OCR AS chemistry unit 2

Pregunta	Respuesta
Functional Group	a group of atoms responsible for the characteristic reactions of a compound
molecular formula - what is the molecular formula for pentane?	actual number of atoms of each element in a molecule- C5H12
structural formula- what is the structural formula for 1,4-dibromobutane?	minimal detail that shows arrangement of atoms in a molecule- BrCH2CH2CH2CH2BR
displayed formula	shows position of atoms and bonds between them
empirical formula- what is the empirical formula of ethane?	simplest whole number ratio- CH3
general formula for alkanes	CnH2n+2
general formula for alkenes	CnH2n
general formula for alcohols	CnH2n+1OH
a homologous series	a series of organic compounds having the same functional group but with each successive member differing by CH2
skeletal formula	shows the skeleton of carbon atoms and functional groups
Structural isomers	compounds with the same molecular formula but different structural formula
stereoisomers	compounds with the same structural formula but a different arrangement in space (restricted rotation around double bond)
E/Z isomerism E isomers Z isomers	occurs due to restricted rotation around double bond when two different groups are attached to each carbon atom. E isomers - groups on different sides. Z isomers groups on same side
cis-trans isomerism	two of the same groups are attached to each carbon atom. cis isomers are on the same side. trans isomers on different sides
chemical yield calculate percentage yield	chemical yield is the maximum amount of a product that can be produced. Percentage Yield= (actual yield/theoretical yield) x 100
atom economy	Mr of the desired product/ Mr of all products x 100
which reactions have an atom ecnomy of 100%?	addition reactions have a atom economy of 100% because there is only one product.
reactions can have a high percentage yield but low atom economy	high percentage yield means that most of the products formed are useful whereas low atom economy means that the desired product has a low proportion of atoms
why do scientists choose to use reactions with high atom economies?	a low atom economy means there is a lot of waste produced so it costs money to separate the desired from waste and costs to dispose of waste safely. high atom economies have less waste and therefore less costs
hydrocarbon	contains only hydrogen and carbon atoms
Are alkanes and cycloalkanes saturated or unsaturated?	saturated-they dont have double bonds
name the first ten alkanes (alkanes end in ane)	1. methane, 2.ethane, 3. propane, 4.butane, 5.pentane, 6. hexane, 7. heptane, 8. octane, 9. nonane, 10. decane
how to name branched alkanes- name CH3 CH2(CH3) CH2 CH3	1. count no. of carbons in longest chain for the stem 2. the branches left out take prefix methyl/ethyl/propyl/butyl etc. 3. which carbon atom is it on 4. if more than one name in alphabetical order and if two of the same then its di-. answer: 2-methyl butane
what is the shape around each carbon atom in alkanes?	tetrahedral- four bonding pairs
explain the trend in boiling point in alkanes. what is the difference in boiling points for straight alkanes and branched alkanes?	the smaller the alkane the lower the b.p due to a smaller van der waals force less energy is required. straight alkanes have a higher b.p than branched because there is a larger surface area so more van der waals are acting .
products of combustion of alkanes	complete combustion co2 and h20 incomplete combustion: CO and h20
why are alkanes burned?	burning alkanes releases energy when the products are formed this is why alkanes are used as fuels because they release more energy when forming bonds than absorb energy when breaking bonds
what are the dangers of incomplete combustion of alkanes?	incomplete combustion produces carbon monoxide which is a poisonous gas. at home we burn alkanes for boilers heaters and stoves and cars, lack of oxygen can lead to the production of carbon monoxide which is a harmful gas.
what is crude oil and what is it used for?	crude oil is a mixture of different hydrocarbons which each provide a use such as fuels e.g petrol, etc.
how are the hydrocarbons in crude oil separated?	fractional distillation separates hydrocarbons according to their boiling points. smaller alkanes are vapourised at the top with a lower b.p and longer chains condense and come back down the column to its boiling point.
what are hydrocarbons used for?	hydrocarbons are used as fuels or processed into petrochemicals (any compound made from crude oil that isnt a fuel)
which alkanes are more useful and how are they obtained?	smaller hydrocarbons are used as fuels like petrol. . the longer chained hydrocarbons are cracked into the useful alkanes by catalytic cracking. this is where heavier fractions are passed over a catalyst at a high temperature to break the fractions
how and why do manufacturers process straight chained hydrocarbons into branched or cyclic isomers?	isomerisation and reforming are the methods used to convert straight hydrocarbons into branched ones.isomerisation heats alkanes with a catalyst to form branched alkanes. this is done because branched and cyclic alkanes have a higher ooctane rating which means they are less likely to auto-ignite so they are burned more efficiently.
what are fossil fuels?	coal, oil and natural gas used to provide energy and raw materials
what effect does burning fossil fuels have on the environment?	burning fossil fuels produces co2 which contributes to global warming and climate change
fossil fuels are non renewable sources of energy. what is the problem with this and why is the development of renewable plant based fuels important?	as they are non renewable they will eventually run out. renewable sources of energy come from plants such as biofuels. these are useful as they will never run out and they dont contribute as much to global warming.
why does the demand for renewable energy have a negative effeect on poorer countries?	richer countries demand more renewable fuels from poorer countries because they have agricultural land that can be used to grow the crops for fuels.however poorer countries will do this to earn money but they use this land for food so not enough food will be grown for them.
what are the different types of covalent bond fission?	heterolytic fission- a bond breaks to form two ions XY>X+ +Y- homolytic fission breaks a bond to form particles that have an unpaired electron (radicals)
in a reaction mechanism what does a curly arrow represent?	a curly arrow represents the movement of an electron pair showing a covalent bond broken/formed
what are substitution reactions used for?	substitution reactions are used for the formation of halogenoalkanes. this is done using ultraviolet radiation to break halogens into free radicals
in a substitution reaction where is homolytic fission used?	homolytic fission is used when the ultraviolet radiation breaks the covalent bond in a halogen into free radicals .
describe the steps of substitution reactions	initiation- an ultraviolet radiation source breaks the bond in a halogen by homolytic fission forming two free radicals. propagation- the free radicals react with other molecules in a chain reaction changing the free radical. termination- when two free radicals react to form a product the reaction is over
what is a limitation of substitution reaction?	a mixture of products are formed at the end which then need to be separated to obtain the desired product and dispose the waste safely.
what are alkenes and cyclealkenes?	unsaturated hydrocarbons
how are the double bonds in alkenes formed?	the double bond is made up of a sigma bond (overlapping s orbitals ) and a pi bind (overlapping of p orbitals above and below)
what is the shape around each double bonded carbon in alkenes?	trigonal planar. due to restricted rotation around the double bond and the 3 regions of negative charge alkenes form this shape.
how does polymerisation occur?	the double bonds in alkenes open up to make long chained polymers
what are the advantages of using polymers?	they are unreactive so they can be used for everyday plastics
how can you dispose of a polymer?	polymers can be buried in landfill, or burned as a fuel or recycled by sorting, cracking and processing into new plastics or sorting and remoulding into new objects
what do chemists do to minimise environmental damage from polymers?	they develop biodegradable polymers so that the toxic waste isnt buried
new methods of developing degradable plastics	photodegradable, more efficient methods for cracking polymers, new ways of making polymers from renewable substances, using higher atom economy etc.
electrophile	electron pair acceptor
addition reactions of alkenes	double bond repels against electrons in x-y bond to create dipoles. double bond then breaks (heterolytic fission) to form bond with positive dipole and x-y bond gives electrons to negative dipole. one carbon is left open as a carbocation which then accepts the negative dipole
addition reactions of alkenes can be used with:	halogens(br test detects double bond), hydrogen halides to form halogenoalkanes, steam in presence of phosphoric acid catalyst to form alcohols, hydrogenation with nickel catalyst.
examples of addition reactions in industry	margarine made by hydrogenating unsaturated vegetable oils
what is the use of alkenes in industry to produce organic compounds?	alkenes like ethene and steam reactions are reversible and the yield is low so unreacted alkenes can be recycled to increase yield.

Siguiente

Descripción

Resumen del Recurso

Similar

	Creado por rooti.shah hace más de 10 años