SC20 Flashcards
SC20a
1) Recall the meaning of the term hydrocarbon.
2) Describe the compounds found in crude oil.
3) Describe the importance of crude oil for the petrochemical industry.
1) A hydrocarbon is a compound that is only formed from hydrogen and carbon.
2) Most of the compounds in crude oil consist of molecules made up of hydrogen and carbon atoms only, we call these type of compounds hydrocarbons.
3) Hydrocarbons can form new compounds. Hydrocarbons from crude oil are used in the petrochemical industry as feedstock (a raw material used to provide reactants for an industrial reaction) in order to make new compounds. These new compounds can form polymers, solvents, lubricants and detergents.
SC20a
1) Explain why crude oil is a finite resource.
2) Recall the names of some common fossil fuels.
1) Crude oil is a finite resource, meaning that one day it will run out, or it is being used at a much faster rate than the rate at which it is being reformed.
2) Coal, oil and natural gas are some common fossil fuels.
SC20c
1) What do oil fractions mostly contain?
2) Describe the main features of an homologous series.
3) Explain why alkanes form an homologous series.
1) Oil fractions mostly contain alkanes.
2) The hydrocarbons in crude oil belong to several different a homologous series. Compounds in a homologous series all share the same general formula. They have molecular formulas that different by CH2 from neighbouring compounds. They show a gradual variation in physical properties.
3) The alkanes are a homologous series of hydrocarbons. This means that they have similar chemical properties to each other and they have trends in physical properties.
SC20f
1) Evaluate hydrogen as an alternative fuel to petrol for cars.
2) Describe what happens during cracking.
1) Burning hydrogen only produces water and does not produce pollutants such as carbon dioxide like burning fossil fuels does. Hydrogen is obtained from water which is a renewable source (so it won’t run out, unlike possibly fuels). More hydrogen can be made from water produced by the fuel cell as a waste product.
2) Cracking involves breaking covalent bonds in hydrocarbon molecules. Crude oil fractions are heated to evaporate them. There is ceramic wool soaked in the alkane that is being cracked. The ceramic wool is heated to evaporate the alkane. The vapours are passed over a catalyst containing aluminium oxide and heated to about 650°C. A porous pot is the catalyst. This speeds up reactions that break down larger hydrocarbon molecules. Smaller, more useful, hydrocarbon molecules form and these can be used as fuels or for making polymers.
SC20f
1) Explain why whether alkanes or alkenes are saturated or unsaturated and why
2) Explain why cracking is necessary.
1) Alkanes and alkenes are both hydrocarbons. Alkanes are saturated because their carbon atoms are joined by single bonds. Alkenes are unsaturated because they contain a carbon-carbon double bond.
2) The amount of some fractions produced does not always meet the demand for those products. More of the product can be produced by cracking longer molecules into smaller, more useful ones.
SC20e
1) Recall the names of the pollutants responsible for acid rain.
2) Explain how some hydrocarbon fuels produce the pollutant responsible for acid rain in use.
1) Sulfur dioxide contributes to acid rain.
2) Hydrocarbon fuels (such as petrol and diesel oil) may contain sulfur compounds. These occur naturally as impurities and are not deliberately added. When the hydrocarbon fuel is burnt, the sulfur reacts with oxygen to form sulfur dioxide gas. This mixture of sulfurous acid and sulfuric acid causes problems when it falls as acid rain.
SC20e
1) Describe some effects of acid rain (state 5)
2) Explain why oxides of nitrogen are produced when fuels are burned in engines.
1) - Acid rain reacts with limestone or marble
- Acid rain corrodes and damages buildings or statues
- Acid rain acidifies lakes and rivers
- Acid rain can kill fish
- Acid rain acidifies soil
2) Nitrogen and oxygen from the air react together at the high temperatures produced by combustion in the engine. The reactions produce various oxides of nitrogen, which are atmospheric pollutants.
SC20d
1) Describe the complete combustion of hydrocarbon fuels.
2) Explain the production of harmful products during the incomplete combustion of hydrocarbon fuels.
1) Complete combustion of a hydrogen is a reaction in which: only carbon dioxide and water are produced, and energy is given out. Complete combustion occurs when there is a plentiful supply air or oxygen.
2) Incomplete combustion happens when there is a limited supply of air or oxygen, such as when the air hole on a Bunsen burner is closed. During the incomplete combustion of a hydrocarbon: water is produced, energy is given out (but less than with complete combustion), and carbon monoxide and carbon are produced.
SC20d
1) Explain why carbon monoxide is toxic.
2) Describe the problems caused by incomplete combustion.
1) Carbon monoxide is a toxic gas. This is because it combines with haemoglobin in red blood cells, preventing oxygen combining. This reduces the amount of oxygen carries in the bloodstream, causing affected people to feel sleepy or to become unconscious. Severe carbon monoxide poisoning can even cause death.
2) Less energy is released than during complete combustion. The carbon is released as fine black particles. We see this in smoky flames, and it is deposited as soot. Soot can cause breathing problems and it blackens buildings.
SC20b
1) Describe how crude oil is separated by fractional distillation.
2) Explain how fractional distillation of crude oil works.
1) At the beginning of the fractional distillation process, crude oil is heated and most of it evaporates. It enters the fractionating column as a gas. As the gas rises up the column, the crude oil fractions cool and condense out at different levels, depending on their boiling points. Fractions can be used as fuels.
2) The industrial fractional distillation of crude oil happens in a tall metal fractionating column. Crude oil is heated strongly to evaporate it, and the hot vapours are piped into the bottom of the column, where:
- the column is hottest at the bottom and coldest at the top
- the vapours rise through the column and cool down
- the vapours condense when they reach a part of the column that is cool enough (below their boiling points)
the liquid falls into a tray and is piped away
- the vapours with the lowest boiling points do not condense at all and leave at the top as a mixture of gases
bitumen has the highest boiling point and leaves at the bottom as a hot liquid.
The separated liquids and gases are called oil fractions because they are only parts of the original crude oil.
SC20b
1) Recall the names and uses of fractions from crude oil.
2) Describe how fractions differ from each other.
3) Explain why the properties of different fractions differ.
1) The fraction names are: refinery gases (also known as liquid petroleum gases), gasoline, kerosene, diesel, fuel oil and bitumen.
These are the uses for the fractions:
Refinery gases - domestic heating and cooking
Petrol - fuel for cars
Kerosene - fuel for aircraft
Diesel oil - fuel for some cars or trains
Fuel oil - fuel for large ships and power stations
Bitumen - surfacing roads and roofs
(Mnemonic to remember Randy’s Gassy Pet Kangaroo Dances Freely, But Sometimes Bites)
2) Each fraction is a mixture of hydrocarbons, rather than a pure hydrocarbon. However, the hydrocarbons in a given fraction have similar numbers of boiling points.
3) Different fractions have different uses because they have different properties.
- The hydrocarbons in the gases fraction have the lowest viscosity (they flow easily) and are easiest to ignite (they are easily set alight), making them suitable for use as fuels
- Bitumen is solid at room temperature, and waterproof, making it suitable for surfacing roads and roofs.
- The other fractions are liquids at room temperature.
SC20c
1) What links the compounds in a homologous series?
2) Explain why the incomplete combustion of alkanes can produce carbon monoxide as one of the products
1) The compounds in a homologous series have the same general formula.
2) There is insufficient oxygen to oxidise all the carbon to carbon dioxide.
