1 What do you understand by the term hydrocarbon?2 All living organisms are composed of compoundswhich contain carbon. Why do you think carbonchemistry is often called ‘organic chemistry’?3 List the main fractions obtained by separatingthe petroleum mixture and explain how they areobtained in a refinery.4 Which of the fractions obtained from petroleumcould be used for producing:a waxesb fuel for aeroplanesc polymers?5 Describe how the properties of fractions obtainedfrom petroleum change as they are collected in afractionating column from the bottom to the top ofthe column, in terms of their:a chain lengthb volatilityc viscosityd boiling po

Hydrocarbons are organic compounds that are made up of only hydrogen and carbon atoms. They can be found in many forms such as alkanes, alkenes, and alkynes. They are the primary constituents of petroleum and natural gas.

Carbon chemistry is often called 'organic chemistry' because it is the study of the structure, properties, composition, reactions, and synthesis of organic compounds, which contain carbon atoms. Carbon atoms have the unique ability to form strong covalent bonds with other carbon atoms and with other elements, which allows the formation of a huge variety of compounds that are central to life processes.

The main fractions obtained by separating the petroleum mixture in a refinery are:

• Gasoline: used as fuel in internal combustion engines.
• Kerosene: used as jet fuel and in lamps and heaters.
• Diesel: used as fuel in diesel engines.
• Lubricating oil: used for lubrication in machinery.
• Fuel oil: used for heating and to power ships.
• Bitumen: used in road surfacing and roofing. These fractions are obtained through a process called fractional distillation, where the petroleum mixture is heated until it vaporizes, then cooled so it condenses into different fractions based on the boiling points of its components.

The fractions obtained from petroleum that could be used for producing:

• Waxes: Lubricating oil fraction
• Fuel for aeroplanes: Kerosene fraction
• Polymers: Naphtha fraction

As the fractions are collected in a fractionating column from the bottom to the top:

• Chain length: The chain length of the hydrocarbons decreases. The fractions at the bottom have long-chain hydrocarbons while those at the top have short-chain hydrocarbons.
• Volatility: The volatility increases. The fractions at the bottom are less volatile while those at the top are more volatile.
• Viscosity: The viscosity decreases. The fractions at the bottom are more viscous while those at the top are less viscous.
• Boiling point: The boiling point decreases. The fractions at the bottom have a high boiling point while those at the top have a low boiling point.