Crude Oil (Edexcel IGCSE Science (Double Award): Chemistry): Flashcards
Exam code: 4SD0
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Define fractional distillation.
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Define fractional distillation.
Fractional distillation is the industrial process used to separate crude oil into groups of hydrocarbons called fractions, based on differences in their boiling points.
In a fractionating column, hydrocarbons with higher boiling points condense .......... the column, while those with lower boiling points condense .......... .
In a fractionating column, hydrocarbons with higher boiling points condense towards the bottom of the column, while those with lower boiling points condense towards the top.
True or False?
Crude oil is a pure substance made up of a single hydrocarbon.
False.
Crude oil is a mixture of hydrocarbons. The different hydrocarbons are separated into fractions by fractional distillation because they have different boiling points.
What property of a hydrocarbon fraction determines where it condenses in the fractionating column?
A fraction condenses at the point in the column where the temperature matches its boiling point. Fractions with higher boiling points (longer chains) condense lower down; those with lower boiling points (shorter chains) rise higher before condensing.
Define fraction (crude oil).
A fraction is a group of hydrocarbons separated from crude oil during fractional distillation, each consisting of molecules with similar chain lengths and boiling points.
Name the six main fractions obtained from crude oil, in order from shortest to longest carbon chain.
The six main fractions are:
(Shortest) Refinery gas
Gasoline
Kerosene
Diesel
Fuel oil
(Longest) Bitumen
As the carbon chain length of a crude oil fraction increases, its boiling point .........., its viscosity .......... and its colour becomes .......... .
As the carbon chain length of a crude oil fraction increases, its boiling point increases, its viscosity increases and its colour becomes darker.
True or False?
Kerosene is used as a fuel for jet aircraft.
True.
Kerosene (also called paraffin) is the crude oil fraction used as jet fuel. It has a carbon chain length of roughly 12–16 atoms.
What is bitumen used for and why is it suitable for that use?
Bitumen is used for surfacing roads and roofs. Its very long carbon chains (70+ C atoms) make it extremely viscous and solid at room temperature, giving it good waterproofing and load-bearing properties.
Why does volatility decrease as the carbon chain length of a hydrocarbon fraction increases?
Longer chains have stronger intermolecular forces between molecules. More energy is needed to overcome these forces, so the fraction is less likely to vaporise, making it less volatile.
Define fuel.
A fuel is a substance that, when burned, releases heat energy in an exothermic reaction.
Complete combustion of a hydrocarbon occurs when there is .......... oxygen, producing .......... and water.
Complete combustion of a hydrocarbon occurs when there is excess oxygen, producing carbon dioxide and water.
True or False?
Incomplete combustion of hydrocarbons can produce carbon particulates (soot).
True.
Incomplete combustion occurs when oxygen supply is insufficient. Products can include carbon monoxide, unburned hydrocarbons and carbon particulates (soot), as well as water.
What gases are released when fossil fuels burn and contribute to atmospheric pollution?
Burning fossil fuels releases carbon dioxide, carbon monoxide, oxides of nitrogen and oxides of sulfur. Incomplete combustion also produces unburned hydrocarbons and carbon particulates.
Define carbon monoxide.
Carbon monoxide (CO) is a colourless, odourless, toxic gas produced during the incomplete combustion of carbon-containing fuels.
Why is carbon monoxide dangerous to humans?
Carbon monoxide reduces the capacity of blood to transport oxygen around the body. Because it is colourless, odourless and tasteless, it can be inhaled without detection.
True or False?
Carbon monoxide is easy to detect because it has a strong, distinctive smell.
False.
Carbon monoxide is odourless, colourless and tasteless, which makes it particularly dangerous — a person can inhale dangerous concentrations without realising it.
Carbon monoxide is dangerous because it reduces the ability of .......... to transport .......... around the body.
Carbon monoxide is dangerous because it reduces the ability of blood to transport oxygen around the body.
Where is incomplete combustion most likely to occur in everyday situations?
Incomplete combustion occurs where oxygen supply is limited, such as in boilers, stoves and internal combustion engines in vehicles.
Define nitrogen oxides.
Nitrogen oxides are a group of compounds (including NO and NO2) formed when nitrogen and oxygen from air react together at the high temperatures reached inside car engines.
Why do car engines produce nitrogen oxides?
Car engines reach high enough temperatures and pressures for nitrogen and oxygen in air to react with each other, forming nitrogen oxides such as NO and NO2.
True or False?
Sulfur dioxide forms when fossil fuels containing sulfur impurities are burned.
True.
Fossil fuels often contain sulfur impurities. When these fuels are combusted, the sulfur is oxidised to produce sulfur dioxide (SO2).
When fossil fuels with sulfur impurities burn, the sulfur reacts with .......... to form .......... .
When fossil fuels with sulfur impurities burn, the sulfur reacts with oxygen to form sulfur dioxide (SO2).
How does sulfur dioxide contribute to acid rain?
SO2 dissolves in rainwater droplets and reacts with oxygen to form sulfuric acid (H2SO4), which falls as acid rain.
Nitrogen dioxide reacts with rainwater to form a mixture of .......... and .........., which contribute to acid rain.
Nitrogen dioxide reacts with rainwater to form a mixture of nitrous acid and nitric acid, which contribute to acid rain.
True or False?
Nitrogen oxides from car exhausts can cause photochemical smog.
True.
Nitrogen oxides are a component of photochemical smog and can also cause breathing difficulties, particularly for people with asthma.
State three harmful effects of acid rain on the environment.
Corrodes metal structures and buildings made of carbonate rock
Damages aquatic organisms
Pollutes water supplies
Define acid rain.
Acid rain is precipitation with a pH lower than normal, caused by sulfur dioxide and nitrogen oxides dissolving in rainwater to form sulfuric acid and nitric acid.
Define cracking.
Cracking is an industrial process in which long-chain hydrocarbon molecules are broken down into shorter-chain alkanes and alkenes using heat and a catalyst.
Why is cracking necessary in the oil industry?
Demand for short-chain fractions such as petrol exceeds their supply from fractional distillation, so cracking converts surplus long-chain fractions into more useful shorter-chain products.
In catalytic cracking, hydrocarbon vapours pass over a hot catalyst of .......... at a temperature of .......... °C.
In catalytic cracking, hydrocarbon vapours pass over a hot catalyst of aluminium oxide at a temperature of 600–700 °C.
True or False?
Cracking is an endothermic reaction.
True.
Cracking requires a continuous input of heat energy to break the covalent bonds in long-chain hydrocarbons, making it an endothermic reaction.
What types of product are formed when a long-chain alkane is cracked?
Cracking produces a mixture of shorter-chain alkanes and alkenes. The alkenes contain carbon-carbon double bonds and the alkanes contain only single bonds.
Define alkene.
An alkene is an unsaturated hydrocarbon containing at least one carbon-carbon double bond, produced alongside shorter alkanes during the cracking of long-chain hydrocarbons.
True or False?
Catalytic cracking uses nickel as the catalyst.
False.
Catalytic cracking uses aluminium oxide (or silica) as the catalyst, not nickel.
Cracking is used to convert .......... fractions with low demand into .......... fractions with high demand.
Cracking is used to convert long-chain fractions with low demand into short-chain fractions with high demand.
What temperature range is used in catalytic cracking?
Catalytic cracking is carried out at 600–700 °C, which is hot enough to vaporise the hydrocarbon molecules before they contact the catalyst.
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