Organic Chemistry Flashcards
What is Crude oil?
A non renewable source made up of a mixture of hydrocarbons
What is a hydrocarbon?
A molecule made up only of hydrogen and carbon
What is a fraction?
A type of hydrocarbon with a specific range of boiling points
What is a homologous group?
A group of chemicals with similar characteristics and a trend seen. They have the same general formula.
How does fractional distillation work?
The crude oil is put in a very hot furnace, where it vaporises. It is then transferred to the column, with a temperature gradient, where vapour rises up column and the fractions separate. When a fraction reaches its boiling point it reliquifies, so it can be collected for use.
What trends do you see as the molecule size increases?
- boiling point increases, a larger molecule w greater intermolecular forces ∴ more energy needed to break them
- viscosity increases; liquids w large molecules stickier as inter molecular attractions greater
- Volatility decreases- evaporates slower at room temp as bigger molecules more attracted to each other
- Flammability decreases- greater inter molecular forces, so won’t combust as easily
What can we make from crude oil(in order of increasing boiling point)?
- refinery gases
- petrol
- naphtha
- kerosine
- diesel
- fuel oil
- lubricating oil
- bitumen
What are alkanes?
- what crude oil is mainly made of
- homologous series
- general formula CnH2n+2
- saturated(all single bonds)
What is an isomer?
When the molecular formula is the same, but it is arranged in a different way, so the structure is different
Name the first four alkanes
Methane Ethane Propane Butane Pentane
Describe the reaction of methane with bromine.
What is the chemical equation?
In the presence of UV light, methane reacts with bromine to form bromomethane and hydrogen bromide.
CH4 + Br2 => CH3Br + HBr
What are alkenes?
- unsaturated(has a double bond)
* general formula is C2nH2n
What is the test for alkenes?
When added to bromine water it turns from orange to colourless.
Why do we need cracking?
Fractional distillation makes many more long-chain hydrocarbons than can be used, and fewer short-chain hydrocarbons than we need, so we use cracking.
What does cracking produce?
It produces a shorter alkane, and an alkene, from a long chain alkane
What type of reaction is cracking?
Thermal decomposition- breaking down molecules by heating them
What is the process of cracking?
- Long chain hydrocarbon is heated to vaporise it
- Vapour is passed over a catalyst(alumina) at 600-700°C
- The long chain molecules are split apart
What is the equation for complete combustion?
Alkane + oxygen => carbon dioxide + water (+energy)
Why is complete combustion good?
- releases lots of energy
- only produces two, harmless waste products
- clean, blue flame
What is the equation for incomplete combustion?
Alkane + oxygen => carbon + carbon monoxide + CO2 + H2O (+ energy)
Why is incomplete combustion bad?
- less energy is produced
- smoky yellow flame
- carbon monoxide is v toxic, as decreases body’s ability to transport oxygen
- carbon produces sooty marks
How do you avoid incomplete combustion?
Make sure there is a good supply of oxygen when burning fuel
How do car engines contribute to acid rain?
- the temps can be high enough to allow nitrogen and oxygen from the air to react and form nitrous oxides
- this leads to acid rain, as well as SO2
What is a polymer?
Long chain molecules made from lots of smaller molecules joined together
What is a monomer?
Small molecules that join together to make polymers
What is polymerisation?
Formation of long chain molecules from lots of smaller molecules joined together
What is addition polymerisation?
- made of one type of monomer that repeats itself
- must be made of alkenes, as the double C=C bond changes to a single bond
- long chains of hydrocarbons are formed
What are the properties and uses of polyethene?
- low density, flexible; plastic bags
* high density, strong and rigid; plastic bottles
What are the properties and uses of Poly Propene?
Stronger than polyethene. Used for ropes and crates
What are the uses and properties of polychloroethene?
- strong and rigid- window frames, drain pipes
* electrical insulator- electrical insulation
What is condensation polymerisation?
- two different monomer
* form small molecule, normally water, when joined together
What are alcohols?
- homologous series
- -OH functional group
- C2 H2n+1 OH
- can make isomers
Why are polymers bad for the environment?
- they aren’t broken down by bacteria
- they only got smaller, not simpler
- when incinerated, it must be very efficient otherwise it produces toxic substances e.g. Hydrogen cyandide
How does fermentation work?
- zymase left with starch or sugar for several days in warm conditions
- starch/sugar turns into fructose and glucose
- these then turn into ethanol and carbon dioxide
- this is not pure, but can be further purified by fractional distillation
How does hydration work?
- high temperatures and pressures needed (250-350°C and 65 atm)
- ethene passed over catalyst(phosphoric acid) constantly
- this produces ethanol
How do you make ethanol from crude oil?
- extract the crude oil
- use fractional distillation to get alkanes of similar length
- crack long chain alkanes to make an alkene
- hydrate the alkenes to make alcohol
How do you dehydrate ethanol?
- pass it over a catalyst(hot aluminium oxide)
- this removes the OH group and an extra H
- the ethanol is turned into ethene
