Organic Compounds - Fuel

Question 1

Name three fossil fuels

Answer 1

Coal Natural gas Petroleum (crude oil)

Question 2

What is the main constituent of natural gas?

Answer 2

Methane

Question 3

What is a fuel?

Answer 3

A fuel is a substance which when burned, releases heat energy This heat can be transferred into electricity, which we use in our daily lives

Question 4

Petroleum

Answer 4

Petroleum is also called crude oil and is a complex mixture of hydrocarbons which also contains natural gas. It is a thick, sticky, black liquid that is found under porous rock (under the ground and under the sea)

Question 5

Fractional distillation:

Answer 5

The fractions in petroleum are separated from each other in a process called fractional distillation.

Fractional distillation is carried out in a fractionating column
• The fractionating column is hot at the bottom and cool at the top
• Crude oil enters the fractionating column and is heated so vapours rise
• Vapours of hydrocarbons with very high boiling points will immediately turn into liquid and are tapped off at the bottom of the column
• Vapours of hydrocarbons with low boiling points will rise up the column and condense at the top to be tapped off
• The different fractions condense at different heights according to their boiling points and are tapped off as liquids
• The fractions containing smaller hydrocarbons are collected at the top of the fractionating column as gases
• The fractions containing bigger hydrocarbons are collected at the lower sections of the fractionating column

Question 6

What are the differences between hydrocarbons at each fraction?

Answer 6

VEN BP

• Boiling points - Ease of ignition - Viscosity - Number of hydrogen and carbon atoms in the molecules.

Question 7

Where in the fractionating column do hydrocarbons with the highest viscosity condense?

Answer 7

Viscosity is how thick and sticky a substance is. The hydrocarbons with the highest viscosity (like bitumen) are collected at the bottom of the fractionating column.

Question 8

Viscosity?

Answer 8

This refers to the ease of flow of a liquid. High viscosity liquids are thick and flow less easily. If the number of carbon atoms increases, the attraction between the hydrocarbon molecules also increases which results in the liquid becoming more viscous with the increasing length of the hydrocarbon chain. The liquid flows less easily with increasing molecular mass.

Question 9

Colour?

Answer 9

As carbon chain length increases the colour of the liquid gets darker as it gets thicker and more viscous

Question 10

Melting point/boiling point?

Answer 10

As the molecules get larger, the intermolecular attraction becomes greater. So more heat is needed to separate the molecules. With increasing molecular size there is an increase in boiling point

Question 11

Volatility

Answer 11

Volatility refers to the tendency of a substance to vaporise. With increasing molecular size hydrocarbon liquids become less volatile. This is because the attraction between the molecules increases with increasing molecular size

Question 12

Trend in boiling point of the main fractions (Pic)

Answer 12

Question 13

Which fraction of petroleum is used for road surfacing and roofs?

Answer 13

Bitumen

Question 14

Homologous Series

Answer 14

This is a series or family of organic compounds that have similar features and chemical properties due to them having the same functional group

Question 15

What are the general characteristics of a homologous series?

Answer 15

• The same general formula
• Same functional group
• Similar chemical properties
• Gradation in their physical properties