Flashcards in GCSE Chemistry unit 1 chapter 4-6 Deck (43)
What is cracking?
Cracking is when fuels (made from a mixture of hydrocarbons molecules) are not efficient enough and are cracked to allow large hydrocarbon molecules to broken down into smaller ones.
How does cracking work?
Cracking is thermal decomposition reaction. The first step is to heat the long chain hydrocarbon to vapourise it. Then the vapour is passed over a powdered aluminium oxide catalyst at a temperature of 700-800 Celsius.
What does cracking make?
Shorter chain alkanes and alkenes.
What is fractional distillation?
Fractional distillation is when crude oil (a mixture of hydrocarbons) is split into the different chain lenghths which have different properties.
Is crude oil mostly alkanes or alkenes?
What is the general formula of an Alkene?
What are the properties of shorter chains lengths?
- less viscous
-lower boiling point
- more flammable
What are the uses of long chain hydrocarbons?
Lubricating engine parts + covering roads because its very gloopy.
What are the uses of shorter chain hydrocarbons?
Petrol for cars because its easy to store and combust.
What can cause acid rain, global warming and global dimming?
Burning fuels. If the fuel contains sulfur impurities it can cause acid rain. Particulates cause global dimming and CO2 causes global warming.
What is the general formula for an alkene?
What is different from an alkene to and alkane?
alkenes are not saturated with hydrogens and have a double bond.
How can you tell a alkene from an alkane?
Bromine water. Alkenes decolourise the bromine water because the double bond opens up.
How can ethene be used to make ethanol?
Ethene can be hydrated with steam in the presence of a catalyst.
Why is making ethanol with ethene good?
Cheap process, continuous process,very pure product, faster process.
Why is making ethanol with ethene bad?
Not renewable, Lots of energy needed for steam and pressure.
How can you use sugar to make ethanol?
Sugar is fermented and converted to ethanol using yeast.
Why is making ethanol by fermentation bad?
Doesn't make pure ethanol, fermentation is slow, large volume of ethanol needed to make small amounts of ethanol, lots of land is needed.
why is making ethanol be fermentation good?
sugar is a renewable source, carbon neutral, good for LEDC because less technology is needed.
How can alkenes be used to make polymers?
joining together lots of small alkene molcules (monomers) to form very large molecules called polymers.
Why do different polymers have different physical properties?
The physical properties of a polymer depend on what its made on, and the temperature and pressure of polymerisation.
What is the main disadvantage of polymers?
They aren't biodegradable. This means they are not broken down by micro-organisms. Furthermore this makes them hard to get rid of so its best to re-use them as many times as possible and then recycle them if you can.
How are biodegradable plastics made?
By using granules of corn starch in the plastic, micro-organisms eat the corn starch and break the bits of plastic more quickly.
What are light sensitive plasters?
A smart material. Peel the top layer off and light reduces the stickiness which prevents irritation to the skin.
What are shape memory polymers?
A smart material. Polymers react to stimulus to become elactic and then return to its original shape. Cheaper than shape memory alloys.
What is a hydrogel?
A smart material. It can change its structure in response to salt concentration, pH and temperature. They absorb water which makes them good for contact lenses, nappies and wound dressings.
What is Crushing?
A way to extract a plant oil; a seed it squashed to release oil.
How does distillation extract plant oils?
Refines the oil and removes water, solvents and impurities due to different boiling points.
What can vegetable oils be used for?
In food: provide a lot of energy + other nutrients
Contain essential fatty acids
higher boiling point than water, faster cooking
Vegetable oils can also be used as a fuel.