Crude Oil And Fuels

Question 1

What type of resource is crude oil? Where is it found?

Answer 1

A finite resource. It is found in rocks as the remains of ancient animals and plants.

Question 2

What is crude oil made of?

Answer 2

It is a mixture made of many different compounds that boil at different temperatures.

Question 3

Why is crude oil separated?

Answer 3

To make useful fuels.

Question 4

What type of separation is used with crude oil? What are the liquid mixtures called?

Answer 4

Fractional distillation. The different liquid mixtures are called fractions.

Question 5

What are most of the compounds in crude oil?

Answer 5

Hydrocarbons.

Question 6

What does the boiling point of a hydrocarbon depend on?

Answer 6

The size of the molecules. The larger the molecule, the higher the boiling point.

Question 7

What is the process of fractional distillation? What is the order of the fractions produced?

Answer 7

• The oil is vapourised at 350*C.
• The temperature of the fractionating column decreases as it goes up. The oil vapour rises.
• The hydrocarbons condense to liquids when they reach the level that is at their boiling point.
• The different liquids are collected on the trays.
• The hydrocarbons with the smallest molecules have the lowest boiling points, and so are collected at the top.

Question 8

How do the size of the molecules affect boiling point, viscosity, volatility and flammability?

Answer 8

Fractions with smaller molecules have:

• Low BP
• High volatility
• Low viscosity
• High flammability

Question 9

What is the word equation for the complete combustion of alkanes?

Answer 9

alkane + oxygen = carbon dioxide + water

Question 10

How do you test whether complete combustion has taken place?

Answer 10

Water: use blue cobalt chloride paper which will turn pink in contact with water.

Carbon dioxide: Limewater will turn cloudy.

If the combustion is not complete, the fuels are not burnt completely, so it may produce a toxic gas, carbon monoxide.

Question 11

What is cracking?

Answer 11

Where large hydrocarbon molecules are broken down into smaller molecules.

Question 12

What two ways can cracking be done?

Answer 12

• Steam cracking (heating a mixture of hydrocarbon vapours and steam to a very high temperature).
• Catalytic cracking (passing hydrocarbon vapours over a hot catalyst).

Question 13

Why do oil companies use cracking?

Answer 13

Alkanes with smaller molecules are more useful as fuels.

Question 14

What is the order of oils collected in fractional distillation?

Answer 14

From bottom to top:

• Residue
• Diesel oil/gas oil
• Kerosene
• Gasoline/petrol
• refinery/petroleum gas