Topic 7 - Organic chemistry Flashcards
What is crude oil in as much detail as possible?
- – Crude oil is a fossil fuel found in rocks formed from the remains of ancient biomass (plants and animals). It is a finite resource.
- – Crude oil is a mixture of lots of different hydrocarbons, most of which are alkanes.
What is the general formula for the homologous series of alkanes? Also, what are the first four members of the series?
General formula:
C(n) H(2n+2)
First four members:
- – Methane (CH4)
- – Ethane (C2H6)
- – Propane (C3H8)
- – Butane (C4H10)
NOTE: alkanes have all C-C single bonds
How does fractional distillation work in terms of evaporation and condensation?
- – Oil is heated until most of it turns to a gas which then enters a fractionating column.
- – There is a temperature gradient in the column which is hot at the bottom and cool towards the top
- – The longer hydrocarbons have higher boiling points and therefore condense into a liquid and drains out the fractionating column early on
- – The shorter hydrocarbons have lower boiling points therefore they evaporate more and condense back into a liquid towards the top of the column where it is much cooler
- – The result is that the crude oil mixture is separated into different fractions each with a similar number of carbon atoms and therefore similar boiling points.
What are the names and uses of the different fuels in a fractionating column from the bottom upwards?
- – Bitumen: roads
- – Heavy fuel oil
- – Diesel: lorries
- – Kerosene: aircrafts
- – Petrol: cars
- – LPG (Liquefied petroleum gas)
How do the properties of hydrocarbon change as the chain gets longer?
As the hydrocarbon chain gets longer:
- – Boiling point increases
- – It gets less runny so more viscous (gloopy)
- – It gets less flammable
What is the word equation for the complete combustion of a hydrocarbon in oxygen?
Hydrocarbon + oxygen —> carbon dioxide + water (+energy)
What is cracking and why is it used? What are the products of cracking?
Cracking:
- – The process of splitting up long-chain hydrocarbons into smaller more useful molecules.
- – It is used as short-chain hydrocarbons make good fuels due to the fact they are flammable. They are also high in demand.
- – The products of cracking are alkanes and alkenes.
What are the two methods of cracking? Explain them in detail.
Catalytic cracking:
- – Heat long-chain hydrocarbons to vaporise them
- – Pass the vapour over a hot powdered aluminium oxide catalyst
- – The long-chain molecules split apart on the surface of the catalyst
Steam cracking:
- – Vaporise the hydrocarbon
- – Mix vapour with steam
- – Heat to a very high temperature
How does modern life depend on the uses of hydrocarbons?
- – Oil provides fuel for most transport
- – Petrochemical industry uses hydrocarbons as feedstock to make new compounds for use in things like polymers, solvents, lubricants and detergents
Why are alkanes saturated and alkenes unsaturated?
In an alkane, each carbon atom forms four single covalent bonds whereas alkenes have a double carbon bond so they have two fewer hydrogen atoms and are unsaturated.
What is the general formula for alkenes? What are the first four alkenes and their formulas?
General formula: C(n)H(2n)
First four:
- – Ethene: C2H4
- – Propene: C3H6
- – Butene: C4H8
- – Pentene: C5H10
Alkenes undergo incomplete combustion as they require a huge amount of oxygen to combust completely. They burn in air with smoky yellow flames due to this incomplete combustion. What is the word equation of incomplete combustion with alkenes?
Alkene + oxygen —> carbon + carbon monoxide + carbon dioxide + water (+energy)
How do you test for alkenes?
Add bromine water to the solution. If the colour changes from orange to colourless then an alkene is present however if it stays bright orange then an alkane is present.
What is the functional group for an alkene? What reactions do alkenes undergo and what happens to the double carbon bond when it reacts?
Functional group: C=C
Alkenes undergo addition reactions. The C=C bond opens up to form a single carbon bond.
Describe the reaction and conditions for the addition of hydrogen, water and halogens to alkenes.
Addition of hydrogen:
- – Double bond opens up to form a single bond
- – Becomes a saturated alkane
- – Reacts in the presence of a catalyst
- – Known as hydrogenation
Addition of water/steam:
- – Steam is added to the alkene then it is passed over a catalyst
- – Forms an alcohol
Addition of halogen:
- – Halogen such as bromine, chlorine or iodine is added to an alkene
- – Forms saturated compund called di…
- – e.g. bromine + ethene = dibromoethane
