioxide () and water ().
The chemical equation is :

In test tube B:
The carbon dioxide produced in test tube A reacts with the lime water (calcium hydroxide, ) in test tube B, forming calcium carbonate (), which is insoluble in water and gives a milky appearance. The chemical equation is: 

(c) No, we would not expect the same change if ethanol () is used instead of ethanoic acid (). Ethanol does not react with sodium carbonate () to produce carbon dioxide. Therefore, no carbon dioxide would be released, and there would be no reaction in tube B. The lime water would remain clear.

(d) A solution of lime water can be prepared in the laboratory by the following method:

(i) Take a small amount of calcium hydroxide (), commonly called slaked lime.

(ii) Add distilled water to the calcium hydroxide and stir the mixture thoroughly.

(iii) Allow the mixture to settle for some time. The undissolved calcium hydroxide will settle at the bottom of the container.

(iv) Decant the clear solution at the top, which is lime water.

This clear solution is now a dilute solution of calcium hydroxide (lime water) and can be used for testing carbon dioxide.

54. How would you bring about the following conversions? Name the process and write the reaction involved.

(a) ethanol to ethene.

(b) propanol to propanoic acid.

Write the reactions.

Answer : (a) Dehydration: When ethanol is heated to 443 K with excess concentrated sulphuric acid, ethene and water are produced.

   

(b) Oxidation : When propanol is heated with alkaline potassium permanganate or acidified potassium dichromate, it produces propanoic acid.

   

55. Draw the possible isomers of the compound with molecular formula  and also give their electron dot structures.

Answer : There are two isomers of the compound  .

(i) Propanol :

     

Electron dot structure :

(ii) Propanone :

   

Electron dot structure :

 

56. Explain the given reactions with the examples

(a) Hydrogenation reaction

(b) Oxidation reaction

(c) Substitution reaction

(d) Saponification reaction

(e) Combustion reaction

Answer : (a) Hydrogenation Reaction : A hydrogenation reaction involves the addition of hydrogen (H₂) to another compound, usually in the presence of a catalyst (such as nickel, platinum, or palladium). This process is commonly used to convert unsaturated compounds, such as alkenes and alkynes, into saturated compounds by adding hydrogen to carbon-carbon double or triple bonds.

Example: Hydrogenation of ethene (C₂H₄) to ethane (C₂H₆) in the presence of a nickel catalyst:

(b) Oxidation Reaction : An oxidation reaction is a chemical process in which a substance loses electrons (or gains oxygen or loses hydrogen). Oxidation reactions are usually accompanied by reduction reactions, where another substance gains the electrons that are lost. Oxidation can also involve the increase in the oxidation state of a molecule, atom, or ion.

Example: Oxidation of ethanol () to acetic acid () :

In this reaction, ethanol loses hydrogen atoms (or equivalently gains oxygen), leading to the formation of acetic acid.

(c) A substitution reaction occurs when one atom or group of atoms in a molecule is replaced by another atom or group. Saturated hydrocarbons (alkanes), while generally unreactive, can undergo substitution reactions with chlorine in the presence of sunlight. In this reaction, chlorine atoms replace hydrogen atoms in the hydrocarbon one by one, forming multiple products.

For example, methane  reacts with chlorine  to form chloromethane and hydrogen chloride.

(d) Saponification Reaction : Saponification is a chemical reaction in which an ester reacts with sodium hydroxide (an alkali) to form an alcohol and the sodium salt of a carboxylic acid. This reaction is significant in soap-making, as it converts fats (which are esters) into soap, which are sodium or potassium salts of long-chain carboxylic acids.

Example :  The reaction of esters with NaOH to produce ethanol and Sodium ethanoate (soap).

 

(e) Combustion Reaction : A combustion reaction involves the burning of carbon and its compounds in oxygen to form carbon dioxide, releasing heat and light. Saturated hydrocarbons burn with a clean flame, while unsaturated hydrocarbons produce a yellow, smoky flame. Incomplete combustion, due to limited air, also results in a sooty flame. Efficient combustion, like in gas stoves, requires sufficient air supply, preventing soot buildup. However, burning fuels like coal and petroleum releases nitrogen and sulphur oxides, contributing to environmental pollution.

Example: Methane   reacts with oxygen to produce carbon dioxide, water, and a large amount of heat.

  heat and light

57. An organic compound A on heating with concentrated  forms a compound B which on addition of one mole of hydrogen in presence of Ni forms a compound C. One mole of compound C on

combustion forms two moles of   and 3 moles of  . Identify the compounds A, B and C and write the chemical equations of the reactions involved.

Answer : The given information suggests the conversion of an organic compound A to compounds B and C through a series of reactions.

A: Organic compound

B: Formed on heating A with concentrated  .

C: Formed by adding one mole of hydrogen in the presence of Ni to B

A: Ethanol () B: Ethene () C: Ethane ()

The reactions are :

Formation of B from A (Dehydration):

   

Addition of one mole of hydrogen to B (Hydrogenation): 

Combustion of one mole of C:

This series of reactions represents the conversion of ethanol (A) to ethene (B) by dehydration, and then the addition of hydrogen converts ethene to ethane (C). The combustion of ethane produces carbon dioxide and water.