P2 7 Organic chem (crude oil) Flashcards
describe how crude oil forms
- fossil fuel formed over millions of years
- biomass (mainly dead plankton) falls to sea bed, covered in layers of mud
- mud turns into rock and dead organisms decay forming oil
describe the composition of crude oil
- a mixture of many different compounds
- mostly hydrocarbons- most found in crude oil are alkanes
state the formula for alkanes
C(n) H(2n+2)
state the first four alkanes
CH4 methane
C2H6 ethane
C3H8 propane
C4H10 butane
describe the process of fractional distillation of crude oil
- crude oil vaporised (heated) so most alkane molecules turn into a gas
- gas put in the bottom of a fractionating column where it is hottest
- (as it is gas) they rise up the column and start to cool, once an alkane reaches its boiling point it condenses into a liquid and is collected
-> crude oil molecules with extremely high boiling points will not vaporise, so are collected at the bottom of the column as a thick/sticky liquid
-> long-chain hydrocarbons have higher boiling points so condense quicker+ will be collected near the bottom of the column
describe the temperature gradient of a fractionating column
gets cooler as you move up the column
(oil begins as a gas and condenses as a liquid)
describe the fractions produced from crude oil by fractional distillation (from long to short chain hydrocarbons / bottom to top of column)
- bicumin (unvaporised molecules remain as liquid, thick/sticky mixture) - tar for roads/roofs
- fuel/diesel oil - ships, power stations, cars
- kerosene - aircraft fuel
- petrol - cars
- refinery/petroleum gas (doesn’t condense) - liquified for fuel or burned for domestic heating/cooking (methane/ethane..)
define volatility+ volatile
volatility- how easily a liquid vaporises
volatile- a chemical that vaporises easily (so also easily flammable)
describe the boiling point of short vs long chain hydrocarbons
short - low as they are volatile (collected at top of column)
long - high (collected at bottom of column)
describe the flammability of short vs long chain hydrocarbons
short - high (as they are volatile)
long - low
define viscosity and viscous
viscosity - how easily a liquid flows (how thick it is)
viscous - a chemical that doesn’t flow easily, gloopy/thick
describe the viscosity of short vs long chain hydrocarbons
short - low, runny
long - high (viscous), thick
state the equation for the complete combustion of hydrocarbons
CnH2n+2 + O2 -> CO2 + H2O
hydrocarbon + oxygen -> carbon dioxide + water
describe the main use of hydrocarbons
- used for fuels
- shorter-chain hydrocarbon molecules are best as they are more flammable so require less energy
- hydrocarbons are oxidised during combustion -> produces carbon dioxide + water + ENERGY released
state the equation for the incomplete combustion of hydrocarbons
hydrocarbon + oxygen -> carbon monoxide OR carbon (soot) + water
describe why cracking is used on hydrocarbons
- long-chain hydrocarbons are broken down into smaller-chain molecules
-> smaller molecules are more useful for fuels as they are more flammable - also produces alkenes which are used to make polymers (plastic)
state the equation for cracking
long-chain alkane -> shorter-chain alkane + alkene
are alkenes more/less reactive than alkanes
(also hydrocarbons)
more reactive than alkanes as they contain a double carbon bond (C=C)
-> used to make polymers (plastics)
describe the test for alkenes
bromine water changes from orange-brown to colourless for a positive result
-> alkanes don’t react with bromine water
describe catalytic cracking (4)
- used to crack long-chain alkanes
- produces moderate-chain alkanes used for fuels
- requires a lower temperature
- uses a catalyst (silica, SiO2) in powder form, increases SA to speed up the breakdown
describe steam cracking (3)
- used to crack moderate-chain alkanes
- produces short-chain alkanes used for petrochemicals
- requires a higher temperature
- also produces alkenes used for polymers (plastics)
