Edexcel GCSE 9-1 Chemistry: SC20/21- Fuels + Complete and incomplete combustion

Paper 2 ---------- Specification: https://www.wardleacademy.co.uk/wp-content/uploads/2020/09/Chemistry-KS4-GCSE-Specification.pdf

SC20a - Hydrocarbons in crude oil and natural gas

Recall the meaning of the term hydrocarbon

Hydrocarbon - a compound that contains hydrogen and carbon atoms only

Describe the compounds found in crude oil

Crude oil is a mixture of hydrocarbon compounds (i.e. paraffins) and small amounts of organic compounds (i.e. sulphur)

Describe the importance of crude oil for the petrochemical industry

• an important source of fuels: petrol, kerosene, heavy fuel oil and liquefied petroleum gas

• used as feedstock (the raw material): plastic, rubber, solvents, lubricants and detergents.

Explain why crude oil is a finite resource

• forms extremely slowly over millions of years

• being used much faster than it can be replaced

Recall the names of some common fossil fuels

• Coal

• Natural gas

• Oil

SC20b - Fractional distillation of crude oil

Describe how crude oil is separated by fractional distillation.

Industrial f/d of crude oil happens in a fractionating column.

• Hot vapours are piped into the bottom of the column

• Base is hotter than the top of the column

• Vapours rise through the column and cool down

• Vapours condense when they reach a point that is cool enough

• Liquid falls into a tray and is piped away

• Vapours with lowest bpt don’t condense and leave from the top as a mixture of gases

  • Bitumen has the highest bpt and leaves from the bottom as a hot liquid

Recall the names and uses of fractions from crude oil.

TOP

• Gases: domestic heating and cooking

• Petrol: car fuel

• Kerosene: aircraft fuel

• Diesel oil: car + train fuel

• Fuel oil: large ships + power station fuel

• Bitumen: surfacing roads and roofs

BOTTOM

Describe how fractions differ from each other

Different fractions have different uses because they have different properties

• Hydrocarbons in gases have low viscosity and easy ignition making them suitable as fuels

• Bitumen is solid at room temp; + waterproof making it suitable to surface roads and roofs

The other fractions are liquids at room temp.

Explain why the different properties of different fractions differ

• Number of atoms decrease as you go UP the column

• Bpts increase as you go DOWN the column

• Ignition increases as you go UP the column

• Viscosity decreases as you go DOWN the column

  • More carbon atoms = more IMF

SC20c - The alkane homologous series

Describe that oil fractions mostly contain alkanes

Oil fractions mostly contain alkanes

Describe the main features of a homologous series

• Molecular formulae of neighbouring compounds differ by CH₂

• They follow the same general formula

• Gradual variation in physical properties (

  • i.e. boiling points

• Similar chemical properties

Explain why alkanes form a homologous series

• Follow the same general formula

  • C_n + H_n+2

• Gradual variation in physical properties

  • As no. of C atoms increase, bpt increases too

• Similar chemical properties

  • React with O₂ → CO₂ + H₂O

    • propane is found in camping gas

SC20d - Complete and incomplete combustion

Describe the complete combustion of hydrocarbon fuels

Hydrocarbon + oxygen → carbon dioxide + water

Explain the production of harmful products during the incomplete combustion of hydrocarbon fuels

Hydrocarbon + O₂ → CO₂ + H₂O

Hydrocarbon + O₂ → C₂ + H₂O

Explain why carbon monoxide is toxic

It binds to haemoglobin and prevents red blood cells from carrying oxygen to cells in your body

Describe the problems caused by incomplete combustion

• Carbon monoxide is a poisonous gas which binds to haemoglobin in your red blood cells, preventing them from carrying oxygen to the cells in your body

• Colourless and has no smell, so it is very difficult to tell if you are breathing it in

SC20e - Combustible fuels and pollution

Explain how some hydrocarbon fuels produce sulphur dioxide in use

• Many fossil fuels. contain sulphur impurities.

• When these fuels are burned, the sulphur is oxidised to form sulphur dioxide.

Recall the name of the pollutants responsible for acid rain

• Sulphur dioxide - SO₂

• Nitrogen oxide - NO

Describe some effects of acid rain

• Dead / dying plants

• Leaches aluminium from soil which is harmful to wildlife

• Removes minerals from soil that plants use to grow

Explain why oxides of nitrogen are produced when fuels are burnt in engines

• Fuel is mixed with air and ignited in the engine

• Nitrogen and oxygen react with each other

• Reaction produces various oxides of nitrogen (NO_x)

  • Atmospheric pollutants

SC20f - Breaking down hydrocarbons

Evaluate hydrogen as an alternative fuel to petrol for cars

• By product of methane

• Hydrogen combustion only produces water vapour (environmental benefits)

• Hydrogen is a gas at room temp which makes it harder to store in large amounts

  • unless compressed under high pressure or liquified by cooling = $$!

Describe what happens during cracking

• Short for catalytic cracking

• Requires high temp + catalyst to break less useful long chain alkanes into more useful short chain alkanes (alkenes)

Explain why alkanes are saturated and alkenes are unsaturated

Alkanes: they only contain SINGLE bonds

Alkenes: have a C=C (DOUBLE bond)

Explain why cracking is necessary

• Allows for the production of smaller, more useful products from larger, less valuable ones

• Breaks into more manageable chunks

  • Makes it possible to produce fuels and chemicals that are more useful and versatile

SC21a - The early atmosphere

Describe how the Earth’s early atmosphere was formed

• Mainly CO₂ + H₂O + other gases

• Lots of volcanic activity on Earth

• Earth, Venus + Mars are rocky volcanic planets: both Venus and Mars’ atmosphere are mainly CO₂

Draw conclusions from evidence about Earth’s early atmosphere

• Earth, Venus + Mars are rocky volcanic planets: both Venus and Mars’ atmosphere are mainly CO₂

• 2.4 billion years ago, rocks containing bands of iron oxide start to form

  • Oxidation of iron shows that O₂ levels increased at that time

• From microorganisms which reacted with iron in the early oceans produce insoluble Fe₂O₃ on seabed

Explain how the oceans are thought to have formed

About 4 billion years ago the Earth cooled down, causing water vapour in the atmosphere to condense to liquid water which formed the oceans

SC21b - The changing atmosphere

Describe how the formation of the oceans influenced the composition of the atmosphere

• CO₂ may have dissolved in the oceans which reduced CO2 in atmosphere

  • Sea creatures used CO₂ to form shells made of CaCO₃ which allowed more CO₂ to dissolve in oceans

Explain how photosynthetic organisms (including plants) changed the composition of the atmosphere

• 3 billion year old stromatolites are proof of photosynthetic organisms were living → rise of O₂ levels in the atmosphere

State the chemical test for oxygen

If a glowing splint relights in a test tube, oxygen is present

SC21c - The atmosphere today

Recall the names of significant greenhouse gases

• Carbon dioxide (CO₂₎

• Carbon monoxide (CO)

• Methane (CH₄)

• Nitrous oxide (NO)

Describe the processes involved in the greenhouse effect

• Energy from Sun is transferred to Earth by infrared

• Some energy is absorbed by the Earth

• Warm Earth emits infrared

• Some gases in the atmosphere absorb infrared and re emit energy → some goes back to Earth’s surface and warms it

Describe how human activity increases the concentration of greenhouse gases

• Since 1850 there has been a steady increase in the use of fossil fuels

• Earth’s temperature is increasing

• Overpopulation (respiration)

• Cattle farming (cattle release CH₄₎

• Oil and natural gas extraction

• Deforestation removes plants which are climate regulators

Evaluate the correlation between atmospheric carbon dioxide concentrations and fossil fuel use

When fossil fuels are combusted, they release CO₂

Evaluate the evidence for increased atmospheric gas concentrations being part of the cause of global warming and climate change

Since preindustrial times, the atmospheric concentration of:

• CO₂ has increased by over 40%

• Methane has increased by more than 150%, and

• Nitrous oxide has increased by roughly 20%

SC21d - Climate change

Suggest possible effects on the climate of increased levels of carbon dioxide and methane

• Keeps Earth’s surface warm

• CO2 dissolves in seawater which lowers its pH

  • Can lead to coral bleaching

Describe the projected effects of climate change

• Earth’s temp increases

  • Ice melts → loss of habitat + rising sea levels

  • Potential extinction of animals → decrease in biodiversity

  • Frequency of extreme temperatures increase

• Coral bleaching

• Increase in natural disasters

Describe how the potential harmful effects of climate change can be addressed and limited

• Using renewable + sustainable energy

• Capture CO2 and bury it underground

• Global effort!!

• Helping local people adapt to new conditions

  • Ecotourism + work WITH the environment, not AGAINST