Organic Chemistry Flashcards
What is crude oil made from?
Different length Hydrocarbons
List four alkanes.
Methane, Ethane, Propane, Butane
‘draw’ (imagine) the following alkanes:
a). C2H6 b). C4H10
H H H H H H
H — C —C —H H - C— C — C — C - H
H H H H H H
What is the formula for alkanes?
Cn + H2n +2
Describe how crude oil is made.
From the remains of dead plankton and other animals and plants that fall to the bottom of the sea and get covered in layers of mud and other substances.
What is the combustion equation?
Hydrocarbon + Oxygen —> Carbon
dioxide +
water
What are the uses of crude oil?
Fuel for transport e.g. petrol and diesel.
Used to make other compounds such as polymers, lubricants, solvents, detergents
Describe the process of fractional distillation.
Crude oil is a mixture of hydrocarbons and they are heated to form a gas. They all have different boiling points so separate out at different temperatures. Long chain hydrocarbons have high boiling points, short chain molecules have low boiling points.
How does the length of the hydrocarbon affect the boiling point?
The longer the hydrocarbon the higher the boiling point - more energy is needed to break up the molecules
What is bromine water a test for?
What colour does it go and what is the original colour?
Alkene
Goes from orange to colourless
Describe alkanes.
Alkanes are saturated (no C=C double bond) so they contain as many hydrogen atoms as possible
Describe alkenes.
Alkenes are unsaturated so we could add more hydrogen atoms to them
What are the products of incomplete combustion and what are the problems with these?
1: Carbon monoxide
Problem: Poisonous gas, binds to our haemoglobin instead of oxygen
2: Carbon (soot)
Problem: causes respiratory diseases if breathed in
Describe cracking.
Cracking is a type of thermal decomposition. A long chain alkane is broken into one shorter alkane and one or more alkene.
What is the point of cracking?
Long alkanes aren’t very useful (they don’t burn well and can’t make consumer products from them) so they get turned into more useful compounds:
Short alkanes are better fuels
Alkenes can be used to make plastics
What is cracking?
The breaking down of large chain hydrocarbons into shorter chains.
Draw (imagine) a diagram for an alkene.
H H
C=C
H H
What is the formula for alkenes?
C2H2n
What are the two methods of cracking?
Describe them.
Steam - heated in vapour, mixed with steam, heated at very high temperature
Catalytic - heated into a gas, passed over aluminium oxide catalyst, molecules split
What are hydrocarbons?
Molecules made from only hydrogen and carbon atoms
Describe the properties of a larger hydrocarbon.
- More viscous
- High boiling point
- Less volatile
- Less flammable
In the process of fractional distillation, what does crude oil get separated into?
Different fractions containing hydrocarbon molecules with a similar number of carbon atoms. Most hydrocarbons obtained are alkanes
Describe the process of fractional distillation.
- First the crude oil is heated until it evaporates
- The vapour moves up the fractioning column
- The top of the column is much colder than the bottom
- Shorter hydrocarbon molecules can reach the top of the fractioning column before they condense and are collected
- Lower hydrocarbon molecules condense at higher temperatures and are collected lower down the column
Are alkanes reactive or unreactive?
Unreactive but they burn well
How are shorter chain alkanes different from longer chain alkanes?
Shorter chain alkanes release energy more quickly by burning so there is greater demand for them as fuels
What happens during combustion (burning) of hydrocarbon fuels?
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