organic chemistry Flashcards
what resource is crude oil and where is it found
a finite resource found in rocks
what is crude oil
the remains of an ancient biomass consisting mainly of plankton that was buried in mud
what is crude oil a mixture of
a very large number of compounds, mostly hydrocarbons
what are hydrocarbons
molecules made up of hydrogen and carbon atoms only
general formula for homologous series of alkanes
CₙH₂ₙ₊₂
first four alkanes
Mouses Eat Peanut Butter
Methane, Ethane, Propane, Butane
define a homologous series
a series of hydrocarbons with similar properties and that react in a similar way
what compounds are alkanes and why
saturated compounds because they have no double bonds (all of its electrons are being used for bonding)
what type of bonding is in hydrocarbons
covalent, because both atoms are non-metals (hydrogen and carbon)
what can the hydrocarbons in crude oil be separated into
fractions, each of which contains molecules with a similar number of carbon atoms, by fractional distillation
what can the fractions be processed to produce
fuels and feedstock for the petrochemical industry
what oils are produced from crude oil (in order from top to bottom of fractional column)
many of the fuels on which we depend for our modern lifestyle, e.g., liquefied petroleum gases (camping stoves), petrol (cars), kerosene (jet fuel), diesel oil (larger cars and vans) and heavy fuel oil (ships)
what is produced by the petrochemical industry
many useful materials on which modern life depends, such as solvents, lubricants, detergents and polymers
why is there a vast array of natural and synthetic carbon compounds
due to the ability of carbon atoms to form families of similar compounds
why do we separate the different hydrocarbons in crude oil
because they all contain different properties useful for different purposes - crude oil without separation is useless
method for separating crude oil
fractional distillation
1) heat crude oil until becomes vapour and feed it into fractionating column - hot at bottom, cooler at top
2) each fraction of hydrocarbon gases within the vapour condense into liquid at different points along the fractionating column bc they all have different boiling points so will condense at different temps
3) this separates the crude oil into diff fractions, each with similar number of carbon atoms
4) longer chain hydrocarbons have higher boiling points bc larger molecule so condense into liquid at bottom of column, while shorter chain hydrocarbons have lower boiling points so condense at top of column - some won’t condense at all and will remain gas, producing LPG (liquified petroleum gas)
factors affecting properties of hydrocarbons
size of molecules:
- boiling point
- viscosity
- flammability
how does fractional distillation for crude oil work
each fraction of hydrocarbons has diff boiling point so condenses at diff heights of column
how does viscosity affect properties of hydrocarbons
more viscous fluid flows more slowly
- as size of hydrocarbon molec increases, viscosity increases
TO HELP REMEMBER (dont say in exam)
- bigger = more intermolecular forces so stick together and more viscous
how does flammability affect properties of hydrocarbons
tells us how easily hydrocarbon combusts
- as size of hydrocarbon molec increases, flammability decreases, so short chain hydrocarbons v flammable
TO HELP REMEMBER
methane is main component in natural gas used to heat homes - high flammability, short chain hydrocarbon
how does boiling point affect properties of hydrocarbons
temperature when liquid -> gas
- as size of hydrocarbon increases, boiling point increases, so short chain hydrocarbons are gases at room temp
TO HELP REMEMBER
methane is gas so very low boiling point
what does the combustion of hydrocarbon fuels release
energy
what happens during combustion of hydrocarbons
the carbon and hydrogen in the fuels are oxidised, because the hydrogen is combining with oxygen to form water and the carbon is combining with the oxygen to form carbon dioxide
equation for complete combustion of a hydrocarbon
hydrocarbon + oxygen -> carbon dioxide + water
what type of reaction is complete combustion
exothermic as lots of energy is released in the process
what is cracking
hydrocarbons being broken down to produce smaller, more useful molecules
why is cracking important
long-chain hydrocarbons tend to have much lower demand, as they are less flammable than short-chain so less effective as fuels
what is the issue with high demand for short-chain hydrocarbons and how is this resolved
most hydrocarbons found in crude oil are long-chain - so to meet demand and produce more useful molecule, they undergo cracking
two methods used for cracking
- catalytic cracking; high temp and catalyst
- steam cracking; high temp and steam
what is catalytic cracking
we pass the hydrocarbon vapour over a hot catalyst causing the long-chain hydrocarbon to split into two or more shorter hydrocarbons
what is steam cracking
we mix the hydrocarbon vapour with steam and heat it to a very high temperature in order to split it into two or more shorter hydrocarbons
what is the difference between alkanes and alkenes
alkenes have a double bond (C=C) whereas alkanes only have single bonds - this means alkanes are saturated whereas alkenes are unsaturated molecules
why are alkenes more reactive than alkanes
alkenes are unsaturated, meaning this double bond can open up and bond to 2 other atoms, making it more reactive
what are the products of cracking
alkanes and alkenes
what do alkenes react with
bromine water
what is the positive test for alkenes
adding bromine water to a solution - if it turns from orange to colourless, alkenes are present
why does bromine water remain orange in the presence of alkanes
alkanes are saturated so cannot react with bromine
what are alkenes used for
- to produce polymers
- as starting materials for the production of many other chemicals
how can alkenes produce polymers
the double bond means that alkenes can bond together to form polymers bc double bond breaks up to form 2 bonds that allow alkene to bond to adjacement molecules
what are alkenes
hydrocarbons with a double carbon-carbon bond
general formula for homologous series of alkenes
CₙH₂ₙ
why are alkene molecules unsaturated
they contain two fewer hydrogen atoms than the alkane with the same number of carbon atoms
first four members of the homologous series of alkenes
Elephants Pack Butter Pants
ethene, propene, butene and pentene
functional group of alkenes
C=C
what determines the reactions of organic compounds
the generality of reactions of functional groups
how many bonds can a carbon atom have in alkenes
4
why can alkenes undergo addition reactions
because the C=C bond can open up to allow it to bond to 2 more atoms of another molecule, so we can add other molecules to the alkene
describe the reaction of an alkene with hydrogen gas
in the presence of a nickel catalyst and heat, it will form an alkane because the double bond will break apart to bond with the 2 extra hydrogen atoms to form the alkane counterpart which is saturated (no double bond)
e.g. pentene can undergo hydrogenation to form pentane
describe the reaction of an alkene with water (steam)
in the presence of a catalyst and high temps (water vapour) to produce an alcohol, because the double bond breaks apart to react to the H and Oh to form an OH functional group and an extra hydrogen atom
HENCE we need a catalyst, high temperatures and high pressures
properties of an alcohol produced from an alkene reaction
- saturated
- no double bonds
what is the functional group of an alcohol
-OH
how can we industrially produce ethanol
the alkene reaction with steam is reversible, so any unreacted ethene gas is recycled back into the reactor
describe the reaction of alkenes with halogens
similar to hydrogen except no catalyst or temperature or pressure required. most common example is reacting ethene with bromine to form dibromoethane (colourless). as bromine used up, alkene causes colour change from orange to colourless; the two halogen atoms have added across double bond, making it single bond
describe the combustion of alkenes in air
it produces unburnt carbon particles due to incomplete combustion, meaning they burn in air with smoky flames. they produce carbon monoxide and carbon in addition to carbon dioxide and water
when would alkenes completely combust
in the presence of a large amount of oxygen, but with air, some incomplete combustion also takes place
incomplete combustion equation
alkene + oxygen -> carbon dioxide + water + carbon monoxide + carbon
first four members of a homologous series of alcohols
methanol, ethanol, propanol, butanol
why are alcohols not hydrocarbons
bc they contain oxygen
difference between alkanes and alcohols
they look identical except alcohols have an -OH functional group instead of one of the hydrogens
evaluate of hydration of ethene
PROS
- produces a high yield of ethanol
CONS
- requires high temp so lots of energy
- therefore expensive and less cost-effective
- ethene comes from non-renewable crude oil, will run out
how can we produce aqueous solutions of ethanol other than hydration of ethene
when sugar solutions are fermented using yeast
describe fermentation of sugar using yest
at 30º, anaerobic conditions and in the presence of yeast, glucose breaks down to form ethanol and carbon dioxide
evaluate production of ethanol via fermentation
PROS:
- low temp means not a lot of energy needed
- sugar comes from plants so renewable resource
CONS:
- product is an aqueous solution of ethanol, so to extract it, we need to carry out distillation which requires heat energy
fermentation of ethanol equation
sugar —(yeast)—> carbon dioxide + ethanol
properties of alcohol
- very flammable unlike alkenes
- therefore undergo complete combustion when burned in air
- produce carbon dioxide and water in complete combustion reactions
how do you balance combustion equations of alcohols
- start by balancing the carbon atoms
- then the hydrogen atoms
- then the oxygen atoms
what are alcohols soluble in
aqueous solutions and produce pH7 solutions
functional group of carboxylic acids
-COOH
first four members of a homologous series of carboxylic acids
methanoic acid, ethanoic acid, propanoic acid, butanoic acid
what happens when we add an oxidising agent to an alcohol
we produce a carboxylic acid and water
what happens when we react alcohols with sodium (use example of ethanol)
sodium ethoxide and hydrogen gas are produced, so we would observe effervescence
why are carboxylic acids weak in terms of ionisation and pH
they only partially ionise when dissolved in aqueous solutions, meaning not all carboxylic acid molecules will dissociate and produce H+ ions; relatively low conc of H+ ions produced in comparison to a strong acid, hence has a higher pH than a strong acid of the same concentration
what happens when a carboxylic acid reacts with carbonates
acid + carbonate -> salt + water + carbon dioxide
what happens when a carboxylic acid reacts with alcohols
an ester and water are produced
e.g. ethanoic acid + ethanol -> ethyl ethanoate
why are esters really useful molecules
- pleasant smell
- often used in food flavourings and perfumes
- volatile (evaporate easily)
what can alkenes be used to make
polymers by addition polymerisation
how is a polymer formed
by joining lots of small, identical repeating units called monomers
2 types of polymers
- addition polymers
- condensation polymers
in an addition polymer what will the monomer always be and why
an alkene because alkenes have a double bond so can open it up to react with adjacent alkene molecules to form the polymer
why in addition polymers does the repeating unit have the same atoms as the monomer
because no other molecule is formed in the reaction
suffixes for all groups e.g., alcohols, carboxylic acids
ALCOHOLS:
- ol
- diol (CP)
CARBOXYLIC ACIDS
- oic
- dioic (CP)
what does condensation polymerisation involve
monomers with two functional groups (meaning they’re not alkenes like AP)
what happens when the monomers of condensation polymers react
small molecules such as water are usually lost, making them condensation reactions
how are the simplest polymers produced
from two different monomers with two of the same functional groups on each monomer
what is glycine
an example of an amino acid
what do all amino acid molecules have
two different functional groups e.g., glycine has the amino and carboxyl group
how do amino acids produce polypeptides
they react by condensation polymerisation
how are proteins produced
by combining different amino acids in the same chain
how can we tell that a condensation polymer is formed
because a small molecule (usually water) is produced
what happens when you react a lot of glycine molecules in a condensation polymerisation reaction
we form a glycine polypeptide
DNA stands for
deoxyribonucleic acid
what is DNA
an example of a large naturally-occurring polymer essential for life
what does DNA encode
genetic instructions for the development and functioning of living organisms and viruses
structure of DNA molecules
they’re two polymer chains, made from four different nucleotide monomers (ATGC) in the form of a double helix
examples of naturally occurring polymers important for life
- DNA
- protein
- starch
- cellulose
what monomers make up proteins
amino acids
what monomers make up starch and cellulose
glucose
