hydrocarbons - organic chemistry Flashcards
(27 cards)
what is a hydrocarbon?
A hydrocarbon is a compound that is made out of only hydrogen atoms and carbon atoms.
what is crude oil
crude oil is a mixture of hydrocarbons
whats a functional group
A functional group is defined as a particular group of atoms which are responsible for how the molecule reacts
what is an alkane
The alkanes are a homologous series of hydrocarbons. A compound that contains hydrogen and carbon only.. This means that they have similar chemical properties to each other and they have trends in physical properties. For example, as the chain length increases, their boiling point increases.
whats a homologous series
Homologous series are families or groups of organic compounds that have similar features and chemical properties due to them having the same functional group.
what is an alkene?
Alkenes are a homologous series of hydrocarbons that contain a carbon-carbon double bond
how do you name alkanes
number of carbons:
1- meth
2 - eth
3 - prop
4 - but
5 - pent
6 - hex
number the carbons to give the branch the smallest number possible
the branch is named by taking the code (from above) and adding -yl.
example:
2 - methyl propane
how do you name alkenes
5 - methyl - 2 - hexene
5-methyl:
methyl - branch length
5 - location of branch
2-hexene:
hexene - longest chain length
2 - location of double bond
double bond takes priority when minimising number (eg. 5-methyl-2-hexene instead of 2-methyl-5-hexene)
what is the general formula for alkanes
C(n)H(2n+2)
what is the general formula for alkenes
C(n)H(2n)
what does it mean if a hydrocarbon is saturated?
hydrocarbons with only single bonds
what is isomerism
Isomerism is the phenomenon in which more than one compounds have the same chemical formula but different chemical structures.
how can bromine be used to distinguish between an alkane and an alkene?
bromine water will go colourless when mixed with an alkene
what is the difference with melting and boiling points between a pure substance and a mixture
a pure substance has a fixed melting and boiling point
a mixture may melt or boil over a range of temperatures
what is the industrial process used to separate crude oil into fractions and how?
it is called fractional distillation
During the fractional distillation of crude oil:
heated crude oil enters a tall
fractionating column
, which is hot at the bottom and gets cooler towards the top
vapours
from the oil rise through the column
vapours
condense
when they become cool enough
liquids are led out of the column at different heights
Small hydrocarbon molecules have weak
intermolecular forces
, so they have low boiling points. They do not condense, but leave the column as gases. Long hydrocarbon molecules have stronger intermolecular forces, so they have high boiling points.
what are the names and uses of the main fractions obtained from crude oil?
refinery gases - bottled gas (30 degrees, black/dark brown)
gasoline - fuel for car engines (100-150 degrees, transparent yellowish)
kerosene - fuel for aircraft and stoves (200-300 degrees, pale, yellow or colourless)
diesel - fuel for road vehicles and trains (200-300 degrees)
fuel oil - fuel for ships, heating and power stations (350-450 degrees, dark brown)
bitumen - road surface and roofing (above 500, black)
gets darker as boiling point increases. viscosity increases as well.
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what is a fuel
a substance that, when burned, releases energy
what is complete and incomplete combustion
In complete combustion, there is a sufficient supply of oxygen which is able to react with the burning hydrocarbon allowing the reaction products H2O and CO2 to be formed. In incomplete combustion there is a lack of oxygen so when heat is applied carbon monoxide is released.
possible products of incomplete:
- carbon monoxide
- carbon particles
- water
possible products of complete:
- water vapour
- carbon dioxide
why is carbon monoxide poisonous?
Carbon monoxide is a poisonous gas which binds to haemoglobin. in your red blood cells, preventing them from carrying oxygen to the cells in your body.
what happens in car engines to nitrogen and oxygen?
nitrogen and oxygen in the air react, forming oxides of nitrogen due to the high temperature reached
what can happen in the combustion of some impurities in hydrocarbon fuels
the formation of sulfur dioxide of nitrogen oxide. these contribute to acid rain
what is cracking
long-chain alkanes are converted to alkenes and shorter-chain alkanes by catalytic cracking (using silica or alumina as the catalyst and a temperature in the range of 600-700 degrees)
why is cracking necessary
helps deal with the balance between supple and demand for different fractions
what happens when alkenes react with bromine
they produce dibromoalkanes. For example, ethene reacts with bromine to produce dibromoethane. The double bond between the two carbon atoms breaks and the bond between the bromine atoms in the bromine molecule breaks.
