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Aqa a level chemistry > Topic 9: Alkanes and haloalkanes > Flashcards

Topic 9: Alkanes and haloalkanes Flashcards

1
Q

what are organic compounds classified into

A

families or series

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2
Q

functional group of alkanes, alkenes and alcohol

A

alkanes = c-c
alkenes = c=c
alcohol = OH

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3
Q

define functional group

A

Functional group –> a group of atoms responsible for the chemical properties of a compound

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4
Q

Types of hydrocarbons

A

-compound containing hydrogen and carbon atoms only

-Hydrocarbons can be described as straight chained, branched, or cyclical

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5
Q

prefix of alkanes and alkenes depends on the number of carbon atoms

A

Meth = 1

Eth = 2

Prop = 3

But = 4

Pent = 5

Hex = 6

Hept = 7

Oct = 8

Non = 9

Dec = 10

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6
Q

why does ethene have different properties to ethanol despite their similar structures

A

different functional group
same homologus series

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7
Q

justify why the following molecules are all part of the same homologous series

A

different atoms (chain length) but same functional group

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8
Q

forms of representing different compounds

A

molecular
empirical
general
displayed
structural
skeletal

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9
Q

calculating alkanes

A

CnH2n+2

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10
Q

calculating alkenes

A

CnH2n

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11
Q

general formula for cycloalkanes

A

The formula for cycloalkanes is the same as the general formula for alkenes (CnH2n)

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12
Q

functional groups

A

-Two compounds would have different functional groups because different atoms are attached to the carbon chain

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13
Q

homogolous series

A

A homologous series is a group of molecules with the same functional group (chemical properties/atoms) but different number of CH2 groups.

-methanol, ethanol and 1-propanol have different properties because they are part of a homologous series (same functional group) but different chain lengths

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14
Q

what do functional groups affect

A

properties of a compound and its reactions

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15
Q

alkene

A

c=c e.g propene

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16
Q

haloalkane

A

c-x (halogen)

chloroethane

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17
Q

amine

A

H2N e.g ethylamine

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18
Q

nitrile

A

c triple bond n

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19
Q

alcohol

A

OH e.g ethanol

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20
Q

aldehyde

A

H-C=O e.g ethanal

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21
Q

carboxylic acid

A

COOH e.g ethanoic acid

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22
Q

ketone

A

C=O e.g propanone

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23
Q

ether

A

C-C-O

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24
Q

molecular formula

A

e.g heptane = C7H16

Ethanol = C2H6O

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25
Q

empirical formula

A

-propene = C3H6 = C2H3

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26
Q

displayed formula

A

-shows the arrangement of atoms in a molecule as well as ALL the bonds –> different structures but same molecular formula

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27
Q

structural formula

A

-Shows how atoms are arranged in a molecule and which functional groups are present

e.g ethanol (alcohol)

Molecular = C2H6O

Structural = CH3CH2OH

e.g 2-chloropropane (alkane)

Molecular = CH7Cl

Structural = CH3CHClCH3

Methanoic acid = HCOOH

Ethanoic acid = CH3COOH

CHO = aldehyde

COOH = carboxylic acid

Methanoic acid = HCOOH

Ethanoic acid = CH3COOH

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28
Q

skeletal formula

A

-Represents large complex molecules and also different functional groups

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29
Q

how are c bonds represented

A

lines

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30
Q

what dont you show for skeletal

A

For skeletal formula you don’t show C-H bonds but can still show hydrogen

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31
Q

root vs prefix

A

Root = length of carbon chain

Prefix = branching and functional group

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32
Q

suffix of functional groups

A

alkene ene

haloalkane Ane

alcohol -O

aldehyde al

ketone One

Carboxylic acid Oic acid

amine amine

nitrile nitride

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33
Q

naming alkanes

A

1) Look for longest unbranched chain of carbon atoms then name it

2) identify the alkyl group attached to longest unbranched chain

3) Number carbon atoms in the main chain to identify side groups

4) Name compound using longest unbranched chain (no in name must take lowest no.

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34
Q

alkyl groups

A

Akyl groups are alkane molecules minus one hydrogen atom

Methyl – CH3

Ethyl – C2H5

Propyl = C3H7

2 CH3 = 2 methyl groups

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35
Q

what is given the highest priority

A

The functional group with the highest priority will be the one which gives its suffix to name the molecule

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36
Q

IUPAC

A

Highest priority:

-Carboxylic acid

-ester

-acid chloride

-amide

-nitrile

-aldehyde

-ketone

-alcohol

-thiol

-amine

-alkene

-alkyne

-alkane

-ether

-alkyl halide

-nitro

Lowest priorty

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37
Q

state 3 characteristics of a homologous series

A

-same/own general formula
-same functional group
-similar chemical properties

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38
Q

Butane and 2-methylpropane are isomers –> suggest which type and why

A

chain isomers
-same molecular formula but different chains of carbon atoms which are arranged differently
-different spatial arrangement

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39
Q

define an isomer

A

isomers are molecules with the same molecular formula but the arrangement of atoms are different

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40
Q

steps to drawing isomers

A

1) Draw straight chain alkane

2) Usually other isomer is a branched version

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41
Q

what are the two main categories of isomerism

A

structural isomerism and stereoisomerism

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42
Q

structural isomerism

A

Structural isomers have different structural formula but same molecular

The three types of structural isomerism are chain, positional and functional group isomerism

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43
Q

stereoisomerism

A

Stereoisomers have the same structural formula but the 3D arrangement of atoms is different.

The two types of stereoisomers are geometric and optical isomerism

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44
Q

chain isomer

A

different chains of carbon atoms

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45
Q

position isomer

A

different positions of the same functional group

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46
Q

functional group isomer

A

have different functional groups

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47
Q

what is CH2O the empirical formula of

A

methyl methanoate

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48
Q

explain why the melting point of dodecane is higher than the melting point of straight chain alkane produced by cracking dodecane

A

-dodecane = longer
-more and stronger van der waals

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49
Q

state the meaning of a fraction

A

a group of hydrocarbons that have similar boiling points

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50
Q

state the property which allows fractions to be separatedd

A

different boiling points

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51
Q

outline the essential features of the fractional distillation of crude oil that enable crude oil to be separated into fractions

A

-temperature gradient
-cooler at top, warmer and bottom
-fractions have diff boiling points
-bp depends on chain length

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52
Q

Name a lab technique that could be used to separate isooctane from a mixture of octane and isooctane

A

-fractional distillation

-isooctane and octane have diff boiling points
-isooctane is branched so condenses higher up the fractionating column

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53
Q

iso

A

branched

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54
Q

complete the equation to show the cracking of one molecule of hexadecane to form hexane and cyclopentane only

A

C16H34 –> C6H14 + 2C5H10

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55
Q

2g mol less =

A

2 less hydrogens or 2 less of mr

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56
Q

write an equation for the cracking of hexane to form hexene and one other product

A

C6H14 –> C6H12 + H2

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57
Q

role of fractional distillation and thermal cracking

A

FD –> separate compounds with similar boiling points
Cracking –> make shorter alkenes

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58
Q

two conditions of thermal cracking

A

high temp and high pressure

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59
Q

catalyst used in cracking

A

zeolite

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60
Q

explain why oil companies need to crack suitable heavy fractions

A

-shorter fractions are more in demand but are in lower supply

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61
Q

saturated vs unsaturated

A

-Alkanes are saturated whilst alkenes are unsaturated

Saturated = single carbon bonds only (c-c)

Unsaturated = double carbon bonds (c=c)

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62
Q

boiling point of alkanes

A

-As chain length increases, boiling and melting point increases because number of contact points increases so more/stronger van der waal forces which require larger amounts of energy to overcome

-Straight chains have higher boiling point than branched chains due to more points of contact in straight chains

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63
Q

alkanes and cycloalkanes

A

Both alkanes and cycloalkanes are saturated hydrocarbons

General formula for alkanes = CnH2n+2

General formula for cycloalkanes = CnH2n

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64
Q

fractional distillation of crude oil

A

-crude oil is one of the most important naturally occuring raw materials coming from plankton and ancient biomass

-crude oil is a complex mix of hydrocarbons (alkanes)

-crude oil must undergo fractional distillation but also 2 more processes to meet the demand called cracking and reforming

-hydrocarbons with diff boiling points are separated using fractional distillation

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65
Q

purpose of fractional distillation

A

separate crude oil into fractions based on their boiling points

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66
Q

describing fractional distillation

A

-fractional distillation relies on the fact that hydrocarbons have different boiling points

-there is a temperature gradient in the fractionating column where it is cooler at the top

-the higher the boiling point the lower down the column

-heavier molecules form and condense at the bottom

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67
Q

issues with fractional distillation

A

-fractional distillation produces a larger supply of the heavier fraction than needed but a lower supply of the fractions most in demand

-there is a larger supply of longer chains but a greater demand of shorter chains

-cracking can be used to solve this problem

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68
Q

define cracking

A

Cracking –> converting heavier fractions into more useful smaller ones by breaking down the longer chains

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69
Q

process of cracking in a lab

A

1) alkane is heated

2) when it is heated it evaporates forming a gas

3) the gas then passes over the hot porcelain chips (solid aluminium oxide) which causes it to crack

4) large alkane then forms smaller alkanes and alkenes

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70
Q

catalyst in cracking

A

A catalyst can be used during cracking –> Zeolite or Aluminium oxide

A catalyst speeds up rate of reaction by lowering activation energy and provides surface area for reaction to occur

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71
Q

thermal cracking

A

-alkenes only

-high temperature

-high pressure

-no catalyst

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72
Q

catalytic cracking

A

-high temperature

-low pressure

-zeolite catalyst used

-motor fuels, aromatic hydrocarbons, cyclic alkanes, branched alkanes

-cheaper

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73
Q

complete combustion of alkanes

A

-the complete combustion of fuels containing alkanes provided energy to heat homes and to power vehicles

Combustion –> reaction when a fuel with oxygen releases heat energy

Complete combustion –> hydrocarbon + oxygen –> water + carbon dioxide

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74
Q

incomplete combustion

A

-occurs when oxygen is insufficient

-either CO and H2O produced or C and H2O

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75
Q

explain why incomplete combustion can occur

A

limited supply of oxygen

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76
Q

suggest a reason why oil companies reform alkanes such as heptane

A

has more efficient combustion

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77
Q

what is a fuel

A

substance that produced energy or heat

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78
Q

why do calculations of global warming exclude the effect of water vapour in the atmosphere

A

water vapour is much less potent greenhouse gas than carbon dioxide

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79
Q

explain how greenhouse gases cause global warming

A

greenhouse gases absorb and re-emit radiation from the earth

80
Q

Describe how SO2 and NO2 come to present in the atmosphere and explain how they can damage a limestone building

A

-SO2 and NO2 is formed when fossil fuels are burnt
-they react with water to form sulfuric acid which reacts with limestone
-limestone and sulfuric acid takes part in neutralisation

81
Q

show the reaction between ethanethiol and hydrogen gas

A

C2H5SH + H2 –> C2H5 (useful) + H2S (removed)

82
Q

global warming

A

-The main problem with the complete combustion of alkanes is global warming. This is due to increasing concentrations of CO2 in the atmosphere which is a greenhouse gas.

-Greenhouse gases trap the heat radiation from the earth. This results in rising sea levels and melting ice caps

83
Q

impurities in fuel

A

Impurities in the fuel:

-sulfur compounds are the main impurities in crude oil

-These need to be removed before the petroleum products are used as fuels

84
Q

primary and secondary problems of sulfur compounds

A

-If sulfur compounds were not removed then sulfur dioxide emissions would be produced.

Sulfur dioxide results in the formation of acid rain

A secondary problem of alkane combustion is the production of the pollutants –> Nitrogen oxides, Sulfur oxides and unburnt hydrocarbons

85
Q

sulfur dioxide

A

-sulfur is found as an impurity in crude oil and other fossil fuels. It burns in oxygen to form sulfur dioxide

S(s) + O2 (g) –> SO2 (s)

86
Q

sulfur trioxide

A

-Sulfur dioxide may be oxidized to form sulfur trioxide:

2SO2 (g) + O2 (g) –> 2SO3 (g)

87
Q

formation of acidic solutions

A

-Both Sulfur dioxide and trioxide dissolve in water to form acidic solutions

SO2 (g) + H2O (l) –> H2SO2 (aq)

SO3 (g) + H2O (l) –> H2SO4 (aq)

88
Q

nitrogen oxides

A

-The temperature in an internal combustion engine can reach over 2000 degrees, here nitrogen and oxygen combine at high temps to form nitrogen monoxide:

N2 (s) + O2 (g) –> 2NO (g)

89
Q

formation of nitrogen dioxide

A

Nitrogen monoxide reacts further forming nitrogen dioxide:

2NO (g) + O2 (s) –> 2NO2 (g) + CO2 (g)

90
Q

formation of nitric acid

A

Nitrogen dioxide gas reacts with rain water and more oxygen to form nitric acid which contributes to acid rain:

4NO2 (g) + 2H2O (l) + O2 (g) –> 4HNO3 (aq)

91
Q

removal of impurities in fuels

A

-sulfur impurities can be removed from the crude oil by mixing it with hydrogen and passing it over a hot catalyst

-Any sulfur compounds that are present react with hydrogen to form hydrogen sulfide and a hydrocarbon

Or Removing sulfur from coal before it is burnt is not practical so acidic sulfur oxides are removed from the water gases using a base such as calcium oxide

92
Q

why are radicals extremely reactive

A

radicals have unpaired electrons and therefore react quickly in order to gain a pair of electrons once again

93
Q

explain which part of the earth’s atmosphere will have the highest concentration of radicals

A

-stratosphere will have the highest concentration of radicals
-UV light filtered via ozone layer
-trosophere recieves less UV
-UV required for initiation

94
Q

alkanes can undergo substitution reactions

A
  • Alkanes can undergo substitution reactions

e.g CH4 + Cl2 –> CH3Cl + HCL

Alkane + halogen –> haloalkane + hydrogen halide

95
Q

define substitution reaction

A

reactions in which one atom in a molecule is replaced by another atom or group of atoms

We can recognize substitution reactions as having two reactants and two products. If only one product is formed and no element replaces the other then it is not a substitution reaction

96
Q

substitution into alkanes

A

-alkanes can react with chlorine and bromine. This reaction can happen when they have been heated or if they have been exposed to UV light

e.g CH4 + 2CL2 –> CH2Cl2 + 2HCl (methane –> dichloromethane)

-hydrogen atoms in alkane replaced by halogen atoms

-multiple products can be formed

-For every one H atom that is replaced, one halogen molecule is used and one haloalkane is formed

97
Q

equation - substitution

A

CnH2n+2 + X2 –> CnH2n+1X + HX

98
Q

chloromethane –> dichloromethane

A

CH3Cl + Cl2 –> CH2Cl2 + HCl

99
Q

halogenation of alkanes

A

-the halogenation of alkanes takes place through a radical substitution reaction

-all radical reactions take place involving radicals and three distinct steps

100
Q

radicals

A

Radicals –> atoms, molecules or ions that have an unpaired outer electron. They tend to be extremely reactive

Radicals = element or compound with a dot

101
Q

steps for halogenation of alkanes

A

1) initiation

2) propagation

3) termination

102
Q

UV light + homolytic fission

A

-producing free radicals (initiation) requires UV light or heat

-covalent bonds involve a shared pair of electrons between atoms and therefore the UV light provides energy to break these

-this bond breaks homolytically by homolytic fission in the presence of UV light

103
Q

initiation

A

-formation of radicals is not energetically favourable, it requires a large amount of energy. Radicals cannot form in the dark as the molecules do not have enough energy for the bonds to break when they collide

-2 free radicals produced

Molecule –> radical + radical

104
Q

propagation

A

-Radicals go on to react as they are highly reactive and need to gain paired electrons

Original radical + molecule –> new radical + molecule

-1 free radical produced

-propagation can occur in multiple steps and the reaction would continue until either all Cl2 is used up or all of the CH4 is used up

105
Q

termination

A

-radical based reactions must come to an end and this happens through a process called termination

-termination reactions release large amounts of energy and is exothermic reaction

-0 free radicals produced

Radical + radical –> molecule

106
Q

testing for alkenes

A

bromine water
brown –> colourless

107
Q

cracking

A

Cracking involves breaking C–C bonds in alkanes.

108
Q

rotation

A

double carbon bonds cant usually rotate but single carbon bonds can

109
Q

structural isomers chemical vs physical properties

A

chain = same chemical, different physical (boiling point)

Positional = diff chemical and physical

Functional = similar chemical and physical

110
Q

C=O

A

ketone

111
Q

state the property of SO2 that causes pollution when it enters rivers

Give an equation to show the reaction of SO2 with water

A

-acidic

SO2 + H2O –> H2SO3

112
Q

explain why cyclohexane would not be a suitable solvent to extract the iodine from the aqueous layer

A

-it would react with iodine
-it is unsaturated

113
Q

state the meaning of the term fraction

A

mixture of compounds with similar boiling points

114
Q

give one reason why CO2 absorbs infrared radiation

A

C=O bonds are polar

115
Q

state on evironmental problem that No caues and what is used to remove it

A

-acid rain

-catalytic converter

116
Q

state what is meant by the term carbon neutral

A

no net emissions of CO2

117
Q

state why the rates are different

A

-iodide ions produced more rapidly than bromide ions as C-I is weaker than C-Br

118
Q

explain how your answer suggest that the alchohol is butan-1ol

A

-incomplete combustion os experiment must be less exothermic

119
Q

state why the C-Cl bonds are polar

A

different electronegativies

Cl = more electronegative

120
Q

describe the hydrogen bonding in propan-1-ol

A

-attraction between O lone pair and H+ on another molecule alcohol group

121
Q

formation and breaking of a covalent bond

A

the formation of a covalent bond is shown by a curly arrow that starts from a lone electron pair or from another covalent bond
the breaking of a covalent bond is shown by a curly arrow starting from the bond.

122
Q

E-Z isomerism

A

E–Z isomerism is a form of stereoisomerism and occurs as a result of restricted rotation about the planar carbon–carbon double bond.

123
Q

cracking

A

Cracking involves breaking C–C bonds in alkanes.

124
Q

highest priority

A

takes the suffix (end) and lower priorities take the prefix (beginning)

Carboxylic acids >aldehydes>ketones>alcohols>alkenes>halogenoalkanes

alcohol = hydroxy prefix

125
Q

aldehyde

A

An aldehyde’s name ends in –al
It always has the C=O bond on the first carbon of
the chain so it does not need an extra number. It is
by default number one carbon on the chain

126
Q

homolytic fission

A

each atom gets one electron from the covalent bond

127
Q

alkene isomers

A

Alkenes can exhibit a type of isomerism
called E-Z stereoisomerism

128
Q

why do stereoisomers arise

A

(a) There is restricted rotation around the C=C double bond.
(b) There are two different groups/atoms attached both ends of the
double bond.

129
Q

soot

A

global dimming and respitory problems

130
Q

greenhouse gases

A

Carbon dioxide (CO2
), methane (CH4
) and water vapour (H2O) are all greenhouse gases

131
Q

greenhouse effect

A

UV wavelength radiation passes through the atmosphere to the Earth’s surface and heats up Earth’s surface.
The Earth radiates out infrared long wavelength radiation.
The C=O Bonds in CO2 absorb infrared radiation so the IR radiation does not escape from the atmosphere.
This energy is transferred to other molecules in the atmosphere by collisions so the atmosphere is warmed.

132
Q

why do CO2 levels increased

A

increased burning of fossil fuels

133
Q

HCl

A

always side product when forming products in free radical substitution

134
Q

homolytic fission

A

breaking of a covalent bond where each atom recieves one electron

135
Q

Free radical subsitution of CH3Cl and Cl2

A

1) Cl2 –> Cl + Cl (radical)

2) CH3Cl + Cl (radical) –> CH2Cl (radical) + HCl

3) CH2Cl (radical) + Cl2 –> CH2Cl + Cl2 (radical)

4) CH3Cl (radical)+ Cl2 (radical) –> CH2Cl2 + HCl

136
Q

suggest the formulae of 2 bromine containing organic compounds formed when CH2Br2 reacts with bromine

A

CHBr3

CBr4

137
Q

true or false - use structural formula for free radical subsitution

A

true

138
Q

identify a catalyst used in a catalytic converter

A

platinum

139
Q

write an equation to show how nitrogen monoxide is removed from the exhuast gases as they pass through a catalytic convertor

A

2NO –> N2 + O2

140
Q

give 2 reasons why boilers are designed to ensure complete combustion

A

-prevents release of CO
-more energy efficient

141
Q

suggest how and engineer could demonstrate that the combustion of hexane was incomplete

A

detect CO gases in exhaust particles

142
Q

suggest why the product Z has more commerical value than hexane

A

can be made into polymers

143
Q

outline the essential features of the fractional disillation of crude oil

A

-fractions have different boiling points
-boiling point depends on chain length
-temperature gradient
-larger molecules with higher boiling points at the bottom

144
Q

why are alkanes unreactive

A

-same electronegativity (non-polar)
-strong bonds that require energy to break

145
Q

shapes of alkenes vs alkanes

A

alkenes = tetrahedral
alkanes = trigonal planar

146
Q

write two equations to show how chlorine atoms catalyse the decomposition of ozone

A
  1. Cl (radical) + O3 –> ClO (radical) + O2
  2. ClO (radical) + O3 –> 2O2 + Cl (radical)
147
Q

explain why bromine, a non-polar molecule is able to react with propene

A

electron dense C=C causes induced dipole in Br2

148
Q

electron pair donor vs acceptor

A

donor = nucelophile

acceptor = electrophile

149
Q

state and explain the role of the cyanide ion above

A

nucelophile since it is an electron lone pair donor

150
Q

name two reagents which could react to form ethanol

A

-chloroethane
-aqueous sodium hydroxide

151
Q

state the organic product from a hot concentrated solution of sodium hydroxide in ethanol is added to bromoethane

A

ethene

152
Q

organic product when a warm dilute solution of KOH (aq) is added to 2 chloropentane

A

pentan-2-ol

153
Q

organic product when saturated ethanolic KOH is added to 2-iodobutane

A

but-1-ene and but-2-ene

154
Q

2-bromopentane can undergo elimination to form an alkene. Name the reagents for this reaction

A

hot ethanolic potassium hydroxide

155
Q

what type of reaction is nucleophilic subsitution

A

hydrolysis

156
Q

what type of reaction is electrophillic addition

A

hydrogenation

157
Q

define a haloalkane

A

an alkane where one or more hydrogens are replaced by a hydrogen

158
Q

prefixes of halogens

A

Fluorine – fluoro-

Chlorine – chloro-

Bromine – bromo-

Iodine – iodo-

159
Q

primary, secondary, tertiary haloalkanes

A

The terms primary, secondary and tertiary can be used with haloalkanes to describe the position of the functional group e.g primary haloalkane = halide attached to 1 carbon atom

160
Q

haloalkane synthesis

A

haloalkanes can be formed by alkenes and alkanes

161
Q

free radical subsituion and electrophillic addition

A

1) Free radical substitution (CH4 + Cl2 –> CH3Cl + HCl) or 2)

electrophillic addition (C2H4 + HBr –> C2H5Br)

162
Q

what are the two ways of forming haloalkanes

A

Free radical subsitution = alkanes to haloalkanes

Electrophillic addition = alkenes to haloalkanes

163
Q

chemical reactions of haloalkanes

A

-C-X bond is polarised meaning the carbon is slightly electron deficient and will have a partially positive charge

Nucleophilles will attack regions with a partially positive charge

The carbon-halogen bond in halogenoalkanes is polar bc all halogens are more electronegative than carbon

164
Q

nucelophilles

A

Nucleophiles -> a species with a lone pair of electrons that is attracted to regions of positive charge (NH3, OH, CN)

NH3 = ammonia

OH = hydroxide

CN = cyanide

165
Q

nucelophilic subsitution of haloalkanes

A

-nucleophiles attack the carbon of a carbon-halogen bond because the lone pair on the nucelophille is attracted towards the partial positive charge in the carbon

1) Electrons in C-X bond are repelled as the nucleophile approaches the carbon atom

2) The nucleophile bond breaks to the carbon and the C-X bond breaks. Two electrons move to halogen forming a halide ion

-2 products formed

166
Q

nucelophillic reaction with water

A

-cold water slowly hydrolyses halogenalkanes replacing the halogen atoms with an OH group to form an alcohol

-if NaOH is used as the nucelophille an alcohol will form with the same mechanism as water

167
Q

nucelophillic subsituiton by cyanide ions

A

-cyanide (CN) acts as a nucelophille which increases the length of the carbon chain

-there is a triple bond between the C and N atoms in a cyanide molecule

-lone pair is on the carbon atom

-A nitrile is formed when cyanide is the nucelophile

168
Q

naming a nitrile

A

-when naming a nitrile add 1 carbon e.g if reactants is bromoethane then propanitrile will be formed

169
Q

nucelophillic subsitution by reaction with ammonia

A

-if we warm a haloalkane with a concentrated solution of ammonia in ethanol a new product is formed

-amine is formed e.g ethylamine (C2H5NH2)

-test tube must be sealed so gases don’t escape

1) the ammonia will attack the partially positive C atom on the haloalkane

2) a secondary molecule of ammonia removes additional hydrogen from one product to form ammonium salt

NH4X and RNH2 = products e.g ammonium chloride (NH4Cl) and ethylamine (CH3NH2) from chloroethane and ammonia

170
Q

naming products

A

1) NaOH and 1-chloropropane = propan-1-ol and sodium chloride

2) 1-iodobutane and potassium cyanide = pentanitrile and potassium iodide

3) chloroethane and ammonia = ethylamine and ammonium chloride

4) potassium hydroxide and 2-bromobutane = butan-2-ol and potassium bromide

5) KCN and CH3Cl = potassium chloride and ethanitrile

Aqueous NH3 = heat and pressure

KCN (aq) = nucleophillic substitution

KOH (aq) = nucelophillic substitution

171
Q

other haloalkane reactions

A

-When aqueous potassium hydroxide is reacted with a halogenoalkane an alcohol is formed due to nucelophilic subsitution where OH acts as a nucelophile

-However, when hot ethanolic potassium hydroxide is reacted a different reaction occurs

172
Q

hot ethanolic acid

A

Hot ethanolic acid = haloalkane + OH- –> alkene + water + halide ion

OH- ion acts as a base in this reaction

173
Q

temperature, concentration, solvent

A

Temperature = hotter temperatures favour elimination whereas subsitution is warmer conditions

Concentration = dilute KOH favours substitution whereas elimination favours concentrated KOH

Solvent = Aqueous solutions of KOH in substitution whereas KOH dissolved in ethanol favours elimination

174
Q

role of hydroxide ions in subsitution vs elimination

A

In substituion hydroxide ions act as a nucelophile (electron donor) but in elimination hydroxide ions act as base since they accept a proton

175
Q

Elimination products

A

-occasionally, a mixture of structural isomers may be formed as H can be eliminated from either side of the double bond

-longer chain = greater mixture of products

g double bond can form on 1st or 2nd carbon

Haloalkanes undergo elimination in the presence of concentrated strong base such as KOH or NaOH in ethanol. An alkene is formed along with water and a halide ion

176
Q

what can haloalkanes by hydrolysed into

A

haloalkanes can be hydrolysed in the presence of Oh- to form an alcohol

Haloalkanes react with water to form an alcohol and a hydrogen halide. The water causes the C-X bond to break do reaction is a hydrolysis reaction

-the rate at which hydrolysis occurs is different for different halogenoalkanes

RX + H2O –> ROH + H+ + X-

177
Q

end product of hydrolysis

A

The end product of the hydrolysis reaction forms a hydrogen halide (Cl = white Br = cream I = yellow)

Test for presence of a halide = silver nitrate

-if the precipitate appears quickly, hydrolysis is rapid

-if the precipitate takes a long time to appear, hydrolysis is slow

178
Q

investigating rates of hydrolysis

A

-rate of hydrolysis of different primary haloalkanes can be investigated by warming each haloalkane with ethanol and then adding warm silver nitrate solution

1-iodopropane reacts the fastest

1/time

C-X bond enthalphy decreases down the group, so does bond strength

179
Q

thermal vs catalytic cracking

A

Thermal cracking takes place at high pressure and high temperature and produces a high percentage of alkenes (mechanism not required).

Catalytic cracking takes place at a slight pressure, high temperature and in the presence of a zeolite catalyst and is used mainly to produce motor fuels and aromatic hydrocarbons (mechanism not required).

180
Q

why can sulfur dioxide be removed from flue gases using calcium carbonate or calcium oxide

A

We can remove sulfur dioxide by reacting with calcium oxide or calcium carbonate. This is because sulfur dioxide is acidic and calcium oxide is basic.

181
Q

what bonds do haloalkanes contain

A

polar bonds

182
Q

why is UV light needed

A

provides energy to break the covalent bond in chlorine

183
Q

what does ozone absorb

A

UV radiation

184
Q

CFCs

A

Ozone, formed naturally in the upper atmosphere, is beneficial because it absorbs ultraviolet radiation.

Chlorine atoms are formed in the upper atmosphere when ultraviolet radiation causes C–Cl bonds in chlorofluorocarbons (CFCs) to break.

Chlorine atoms catalyse the decomposition of ozone and contribute to the hole in the ozone layer.

185
Q

equation for ozone decomposition

A

Cl* + O3 → ClO* + O2

and ClO* + O3 → 2O2 + Cl*

186
Q

suggest one reason other than the use of mean bond enthalpies, why a value for the enthalphy of combustion of a liquid alkane is different to the value obtained

A

alkane is not gaseous

187
Q

what statement is correct about the production and use of ethanol as biofuel

A

biofuel ethanol is purified by fractional distillation

188
Q

stereoisomer and structural isomers of C4H8

A

stereo = Z-but-2-ene

chain = but-1-ene and methylpropene

positional = but-2-ene

functional = cyclobutane

189
Q

which statement is not correct about ozone

A

its decomposition is catalysed by chlorine molecules

190
Q

combustion of alkanes

A

burn with a blue flame
combustion tends to be less complete as number of C atoms increases (stronger van der waals) so will be a smoky yellow flame

191
Q

chlorination of alkanes

A

free radical subsitution

192
Q

ozone layer =

A

blocks UV light

Cl. + O3 –> ClO. + O2
ClO- + O3 –> Cl. + 2O2

193
Q

are haloalkanes soluble

A

no insoluble in water
R group is non-polar

C-F = most polar

194
Q

test for HBr

A

ammonia = NH4Br = white fumes

195
Q

making haloalkane

A

C6H14 + Br2 –> C6H13Br + HBr

196
Q

explain with the aid of equations, why a single radical can cause the decomposition of many molecules of ozone

A

radical = Cl ;

Cl; + O3 –> ClO; + O2
ClO; + O3 –> Cl; + 2O2

Cl radical is regenerated causing the decomposition of the ozone

197
Q

nucleophilic subsitution =

A

excess NH3

Aqa a level chemistry (23 decks)

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