organic chemistry Flashcards
what is crude oil?
Crude oil a fossil fuel formed mostly from dead sea creatures (eg. plankton). It is the source of many fuels and other chemicals such as plastic.
what is crude oil a mixture of
hydrocarbons
what are hydrocarbons?
compounds made up of only hydrogen and carbon atoms
what are alkanes made up of?
a chain of hydrocarbons
fill in a table for the first 4 alkanes. include the number of carbons in the chain, displayed formula, the molecular formula and the name.
google it
what’s the general formula for alkanes?
CnH2n+2
take the number of C atoms, x2 and +2 to get H atoms
how do the properties of alkanes change?
the properties of alkanes change with the number of carbons in the molecule
what happens as the number of C atoms increases in an alkane
- boiling point increases
- viscosity increases
- flammability decreases
- amount of soot/ smoke released when burned increases
why does fractional distillation take place?
crude oil is not useful as a mixture of hydrocarbons. it needs to be seperated into different fractions of alkanes and different chain lengths.
describe the method of fractional distillation in 6 steps.
- the crude oil is heated to 350°c
- most of the alkanes evaporate
- the different alkane vapours rise up the distillation column (the longest chains flow down the bottom)
- the column gets colder further up
5.when the alkane/ fraction cools down below its boiling point, it condenses back into a liquid and flows through a pipe - the smallest alkanes (eg methane) stay as gases and leave the column at the very top.
what happens when alkanes are burned in a plentiful supply of oxygen?
the carbon oxidises into carbon dioxide and the hydrogen oxidises into water. this is called complete combustion.
what does the complete combustion of an alkane produce?
carbon dioxide + water
what happens when alkanes are burned without enough oxygen?
incomplete combustion takes place and carbon monoxide or soot is made.
long alkanes can be split into a _______ _____________ reaction called cracking
thermal decomposition
long alkanes, which are in ____ demand but _____ supply, are cracked to make shorter alkanes, which are ____ in demand but _____ supply.
long alkanes, which are low in demand but high supply are cracked to make shorter alkanes which are high in demand but low in supply
catalytic cracking
high temperature & the long alkane vapours passed over a catalyst.
steam cracking
long alkane mixed with very high temp & high pressure steam
what are the 2 products of cracking an alkane?
1 alkane and 1 alkene
draw the cracking of C9H20
makes C6H14 and C3H6
alkanes are [saturated / unsaturated]
alkenes are [saturated / unsaturated]
alkanes are saturated, alkenes are unsaturated
what can the smaller alkanes be used for after cracking?
better fuels. eg. gasoline, kerosene jet fuel, diesel heating oil
draw a table of alkenes 2-5 including the number of C atoms, displayed formula, molecular formula and the name.
google it