C7 - Organic Chemistry Flashcards
What is a hydrocarbon?
- A compound that is formed from carbon and hydrogen atoms only
What are alkanes?
- The simplest type of hydrogencarbons (saturated hydrocarbons)
- A homologous series (a group of organic compounds that react in a similar way)
What is the general formula for alkanes?
C (n) H (2n +2)
What are the first four alkanes?
- Methane
- Ethane
- Propane
- Butane
What happens to the viscosity as the length of a hydrocarbon increases?
- Increases as well (becomes more gloopy)
What happens to the volatility of hydrocarbons as the length increases?
- They become less volatile, and have higher boiling points
What happens to the flammability of a hydrocarbon as the length increases?
- It makes it harder to ignite
What is the complete combustion of hydrocarbons?
hydrogen + oxygen -> carbon dioxide + water
What happens during combustion?
- Both carbon and hydrogen from the hydrocarbons are oxidised
What are hydrocarbons used for?
- Fuels due to the amount of energy they release when they combust completely
What is crude oil and how is it formed?
- Fossil fuel
- It is formed from the remains of plants and animals, mainly plankton, that died millions of years ago and were burried in mud
- Over millions of years, with high temperature and pressure, the remains turn to crude oil, which can be drilled up from the rocks where it’s found
What are non-renewable fuels?
- Coal, oil and gas are called non-renewable fuels as they take so long to make that they’re beings used up much faster than they’re being formed (finite resources) so one day they will run out
What is the process of separating crude oil into it’s different compounds (as crude oil is a mixture)?
Fractional distillation
How does fractional distillation work?
- The oil is heated until most of it has turned into gas (they enter a fractionating column)
- In the column there’s a temperature gradient (it’s hot at the bottom and cooler as you go up)
- The longer hydrocarbons have high boiling points, so they condense back into liquids and drain out of the column early on, when they’re near the bottom. Similarly it’s the opposite but the same concept for the shorter hydrocarbons
What is at the top of the FD chain?
LPG (liquified petroleum gas)
What is the 2nd compound in FD?
Petrol for cars
What is the 3rd compound in FD?
Kerosene fuel for planes
What is the 4th compound in FD?
Diesel for cars
What is the 5th compound in FD?
Heavy fuel oil for heating, fuel or lubricating
Why is crude oil important?
- Provides the fuel for most modern transport
- The petrochemical industry uses some of the hydrocarbons from crude oil as a feedstock to make new compounds for use in things like polymers, solvents, lubricants and detergents
Why are short-chain hydrocarbns in high demand?
- The flammability make good fuels
What is cracking
The process that breaks down long-chain hydrocarbons into shorter-chain molecules that are more useful (thermal decomposition)
Why is cracking useful?
- Long hydrocarbons form thick gloopy substances like tar, so they can be broken down into smaller chains of hydrocarbons
What can cracking produce?
- Alkenes which are a lot more reactive than alkanes
- They are often used as a starting material when making lots of other compounds and can be used to make polymers
What can be used to test for alkenes?
Bromine water
What are the colour tests for Bromine water and alkenes?
- When orange bromine water is added to an alkane, no reaction will happen and it’ll stay bright orange
- If it’s added to an alkene, the bromine reacts with the alkene to make a colourless compound - so that bromine water is decolourised
What is cracking?
Thermal decomposition reaction, where you break down molecules by heating them
What are the steps to cracking?
- Heat long-chain hydrocarbons to vaporise them
- Pour the vapour over a hot powdered aluminium oxide catalyst
- The long-cain molecules split apart on the surface of the specks of catalyst (catalytic catalyst)
- You can also crack hydrocarbons if you vapourise them, mix them with steam and then heat them to a very high temperature (steam cracking)
