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Properties of Hydrocarbons

Properties of Hydrocarbons

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Polarity
• Alkanes are not polar, as there is no electronegativity between C-H bonds
• Alcohols and water are polar because they contain –OH bonds, with a difference in electronegativity
• The only force present in hydrocarbons are Van Der Waals
Reactivity
• Alkenes are more reactive than alkanes due to their double bonds which break in the reaction releasing more energy
• Alkanes are not reactive but can be combusted as fuels for engines.
Solubility
• Alkanes are non-polar and therefore do not mix and dissolve into polar liquids such as water. They are unable to form hydrogen bonds between each molecule. Water also has strong hydrogen bonds between each H2O molecule and therefore not want to move apart to allow for the alkane in
Boiling Points
• The increase in the chain of the atoms in an alkane, increases the boiling points as a result of there being more Van der Waal forces between each molecule. (A CH4 molecule has a boiling point of -161.5 °C, where are C10H22

Polarity
• Alkanes are not polar, as there is no electronegativity between C-H bonds
• Alcohols and water are polar because they contain –OH bonds, with a difference in electronegativity
• The only force present in hydrocarbons are Van Der Waals

Reactivity
• Alkenes are more reactive than alkanes due to their double bonds which break in the reaction releasing more energy
• Alkanes are not reactive but can be combusted as fuels for engines.

Solubility
• Alkanes are non-polar and therefore do not mix and dissolve into polar liquids such as water. They are unable to form hydrogen bonds between each molecule. Water also has strong hydrogen bonds between each H2O molecule and therefore not want to move apart to allow for the alkane in

Boiling Points
• The increase in the chain of the atoms in an alkane, increases the boiling points as a result of there being more Van der Waal forces between each molecule.

Polarity
• Alkanes are not polar, as there is no electronegativity between C-H bonds
• Alcohols and water are polar because they contain –OH bonds, with a difference in electronegativity
• The only force present in hydrocarbons are Van Der Waals

Reactivity
• Alkenes are more reactive than alkanes due to their double bonds which break in the reaction releasing more energy
• Alkanes are not reactive but can be combusted as fuels for engines.

Solubility
• Alkanes are non-polar and therefore do not mix and dissolve into polar liquids such as water. They are unable to form hydrogen bonds between each molecule. Water also has strong hydrogen bonds between each H2O molecule and therefore not want to move apart to allow for the alkane in

Name of Alkene

Number of Carbons

Chemical Formula

Boiling Point in °C
(degrees centigrade)

State at “Room Temperature” (20°C)

Melting Point in °C
(degrees centigrade)

Ethene

2

C2H4

-104

gas

-169

Propene

3

C3H6

-47

gas

-185

Z-Butene

4

C4H8

0.9

gas

-138.9

E-Butene

4

C4H8

3.7

gas

-139.7

1-Pentene

5

C5H10

30

gas

-165

Z-2-Pentene

5

C5H10

36

gas

-135

E-2-Pentene

5

C5H10

37

gas

-180

1-hexene

6

C6H12

63

liquid

−139.8

1-Heptene

7

C7­H14

115

liquid

-119

3-octene

8

C8H16

122

liquid

-101.9

3-nonene

9

C9H18

147

liquid

-84.4

5-decene

10

C10H20­

170

liquid

-66.3

 

Name of Alkane

Number of Carbons

Chemical Formula

Boiling Point in °C
(degrees centigrade)

State at “Room Temperature” (20°C)

Melting Point in °C
(degrees centigrade)

Methane

1

C H4

-162

gas

-183

Ethane

2

C2H6

-89

gas

-172

Propane

3

C3H8

-42

gas

-188

Butane

4

C4H10

0

gas

-138

Pentane

5

C5H12

36

liquid

-130

Hexane

6

C6H14

69

liquid

-95

Heptane

7

C7H16

98

liquid

-91

Octane

8

C8H18

126

liquid

-57

Nonane

9

C9H20

151

liquid

-54

Decane

10

C10H22

174

liquid

-30
Fractional Distillation of Crude Oil

Fractional Distillation of Crude Oil

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Fractional distillation allows us to separate different lengths hydrocarbons, mainly alkanes, from a mixture, as they are found in crude oil. Different hydrocarbons have different uses:

Fraction

Length of atom chains

Uses

Gas

1-4

Bottled gases for camping etc.

Petrol

5-12

Petrol for combustion engines

Naphtha 

7-14

Petrochemicals

Kerosene

11-15

Plane fuels

Diesel

15-19

Combustion engines

Mineral Oils

20-30

Lubricating oils

Fuel Oils

30-40

Ship fuel and Power stations

Wax

40-50

Candles and lubrication

Bitumen

50+

Road surfaces

Cracking in Industry

  • Crude oil is heated to 350°c and pumped into the bottom of the distillation column
  • The crude oil vaporises, the smaller hydrocarbon molecules with their lower boiling points, rise and condense higher up the column
  • Going down the column the different hydrocarbon chains grow larger, going from gases to more viscous substances such as bitumen. The largest hydrocarbons do not vaporise as their boiling points are higher than 350°c and therefore collect at the bottom forming a thick residue.
  • As the crude oil rises it reaches its fractions, and being far away from the heat source and falls below its boiling point and condenses on to it. This follows a temperature gradient
  • Some gases do not do condense (e.g. propane, ethane) and are just collected at the top.

Cracking in a lab

The difference between industry and on a smaller scale in a lab is minimal however necessary due to the limitation of height and temperature.

  • Put the hydrocarbon mixture in the bottom of the distillation column.
  • Using an electric mantle, as they will heat the mixture to a constant set temperature which a Bunsen burner cannot achieve easily, heat the mixture
  • The mixture that you want to obtain from the set temperature will vaporise and rise up the column.
  • At the top of the column a condenser is used to lower the temperature of the vaporised liquid down, so it can therefore condense back into a liquid. The condenser has a cold circulation of water running through it.
  • A collection beaker is used to collect the required fraction.
  • After no more of the fraction is being collected, raise the temperature and use a different beaker to collect the next fraction.