organic chem Flashcards
what are hydrocarbons
A substance with molecules that contain only carbon and hydrogen atoms.
how many bonds can a carbon atom form
4
why are alkanes saturated
they contain the maximum number of hydrogen atoms for each carbon atom.
how many bonds are between carbon atoms in alkenes
double bond (C=C)
why does methene not exist
bc meth has only 1 carbon bond, methane exists bc alkanes have only 1 carbon bond
name the first 4 alkanes
methane,ethane,propane,butane
why are alkenes unsaturated
they contain less than the maximum number of hydrogens per carbon.
whats the general formula for alkenes
CnH2n
define voltality
the tendency of a substance to turn from liquid to gas (evaporate)
whats the general formula for alkanes
CnH2n+2
viscosity
a liquids resistance to flow
whatre the properties of short chain hydrocarbons
-lower boiling point and viscosity
-higher volatility and flammability
whatre the properties of long chain hydrocarbons
- high boiling point and viscosity
-lower volatility and flammability
whatre the steps in fractional distillation
1- crude oil is heated then vapourised -> goes into bottom of fractional tower
2-short chain hydrocarbons vapourise then cool as thet rise due to a lower boiling point
3- long chain hydrocarbons vapourise and condense at the bottom as they have a higher boiling point
the bottom of tower is hotter than top
4- fractions condense and cool
why do we use fractional distilation
to seperate different fractions of hydrocarbons in crude oil depending on their boiling point, short chains are more useful
which comes first, cracking or fractional distilation
fractional distilation, cracking breaks down larger fractions from the top of fractionating tower into more usefull shorter hydrocarbons
what are the 2 types of cracking
- steam cracking and catalyctic cracking
what gases are released when fuels are burnt
- carbon dioxide
- water vapours
-carbon monoxide (odourless and colourless gas) - sulfer dioxide
-nitrogen oxides (formed at high temp) - solid particles (soot(carbon) and unburnt fuels)
whatre the 3 effects of burning fuels
- acid rain (nitrogen oxide and sulfer dioxide)
- climate change (carbon dioxide)
-global dimming (solid particles)
what happens during the combusion of hydrocarbons
- carbon and hydrogen are oxidised(gains oxygen )
-fuels release energy
hydrocarbons + oxygen ->
carbon dioxide+ water
hydrocarbon + low oxygen supply
carbon monoxide
carbon with no oxygen
carbon particles (soot)
whatre the 2 ways ethanol (a biofuel) can be made
1- reacting ethene with steam (uses phosphoric acid catalyst but ethene is from crude oil which is nonrenewable)
2- fermenting glucose at 20-35 degrees (using enzymes in yeast which is a natural catalyst and renewable resource)
whatre the advantages of using biofuels
- biodiesel spillage is less harmful than spilling crude oil since it burns cleanly and reduces sulfer dioxide emissions
- biofuels will become cheaper
- carbon nutral since co2 in=co2 out
what are the disadvantages of biofuels
-famland used to grow biofuels instead of food will cause famine(starvation) in poorer countries
-habitats destroyed from deforestation which decreases biodiversity
describe the cracking process
- heat then vapourise the hydrocarbon
- vapours are either passed over a hot catalyst or steam with very high pressure
how can alkenes be told apart from alkanes
bromine water turns colourless
which hydrocarbon can make polymers,give an example
- alkenes
- ex poly(ethene)
what happens in polymerisation reactions
many monomers (smaller molecules) join together to form polymers
what do properties of polymers depend on
conditions theyre made under and what theyre made of
what are thermosoftening polymers
polymers that consist of tangled polymer chains with no crosslinks between them
why do thermosoftening polymers melt easily
they have weak intermolecular forces which allows them to be easily remoulded
whatre cross links
strong covalent bonds
what are thermosetting polymers
polymers that consist of polymer chains with cross linkks between them
why do thermosetting polymers not melt easily
they have strong covalent cross link bonds that require loads of energyt o seperate/ break apart
why is it an issue if polymers arent biodegradable (break down by microbes)
theyre desposed but dont break up for years which causes them to be carried by oceans to form garbage patches which marine animals consume
why are plastic bangs made of polymers and cornstarch
so they become biodegradabke and break down easily so less damage is caused to the environment
what functional group do alcohold contain
-OH
whatre the uses and properties of alcohols
- flammable and can undergo complete combustion
-soluble (dissove in water to form neutral solutions)
-burn in air
-used as fuels and solvents
ethanol used in alcoholic drinks
whatre the 2 ways ethanol can be oxidised to form ethanoic acid
-chemical oxidising agents
-microbial actions
whats the main acid in vinegar
ethanoic acid
whats the functional group for carboxylic acids
-COOH
whatre the properties of carboxylic acids
they react with cabonates to form carbon dioxide
dissolve in water to form acidic solutions
react with alcohols in the presence of acid catalyst to form esters
dont ionise completely so theyre weak acids
whats the functional group for esters
coo
how is ethanyl ethanoate formed
by reacting ethanol and ethanoic acid with the presence of an acid catalyst
why are esters used as flavourings and perfumes
cause they have distinctive smells and are voltalite
