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A-Level Chemistry > Organic Unit 3 All > Flashcards

Organic Unit 3 All Flashcards

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1
Q

define empirical formula

A

the formula that shows the simplest whole number ratio of atoms of each element in a compound

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2
Q

define molecular formula

A

the formula that shows the actual number of atoms of each element in a compound

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3
Q

define general formula

A

members of the same homologous series have the same general formula

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4
Q

define structural formula

A

the formula that shows the arrangement of atoms within a molecule

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5
Q

define displayed formula

A

the formula that shows all bonds b/w atoms of each element in a molecule

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6
Q

define skeletal formula

A

the formula that does not show c-h bonds
each vertex represents a carbon atom bonded to the max # of hydrogen atoms

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7
Q

what are the characteristics of a homologous series?

A

same functional group
same general formula
similar chemical properties
trend in physical properties
differ by ch2

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8
Q

what are the iupac nomenclature rules?

A

name is based around the longest carbon chain which contains the functional group
functional group is indicated by prefix or suffix
position of functional group is given by a # - from the end that gives the lowest #
where there are 2 or more of the same groups, di-, tri-, tetra- etc. are used
if there is more than one functional group, the groups are in alphabetical order & #s are separated by commas
#s only included if needed

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9
Q

what are the prefixes/suffixes for as functional groups?

A

alkanes: -ane
alkenes: -ene
alcohols: -ol, hydroxy-
haloalkanes: fluoro-, chloro-, bromo-, iodo-
aldehydes: -al
ketones: -one, oxo-
carboxylic acids: -oic acid
nitriles: -nitrile
amines: -amine, amino-
ethers: alkoxy-, -ether

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10
Q

what are the functional groups of:
alkenes
alcohols
haloalkanes
aldehydes
ketones
carboxylic acids
nitriles
amines
ethers?

A

see table in organic nomenclature booklet

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11
Q

what are reaction mechanisms?

A

explains the steps of the reactions of organic compounds

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12
Q

what is the formation of a covalent bond shown by?

A

a curly arrow that starts from a lone electron pair or from another covalent bond

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13
Q

what is the breaking of a covalent bond shown by?

A

a curly arrow starting from the bond

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14
Q

what are isomers?

A

molecules with the same molecular formula, but different arrangement of atoms

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15
Q

what are structural isomers?

A

molecules with same molecular formula, but different structural arrangement of atoms (structural, displayed or skeletal formula)
includes chain, position & functional group isomers (can overlap)

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16
Q

what are chain isomers?

A

molecules with same molecular formula, but different carbon chain branches

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17
Q

what are position isomers?

A

molecules with same molecular formula, but the functional group is on a different carbon atom

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18
Q

what are functional group isomers?

A

molecules with same molecular formula, but different functional group

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19
Q

what are the pairs of homologous series that can be functional group isomers?

A
  1. alcohol & ether
  2. aldehyde & ketone
  3. alkenes & cycloalkanes
  4. carboxylic acids & esters
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20
Q

what are alkanes?

A

homologous series of saturated hydrocarbons with the general formula CnH2n+2
very unreactive

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21
Q

what is the trend in boiling points in alkanes?

A

the longer the carbon chain, the higher the boiling point
bc more e-s so stronger vdw b/w molecules (only have vdw)

for alkanes that are isomers, the more branched the carbon chain, the lower the boiling point
bc molecules cannot pack as closely together so weaker vdw b/w molecules

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22
Q

what is petroleum?

A

mixture containing mainly alkanes that can be separated by fractional distillation

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23
Q

what is crude oil?

A

mixture of hydrocarbons, mainly alkanes

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24
Q

how is crude oil formed?

A

slow decay of marine animals and plants over millions of years, under heat & pressure & anaerobic conditions

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25
Q

describe the process of fractional distillation of crude oil

A
  1. crude oil is vaporised & passed into a fractionating tower
  2. that is hotter at the bottom
  3. hydrocarbons condense at different heights according to their different boiling points
  4. as the vapour rises, it cools
  5. shorter/smaller hydrocarbons have lower boiling points so condense nearer the top
    the fractions contain hydrocarbons with similar boiling points
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26
Q

what is the order of heights of fractions & their uses?

A

refinery gases - domestic gas
gasoline - car fuel
kerosene - jet fuel
diesel - fuel for cars, lorries etc. w diesel engines
fuel oil - fuel for ships
bitumen - tarmac for roads

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27
Q

what does cracking involve?

A

breaking c-c bonds in alkanes

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28
Q

why is cracking useful?

A

cracking breaks up long chain, less useful alkanes, of which there are an excess for the demand, into more useful shorter alkanes (fuels) & alkenes (to make polymers), of which there are not enough to satisfy the demand

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29
Q

what are the products of & conditions for thermal cracking?

A

products: alkenes
high temp: 900C
high pressure: 70atm
no catalyst

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30
Q

what are the products of & conditions for catalytic cracking?

A

products: motor fuels (branched alkanes, cyclic alkanes, aromatics)
high temp: 450C
slight pressure: 1-2atm
catalyst: zeolite

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31
Q

alkanes are used as fuels

A
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32
Q

what is formed in complete combustion of alkanes & why is it harmful?

A

plentiful supply of O2
hydrocarbon + O2 —> CO2 + H2O
CO2 is a greenhouse gas that contributes to global warming

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33
Q

what is formed in incomplete combustion of alkanes?

A

insufficient supply of O2
hydrocarbon + O2 —> CO + H2O
hydrocarbon + O2 —> C (soot) + H2O

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34
Q

what pollutants does the internal combustion engine (incomplete combustion) produce & why are they harmful?

A

NOx - nitrogen reacts with oxygen in air because of the high temperatures in car engines
e.g. NO2 - toxic, asthma attacks, forms HNO3 which reacts with water & oxygen to form acid rain
CO - toxic, binds to haemoglobin in blood which reduces the body’s carrying capacity for O2
C - toxic, respiratory irritant
unburnt hydrocarbons - wastes fuel

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35
Q

what does combustion of substances containing sulfur impurities lead to?

A

SO2 - forms acid rain & causes air pollution

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36
Q

how are gaseous pollutants from internal combustion engines removed?

A

catalytic converters
flue gas desulfurisation

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37
Q

how do catalytic converters work?

A

function: to reduce the emission of CO & NO by allowing them to react together to make harmless products & remove unburnt hydrocarbons
structure of machine: ceramic coated with platinum, palladium or rhodium
honeycomb structure with large surface area for increased rate of reaction

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38
Q

what are the equations of the reactions that happen inside a catalytic converter (with state symbols)?

A

2CO(g) + 2NO (g) —> 2CO2 (g) + N2(g)
C8H18(g)(petrol) + 25NO(g) —> 8CO2(g) + 12 1/2N2(g) + 9H2O(g)

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39
Q

how does flue gas desulfurisation work?

A

when in combustion reaction:
SO2 + H2O —> H2SO3 (calcium sulphite)
H2SO3 + 1/2O2 —> H2SO4

desulfurisation uses calcium oxide or calcium carbonate to form calcium sulfate (CaSO4)
dry: CaO(s) + SO2(g) –> CaSO3(g)
CaCO3(g) + SO2(g) –> CaSO3(g) + CO2(g)

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40
Q

how do gases affect global warming?

A

in troposphere, several gases absorb infrared radiation & re-radiates it in all directions, which increases the temperature inside the atmosphere

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41
Q

what are the steps in the free-radical substitution mechanism?

A

alkanes react with halogens in the presence of uv light to form halogenoalkanes (haloalkanes)
1. initiation - 1 reaction
2. propagation - 2 reactions
3. termination - 3 reactions (only use 2)
see notes

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42
Q

what happens in initiation?

A

halogen breaks down (in the presence of uv) to form 2 free-radicals

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43
Q

what happens in propagation?

A

a hydrogen is replaced by a halogen atom & .Cl radical is reformed by:
1. free-radical reacts to form a alkyl free-radical
2. free-radical reforms
free-radical is acting as a catalyst

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44
Q

what happens in termination?

A

2 free-radicals combine, forming a covalent bond & a stable compound, which ends the chain reaction

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45
Q

what is further substitution & when does it occur?

A

more than one H atom is replaced by a halogen atom

if halogen is in excess
presence of uv

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46
Q

what are the equations for further substitution?

A

see sheet

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47
Q

why does nucleophilic substitution happen?

A

the C-halogen bond is polar/has a dipole

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48
Q

define nucleophile

A

species that donates a lone pair of e-s

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49
Q

what are the conditions for nucleophilic substitution?

A

warm, aqueous

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50
Q

with what nucleophiles do haloalkanes undergo nucleophilic substitution?

A

OH-, CN-, NH3

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51
Q

draw mechanisms for nucleophilic substitution

A

see notes

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52
Q

how does the C-halogen bond enthalpy affect the rate of reaction?

A

C-F highest bond energy
least reactive
as bond enthalpy increases, rate of reaction decreases
shared pair of e-s in covalent bond is closer to & more strongly attracted to the halogen nucleus so the bond requires more energy to be broken

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53
Q

what haloalkanes can nucleophilic substitution happen in?

A

only primary & secondary

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54
Q

draw mechanisms for elimination with OH-

A

see notes

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55
Q

what are the conditions for elimination?

A

hot, ethanolic, high concentration of hydroxide

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56
Q

what happens during elimination?

A

nucleophile acts as a base & accepts a proton, removing a hydrogen atom from the molecule

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57
Q

what haloalkanes can elimination happen in?

A

only secondary & tertiary

58
Q

what are the roles of OH- in elimination?

A

nucleophile - donates a lone pair of e-s
base - accepts a proton

59
Q

what is ozone & why is it beneficial?

A

O3 that naturally forms in the atmosphere
absorbs uv radiation

60
Q

how are chlorine atoms formed in the atmosphere?

A

when uv radiation causes C-Cl bonds in CFCs (chlorofluorocarbons) to break, forming chlorine free radicals

61
Q

what do chlorine atoms do in the atmosphere?

A

catalyse the decomposition of ozone & contribute to the hole in the ozone layer

62
Q

what did results of research by different groups in the scientific community provide?

A

evidence for legislation to ban the use of CFCs as solvents & refrigerants
chemists have now developed alternative chlorine-free compounds.

63
Q

what are the equations for the formation of ozone?

A

see notes

64
Q

what are the equations (initiation & propagation) for the depletion of ozone?

A

see notes

65
Q

what is the solution to the depletion of ozone?

A

use hydrogen fluorocarbons instead
CFCs unreactive
HFCs more reactive so might not reach the stratosphere
C-F bond too strong for UV to break

66
Q

why is a hole in the ozone layer forming?

A

the decomposition of ozone is faster than ozone formation

67
Q

what are alkenes?

A

unsaturated hydrocarbons
contain at least 1 c=c double bond

68
Q

describe the c=c

A

electron dense

69
Q

define stereoisomer

A

substances with the same molecular formula & structural formula but different 3d arrangement of atoms in space

70
Q

what is the difference b/w e & z isomers?

A

e: highest priority groups on different sides
z: highest priority groups are on the same side

the higher the atomic # of the group, the higher its priority

71
Q

why does stereoisomerism occur?

A

no free rotation around the planar c=c double bond

72
Q

how do alkenes react?

A

addition reactions

73
Q

what type of reaction is alkenes + HBr, H2SO4 & Br2?

A

electrophilic addition

74
Q

define electrophile

A

species attracted to the double bond
e- pair acceptors
+ve ions or polar species

75
Q

how is bromine used to test for unsaturation?

A

add bromine water to alkene
shake
bromine is added across the c=c to form colourless dibromoalkane
by electrophilic addition

76
Q

what are the major & minor products in addition reactions (of unsymmetrical alkanes)?

A

higher % of major product formed than minor product

77
Q

why are there major & minor products?

A

carbocations with 3 structure are more stable than 2 structure, which is more stable than 1 structure

78
Q

outline the mechanism for electrophilic addition of HBr

A

see notes

79
Q

outline the mechanism for electrophilic addition of H2SO4

A

see notes

80
Q

outline the mechanism for electrophilic addition of Br2

A

see notes

81
Q

define polymer

A

long chain molecules formed by monomers joining together

82
Q

define monomer

A

small, individual molecules that are repeated/joined together to form a polymer

83
Q

define addition polymers

A

formed from alkenes & substituted alkenes
c=c double bonds open up & join together

84
Q

what are the intermolecular forces of polyalkenes?

A

polyalkenes are often non-polar so VDW only
the longer the polymer & the closer the polymer chains, the stronger the VDW
polyalkenes made up of long, straight chains are strong & rigid vs short, branched chains are weaker & flexible

85
Q

describe the reactivity of addition polymers & why

A

unreactive
saturated
no c=c double bond

86
Q

knowledge & understanding of the production & properties of polymers has developed over time

A
87
Q

what is PVC & its uses?

A

poly(chloroethene)
rigid PVC: drainpipes, window frames
plasticised PVC: cable insulation, clothing

88
Q

what are plasticisers?

A

small molecules, often esters, that are added to polymers to change their properties
they get in b/w chains of polymers & let chains slide over each other so the polymer becomes more flexible
they stop covalent bonds or intermolecular forces forming b/w chains

89
Q

what is the repeating unit of a polymer

A

opened bond
brackets
2 Cs across

90
Q

what is the structure of a polymer

A

opened bond
brackets
2Cs across
n

91
Q

why are addition polymers unreactive?

A

main C chain is non-polar bc only contains c-c single bonds

92
Q

why is there an attraction b/w c=c & Br2?

A

c=c is electron dense
Br2 is polar/has an induced dipole
attraction b/w c=c & delta + Br atom

93
Q

water is added to the hydrogen sulfate to reform H2SO4, leaving an alcohol

A

H2SO4 is a catalyst

94
Q

what are the 2 methods for producing alcohols?

A

hydration of alkenes (reacting with steam) using an acid catalyst = hydrolysis
ethanol produced by fermentation of glucose

95
Q

what are the conditions needed for direct hydration of ethene?

A

350C
60-70atm
conc. phosphoric acid catalyst

96
Q

what is the raw material for direct hydration of ethene & what is its source?

A

raw materials: ethene
source: thermal cracking larger alkanes from petroleum

97
Q

is direct hydration of ethene renewable?

A

non-renewable
finite resources based on crude oil

98
Q

what type of process is direct hydration of ethene?

A

continuous
products removed constantly
stream of reactants passed continuously over catalyst
= more efficient

99
Q

what is the cost, purity & rate of direct hydration of ethene?

A

more expensive
pure/high % yield - nearly 100% ethanol
faster (minutes)

100
Q

what are the conditions needed for fermentation of glucose?

A

35C
zymase (yeast) catalyst
anaerobic - absence of O2
(1 atm - not on ms)

101
Q

what are the raw materials for fermentation & what are their sources?

A

raw materials: glucose, zymase
source: glucose from sugar cane/plant material, zymase from yeast

102
Q

is fermentation of glucose renewable?

A

renewable
ethanol used as a biofuel
plant material can be regrown

103
Q

what type of process is fermentation of glucose?

A

batch
reactants allowed to react for a fixed time
then process is repeated

104
Q

what is the cost, purity (how separated)& rate of fermentation of glucose?

A

cheaper
impure/low % yield - majority is H2O - ethanol separated by fractional distillation
slower (days)

105
Q

what are the advantages & disadvantages of batch vs continuous processes?

A

batch:
cost-effective, better quality control
but higher setup cost, slower, higher energy input

continuous:
faster, lower energy input
inflexible, expensive resources (machinery)

106
Q

define biofuel

A

fuel derived from living matter

107
Q

what are the equations for fermentation of glucose & direct hydration of ethene?

A

see notes

108
Q

define carbon neutral

A

an activity which has no net CO2 emissions to the atmosphere
(same amount of CO2 released into atmosphere as taken in)

109
Q

what are the equations that show fermentation of glucose is carbon neutral?

A

see notes
photosynthesis makes glucose & uses up CO2
fermentation & combustion of ethanol releases CO2

110
Q

why is fermentation not actually carbon neutral?

A

other processes involved in the production of ethanol by fermentation that release CO2:
fuel for machinery (to heat to 35C) & transport

111
Q

what is the mechanism for the formation of ethanol from ethene & steam with presence of acid catalyst?

A

see notes
be able to do for any alcohol from the alkene

112
Q

what are primary alcohols oxidised to & by what oxidation agent?

A

aldehydes (obtained by distillation), which are further oxidised to carboxylic acids (obtained by reflux)

oxidising agent is acidified potassium dichromate orange –> green

113
Q

when is water produced in oxidation of alcohols?

A

alcohol –> aldehyde
NOT aldehyde –> carboxylic acid

114
Q

what are secondary alcohols oxidised to?

A

ketones

oxidising agent is potassium dichromate orange –> green
distillation (or reflux)

115
Q

what are tertiary alcohols oxidised to?

A

not easily oxidised

116
Q

describe the oxidation of ethanol

A

primary alcohol

ethanol is oxidised to ethanal, which is further oxidised to ethanoic acid
oxidising agent is acidified potassium dichromate - colour change orange –> green

IMFs: ethanol - hydrogen bonds
ethanal - dipole-dipole (so lowest bp)
ethanoic acid: hydrogen bonds

ethanol –> ethanal = distillation
ethanol –> ethanoic acid = reflux

117
Q

what are the equations for the oxidation of ethanol?

A

see notes

118
Q

describe the process of reflux

A

vertical condenser
heat reactants –> vapour
vapour continually condenses in condenser

119
Q

what is the chemical test for aldehydes?

A

add Fehling’s solution
heat in hot water bath
blue solution –> red precipitate

Tollen’s reagent forms a silver mirror
add silver nitrate
add dilute sodium hydroxide - light brown precipitate forms
add dilute ammonia solution until brown precipitate just dissolved

120
Q

what is the chemical test for carboxylic acids?

A

add small amount of Mg
produces gentle bubbles of H2 - slow rate bc weak acid

121
Q

what is the chemical test for alkenes?

A

add bromine water & shake
orange –> colourless
tests for presence of c=c double bond
forms dibromoalkane

122
Q

how are alkenes formed from alcohols?

A

elimination reactions
dehydration
acid catalyst - conc. sulfuric or phosphoric acid

123
Q

what can alkenes formed by this process be used for?

A

making addition polymers without using monomers derived from crude oil

124
Q

what is the mechanism for the dehydration of alcohols?

A

see notes

125
Q

what is the test-tube test for alkenes?

A

add bromine water
shake
positive result: solution turns from orange to colourless

126
Q

what are the test-tube tests for aldehydes?

A

Tollen’s reagent:
add to solution being tested & warm gently
positive result: colourless solution –> silver mirror

Fehling’s reagent:
add Fehling’s solution to solution being tested
heat in hot water bath
positive result: blue solution turns to brick red ppt

127
Q

what is the test-tube test for alcohols?

A

add acidified potassium dichromate
positive result: for 1 & 2 alcohols, solution will turn from orange to green
3 alcohols remain orange

128
Q

what is the test-tube test for carboxylic acids?

A

either add a small amount of Mg
positive result: bubbles of H2
or
add sodium carbonate
positive result: bubbles of CO2 - bubble through limewater & solution turns from colourless to white cloudy

129
Q

what is mass spectrometry used for?

A

% abundance of isotopes
high resolution can determine the molecular formula of a compound

130
Q

how does high resolution ms work?

A

elements contain different isotopes with different masses so Ar will not be a whole number

131
Q

what is the first species formed in ms?

A

molecular ion - has a +ve charge & a radical

132
Q

on the spectra graph, what shows the Mr?

A

peak with greatest m/z value

133
Q

what is the % abundance of each Cl & Br isotope?

A

35Cl = 75%
37Cl = 25%

79Br = 50%
81Br = 50%

134
Q

practise identifying compounds by high res. ms

A

see notes booklet

135
Q

how does infrared spectroscopy work?

A

bonds in a molecule absorb ir radiation at characteristic wave numbers
all bonds vibrate at a characteristic frequency

136
Q

what does ‘fingerprinting’ do?

A

allow identification of a molecule by comparison of spectra
fingerprint region is below 1500
computerised comparison

137
Q

what are the labels for the spectra axes for ir spectroscopy?

A

x = wave number
y = transmittance

138
Q

functional group signals

A

above 1500

139
Q

what are the shapes & positions of characteristic peaks?

A

see notes sheet

140
Q

compound with a bigger bp…

A

means more interference of C-H bond

A-Level Chemistry (12 decks)

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