Crude Oil

Question 1

What is Crude Oil?

Answer 1

Crude oil is a mixture of compounds called hydrocarbons

Question 2

How can crude oil be separated?

Answer 2

Fractional Distillation

Question 3

What is a hydrocarbon?

Answer 3

It is a compound made up of hydrogen and carbon atoms joined by covalent bonds. Most of the hydrocarbons in crude oil are alkanes.

Question 4

An example of a hydrocarbon

Answer 4

Ethane C2H6 two C’s and six H’s

Question 5

What are alkanes?

Answer 5

Alkanes are saturated hydrocarbons. This means that their carbon atoms are joined to each other by single bonds. This makes them relatively unreactive, apart from burning or combustion, which is their reaction with oxygen in the air.

Question 6

What is distillation and how does it work?

Answer 6

Distillation is a process that can be used to separate a pure liquid from a mixture of liquids. It works when the liquids have different boiling points.

Question 7

The sequence of events in distillation

Answer 7

heating → evaporating → cooling → condensing

Question 8

How is fractional distillation different to distillation?

Answer 8

It separates a mixture into a number of different parts, called fractions.

Question 9

How does fractional distillation work?

Answer 9

A tall column is fitted above the mixture, with several condensers coming off at different heights. The column is hot at the bottom and cool at the top. Substances with high boiling points condense at the bottom and substances with lower boiling points condense on the way to the top. The crude oil is evaporated and its vapours condense at different temperatures in the fractionating column. Each fraction contains hydrocarbon molecules with a similar number of carbon atoms.

Question 10

How do oil fractions work?

Answer 10

The top of the column is cool (25 degrees Celsius). Fractions taken from here have small molecules, low boiling points, are very volatile, flow easily and ignite easily. Crude oil enters at the bottom of the column and is heated to 350 degrees Celsius. Fractions taken here have large molecules, high boiling points, are not very volatile, and don’t flow or ignite easily. From top to bottom the fractions are: Refinery gases (bottled gas), gasoline (petrol), naphtha (used for making chemicals), kerosene (aircraft fuel), diesel oil (fuel for cars, and lorries, etc.), fuel oil (fuel for ships, power stations), residue (bitumen for roads and roofs).

Question 11

Fractioning column

Answer 11

As you go up the fractionating column, the hydrocarbons have: lower boiling points lower viscosity (they flow more easily) higher flammability (they ignite more easily). This means that in general hydrocarbons with small molecules make better fuels than hydrocarbons with large molecules.

Question 12

What is complete combustion?

Answer 12

Fuels burn when they react with oxygen in the air. If there is plenty of air, complete combustion happens. Coal is mostly carbon. During complete combustion, carbon is oxidised to carbon dioxide: carbon + oxygen → carbon dioxide

Question 13

What kind of gas is carbon dioxide?

Answer 13

A greenhouse gas

Question 14

What happens to hydrogen during combustion?

Answer 14

Hydrocarbon fuels contain carbon and hydrogen. During combustion, hydrogen is oxidised to water (remember that water, H2O, is an oxide of hydrogen). In general: hydrocarbon + oxygen → carbon dioxide + water

Question 15

What is incomplete combustion?

Answer 15

If there is insufficient air for complete combustion, incomplete combustion (also called partial combustion) happens. Hydrogen is still oxidised to water, but carbon monoxide forms instead of carbon dioxide. Carbon monoxide is a toxic gas, so adequate ventilation is important when burning fuels. Solid particles (particulates) are also released. These contain carbon and are seen as soot or smoke.

Question 16

What do particulates cause?

Answer 16

Global dimming and they reduce the amount of light reaching the Earth’s surface.

Question 17

What are the effects of acid rain?

Answer 17

Acid rain reacts with metals and rocks such as limestone, causing damage to buildings and statues. Acid rain damages the waxy layer on the leaves of trees. This makes it more difficult for trees to absorb the minerals they need for healthy growth and they may die. Acid rain also makes rivers and lakes too acidic for some aquatic life to survive.

Question 18

What happens to the sulphur in fuel when it burns?

Answer 18

sulphur + oxygen → sulphur dioxide This gas dissolves in water to form an acidic solution. It is a cause of acid rain.

Question 19

Are crude oil and coil renewable or non-renewable resources?

Answer 19

Non-renewable, they take so long to form that they cannot be replaced once they have all been used up. This means that these fossil fuels are likely to become more expensive as they begin to run out.

Question 20

Which substances are produced when fuels made from crude oil are burned?

Answer 20

Petrol, diesel and other fuels produced from crude oil make a range of harmful substances when they are burned, including: carbon dioxide carbon monoxide water vapour particulates (solid particles) sulphur dioxide oxides of nitrogen or NOx.

Question 21

What are biofuels?

Answer 21

Biofuels are fuels produced from plant material. They have some advantages and disadvantages compared to fossil fuels.

Question 22

What is biodiesel made from?

Answer 22

Biodiesel is made from rapeseed oil and other plant oils. It can be used in diesel-powered vehicles without needing any modifications to the engine.

Question 23

What is bioethanol?

Answer 23

Ethanol, C2H5OH, is not a hydrocarbon because it contains oxygen as well as hydrogen and carbon. However, it is a liquid fuel that burns well. Bioethanol is made by fermenting sugars from sugar cane, wheat and other plants. It cannot be used on its own unless the engine is modified. However, modern petrol engines can use petrol containing up to 10 percent ethanol without needing any modifications, and most petrol sold in the UK contains ethanol.

Question 24

What are some ethical issues surrounding the use of biofuels?

Answer 24

There are ethical issues surrounding the use of biofuels. For example, crops that could be used to feed people are used to provide the raw materials for biofuels instead. This could cause food shortages or increases in the price of food. There are other economic issues surrounding the use of biofuels, including: human resources -more people are needed to produce biofuels than are needed to produce petrol and diesel increased income - for farmers lower fuel prices - biofuels limit the demand for fossil fuels, helping to reduce increases in fuel prices.

Question 25

What are the environmental issues with biofuels?

Answer 25

There are environmental issues surrounding the use of biofuels. Biodiesel naturally contains little sulphur. For example, it may be said that they are carbon neutral – the amount of carbon dioxide released when they are used is the same as the amount absorbed by the plants as they grew. If so, this would reduce the production of this greenhouse gas. However, while biofuels produce less carbon dioxide overall, they are not carbon neutral. This is because fossil fuels are used in their production, for example in making fertilisers for the growing plants.