Crude oil (Edexcel IGCSE Chemistry (Modular): Unit 1): Flashcards
Exam code: 4XCH1
1/370Still learning
Know0
Define fractional distillation.
Was this flashcard helpful?
Cards in this collection (37)
Define fractional distillation.
Fractional distillation is the process used to separate crude oil into groups of hydrocarbons called fractions, based on differences in their boiling points.
How does a fractionating column separate crude oil into fractions?
A fractionating column has a temperature gradient — very hot at the bottom and cooler at the top.
Crude oil is heated and vaporised. Hydrocarbons with high boiling points condense lower down the column, while those with lower boiling points rise higher before condensing.
Each fraction of crude oil contains hydrocarbons with similar .......... lengths, and the fractions are mostly made up of compounds called .......... which contain only single carbon-carbon bonds.
Each fraction of crude oil contains hydrocarbons with similar chain lengths, and the fractions are mostly made up of compounds called alkanes which contain only single carbon-carbon bonds.
True or False?
Hydrocarbons with longer carbon chains have lower boiling points than those with shorter chains.
False.
Longer carbon chains have greater intermolecular attraction, so more energy is needed to separate the molecules. This means longer chains have higher boiling points.
Why do longer hydrocarbon chains have higher boiling points?
As the chain length increases, the intermolecular forces between molecules become stronger.
More energy is needed to overcome these forces and separate the molecules, so the boiling point increases with increasing molecular size.
Define viscosity.
Viscosity is a measure of how easily a liquid flows. A high-viscosity liquid is thick and flows less easily.
Viscosity increases as the carbon chain length of a hydrocarbon increases.
Complete the table of crude oil fractions and their main uses.
Fraction
Main use
Liquified petroleum gas
Petrol
Kerosene
Diesel
Heavy fuel oil
Bitumen
Fraction
Main use
Liquified petroleum gas
Domestic heating and cooking
Petrol
Fuel for cars
Kerosene
Jet fuel
Diesel
Diesel engines
Heavy fuel oil
Ships and power stations
Bitumen
Surfacing roads and roofs
True or False?
Bitumen contains more than 70 carbon atoms and is used to surface roads and roofs.
True.
Bitumen is the heaviest fraction from crude oil, with more than 70 carbon atoms per molecule. Its high viscosity makes it ideal for surfacing roads and roofs.
What is volatility, and how does it change as hydrocarbon chain length increases?
Volatility is the tendency of a substance to vaporise.
As chain length increases, the intermolecular forces between molecules become stronger, so longer-chain hydrocarbons are less volatile — they do not vaporise as easily.
As carbon chain length increases, the colour of the hydrocarbon liquid gets .......... and it becomes more .......... in both viscosity and boiling point.
As carbon chain length increases, the colour of the hydrocarbon liquid gets darker and it becomes more viscous, with a higher boiling point.
Define fossil fuel.
A fossil fuel is a non-renewable fuel formed from the remains of ancient organisms. Examples include coal, oil, and natural gas.
Fossil fuels all contain carbon and hydrogen, and small quantities of sulfur.
What are the products when a hydrocarbon burns in excess oxygen?
When a hydrocarbon undergoes complete combustion in excess oxygen, the only products are carbon dioxide (CO2) and water (H2O).
True or False?
Carbon monoxide is a colourless, odourless gas.
True.
Carbon monoxide is both colourless and odourless, which makes it particularly dangerous as it cannot be detected by sight or smell. It is produced by incomplete combustion.
Complete combustion of a hydrocarbon (excess oxygen) produces .......... and water, while incomplete combustion (limited oxygen) produces .......... and unburned carbon particles.
Complete combustion of a hydrocarbon (excess oxygen) produces carbon dioxide and water, while incomplete combustion (limited oxygen) produces carbon monoxide and unburned carbon particles.
Why is carbon monoxide toxic to humans?
Carbon monoxide (CO) binds strongly to haemoglobin in the blood, preventing it from carrying oxygen to the body's organs.
This can cause dizziness, loss of consciousness, and eventually death.
Define complete combustion.
Complete combustion is the reaction of a fuel with excess oxygen, producing only carbon dioxide and water as products.
True or False?
Carbon dioxide is a toxic gas that causes immediate harm by binding to haemoglobin.
False.
Carbon dioxide is not a toxic gas — it is carbon monoxide that binds to haemoglobin and is immediately harmful. CO2 is a pollutant that contributes to global warming and climate change.
Complete the table of fossil fuel uses.
Fuel
Main use
Petrol
Kerosene
Coal
Natural gas
Fuel
Main use
Petrol
Fuel for cars
Kerosene
Fuel for aircraft (jet fuel)
Coal
Power stations and steel production
Natural gas
Heating and cooking (mainly methane)
Why does incomplete combustion occur in some boilers and stoves?
Incomplete combustion occurs when there is an insufficient supply of oxygen to fully burn the fuel.
This produces carbon monoxide and unburned carbon (soot) rather than carbon dioxide, making it both wasteful and dangerous.
How are nitrogen oxides formed in car engines?
Nitrogen oxides (NO and NO2) are formed when nitrogen and oxygen in the air react together under the high temperature and high pressure conditions inside internal combustion engines and blast furnaces.
Define acid rain.
Acid rain is rain that has become acidic due to dissolved pollutants, mainly sulfur dioxide and nitrogen dioxide, which react with water in the atmosphere to form sulfuric acid and nitric acid.
True or False?
Sulfur dioxide is produced when fossil fuels containing sulfur impurities are burned.
True.
Fossil fuels often contain small amounts of sulfur impurities. When they are combusted, the sulfur is oxidised to sulfur dioxide (SO2).
Sulfur dioxide dissolves in rainwater droplets and reacts with oxygen to form .......... acid, which is one of the main components of ...........
Sulfur dioxide dissolves in rainwater droplets and reacts with oxygen to form sulfuric acid, which is one of the main components of acid rain.
What are the harmful effects of acid rain on the environment?
Acid rain can:
Corrode metal structures, buildings, and statues made from carbonate rocks
Damage aquatic organisms and pollute water supplies
Harm crops and irritate the lungs, throats, and eyes of people and animals
What is the role of a catalytic converter?
A catalytic converter is a device fitted to a car's exhaust system that converts harmful exhaust gases (such as nitrogen oxides, carbon monoxide, and unburned hydrocarbons) into less harmful substances.
True or False?
Nitrogen dioxide dissolves in rainwater to form only nitric acid.
False.
Nitrogen dioxide (NO2) reacting with water forms a mixture of both nitrous acid (HNO2) and nitric acid (HNO3), not just nitric acid alone.
Complete the table of air pollutants from burning fossil fuels.
Pollutant
Source
Harmful effect
Sulfur dioxide
Nitrogen oxides
Carbon monoxide
Pollutant
Source
Harmful effect
Sulfur dioxide
Combustion of sulfur-containing fuels
Acid rain
Nitrogen oxides
High-temperature combustion in engines
Acid rain and photochemical smog
Carbon monoxide
Incomplete combustion
Binds to haemoglobin, toxic
Why does burning fossil fuels produce sulfur dioxide?
Fossil fuels contain small amounts of sulfur impurities. During combustion, the sulfur reacts with oxygen and is oxidised to sulfur dioxide (SO2), which is then released into the atmosphere.
Define cracking.
Cracking is an industrial process that breaks long-chain hydrocarbon molecules (low demand) into shorter, more useful hydrocarbon molecules (high demand).
Why is cracking used in the oil industry?
Cracking is used because the demand for short-chain hydrocarbons (such as petrol, kerosene, and diesel) is greater than the supply obtained from fractional distillation.
Excess long-chain fractions (such as fuel oil and bitumen) are cracked to produce more of the useful, shorter-chain products.
In catalytic cracking, the hydrocarbon is heated to around ..........°C to vaporise it, then passed over a hot powdered catalyst of ...........
In catalytic cracking, the hydrocarbon is heated to around 600–700°C to vaporise it, then passed over a hot powdered catalyst of aluminium oxide.
True or False?
Cracking is an exothermic reaction.
False.
Cracking is an endothermic reaction — it requires a continuous input of heat energy to break the covalent bonds in the long-chain hydrocarbon molecules.
What types of molecules are produced when a long-chain hydrocarbon is cracked?
Cracking produces a mixture of shorter alkanes and alkenes.
Alkanes are saturated molecules with only single C-C bonds. Alkenes are unsaturated molecules with a C=C double bond.
Define alkene.
An alkene is an unsaturated hydrocarbon that contains at least one carbon-carbon double bond (C=C).
True or False?
The demand for short-chain hydrocarbons like petrol exceeds the supply obtained from fractional distillation of crude oil.
True.
Fractional distillation produces more long-chain fractions (such as fuel oil) than are needed, while the supply of short-chain fractions like petrol and kerosene is insufficient to meet demand. Cracking is used to address this imbalance.
Complete the table showing supply and demand for crude oil fractions.
Fraction
Demand vs supply
Petrol
Kerosene
Fuel oil
Bitumen
Fraction
Demand vs supply
Petrol
Demand exceeds supply
Kerosene
Demand exceeds supply
Fuel oil
Supply exceeds demand
Bitumen
Supply exceeds demand
What conditions are used in catalytic cracking, and how does the catalyst work?
The hydrocarbon is heated to around 600–700°C to vaporise it, then passed over a hot powdered aluminium oxide catalyst.
The molecules undergo thermal decomposition as they contact the catalyst surface, breaking covalent bonds to form shorter molecules.
Sign up to unlock flashcards
or