Carbon Chemistry: Fuels, Crude Oil, Alkanes, Alkenes and Cracking

1. A hydrocarbon contains 6 carbon atoms and is saturated.

Which formula is possible?

A C6H10
B C6H12
C C6H14
D C6H16

2. Which formula belongs to an alkene with one C=C bond?

A C5H12
B C5H10
C C5H8
D C5H14

3. A hydrocarbon has molecular formula C4H10.

Which statement is correct?

A It is an alkene and decolourises bromine water.
B It is an alkane and burns in oxygen.
C It is unsaturated because it contains more hydrogen than C4H8.
D It contains one carbon-carbon double bond.

4. Which compound is the first member of the alkene homologous series?

A methane
B ethane
C ethene
D propene

5. Which statement about a homologous series is correct?

A Members have different functional groups and different general formulae.
B Members have the same functional group and similar chemical properties.
C Members have the same molecular formula but different structures.
D Members have the same boiling point because they have similar reactions.

6. Which pair are consecutive members of the alkane homologous series?

A CH4 and C2H4
B C2H6 and C3H8
C C3H6 and C4H8
D C4H10 and C6H14

7. Which formula represents the general formula of alkanes?

A CnHn
B CnH2n
C CnH2n+2
D CnH2n-2

8. Which formula represents the general formula of alkenes with one double bond?

A CnH2n
B CnH2n+2
C CnH2n-2
D CnHn+2

9. Which compound has the highest percentage by mass of carbon?

[Ar: C, 12; H, 1]

A CH4
B C2H6
C C3H8
D C4H10

10. Which hydrocarbon has the lowest hydrogen-to-carbon atom ratio?

A methane
B ethane
C ethene
D butane

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

11. A hydrocarbon burns completely to form 8.8 g of carbon dioxide and 5.4 g of water.

[Ar: C, 12; H, 1; O, 16]

What is the empirical formula of the hydrocarbon?

A CH2
B CH3
C C2H5
D C3H8

12. A hydrocarbon has empirical formula CH2 and relative molecular mass 56.

What is its molecular formula?

A C2H4
B C3H6
C C4H8
D C5H10

13. A hydrocarbon contains 85.7% carbon by mass and has relative molecular mass 42.

[Ar: C, 12; H, 1]

Which formula is correct?

A C2H4
B C3H6
C C4H8
D C3H8

14. A hydrocarbon burns completely.

CxHy + 5O2 → 3CO2 + 4H2O

What is the formula of the hydrocarbon?

A C3H4
B C3H6
C C3H8
D C4H8

15. Which equation represents complete combustion of propane?

A C3H8 + 3O2 → 3CO2 + 4H2O
B C3H8 + 5O2 → 3CO2 + 4H2O
C C3H8 + 4O2 → 3CO + 4H2O
D C3H8 + 5O2 → 3CO2 + 8H2O

16. Which equation represents incomplete combustion of methane forming carbon monoxide?

A CH4 + 2O2 → CO2 + 2H2O
B 2CH4 + 3O2 → 2CO + 4H2O
C CH4 + O2 → C + 2H2O
D CH4 + 4O2 → CO + 2H2O

17. Which product is formed during incomplete combustion and is poisonous because it reduces oxygen transport in blood?

A carbon dioxide
B carbon monoxide
C sulfur dioxide
D nitrogen monoxide

18. Which observation suggests incomplete combustion of a hydrocarbon?

A blue flame only and no solid residue
B soot forms and less energy is released
C oxygen is produced and flame goes out
D carbon dioxide is not formed at all

19. A fuel burns with a smoky yellow flame.

Which statement is most likely correct?

A Complete combustion is occurring with excess oxygen.
B Incomplete combustion is occurring and carbon particles may form.
C The fuel contains no carbon.
D Water is the only product.

20. Which fuel produces only water when burned completely?

A hydrogen
B methane
C ethanol
D propane

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

21. Crude oil is best described as:

A a pure compound containing only octane
B a mixture of hydrocarbons with different chain lengths
C a mixture of elements chemically combined in fixed ratios
D an aqueous solution of carbon compounds

22. Why can crude oil be separated by fractional distillation?

A Its hydrocarbons have different melting points only.
B Its hydrocarbons have different boiling points.
C Its hydrocarbons react with oxygen at different rates.
D Its hydrocarbons have the same volatility.

23. In a fractionating column, where do the shortest-chain hydrocarbons mostly leave?

A near the bottom because they have high boiling points
B near the top because they have low boiling points
C exactly in the middle because they are neutral
D from the residue outlet because they are most viscous

24. Which fraction has the highest boiling point?

A refinery gas
B gasoline/petrol
C kerosene/paraffin
D bitumen/residue

25. Which trend is correct as hydrocarbon chain length increases?

A boiling point decreases, viscosity decreases, flammability increases
B boiling point increases, viscosity increases, flammability decreases
C boiling point decreases, viscosity increases, volatility increases
D boiling point increases, viscosity decreases, volatility increases

26. Which fraction is most suitable for road surfacing?

A gasoline/petrol
B refinery gas
C kerosene
D bitumen

27. Which fraction is most suitable as fuel for aircraft?

A bitumen
B kerosene/paraffin
C lubricating oil
D residue

28. Which fraction is most useful as bottled gas for heating and cooking?

A refinery gas
B diesel oil
C fuel oil
D bitumen

29. Which statement about gasoline/petrol compared with fuel oil is correct?

A Gasoline has longer chains and higher boiling point.
B Gasoline is more volatile and more flammable.
C Fuel oil is more volatile and less viscous.
D Fuel oil evaporates more easily.

30. Which property makes long-chain hydrocarbons less useful as fuels in car engines?

A They are too volatile and evaporate instantly.
B They are less flammable and more viscous.
C They have no carbon-hydrogen bonds.
D They cannot undergo combustion.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

31. What is the purpose of cracking?

A to join short-chain hydrocarbons into long-chain hydrocarbons
B to split long-chain hydrocarbons into shorter alkanes and alkenes
C to remove all carbon from hydrocarbons
D to turn hydrocarbons into water and oxygen

32. Which conditions are used for catalytic cracking?

A low temperature and water only
B high temperature and a catalyst
C room temperature and sunlight only
D high pressure and iron catalyst only

33. Which pair of products could be formed by cracking decane, C10H22?

A C5H12 and C5H10
B C5H10 and C5H10
C C6H14 and C4H10
D C10H20 and H2

34. Which equation could represent cracking?

A C12H26 → C8H18 + C4H8
B C8H18 + O2 → CO2 + H2O
C C2H4 + H2 → C2H6
D CH4 + Cl2 → CH3Cl + HCl

35. Dodecane cracks as shown.

C12H26 → C7H16 + X

What is X?

A C5H8
B C5H10
C C5H12
D C6H10

36. Hexadecane cracks to form octane and ethene only.

C16H34 → C8H18 + xC2H4

What is x?

A 2
B 3
C 4
D 5

37. Which product of cracking is most useful for making polymers?

A methane
B ethene
C carbon dioxide
D hydrogen chloride

38. Which statement about cracking is correct?

A It increases supply of more useful short-chain fuels.
B It decreases demand for petrol by forming only bitumen.
C It produces only alkanes.
D It is an example of fractional distillation.

39. A hydrocarbon C7H16 is cracked into propene and one other hydrocarbon.

C7H16 → C3H6 + X

What is X?

A C4H8
B C4H10
C C3H8
D C5H10

40. Which mixture could be produced by cracking C9H20?

A C4H10 and C5H10
B C4H8 and C5H8
C C3H8 and C6H14
D C9H18 and H2O

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

41. Which test distinguishes an alkene from an alkane?

A add limewater
B add bromine water
C add acidified barium chloride
D add aqueous sodium hydroxide

42. What happens when ethene is shaken with bromine water?

A orange/brown bromine water is decolourised
B blue precipitate forms
C white precipitate forms
D no change occurs because ethene is saturated

43. Why do alkenes decolourise bromine water?

A They undergo addition reactions across the C=C bond.
B They undergo substitution reactions with bromine only in ultraviolet light.
C They contain only single bonds.
D They are less reactive than alkanes.

44. Which reaction is typical of alkanes but not usually used as the test for unsaturation?

A addition with bromine water in the dark
B substitution with chlorine in ultraviolet light
C polymerisation at room temperature without catalyst
D neutralisation with sodium hydroxide

45. Methane reacts with chlorine in ultraviolet light.

Which product can form in the first substitution step?

A CH3Cl
B C2H6
C CH2Cl2 only
D HCl only

46. Which equation represents substitution of methane by chlorine?

A CH4 + Cl2 → CH3Cl + HCl
B CH4 + Br2 → CH4Br2
C CH4 + Cl2 → CCl4 + H2
D CH4 + Cl2 → CH2 + 2HCl

47. Which equation represents addition of bromine to ethene?

A C2H4 + Br2 → C2H4Br2
B C2H6 + Br2 → C2H5Br + HBr
C C2H4 + Br2 → C2H3Br + HBr
D C2H4 + Br2 → 2CH2Br

48. Which compound is saturated?

A ethene
B propene
C but-1-ene
D propane

49. Which statement about saturated hydrocarbons is correct?

A They contain at least one carbon-carbon double bond.
B They contain only carbon-carbon single bonds.
C They always decolourise bromine water quickly in the dark.
D They have general formula CnH2n.

50. A hydrocarbon has formula C6H12 and decolourises bromine water.

Which conclusion is safest?

A It is definitely cyclohexane.
B It is an unsaturated hydrocarbon, likely an alkene.
C It is definitely an alkane.
D It contains no carbon-carbon double bond.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

1. C

A wrong: C6H10 is too low in hydrogen for a saturated straight-chain alkane.
B wrong: C6H12 fits an alkene or cycloalkane, not a normal saturated alkane.
C right: Saturated hydrocarbon with 6 carbon atoms follows CnH2n+2, so C6H14.
D wrong: C6H16 has too many hydrogen atoms.

2. B

A wrong: C5H12 is an alkane.
B right: Alkenes with one C=C bond follow CnH2n, so C5H10.
C wrong: C5H8 has fewer hydrogens than a simple alkene with one double bond.
D wrong: C5H14 has too many hydrogens.

3. B

A wrong: C4H10 is not an alkene and does not decolourise bromine water quickly in the dark.
B right: C4H10 is butane, an alkane, and it burns in oxygen.
C wrong: Having more hydrogen means it is saturated, not unsaturated.
D wrong: Alkanes contain only single C–C bonds.

4. C

A wrong: Methane is the first alkane.
B wrong: Ethane is an alkane.
C right: Ethene, C2H4, is the first alkene.
D wrong: Propene is the second alkene.

5. B

A wrong: Members of a homologous series have the same functional group and general formula.
B right: They have the same functional group and similar chemical properties.
C wrong: Same molecular formula but different structures describes isomers.
D wrong: Boiling points usually increase as chain length increases.

6. B

A wrong: CH4 is alkane, C2H4 is alkene.
B right: C2H6 and C3H8 are consecutive alkanes.
C wrong: These are alkenes, not alkanes.
D wrong: C5H12 is missing between them, so they are not consecutive.

7. C

A wrong: CnHn is not the alkane formula.
B wrong: CnH2n is for alkenes with one C=C bond.
C right: Alkanes follow CnH2n+2.
D wrong: CnH2n-2 is too unsaturated for alkanes.

8. A

A right: Alkenes with one double bond follow CnH2n.
B wrong: CnH2n+2 is for alkanes.
C wrong: CnH2n-2 is for compounds with more unsaturation.
D wrong: Not the alkene general formula.

9. D

A wrong: CH4 carbon percentage = 12/16 x 100 = 75.0%.
B wrong: C2H6 carbon percentage = 24/30 x 100 = 80.0%.
C wrong: C3H8 carbon percentage = 36/44 x 100 = 81.8%.
D right: C4H10 carbon percentage = 48/58 x 100 = 82.8%, the highest.

10. C

A wrong: Methane has H:C = 4:1.
B wrong: Ethane has H:C = 6:2 = 3:1.
C right: Ethene has H:C = 4:2 = 2:1, the lowest listed.
D wrong: Butane has H:C = 10:4 = 2.5:1.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

11. B

Moles CO2 = 8.8 / 44 = 0.200 mol
So moles C = 0.200 mol

Moles H2O = 5.4 / 18 = 0.300 mol
So moles H = 0.600 mol

Ratio C : H = 0.200 : 0.600 = 1 : 3
Empirical formula = CH3

A wrong: H ratio too low.
B right: CH3.
C wrong: Same ratio as C2H5 is not correct here.
D wrong: Ratio is not 3 : 8.

12. C

Empirical formula mass of CH2 = 12 + 2 = 14
Multiplier = 56 / 14 = 4
Molecular formula = C4H8

A wrong: Mr = 28.
B wrong: Mr = 42.
C right: Mr = 56.
D wrong: Mr = 70.

13. B

Mass of carbon in 42 g = 85.7% of 42 = 36 g
Moles C = 36 / 12 = 3
Remaining mass H = 42 – 36 = 6 g
Moles H = 6 / 1 = 6

Formula = C3H6

A wrong: Mr = 28.
B right: C3H6.
C wrong: Mr = 56.
D wrong: Carbon percentage is not 85.7%.

14. C

3CO2 means 3 carbon atoms.
4H2O means 8 hydrogen atoms.
So hydrocarbon = C3H8.

A wrong: Hydrogen too low.
B wrong: Hydrogen too low.
C right: C3H8.
D wrong: Carbon too high.

15. B

A wrong: Oxygen is not balanced.
B right: C3H8 + 5O2 → 3CO2 + 4H2O.
C wrong: Carbon monoxide forms in incomplete combustion.
D wrong: Hydrogen is not balanced.

16. B

A wrong: This is complete combustion.
B right: 2CH4 + 3O2 → 2CO + 4H2O is balanced incomplete combustion forming carbon monoxide.
C wrong: This forms carbon, not carbon monoxide.
D wrong: Not balanced and oxygen amount is wrong.

17. B

A wrong: Carbon dioxide is not the poisonous gas that binds to haemoglobin.
B right: Carbon monoxide reduces oxygen transport in blood.
C wrong: Sulfur dioxide causes respiratory problems and acid rain.
D wrong: Nitrogen monoxide is a pollutant but not the product from incomplete combustion of hydrocarbons.

18. B

A wrong: Blue flame suggests more complete combustion.
B right: Soot forms when there is insufficient oxygen, so incomplete combustion occurs.
C wrong: Oxygen is not produced.
D wrong: Some carbon dioxide may still form in incomplete combustion.

19. B

A wrong: Excess oxygen usually gives cleaner combustion.
B right: Smoky yellow flame suggests incomplete combustion and glowing carbon particles/soot.
C wrong: Hydrocarbon fuel contains carbon.
D wrong: Water is not the only product.

20. A

A right: Hydrogen burns to form water only.
B wrong: Methane forms carbon dioxide and water.
C wrong: Ethanol forms carbon dioxide and water.
D wrong: Propane forms carbon dioxide and water.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

21. B

A wrong: Crude oil is not pure octane.
B right: Crude oil is a mixture of hydrocarbons of different chain lengths.
C wrong: Mixtures do not have fixed chemical ratios.
D wrong: Crude oil is not an aqueous solution.

22. B

A wrong: Fractional distillation depends mainly on boiling point differences.
B right: Different hydrocarbons have different boiling points.
C wrong: It does not separate by reaction rate with oxygen.
D wrong: They do not all have the same volatility.

23. B

A wrong: Short-chain hydrocarbons have low boiling points.
B right: They are more volatile and leave near the top of the column.
C wrong: Position is not based on neutrality.
D wrong: Residue is long-chain, high-boiling and viscous.

24. D

A wrong: Refinery gas has the lowest boiling point.
B wrong: Petrol has a relatively low boiling point.
C wrong: Kerosene is higher than petrol but lower than bitumen.
D right: Bitumen/residue has the highest boiling point.

25. B

A wrong: Boiling point and viscosity increase, flammability decreases.
B right: Longer chains have higher boiling points, higher viscosity and lower flammability.
C wrong: Boiling point does not decrease and volatility does not increase.
D wrong: Viscosity does not decrease.

26. D

A wrong: Gasoline/petrol is used as car fuel.
B wrong: Refinery gas is used for heating/cooking.
C wrong: Kerosene is used as aircraft fuel.
D right: Bitumen is used for road surfacing.

27. B

A wrong: Bitumen is too viscous and used for roads.
B right: Kerosene/paraffin is used as aircraft fuel.
C wrong: Lubricating oil is for lubrication.
D wrong: Residue is not aircraft fuel.

28. A

A right: Refinery gas is used as bottled gas for heating and cooking.
B wrong: Diesel oil is used in diesel engines.
C wrong: Fuel oil is used for ships/power stations.
D wrong: Bitumen is used for roads.

29. B

A wrong: Petrol has shorter chains and lower boiling point.
B right: Petrol is more volatile and more flammable than fuel oil.
C wrong: Fuel oil is less volatile and more viscous.
D wrong: Fuel oil does not evaporate more easily.

30. B

A wrong: Long-chain hydrocarbons are less volatile, not too volatile.
B right: They are less flammable and more viscous, making them less suitable for car engines.
C wrong: They do contain C–H bonds.
D wrong: They can combust, but less easily.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

31. B

A wrong: That describes polymerisation-like joining, not cracking.
B right: Cracking splits long-chain hydrocarbons into shorter alkanes and alkenes.
C wrong: Cracking does not remove all carbon.
D wrong: That is not cracking.

32. B

A wrong: Cracking needs high temperature.
B right: Catalytic cracking uses high temperature and a catalyst.
C wrong: Room temperature and sunlight are not cracking conditions.
D wrong: Iron catalyst is associated with Haber process, not cracking.

33. A

A right: C5H12 + C5H10 gives C10H22, and cracking can produce an alkane and an alkene.
B wrong: Total hydrogen = 20, not 22.
C wrong: Total hydrogen = 24, not 22.
D wrong: This does not split the carbon chain into smaller hydrocarbons in the usual cracking sense.

34. A

A right: C12H26 → C8H18 + C4H8 is balanced and forms shorter hydrocarbons.
B wrong: This is combustion, not cracking.
C wrong: This is hydrogenation/addition.
D wrong: This is substitution.

35. B

C12H26 → C7H16 + X
Carbon left = 12 – 7 = 5
Hydrogen left = 26 – 16 = 10
X = C5H10

A wrong: Hydrogen too low.
B right: C5H10.
C wrong: Hydrogen too high.
D wrong: Carbon number too high.

36. C

C16H34 → C8H18 + xC2H4

Carbon remaining after C8H18 = 8 carbon atoms.
Each ethene has 2 carbon atoms, so x = 4.

Check hydrogen: C8H18 + 4C2H4 gives H = 18 + 16 = 34.

A wrong: Carbon and hydrogen too low.
B wrong: Carbon and hydrogen too low.
C right: x = 4.
D wrong: Carbon and hydrogen too high.

37. B

A wrong: Methane is not the main monomer for addition polymers.
B right: Ethene is used to make poly(ethene).
C wrong: Carbon dioxide is not used to make poly(ethene).
D wrong: Hydrogen chloride is not a cracking product used as a polymer monomer here.

38. A

A right: Cracking increases supply of useful short-chain fuels and alkenes.
B wrong: It does not form only bitumen.
C wrong: It forms alkanes and alkenes.
D wrong: Fractional distillation separates; cracking breaks molecules.

39. B

C7H16 → C3H6 + X
Carbon left = 4
Hydrogen left = 10
X = C4H10

A wrong: Hydrogen too low.
B right: C4H10.
C wrong: Carbon too low.
D wrong: Carbon too high.

40. A

A right: C4H10 + C5H10 gives C9H20.
B wrong: Total hydrogen = 16, not 20.
C wrong: Total hydrogen = 22, not 20.
D wrong: Adds oxygen/water, not hydrocarbon cracking.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

41. B

A wrong: Limewater tests for carbon dioxide.
B right: Bromine water distinguishes alkenes from alkanes.
C wrong: Acidified barium chloride tests sulfate ions.
D wrong: Sodium hydroxide tests some cations/ammonium ions.

42. A

A right: Ethene is unsaturated and decolourises bromine water.
B wrong: No blue precipitate forms.
C wrong: No white precipitate forms.
D wrong: Ethene is unsaturated.

43. A

A right: Alkenes undergo addition across the C=C bond, removing bromine’s colour.
B wrong: Substitution in UV is typical of alkanes with halogens.
C wrong: Alkenes contain a C=C double bond.
D wrong: Alkenes are more reactive than alkanes.

44. B

A wrong: Addition with bromine water is typical of alkenes.
B right: Alkanes undergo substitution with chlorine in ultraviolet light.
C wrong: Alkanes do not polymerise like alkenes.
D wrong: Hydrocarbons do not neutralise sodium hydroxide.

45. A

A right: First substitution step can form chloromethane, CH3Cl, and HCl.
B wrong: C2H6 forms from combining methyl radicals, not the first substitution product.
C wrong: CH2Cl2 can form in further substitution, not first step only.
D wrong: HCl forms, but it is not the organic substitution product.

46. A

A right: CH4 + Cl2 → CH3Cl + HCl.
B wrong: Formula and reaction are incorrect.
C wrong: This is not correct first substitution.
D wrong: Incorrect products and balancing.

47. A

A right: Ethene adds bromine to form C2H4Br2.
B wrong: This is substitution of an alkane.
C wrong: This is not the normal addition product.
D wrong: Product formula is not correctly represented.

48. D

A wrong: Ethene is unsaturated.
B wrong: Propene is unsaturated.
C wrong: But-1-ene is unsaturated.
D right: Propane is an alkane and saturated.

49. B

A wrong: That describes unsaturated hydrocarbons.
B right: Saturated hydrocarbons contain only carbon-carbon single bonds.
C wrong: Alkenes decolourise bromine water quickly in the dark, not saturated hydrocarbons.
D wrong: CnH2n is for alkenes/cycloalkanes, not normal alkanes.

50. B

A wrong: Cyclohexane is C6H12 but does not decolourise bromine water like an alkene.
B right: Decolourising bromine water suggests unsaturation, likely an alkene.
C wrong: Alkanes do not quickly decolourise bromine water in the dark.
D wrong: Bromine water decolourisation suggests a C=C bond.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.