organic chemistry Flashcards
Define crude oil
- a finite resource found in rocks.
- the remains of an ancient biomass consisting mainly of plankton that was buried in mud.
What is crude oil a mixture of?
- a mixture of a very large number of compounds.
- chemical properties of each substance in the mixture are unchanged
What is crude oil made up of?
- most of the compounds in crude oil consist of hydrocarbons
- molecules made up of hydrogen and carbon atoms only.
Define homologous series
- A group of organic compounds that react in a similar way
What are the most of the hydrocarbons in crude oil?
- alkanes
What are alkanes?
- saturated hydrocarbons - each carbon atom forms four single covalent bonds
What is the general formula for alkanes?
- CₙH₂ₙ₊₂
What are the first four members of the alkanes?
- methane, ethane, propane and butane
Show how can alkanes be represented
C₂H₆
H H
| |
H—-C—C—-H
| |
H H
How can hydrocarbons in crude oil be separated?
- hydrocarbons in crude oil may be separated into fractions by fractional distillation
- each of which contains molecules with a similar number of carbon atoms
Explain how fractional distillation works
- The oil is heated in the fractionating column and evaporates and condenses at a number of different temperatures.
- In the bottom there is a temp gradient (hot at the bottom, cooler as you go up)
- The longer the hydrocarbons, the higher the b.p so they condense back into liquids and drain out of the column early on.
- Shorter hydrocarbons condense later on
- The fractionating column works continuously
- Heated crude oil is piped in at the bottom.
- The vaporised oil evaporates and rises up the column and the various fractions are constantly tapped off at the different levels where they condense.
- The many hydrocarbons in crude oil can be separated into fractions each of which contains molecules with a similar number of carbon atoms
What can the fractions be processed to produce?
- can be processed to produce fuels and feedstock for the petrochemical industry
What are the uses of crude oil?
- many fuels that we depend on for our modern lifestyle are produced from crude oil
e.g. petrol, diesel oil, kerosene, heavy fuel oil and liquefied petroleum gases
What industry produces useful materials that our modern life depends on?
- the petrochemical industry produces many useful materials that modern life depends on
e.g. solvents, lubricants, polymers, detergents
How does the vast array of natural and synthetic carbon compounds occur?
- due to the ability of carbon atoms to form families of similar compounds
What do the properties of hydrocarbon depend on?
- the size of their molecules, which affects boiling point, viscosity and flammability
- these properties influence how hydrocarbons are used as fuels.
Describe how boiling point changes as the molecular size of hydrocarbons increase
- the shorter the molecules, the lower the temp at which that fraction is vaporised or condensed
- and the lower its boiling point (therefore more volatile)
Describe how viscosity changes as the molecular size of hydrocarbons increase
- the shorter the molecules, the less viscous it is
- the longer the molecules, the more viscous it is
Describe how flammability changes as the molecular size of hydrocarbons increase
- the shorter the molecule, the more flammable it is
Define volatile
- Turns into a gas at a lower temperature
Why are hydrocarbons burnt?
- so that they can be used as fuel since the reaction produces energy
What happens when hydrocarbons are burnt?
- the combustion of hydrocarbon fuels releases energy
- during combustion, the carbon and hydrogen in the fuels are oxidised.
- produces carbon dioxide
and water (complete combustion)
What is the word equation for hydrocarbon, carbon dioxide and water?
hydrocarbon + oxygen –> carbon dioxide + water + energy
How can hydrocarbons produce smaller molecules?
- hydrocarbons can be cracked (broken down) to produce smaller, more useful molecules
What type of reaction is cracking?
- Thermal decomposition (breaking molecules down by heating the,?
What are the two methods of cracking?
- catalytic cracking and steam cracking
What happens during catalytic cracking?
- Heat long-chain to vaporise them
- Vapour passed over a hot powdered aluminium oxide catalyst
- Long-chain molecules split apart on the surface
What happens during steam cracking?
- mixes with steam and heated to a very high temp so that thermal decomposition reactions can occur
What are the products of cracking?
- alkanes and alkenes.
Which is more reactive, alkenes or alkanes?
- alkenes are more reactive than alkanes due to their C=C
- they react with bromine water (used as a test for alkenes)
What happens when bromine water reacts with an alkene?
- react with bromine water, turning it from orange to colourless
Why are the products of cracking useful as fuels?
- because there is a high demand for fuels with small molecules
- products of cracking have shorter chains making them more flammable
What are alkenes used to produce?
- polymers
- as starting materials for the production of many other chemicals.
How to balance cracking equations
- same number of carbons and hydrogens on each side of the equation
- going from a bigger molecule to usually 2 smaller molecules
Why is cracking useful?
- Short-chain hydrocarbons are flammable so make good fuels and are in high demand
- Can also be used to produced alkenes as a starting material when making lots of other compounds and can be used to make polymers
- Useful as fuels
What are alkenes?
*unsaturated hydrocarbons with a double carbon-carbon bond
What is the general formula for alkenes?
- CnH2n
Why are alkene molecules unsaturated?
- because they contain two fewer
hydrogen atoms than the alkane with the same number of carbon
atoms
Why are alkenes more reactive than alkanes?
- The C=C can open up to make a single bond, allowing the two carbon atoms to bond with other atoms