Topic 5 - Fuels

Question 1

What is crude oil and how is it formed?

Answer 1

Crude oil is a mixture of different sized hydrocarbon molecules. Because it is a mixture, the different hydrocarbon molecules aren’t chemically bonded so they keep their original properties. It is formed from the buried remains of plants and animals - it is a fossil fuel.

Question 2

What is a hydrocarbon?

Answer 2

Fuels such ad petrol and diesel that are made of just carbon and hydrogen.

Question 3

What is the fractionating column? How does it work?

Answer 3

It is crude oil split into seperate groups of hydrocarbons. The diagram below summarises the main fractions from crude oil and their uses, and the trends in properties. Note that the gases condense at the top of the column, the liquids in the middle and the solids stay at the bottom.

Question 4

What is the general equation for complete combustion?

Answer 4

hydrocarbon + oxygen —- carbon dioxide + water

Question 5

What is the symbol equation for the complete combustion of methane?

Answer 5

CH4 + 20² —- 2H²0 + C0²

Question 6

What is the equation for incomplete combustion?

Answer 6

hydrocarbon + oxygen – carbon + carbon monoxide + carbon dioxide + water

Question 7

What colour flame is complete/incomplete combustion?

Answer 7

complete - clean blue flame

incomplete - smoky yellow flame

Question 8

Give 4 things to consider when choosing a fuel

Answer 8

• ease of ignition
• energy value
• ash and smoke
• storage and transport

Question 9

Give 2 of the main ways fossil fuels are burnt?

Answer 9

• power stations
• cars

Question 10

Give the equation for when fossil fuels are burnt

Answer 10

hydrocarbon + oxygen —- carbon dioxide + water vapour

Question 11

What happens if there is not enough oxygen for the fuel to burn?

Answer 11

Particles of soot (carbon) and carbon monoxide are also released along with sulfur dioxide due to the sulfur impurities that are found in petrol and diesel.

Question 12

How does sulfur dioxide cause acid rain?

Answer 12

When the sulfur dioxide mixes with the clouds it forms dilute sulfuric acid which then falls as acid rain.

Question 13

Give 3 way acid rain affects our environment

Answer 13

• it causes lakes to become acidic and many plants and animals die as a result
• acid rain kills treed
• it damages limestone buildings and ruins stone statues

Question 14

Describe the + and - of sulfur being removed from fuels before they are burnt

Answer 14

• most of the sulfur can be removed from fuels before they are burnt
• it is expensive
• takes more energy, this usually comes from burning more fuel which releases more of the greenhouse gas C0²

+ petrol and diesel are starting to be replaced by low sulfur versions

-

Question 15

Give 3 ways in which acid rain can be prevented by cleaning up emissions

Answer 15

• power stations now have ‘acid gas scrubbers’ to take the harmful gases out before they release their fumes into the atmosphere
• most cars are now fitted with catalytic converters to clean up their exhaust pipes
• reduce use of fossil fuels

Question 16

What is the effect of greenhouse gases?

Answer 16

The temperature of the Earth is a balance between the heat it gets from the Sun and the heat it radiates back out into space.

Gases in the atmoqphere like C0², methane and water vapour naturally act like an insulating layer. They absorb most of the heat that would normally be radiated out into space and re-radiate it in all directions - including back towards the Earth. The earth is gradually heating up.

Question 17

Describe how deforestation is affecting carbon dioxide levels

Answer 17

• deforestation for timber and land for farming
• C0² is released when trees are burnt to clear land (carbon in wood is locked up and is relased when burning)
• microogranisms feeding on bits of dead wood relase C0² (as a waste product of respiration)
• trees use C0² for photosynthesis so cutting trees down means less C0² will be taken in by the trees

Question 18

Describe how iron seeding is used to reduce C0² levels

Answer 18

• iron is an element needed by plants for photosynthesis. injecting iron intto the upper ocean promotes the growth of phytoplankton
• these blooms of phytoplankton absorb C0² for photosynthesis
• we have no control what plankton grows and some can be toxic
• microorganisms which decompose dead plankton use 0² and this creates dead zones in the ocean where nothing can live

Question 19

Give what most of the methods scientists are testing to research the possibility of converting waste C0² into hydrocarbons use

Answer 19

high pressure

high temperature

metal catalyst

• short chain hydrocarbons can be egenrated fairly easily but the longer hydrocarbons required for petrol are harder to produce

Question 20

What are biofuels? give the 2 main ones.

Answer 20

fuels made from cehmicals obtained from living gas

• biogas
• ethanol

Question 21

How is biogas produced?

Answer 21

Microorganisms are used to decompose living organisms’ waste or dead plants to create biogas.

Question 22

What is biogas used for?

Answer 22

• It can be burned to heat water or used in central heating systems
• it can power a turbine, which can be used to generate electricity
• fuel for cars and buses

Question 23

Give 4 advantages of biogas

Answer 23

• renewable
• dead plants needed to make biogas photsynthesised when alive, removing C0² from the atmosphere
• fairly clean fuel
• raw material for biogas (plant waste or manure) are cheap and readily available

Question 24

How is ethanol produced?

Answer 24

It can be produced by using yeast to ferment sugars. Materials like sugar cane and sugar beet can be used as a source of sugar in ethanol production.

Question 25

Give 2 uses of ethanol

Answer 25

• can be used as fuel it burns to give just C0² and water
• cars can be adapted to run on a mixture of about 10% ethanol and 90% petrol (gasohol)

Question 26

Give 2 advantages and disadvantages of ethanol

Answer 26

+ using gasohol instead of pire petrol means less crude oil is being used

+ crops needed for ethanol production absorb C0² from the atmosphere in photosynthesis while growing

• distilling the ethanol after fermentation needs a lot of energy
• because large amounts of land are needed to grow the crops used to produce ethanol, there would be les land to grow food

Question 27

What are the lab tests for hydrogen and oxygen? How can hydrogen and odygen be used to produce energy?

Answer 27

hydrogen - lighted splint = squeaky pop

oxygen - relights glowing splint

hydrogen + oxygen produces water - not a pollutant

the reaction releases energy

Question 28

What is a fuel cell?

Answer 28

An electrical cell that’s supplied with a fuel and oxygen and uses energy from the reaction between them to generate electricity.

Question 29

When were fuel cells first developed? Give 4 advantages

Answer 29

Fuel cells were developed in the 1960s as part of a space programme to provide electrical power on spacecraft

+ more practical than solar cells

+ safer than nuclear power

+ don’t run down or need recharging

+ produces energy in the form of electricity and heat as long as fuel is supplied

Question 30

Give 4 advantages of hydrogen - oxygen fuel cells

Answer 30

+ more efficient than power stations or batteries at producing electricity. the electricity is generated from the reaction.

+ not a lot of stages to the process of generating electricity, so less places for energy to be lost as heat

+ unlike a car engine or a fossil fuel burning power stations there are no moving parts so energy isn’t lost through friction

+ don’t produce convential pollutants e.g. greenhouse gases, nitrogen oxides, sulphur dioxide, carbon monoxide.

Question 31

Why could the use of hydrogen - oxygen cells not end convential power stations or our dependance on fossil fuels?

Answer 31

• hydrogen is a gas so it takes up lots of space to store in comparison to liquid fuels like petrol
• it is very explosive so it’s difficult to store safely
• the hydrogen fuel is often made from hydrocarbons (fossil fuels) or by electrolysis of water, which uses electricity (the electricity is usually generated using fossil fuels)

Question 32

How do you calculate mass of fuel burnt? How can this be used to calculate energy content?

Answer 32

final mass of fuel and burned - initial mass of fuel and burner

if you do this same experiment with different fuels, you can compare the energy content. If a fuel has a higher energy content per gram, you need less fuel to cause the same temperature rise.

Question 33

How can you calculate energy content using the calorimetric method?

Answer 33

• REDUCE DRAUGHTS BY USING A SCREEN
• put some fuel in a spirit burner and weigh the burner full of fuel
• measure out e.g. 200cm cubed of water into a copper calorimeter
• take the initial temp of the water the put the bruner under the calorimeter and light the wick
• stir it every now and then to distribute the heat evenly
• when the heat has made the water rise by 20-30°c blow out the spirit burner and male a note of the highest temperature the water reaches
• reweigh the burner and fuel. if you’re comparing two fuels, repeat the procedure with the second fuel

Question 34

What 3 things should stay the same to make the calorimetric method reliable?

Answer 34

• same apparatus
• same amount of water each time
• water should start and finish at the same temperature

Question 35

What type of hydrocarbons are alkanes?

Answer 35

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 their reaction with oxygen in the air, which we call burning or combustion.

Question 36

What is an alkane?

Answer 36

A hydrocarbon made up of chains of carbon atoms with single bonds between them.

Question 37

What are the four alkanes? What are their formulas?

Answer 37

methane - CH4

ethane - C2H6

propane - C3H8

Question 38

What is the general formula for alkanes?

Answer 38

The alkanes are a family of hydrocarbons that share the same general formula. This is:

CnH2n+2

The general formula means that the number of hydrogen atoms in an alkane is double the number of carbon atoms, plus two. For example, methane is CH4 and ethane is C2H6.

Question 39

What is an alkene?

Answer 39

A hydrocarbon made up of chains of carbon atoms with one or more double bonds.

Question 40

What type of hydrocarbons are alkenes?

Answer 40

They are unsaturated hydroczrbons meaning they are hydrocarbons with at least one carbon to carbon double bond.

Question 41

What is the effect of alkanes and alkenes on bromine water?

Answer 41

alkanes - result in bromine water staying brown

alkenes - turn bromine water colourless

Question 42

What are the first two alkenes? What are their formulas?

Answer 42

ethene C2H4
propene C3H6

Question 43

What is the general formula for alkenes?

Answer 43

The alkenes are a family of hydrocarbons that share the same general formula:

CnH2n

The general formula means that the number of hydrogen atoms in an alkene is double the number of carbon atoms. For example, ethene is C2H4 and propene is C3H6.

Question 44

What do ‘meth’, ‘eth’ and ‘prop’ mean?

Answer 44

meth - one carbon atom

eth - two carbon atoms

prop - three C atoms

Question 45

What is cracking?

Answer 45

Cracking is a form of thermal decomposition which just means breaking mpolecules down into simpler molecules by heating them. A lot of the long-chain molecules produced from fractional distillation are not very useful so they are cracked into smaller ones because there’s mpre demqnd for products like petrol than for diesel or lubricating oil. Cracking produces alkenes needed for making plastics.

Question 46

How is cracking used in industry?

Answer 46

In industry, vaporised hydrocarbons are passed over a powdedered catalyst at 400°-700°c. Silicon dioxide (Si02) and aluminium oxide (Al203) are used as catalysts.

Question 47

Describe how parrafin is cracked in the lab?

Answer 47

• heat the parrafin. After a few seconds, move the bunesenburner to heat the porcelain chips. alternate between the two until the parrafin vaporises and the porcelain glows red.
• the heated parrafin vapour cracks as it passes over the heated porcelain.
• the smaller alkanes and alkenes travel down the delievry tube
• the smallest alkanes and alkenes are gases which collect in the gas jar
• you can show that the gas in the gas jar contains alkenes as it decolourises the bromine water.

Question 48

What is polymerisation? use ethene as an example.

Answer 48

Joining together lots of monomers to form very large molecules - these long chain molecules are called polymers.

e.g. ethene molecules can be joined up to produce poly(ethene). molecules form polymers by opening their double bonds.

Question 49

Give examples of how producing biodegradable polymers will help wit problems associated with disposing of them?

Answer 49

• some polythene bags now have starch granules in them. if the plastic is buried, the starch is broken down by microorganisms in the soil, and the bag breaks down into tiny pieces of polyethene
• you can get plastics that break down in sunlight - they tend to be used in agriculture.

Question 50

What are the uses of

• poly(ethene)
• poly(propene)
• poly(chlorethene)
• poly(tetrafluoroethene)

Answer 50

-poly(ethene)
stretchy and light - plastic bags to hose pipes to laminating paper

-poly(propene)
tough but flexible - thermal underwear, carpets, plastic containers

-poly(chlorethene)
flexible and resistant to wear - clothing, electrical cables, pipes

• poly(tetrafluoroethene)

unreactive, flame resistant, v resistant to wear - non-stick coating for pans