C1 Topic 5 - Fuels

Question 1

Which molecules is crude oil made of?

Answer 1

A mixture of different sized hydrocarbons

Question 2

How is crude oil separated?

Answer 2

Fractional distillation
As each size of hydrocarbon has different boiling points, a fractioning column heats the oil to different temperatures to separate each hydrocarbon.

Question 3

Which hydrocarbons can you get from crude oil?

Answer 3

Gas
Petrol
Naphtha
Kerosene
Diesel
Fuel Oil
Bitumen

Question 4

What is the equation for complete combustion?

Answer 4

Hydrocarbon + Oxygen -> Carbon Dioxide + Water (+ energy)

Question 5

What colour is the flame in complete combustion?

Answer 5

Blue

Question 6

What is the equation for incomplete combustion?

Answer 6

Hydrocarbon + Oxygen -> Carbon + Carbon Dioxide + Carbon Monoxide + Water (+ energy)

Question 7

What colour is the flame in incomplete combustion?

Answer 7

Orange

Question 8

What are the four factors to consider when choosing a fuel?

Answer 8

Ease of ignition
Energy value - amount of energy released
Ash and smoke
Storage and Transport

Question 9

What causes acid rain and how does it happen?

Answer 9

Sulphur dioxide is released from power stations as petrol and diesel contain sulphur impurities. When the SO2 reacts with rain water in clouds, it forms dilute sulphuric acid.

Question 10

What problems does acid rain cause?

Answer 10

High acidity in lakes and rivers - kills fish and other animals
Erodes buildings and statues
Kill trees

Question 11

How can acid rain be reduced?

Answer 11

Using low-sulphur versions of petrol and diesel
Acid gas scrubbers to take harmful gases out before they enter atmosphere
Catalytic converters in exhausts to clean exhaust gases
Use less fossil fuels

Question 12

Briefly explain the greenhouse effect.

Answer 12

Gases such as water vapour, carbon dioxide and methane act as an insulating layer in the atmosphere, trapping the heat from the Sun and sending it back to Earth. This is causing the Earth to gradually heat up.

Question 13

How are humans contributing to global warming?

Answer 13

Deforestation

Burning of fossil fuels

Question 14

How can we decrease the amount of CO2 in the atmosphere?

Answer 14

Iron seeding - injecting iron into upper ocean to encourage growth of plankton which photosynthesise and absorb carbon dioxide

Converting CO2 into hydrocarbons - short hydrocarbons are easy to produce, longer ones are harder

Question 15

Describe how biogas is made?

Answer 15

1. Microorganisms decompose organic waste to create biogas.
2. Produces electricity like a gas-fired power station.
3. It’s renewable and won’t run out.
4. Carbon neutral.
5. Fairly clean fuel, not many impurities

Question 16

Describe how ethanol is made?

Answer 16

1. Glucose is fermented using yeast.
2. Cars can be made to run on 10% ethanol and 90% petrol
3. Downside is that large areas of land are needed to grow sugar beet and sugar cane.
4. Distilling ethanol after fermentation needs a lot of energy.

Question 17

What is a fuel cell and how does it work?

Answer 17

A fuel cell uses hydrogen and oxygen to give out energy and water when they react.
So long as they are provided with fuel (hydrogen) and heat, they produce energy without the need to be recharged.
More efficient than power stations or batteries.
Can be more than 80% efficiency if heat is also used.
Only one stage with no moving parts so not many places for energy loss.
No pollutants made, other than water.

Question 18

What are the problems of hydrogen fuel cells?

Answer 18

Hydrogen is a gas so it takes a lot of space to transport, it is also explosive so not very safe.
Often made from hydrocarbons from fossil fuels, or by electrolysis of water, which uses electricity.

Question 18

How can you calculate the energy content of a fuel by heating water?

Answer 18

Calorimetric Method:

1. Aim is to reduce as much draught as possible so use a screen
2. Put some fuel in the spirit burner and weigh the burner full of fuel
3. Measure out 200cm^3 of water into a copper calorimeter.
4. Take the initial temperature of the water, put the burner under the calorimeter and light the wick.
5. While the water is heating up, stir it every now and then to distribute the heat evenly.
6. When the heat from the burner has made the water temperature rise by 20-30°C, blow out the spirit burner and make a note of the highest temperature the water reaches.
7. Reweigh the burner and fuel.
8. Repeat the experiment for every fuel that you are comparing.

To find the mass of the fuel burned, find the difference in the initial and final mass of the burner.

Question 19

What is an alkane?

Answer 19

An alkane is a saturated hydrocarbon, this means that there are no double bonds. They won’t form polymers or turn bromine water colourless for this reason.
The general formula for alkanes is C2H2n+2

Question 20

What is an alkene?

Answer 20

Alkenes are unsaturated hydrocarbons because they all have one double bond. It decolourises bromine water and forms polymers by opening up the double bond. The general formula for alkenes is CnH2n

Question 21

What are the first four prefixes for hydrocarbons?

Answer 21

Meth- One carbon atoms
Eth- Two carbon atoms
Prop- Three carbon atoms
But- Four carbon atoms

Question 22

What is cracking?

Answer 22

Cracking is a process that shortens long chain hydrocarbons into shorter and more useful ones that have a higher demand, such as petrol or ethene etc.

Question 23

Describe the process of cracking.

Answer 23

The long chain hydrocarbon is vaporised and then passed over a powdered catalyst such as silicon dioxide or aluminium oxide at 400 - 700°C. This causes it to ‘crack’ into smaller hydrocarbons.

Question 24

How are alkenes used to make polymers?

Answer 24

Monomers, such as ethene or propene, are mixed with a catalyst and put under pressure, causing them to open their double bond and link up with each other. This is known as polymerisation. Ethene forms polyethene or polyethylene, propene makes polypropene or polypropene etc.

Question 25

What is the environmental problem of plastics?

Answer 25

Plastics don’t rot/aren’t biodegradable and therefore stay in landfill sites for years. Furthermore, when plastic are burnt, they give of toxic VOCs or Volatile Organic Compounds.
Some plastics can be recycled but separating them takes time and can be expensive.

Some biodegradable plastics have been developed though, polyethylene bags can be made with starch granules, so that when they break down, all that is left are very small pieces of polyethylene. Other plastics also break down in sunlight.