Organics 1 - 4th Flashcards
what is crude oil?
- a mixture of hydrocarbons, compounds of hydrogen (H) and carbon (C) only
- the different hydrocarbons in crude oil come in a huge variety of shapes and sizes, which results in crude oil boiling over a very large range of temperatures
why do we need to separate crude oil?
- most of the hydrocarbons are useful, but often for very different purposes
- this means we need to separate the oil into fractions which contain similarly used molecules.
what is each fraction of crude oil?
- a mixture of similar hydrocarbons with similar boiling points
what happens to the fractions of crude oil as the boiling points increase?
- the fractions get darker in colour
- the fractions get more viscous (like treacle)
what happens to the fractions of crude oil as the boiling points increase?
- the fractions get darker in colour
- the fractions get more viscous (like treacle)
what is the boiling point, molecular mass, colour, viscosity and use of refinery gases?
- low BP
- low molecular mass
- light colour
- low viscosity
- used for fuel for home cooking
what is the use of gasoline?
- used for fuel for cars
what is the use of kerosene ?
- used for fuel for aircraft
what is the use of diesel?
- used for fuel for trains
what is the use of fuel oil?
- fuel for ships
what is the boiling point, molecular mass, colour, viscosity and use of bitumen?
- high BP
- high molecular mass
- dark colour
- high viscosity
- used for making roads
how are each of the fractions separated from crude oil?
- by fractional distillation
- done industrially on a large scale
how does fractional distillation work?
- fractionating column is hotter at the bottom and colder at the top
onenote chemistry rev pic
THIS IS HOW IT WORKS: - heated crude oil vapours enter the column
what is the order of each of the fractions from lowest to highest BP/order of fractional distillation?
- refinery gases
- gasoline
- kerosene
- diesel
- fuel oil
- bitumen
what are fractions?
- mixtures containing the hydrocarbons that boil in a particular temperature range
- for example, kerosene contains hydrocarbons that boil between 250 degrees and 350 degrees.
what are alkanes?
- hydrocarbons that fit the general formula C v nH v 2n+2
- (v means subscript)
- made of simple molecules containing C and H atoms held together by covalent bonds
how are alkanes named?
- the start of the name shows how many carbon atoms it has
- the end of the name is ‘-ane’ to show it is an alkane
what is the name and bonding of CH4?
- methane
- *chem rev image
what is the name and bonding of C2H6?
- ethane
- *chem rev image
what is the name and bonding of C3H8?
- propane
- *chem rev image
what is the name and bonding of C4H10?
- butane
- *chem rev image
what is the name and bonding of C5H12?
- pentane
- *chem rev image
what names of alkane bondings come after methane, ethane, propane, butane and pentane?
- names follow the 2d shapes
- hexane, heptane, octane, etc
what are the 4 types of formulae for each alkane?
- displayed formula
- structural formula
- molecular formula
- empirical formula
what does the displayed formula show?
- a diagram showing the position of every atom and every bond
- e.g. chemistry flashcard 21
what does the structural formula show?
- this shows the structure of the molecule in one line, read from left to right like a word
- e.g. CH3CH2CH2CH3
what does the molecular formula show?
- this only shows how many carbon and hydrogen atoms there are
- e.g. C4H10
what does the empirical formula show?
- this only shows the simplest whole-number ratio of carbon to hydrogen
- e.g. C2H5
what are alkanes in terms of homologous series?
- alkanes are a homologous series of organic molecules
what does a homologous series of organic molecules mean?`
- this means they are a family of molecules which have:
- similar chemical reaction
- trends in physical properties (e.g. boiling points, viscosity or colour)
- the same general formula
what are the other series in the IGCSE course ?
- alkanes
- alcohols
- carboxylic acids
- esters
what are isomers?
- isomers are molecules with the same molecular formula but different structural formulae
how many isomers does C4H10 have?
- butane has two isomers
- *chem rev image
how many isomers does C5H12 have?
- pentane has three isomers
- *chem rev image
what makes isomers different?
- the branching in the carbon chain
- you can’t make a different isomer just by bending the molecules
what are most alkanes made of and why?
- most can be used as fuels because they release a lot of energy when combusted
what are the two types of combustion that alkanes can undergo and what is it dependent on?
- depending on how much oxygen is available :
- complete combustion
- incomplete combustion
what is complete combustion?
- this occurs when there is excess oxygen
- it produces only CO2 and H2O
- alkane + oxygen -> carbon dioxide + water
- e.g. the complete combustion of propane
- propane + oxygen -> carbon dioxide + water
- C3H8 + 5O2 -> 3CO2 + 4H2O
what is the equation of complete combustion with alkenes?
- alkane + oxygen -> carbon dioxide + water
what is incomplete combustion?
- this occurs when there isn’t enough oxygen
- instead of CO2 this produces a nasty mixture of:
- carbon monoxide (CO) - a toxic gas which lowers oxygen-carrying capacity of blood
- soot (C) - which causes lung diseases - it also releases less energy so it makes the alkane less useful as fuel
what is the equation of incomplete combustion with alkenes?
- alkene + oxygen -> carbon monoxide + soot
what three significant pollutants does the combustion of alkenes as fuels release into the atmosphere?
- carbon dioxide (CO2)
- nitrogen oxides (NOx)
- sulphur dioxide (SO2)
explain how carbon dioxide is formed as a significant pollutant.
- this forms directly from the combustion of the alkane fuel
- it is a greenhouse gas that traps heat in the atmosphere and causes climate change
explain how nitrogen oxides are formed as a significant pollutant.
- this family of compounds form when nitrogen from the air combusts
- usually nitrogen doesn’t combust but car engines are really, really hot
- they dissolve in rainwater to form acid rain, which corrodes structures and is harmful to plant and aquatic life
explain how sulphur dioxide is formed as a significant pollutant.
- this forms when sulphur impurities in the fuel combust
- like nitrogen oxides, it dissolves in rainwater to form acid rain
how do alkanes react with halogens?
- by swapping one hydrogen atoms for one halogen atom
- for example, when ethane (C2H6) reacts with bromine (Br2)
- C2H6 + Br2 -> C2H5Br + HBr
- *chem rev image
when would the the halogen + alkane reaction work?
- would work with any alkane (e.g. pentane) and any halogen (e.g. chlorine)
- all that happens is a hydrogen swaps with hydrogen
what are the two details you need to know about alkane and halogen reactions?
- it’s a substitution reaction - because the H swaps with Br
- the reaction requires UV light - because the alkane is pretty unreactive
does crude oil contain longer or shorter alkanes?
- contains much longer alkanes than shorter ones
which is more useful - the longer or shorter alkanes?
- the shorter ones
what do we do to get around having more longer alkanes than shorter alkanes?
- the shorter ones are more useful
- to get around this, we take the longer alkanes and do cracking
- cracking breaks down longer alkanes into smaller, more useful ones
under which conditions is cracking conducted?
- temperature: 650 degrees
- catalyst: aluminium oxide(Al2O3)
- it can be conducted without a catalyst but far more energy would need to be provided
what does cracking produce?
- can provide a variety of products, but nearly always it works like this:
- long alkane -> shorter alkane + alkene - for example, it could be pentane -> ethane + propene
- anything is possible as long as it makes an alkene and an alkane and as long as the numbers of C and H add up
what are alkenes?
- they are hydrocarbons that fit the general formula CvnHv2n
- v = subscript
what is the formula, name and bonding of an alkene if n is 2 in the formula?
- formula = C2H4
- name = ethene
- bonding = *chem rev image
what is the formula, name and bonding of an alkene if n is 3 in the formula?
- formula = C3H6
- name = propene
- bonding = *chem rev image
what is the formula, name and bonding of an alkene if n is 4 in the formula?
- formula = C4H8
- name = butene
- bonding = *chem rev image
what is the formula, name and bonding of an alkene if n is 5 in the formula?
- formula = C5H10
- name = pentene
- bonding = *chem rev image
why do the names of alkenes end in ‘-ene’?
- to indicate they have the C=C bond
how is the double bond sometimes shown in a structural formula?
- as ‘=’
- e.g. butene is written:
- CH2 = CHCH2CH3
what are alkenes in terms of homologous series?
- alkenes are a homologous series of organic molecules, like alkanes, but slightly different
- however, they are still a family of molecules which have:
- similar chemical reactions
- trends in physical properties (e.g. boiling points, viscosity or colour)
- the same general formula
what are alkene isomers?
- like alkanes, alkenes also have isomers
- but unlike alkanes, their isomers can differ in more than one way:
- through the branching of the carbon chain (chem rev image)
- because of the position of the C=C in the carbon chain (chem rev image)
how many different isomers does C4H8 have?
- three different isomers
why are alkenes referred to as unsaturated?
- because they have a C=C double bond
why are alkanes referred to as saturated?
- because they don’t have a C=C double bond
how do alkenes release energy?
- like alkanes, they also combust in oxygen to release energy
- same as alkanes - can combust completely and incompletely in the same manner
how do alkenes react with bromine?
- by breaking the C=C and adding the bromine atoms in
- e.g. ethene (C2H4) reacting with bromine (Br2) - *chem rev image
- C2H4 + Br2 -> C2H4Br2
when would the alkene and bromine reaction work?
- with any alkene
- all that happens is the C=C breaks and the Br atoms add in where it was
what are the details you need to know about the alkene and bromine reaction?
- it’s an addition reaction - because you’re adding the bromine atoms into the alkene
- the reaction happens without UV light - because alkenes are more reactive than alkanes
- it works with pure bromine liquid or bromine water (bromine water is orange)
- the mixture turns orange to colourless - because the bromine is used up in the reaction
what is the alkene and bromine reaction used for?
- as a test for the C=C in unsaturated compounds
- *chem rev image
what forms when molecules with a C=C double bond add into chains?
- an addition polymer
- *chem rev image
what are the small molecules which add together to form an addition polymer called?
- monomers
how is an addition polymer usually represented?
- using a repeating unit
- *chem rev image
- the little ‘n’ represents a v.big number
how is the name of an addition polymer formed?
- by putting ‘poly’ in front of the monomer name
- e.g. polymer formed by ethene -> called poly(ethene)
what are the four commonly encountered polymers you should know about?
- poly(ethene)
- poly(propene)
- poly(chloroethene)
- poly(tetrafluoroethene)
what is the monomer, repeating unit and uses of poly(ethene)?
- *chem rev image
- uses: drinks bottles and shopping bags
what is the monomer, repeating unit and uses of poly(propene)?
- *chem rev image
- uses: storage boxes and climbing ropes
what is the monomer, repeating unit and uses of poly(chloroethene)?
- *chem rev image
- uses: wire insulation and drainpipes
what is the monomer, repeating unit and uses of poly(tetrafluoroethene)?
- *chem rev image
- uses: non-stick coating
what does it mean by addition polymers are inert?
- they’re chemically very unreactive
- they don’t break down very easily
what are your only options for disposal of an unwanted addition polymer?
- reuse it, or give it to someone else who will use it
- recycle it, which allows it to be reshaped for another use
- incinerate it, and use the energy released to generate electricity
- chuck it onto landfill, and hope it goes away
