What is cracking?
The splitting up of long chain hydrocarbons.
List three products of cracking and their uses
- Petrol to fuel cars
- Paraffin for jet fuel
- Ethene for making plastic
What kind of reaction is cracking?
Describe the three main steps of cracking
- The long-chain hydrocarbon is heated and vaporised.
- The gas is then passed over a powdered catalyst (aluminium oxide) at a temperature of 400 - 700 degrees
- The long chain molecules will split apart on the surface of the powdered catalyst
What are the products when kerosene (10 carbon atoms) is "cracked"?
Octane (an alkane with eight carbon atoms) and Ethene (an alkene with two carbon atoms)
Can you give an alternative method of splitting up long chain hydrocarbons?
The vapour is mixed with steam at a very high temperature.
What are alkenes?
Hydrocarbons that have a double bond between two of the carbon atoms in their chain
Why are alkenes known as "unsaturated"?
They can make more bonds by the double bond between two carbon atoms opening up.
What is the general formula for alkenes?
How can you test for an alkene?
By adding a substance to bromine water, if the water goes from orange to colourless it means that an alkene is present. The colour change happens because the double bond has opened and formed bonds with the bromine.
How is ethanol produced from ethene and why is this a problem?
Ethene is hydrated with steam in the presence of a catalyst to make ethanol.
Ethene is a product from crude oil, it will eventually become more expensive to make ethanol as crude oil is a non-renewable resource.
What is the process by which ethanol can be produced from renewable resources? Give the word equation
Ethanol is the alcohol in beer and wine, in these products it is created by fermentation. Sugar is converted into ethanol using yeast.
Sugar → Carbon Dioxide + Ethanol
What are the pros (4) and cons (2) of creating ethanol from the fermentation of sugar?
- Needs a lower temperature and simpler equipment than when using ethene
- Sugar is a renewable resource
- Sugar crops are largely grown in poorer areas of the world
- Can be used as a cheap fuel
- The ethanol produced isn't very concentrated so it must be distilled to increase it's strength
- The ethanol produced needs to be purified
Joining together lots of small alkene molecules (monomers) to form very large molecules called polymers
Name the polymers of ethene and propene
Polyethene (or polythene)
What do the physical properties of polymers depend on? (3)
- What its made from eg. polyamides are stonger than polythene
- The temperature of polymerisation
- The pressure of polymerisation
What is the difference between polythene made at 200 degrees and that made at 60 degrees with a catalyst?
- Made at 200 degrees and 2000 atmospheres: flexible and has a low density
- Made at 60 degrees and a few atmospheres pressure with a catalyst: rigid and dense
Name as many uses of polymers as you can (7)
- Elastic polymer fibres are used to make stretchy lycra fibre for tights
- Light stretchable polymers (such as low density ethene) are used to make plastic bags
- Waterproof coating for fabric
- Resin in tooth fillings
- Hydrogel wound dressings
- Biodegradable packaging
- Memory foam
What disadvantages are there to the wide use of polymers? (2)
- They're not biodegradable
- The alkene products their made of come from products of crude oil, a non-renewable resource
How are oils extracted from plants and seeds? (3 different methods) What is distillation?
- The plant material is crushed and then pressed between metal plates, causing the oil to seep out.
- Solvents can be used to get oil from plant material.
Distillation refines oil, removing water, solvents and impurities.
What are the benefits of using vegetable oils in food? (3)
- High energy content
- Vitamins eg. seeds contain Vitamin E
- Contain essential fatty acids that the body need to metabolic processed.
Why are vegetable oils used in cooking?
- Higher boiling points than water
- Intensify flavour (chemicals are soluble in the oil)
- Increases the energy we get from eating the food
What is another use of vegetable oils, other than consumption?
Can be processed to make biofuels like biodiesel - can be used in a normal diesel engine.
What are the molecules in oils and fats like?
They are long-chain molecules with lots of carbon atoms, either saturated or unsaturated.
Unsaturated oils contain what type of bonds between some of their carbon atoms? And what does an unsaturated oil do to bromine water?
Unsaturated oils will decolourise bromine water.
What's the difference between monounsaturated fats and polyunsaturated fats?
Monounsaturated fats contain one C=C double bond in their carbon chains wherease polyunsaturated have more than one.
How can unsaturated oils be hardened?
They are reacted with hydrogen in the presence of a nickel catalyst at 60 degrees. The hydrogen reacts with the double bonded carbons and opens them out. This is known as hydrogenation.
What is margarine made from?
Partially hydrogenated vegetable oils
Why are partially hydrogenated vegetable oils widely used in processed foods and why does this cause concern?
The oils are a lot cheaper than butter and they keep longer.
Partially hydrogenated vegetable oils means you end up with a lot of trans-fats and there's evidence to suggest these trans fats are very bad for health.
Which type of fats tend to be saturated?