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A Level Chemistry > Organic Chemistry 1 - Alkanes to Alcohols > Flashcards

Organic Chemistry 1 - Alkanes to Alcohols Flashcards

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1
Q

What features do a homologous series share?

A

1) same general formula
2) similar chemical properties
((3) have successive members which differ by CH2))
4) have physical properties which show a steady gradation
5) are made by similar methods

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2
Q

What is a functional group?

A

A group of atoms which gives an organic compound its characteristic properties and reactions (e.g. the double bond in alkenes)

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3
Q

What is a hydrocarbon?

A

A compound made up of hydrogen and carbon only

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4
Q

What is a homologous series?

A

A family of compounds which all contain the same functional group and each member of the family contains one CH2 unit more than the previous member

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5
Q

What is a general formula?

A

A formula that represents all members of a homologous series

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6
Q

What is a saturated compound?

A

A compound in which all covalent bonds are single bonds

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7
Q

What is the IUPAC nomenclature of CH4?

A

Methane

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8
Q

What is the IUPAC nomenclature of C2H6?

A

Ethane

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9
Q

What is the IUPAC nomenclature of C3H8?

A

Propane

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10
Q

What is the IUPAC nomenclature of C4H10?

A

Butane

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11
Q

What is the IUPAC nomenclature of C5H12?

A

Pentane

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12
Q

What is the IUPAC nomenclature of C6H14?

A

Hexane

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13
Q

What is the IUPAC nomenclature of C7H16?

A

Heptane

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14
Q

What is the IUPAC nomenclature of C8H18?

A

Octane

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15
Q

What is the IUPAC nomenclature of C9H20?

A

Nonane

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16
Q

What is the IUPAC nomenclature of C10H22?

A

Decane

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17
Q

What is the IUPAC nomenclature of C11H24?

A

Undecane

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18
Q

What is the IUPAC nomenclature of C12H26?

A

Dodecane

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19
Q

What is an isomer?

A

Compounds with the same molecular formula but different structural formula

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20
Q

What is the molecular formula of a methyl side chain?

A

-CH3

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21
Q

What is the molecular formula of an ethyl side chain?

A

-C2H5

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22
Q

What is the molecular formula of a propyl side chain?

A

-CH2CH2CH3

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23
Q

What is the molecular formula of a butyl side chain?

A

-CH2CH2CH2CH3

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24
Q

What is the molecular formula of a methylethyl side chain?

A

-CH(CH3)2

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25
Q

What is the molecular formula of a dimethylethyl side chain?

A

-C(CH3)3

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26
Q

What is the molecular formula of a 1-methylpropyl side chain?

A

-CH(CH3)CH2CH3

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27
Q

What is the molecular formula of a 2-methylpropyl side chain?

A

-CH2CH(CH3)2

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28
Q

What are the rules for naming branched chain alkanes?

A

1) Find the longest chain
2) Identify side chains
3) List side chains alphabetically
4) If more than 1 side chain of the same type is present, prefix it with di, tri etc. Ignore these when deciding alphabetical order
5) Number the side chains according to where they occur on the longest chain. Number the chain in the way that gives the lower number for the first side chain

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29
Q

Explanation for the boiling point graph of alkanes

A

Clear pattern - as the number of carbon atoms increases, the number of electrons increases so the strength of London forces increases, giving a higher boiling point

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30
Q

Explanation for the melting point graph of alkanes

A

1 curve for even numbers of carbon atoms and 1 curve for odd numbers of carbon atoms. Even numbered chains pack together more efficiently than odd numbered chains , so melting points are higher for even numbered carbon chains

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31
Q

Why do branched alkanes have lower boiling temperatures than their straight chain isomers?

A

There are fewer points of contact in branched chain alkanes between adjacent molecules

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32
Q

Would alkanes dissolve in water?

A

No, immiscible liquids

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33
Q

Would alkanes dissolve in non-polar solvents?

A

Yes, similar structures

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34
Q

How is crude oil separated?

A

Crude oil is a mixture of hydrocarbons, mainly alkanes, and so they have different boiling points, so they can be separated using fractional distillation

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35
Q

What apparatus is used in the separation of crude oil?

A

Distillation flask, fractionating column, Liebig condense, receiver (conical flask which is changed to catch each distillate separately)

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36
Q

How is the industrial process of fractional distillation of crude oil different to the laboratory process?

A

Collection is from various points on the fractionating column, the process is continuous rather than batch, and instead of using glass rods in the fractionating column, bubble caps are used

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37
Q

Order of the fractions from top to bottom

A 
Refinery gases 
Gasoline (Petrol)
Naphtha 
Kerosene
Diesel oil
Fuel oil
Residue
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38
Q

Use for refinery gases (fractional distillation)

A

Bottled camping gas

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39
Q

Use for gasoline (fractional distillation)

A

Fuel for cars

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40
Q

Use for naphtha (fractional distillation)

A

Making chemicals

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41
Q

Use for kerosene (fractional distillation)

A

Aircraft fuel

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42
Q

Use for diesel oil (fractional distillation)

A

Fuel for cars, lorries and buses

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43
Q

Use for fuel oil (fractional distillation)

A

Fuel for ships and power stations

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44
Q

Use for reside (fractional distillation)

A

Bitumen for roads and rooves

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45
Q

What are the reactions of note for alkanes?

A

Halogenation, cracking, combustion

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46
Q

Halogenation of methane (chlorine)

A

In presence of sunlight, a violent reaction takes placeto produce hydrogen chloride gas and various liquid halogenoalkanes are formed

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47
Q

What are the products of the halogenation of of methane?

A

Hydrogen chloride gas (always)
- Chloromethane, CH3Cl (if methane is in excess)
- Dichloromethane, CH2Cl2
- Trichloromethane, CHCl3
- Tetrachloromethane, CCl4 (if chlorine is in excess)
Products can be separated using fractional distillation

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48
Q

What is a free radical?

A

A free radical is a neutral species which possesses an unpaired electron

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49
Q

Initiation step of a mechanism

A

Example of homolysis/homolytic fission where a covalent bond is split so that one electron of the pair goes to one group produced after splitting and one elctron goes to the other

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50
Q

Why is a curly arrow used when drawing mechanisms?

A

To differentiate between the straight arrow used for a dative covalent bond

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51
Q

What is the initiation step of the halogenation of methane with chlorine?

A

Cl-Cl splits under UV light to form 2Cl’

Only step of the reaction which requires sunlight so it is called a photolytic reaction

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52
Q

What happens in the propagation steps and then the termination step of the halogenation of alkanes?

A

Propagation - in each step, a free radical reacts with a neutral molecule to give another free radical and a neutral molecule
Termination - ends the reaction by reacting 2 free radicals to form a neutral molecule

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53
Q

Why is it more likely that the reaction will continue rather than terminate? (Halogenation of alkanes)

A

The concentrations of chlorine radicals and methyl radicals are low in comparison with the concentration of neutral molecules, so the chances of a termination step are much lower than the chances of a propagation step. Many thousands of chlorinated molecules are formed for each chlorine molecule decomposed

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54
Q

How do the other halogens react with alkanes?

A

Bromine reacts with methane in a similar way to chlorine. Fluorine reacts vigorously, often breaking down the carbon skeleton to give carbon and hydrogen fluoride. Iodine does not react

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55
Q

What are the products of alkanes burning in excess oxygen?

A

Carbon dioxide and water

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56
Q

What are the products of alkanes burning in limited oxygen?

A

Carbon monoxide and water, or sometimes just carbon (soot)

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57
Q

What is cracking?

A

When an alkane is heated to a high temperature in the absence of air it breaks down to give and alkene and hydrogen, or an alkene and another alkane.

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58
Q

What are the conditions for thermal cracking?

A

A high temperature (500-600°C) and has a free radical chain mechanism with initiation, propagation and termination steps

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59
Q

What are the conditions for catalytic cracking?

A

A slightly lower temperature (400-500°C) and a catalyst of usually silica/silicon oxide or alumina/aluminium oxide and has an ionic mechanism

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60
Q

What are the advantages of catalytic cracking?

A
  • Saves energy by enabling the reaction to be carried out at a lower temperature
  • It allows the way in which the alkane breaks down to be much more controlled and by changing the catalyst you can change the products, as changing the temperature controls the reaction to a degree, but using catalysts does it much more
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61
Q

Why is cracking a useful process?

A

Alkanes can be used as fuels, but alkenes have much more uses such as making solvents and plastics

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62
Q

What is reforming?

A

The processing of straight chain hydrocarbons into branched chain alkanes and cyclic hydrocarbons for efficient combustion

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63
Q

How is reforming carried out?

A

Passing the alkana over a catalyst. Changing the catalyst can change the product formed. A common catalyst is platinum supported on a base of aluminium oxide

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64
Q

Why is reforming useful?

A

Branched chain hydrocarbons burn more smoothly than straight chain hydrocarbons in petrol engines, so they are in higher demand

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65
Q

What properties are necessary for a useful fuel?

A
  • Be abundant or easily manufactured
  • Ignite easily
  • Have high energy output
  • Be easily stored and transferred
  • Be non-toxic
  • Cause minimal environmental damage
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66
Q

What are the properties of fractions with a low boiling point (ie at the top of the fractionating column)?

A
  • Volatile
  • Flow easily
  • Ignite easily
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67
Q

What are the properties of fractions with a high boiling point (ie at the bottom of the fractionating column)?

A
  • Not very volatile
  • Do not flow easily
  • Do not ignite easily
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68
Q

What is a fossil fuel?

A

A mixture of hydrocarbons laid down over millions of years through the anaerobic decay of animal and vegetable matter - coal, natural gas, crude oil

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69
Q

Facts about methane as a fuel - fossil fuels

A
  • Cannot be liquefied until -83°C
  • Found as a natural gas
  • Burns cleanly with few pollutants and least CO2 per unit than any other fuel except hydrogen
  • Can be piped directly into urban areas
  • Not suitable for vehicle fuel as it would have to be stored in large, high pressure cylinders
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70
Q

Facts about hydrogen as a fuel - derived from fossil fuels

A
  • Manufactured from natural gas by passing it over a heated catalyst, or from electrolysis of water (which requires energy)
  • The ways hydrogen is produced means it is a fuel derived from fossil fuels, as means of generating energy to produce it with wind or wave power are too expensive
  • Cannot be stored easily, so cannot be used in vehicles, and is too explosive to be used as a domestic fuel
  • Where energy per unit mass is critical liquid hydrogen (+liquid oxygen) are very good (e.g. in rockets)
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71
Q

Facts about butane as a fuel - fossil fuels

A
  • Found in natural gas and is produced when oil is cracked
  • As a liquid under pressure it is used as a fuel in motor vehicles (LPG - liquid petroleum gas), but cars have to be specially adapted to use it and specialist equipment has to be used
  • Butane produces less CO2 than petrol and leaves fewer unburnt hydrocarbons so is less polluting
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72
Q

Facts about octane + other liquid hydrocarbons - fossil fuels

A
  • Obtained from crude oil
  • Most convenient fuel; easy to transport and store and are not dangerously volatile
  • High yield of energy per unit volume but produce much more CO2 than fuel like methane
  • CO is produced but can be removed by a catalytic converter, but the high pressure in the converter reduces the efficiency of changing chemical energy of the fuel into KE for the vehicle
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73
Q

What is a biofuel?

A

A biofuel is a fuel made from renewable organic materials such as sugar, grain or vegetable oils

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74
Q

Facts about bioethanol as a fuel - biolfuels

A
  • Made by the fermentation of carbohydrates
    > First starch is broken down (from sugar cane, wheat etc) into glucose by heating with an acid catalyst or enzymes
    > Sucrose is converted into a mixture of glucose and fructose by enzymes in yeast
    > Other enzymes ferment glucose and fructose to produce a dilute solution of ethanol
  • The atom economy of the process is a maximum of 67% and the ethanol has to be obtained from the mixture by fractional distillation - energy demanding
  • Energy output is lower than that of petrol
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75
Q

Facts about biodiesel as a fuel - biolfuel

A
  • A vegetable oil is converted into biodiesel by mixing it with methanol and an acid catalyst, causing a transesterification reaction to take place. The methyl esters have similar combustion properties to diesel from crude oil and can be used purely, or mixed with diesel
  • Many crops can be used as a source of vegetable oil, but the fuel used to produce the crops as well as energy used to process the vegetable oil means biodiesel has a carbon footprint
  • Waste vegetable oil can be used as a source
76
Q

What is the main problem with biofuels?

A

The main problem with growing biofuels is that they use land which could be used to grow food, or they require destruction of natural forests.
This can then push up the prices of food crops, affecting the poorest people in society

77
Q

Why do engines that burn petrol and diesel pollute the air?

A
  • They may not burn fuel completely
  • The fuel may contain impurities
  • They run at high enough temperatures that nitrogen and oxygen in the air can react
78
Q

Why is the release of carbon monoxide from car engines harmful?

A

It is a toxic gas which combines strongly with haemoglobin, meaning the blood cannot absorb oxygen and so CO can be fatal in high doses

79
Q

Why is the release of carbon particles/particulates from car engines harmful?

A

The soot formed includes fine particles and nanoparticles which are able to penetrate deep into the lungs, which causes short term symptoms (like headaches and coughing) and long term problems (liek heart disease and lung cancer), however, modern diesel engines use a diesel particulate filter to capture the carbon particles which are then burned

80
Q

Why is the release of unburned hydrocarbons from car engines harmful?

A

Unburned hydrocarbons may include benzene which is carcinogenic. In engines, careful monitoring of the air to fuel ratio entering the engine is used to minimise the release of unused fuel

81
Q

Impurities in fuel - sulfur

A

Sulfur compounds are the main impurities in crude oil which should be removed before fuels are used in order to reduce sulfur dioxide emissions. Sulfur dioxide can cause acid rain and sulfur can damage the catalyst in catalytic converters

82
Q

What are the equations for the formation of acid rain?

A

S + O2 -> SO2 then SO2 + H2O -> H2SO3
or//
SO2 + 1/2O2 -> SO3 then SO3 + H2O -> H2SO4

83
Q

Impurities in fuel - oxides of nitrogen

A

When patrol vapour is burned, the temperature can rise to 2800°C, giving sufficient activation energy for nitrogen to react with oxygen to form nitrogen oxide (N2 + O2 -> 1/2NO).
The NO then reacts to form nitrogen dioxide (NO + 1/2O2 -> NO2)
The nitrogen dioxide can react with water and more oxygen to form nitric acid, leading to the production of acid rain (disproportionation)

84
Q

Why are nitrogen dioxide molecules in the air a problem?

A

In bright sunlight, NO2 molecules break down into NO and oxygen radicals, which combine with oxygen molecules to form ozone. Ozone is a pollutant on its own, but it can also mix with unburned hydrocarbons to form a mix of irritant chemicals which can build up to create a photochemical smog

85
Q

What are catalytic converters?

A

They improve air quality by removing pollutants. In the presence of the catalyst, CO and unburned hydrocarbons react with nitrogen oxides to form CO2, H2O and N2. The converter has a honeycomb of ceramic material with a thin layer of metals (rhodium, platinum and palladium), and the large surface area increases the rate of reaction so that 90% of pollutant gases are removed

86
Q

What is an unsaturated compound?

A

It is a compound which contains a multiple covalent bond e.g. a carbon carbon double bond or triple bond

87
Q

What is the general formula for an acyclic alkene?

A

Cn H2n+2

88
Q

What is the general formula for a cyclic alkene?

A

Cn H2n-2

89
Q

What is the double bond in an alkene made up of?

A

One sigma bond and one pi bond

90
Q

Why are alkenes more reactive than alkanes?

A

When alkenes react, the pi bond is broken, which is much weaker than the sigma bond

91
Q

What is structural isomerism?

A

Compounds with the same molecular formula but different structural formulae

  • Chain isomerism
  • Position isomerism
  • Functional group isomerism
92
Q

What is stereoisomerism?

A

Compounds with the same molecular and structural formula but different arrangements of atoms

93
Q

What is the condition for geometric isomerism to be present in a molecule?

A

There must be 2 different groups attached to each double bonded carbon atom. These isomers occur because of restricted rotation round the carbon-carbon double bond

94
Q

How does the E-Z naming system work?

A

Groups around a carbon carbon or other rigid bond are ranked according to their atomic number. The atom with the higher atomic number has the higher priority. If the 2 high priority groups are on the same side of the double bond it is the Z isomer, and if they are on different sides it is the E isomer

95
Q

How does the cis and trans naming system work?

A

If the 2 alkyl groups are on the same side of the bond then it is the cis isomer and if they are on different sides it is the trans isomer

96
Q

What are the physical properties of the alkenes?

A
  • Slightly lower melting and boiling points than their corresponding alkanes
  • Alkenes with <5 carbon atoms are gases at room temperature, 5-15 are liquids and 15+ are solids
  • Alkenes are soluble in non-polar organic solvents, but are almost completely insoluble in water
97
Q

What is an addition reaction?

A

A reaction that occurs when 2 substances react together to form a single substance

98
Q

What is an electrophile?

A

Electrophiles are species which are electron deficient (delta +) or have a positive charge and so can accept a pair of electrons from an electron rich site forming a new covalent bond

99
Q

Hydrogenation of alkenes

A

Reagent: hydrogen
Conditions: nickel catalyst, 180°C, 2atm
Product: alkane
Reaction type: free radical addition

100
Q

Why is a nickel catalyst used industrially in the hydrogenation of alkenes rather than palladium or platinum?

A

A palladium or platinum catalyst allows the reaction to take place at room temperature and pressure (rather than at 180°C and 2atm with nickel) but are much more expensive, and so are not viable on an industrial scale

101
Q

What does the catalyst do in the hydrogenation of alkenes?

A

It weakens the bonds between the hydrogen atoms which then add on across the double bond

102
Q

Why is the hydrogenation of alkenes of commercial importance?

A

It is used in the manufacture of margarine. Natural vegetable oils are unsaturated, and when reacted with hydrogen some of the C=C bonds become hydrogenated and become C-C, causing the vegetable oil to become a solid

103
Q

Halogenation (Bromination) of alkenes

A 
Reagent: bromine
Conditions: inert solvent (like hexane), room temperature
Product: dibromoalkane
Reaction type: electrophilic addition
Bromine can be substituted for chlorine
104
Q

What are the issues with using iodine or fluorine rather than chlorine or bromine in the halogenation of alkenes?

A

Fluorine reacts very violently to produce CF4 and iodine reacts slowly and incompletely

105
Q

Why is the halogenation of alkenes carried out at room temperature in the absence of sunlight?

A

In order to prevent free radical substitution

106
Q

What is the purpose of using an inert solvent in the halogenation of alkenes?

A

Using a solvent like hexane provides a common solvent for both reagents to dissolve in

107
Q

Why is the second step of an electrophilic addition mechanism faster than the first?

A

There is attraction between oppositely charged ions

108
Q

Why is chlorine not usually used to test for the presence of unsaturation in an organic compound?

A

There would be no obvious colour change even though a reaction occurs

109
Q

Hydrohalogenation of alkenes

A

Reagent: hydrogen halide
Conditions: mix gases at room temperature
Product: halogenoalkane
Reaction type: electrophilic addition

110
Q

What is the order of reactivity of the hydrohalogenation of alkenes?

A

It follows the order of acid strength

HI > HBr > HCl > HF

111
Q

Why is a gaseous hydrogen halide used rather than the hydrohalic acids?

A

In the presence of water, the halogenoalkane may be hydrolysed to form an alcohol

112
Q

How does the rate of reaction change with the reagent used in hydrohalogenation of alkenes?

A

Rate increases HCl < HBr < HI. following order of increased acid strength. The first step of the mechanism determines the rate

113
Q

What are primary carbocations?

A

Carbon cations with 1 alkyl group and 2 hydrogens attached. The least stable carbocations

114
Q

What are seconday carbocations?

A

Carbon cations with 2 alkyl groups and 1 hydrogen attached

115
Q

What are tertiary carobcations?

A

Carbon cations with 3 alkyl groups attached. The most stable carbocations

116
Q

Why do carbocations have an inductive effect?

A

The inductive (electron pushing) effect is explained by the difference in electronegativities of C (2.5) and H (2.1). The carbon of CH3 pushes electrons to the positively charged carbon ion, stabilising the charge on the carbocation

117
Q

Why are tertiary carbocations the most stable carbocation?

A

Alkyl groups tend to release electrons (electron releasing inductive effect) which stabilise carbocations. The more alkyl groups around a positive carbon ion the more it is stabilised, making tertiary carbocations (the one with the most alkyl groups attached) the most stable

118
Q

What is the order of electron releasing effect?

A

(CH3)3C > (C2H5)(CH3)CH > C4H9 > C3H7 > C2H5 > CH3 > H
More carbon atoms in a group = more the group releases electrons, branched chain alkyl groups = better at releasing electrons

119
Q

How can you tell which way a mechanism will proceed?

A

The mechanism proceeds via the more stable carbocation

120
Q

Adding bromine water to alkenes?

A

Reagent: Br2 (aq)
Conditions: room temperature
Product: bromoalcohol
Reaction type: electrophilic addition

121
Q

Testing for unsaturation in a compound

A

Rapid decolorisation of bromine water (orange to colourless). The main product is formed by the addition of OH and Br

122
Q

Reaction of alkenes with potassium manganate

A

Reagent: KMnO4 / dilute H2SO4
Conditions: acidified solution (dilute H2SO4), room temperature
Product: diol
Reaction type: oxidation

123
Q

What happens when potassium manganate is added to an alkene?

A

The alkene is oxidised and the products depend on the conditions. A dilute, acidified solution of potassium manganate (VII) converts an alkene to a diol at room temperature. The purple manganate ions are reduced to pale pink Mn^2+ ion, and the purple colour disappears if there is excess alkene. This means it can be used to differentiate between unsaturated and saturated hydrocarbons

124
Q

Combustion of alkenes

A

Burn in excess oxygen to form CO2 and H2O. In air, they often don’t burn completely and can produce a lot of CO or C, meaning the flame from alkenes is often quite sooty. The higher % of carbon in the hydrocarbon, the sootier the flame

125
Q

Why is the combustion of alkenes not used as a fuel?

A

Despite producing energy when they burn, they are not used as fuels as they are more important in the manufacture of polymers and other chemicals

126
Q

Preparation of alkenes from alcohols by dehydration

A

When ethanol is treated with excess concentrated sulfuric acid (dehydrating agent) at 170°C, the alcohol loses water to form ethene

127
Q

What other reactions take place when alkenes are dehydrated?

A

Concentrated sulfuric acid is also an oxidising agent (as well as a dehydrating agent) and so will oxidise some of the alcohol to CO2 and will be reduced to SO2. The acidic impurities are removed by passing the ethene through aqueous potassium hydroxide before collecting it over water.

128
Q

What is the alternative dehydrating agent to produce ethene from alcohols?

A

Syrupy (concentrated) phosphoric acid can be used and does not undergo the side reactions of sulfuric acid (not an oxidising agent) but is more expensive than sulfuric acid

129
Q

What is another way that alcohols can be dehydrated?

A

By soaking alcohol in rocksil/mineral wool and applying heat to a test tube also containing alumina or pumice stone (to provide a catalytic surface for the reaction), ethene vapour is produced which can be collected over water

130
Q

Preparation of alkenes from halogenoalkanes by dehydrohalogenation

A

If a halogenoalkane is treated with hot, concentrated potassium hydroxide solution in alcohol, it undergoes an elimination reaction to give an alkene, which is collected over water if it is a gas. The halogenoalkane loses the halogen atom and a hydrogen atom from a carbon atom next to the carbon atom with the halogen attached

131
Q

How is the potassium hydroxide solution used in the preparation of alkenes (from halogenoalkanes by dehydrohalogenation) prepared?

A

Potassium hydroxide is usually dissolved in an alcohol containing the same number of carbon atoms as the halogenoalkane.

132
Q

Why can aqueous potassium hydroxide not be used when alkenes are prepared by dehydrohalogenation?

A

It would undergo a substitution reaction rather than an elimination reaction producing an alcohol

133
Q

What is the order of ease of dehydrohalogenation?

A

Iodoalkanes dehydrohalogenate more than bromoalkanes which dehydrohalogenate more easily then chloroalkanes. This is because there is a greater release of steric strain (how much space it takes up in a 3D space) for iodoalkanes
Tertiary halogenoalkanes dehydrohalogenate faster than secondary and primary

134
Q

Production of alkenes from alkanes by cracking

A

Ethene and propene (in particular) are produced in huge amounts by cracking alkanes (heating them in the absence of air). Thermal cracking uses high temperatures of 500-600°C and catalytic cracking uses 400-500°C and a catalyst of chromium oxide, aluminium oxide or silicon oxide

135
Q

What is a polymer and how are they made?

A

When many molecules of a simple compound or 2 different compounds join together to form a molecule, this is called polymerisation, and the large molecule produced (from monomers) is the polymer

136
Q

How does addition polymerisation work?

A

Alkenes undergo addition polymerisation, and the pi bond of the C=C bond breaks and the alkene molecules join onto each other. The polymer then has the same % composition and same empirical formula but higher Mr

137
Q

What are the advantages of PVC?

A
  • Polymer has a long life

- Not easily attacked by bacteria so good or outdoor use (e.g. guttering)

138
Q

What are the disadvantages of PVC?

A
  • If thrown away it stays in the environment for a long time - not biodegradable
  • Disposal by incineration gives toxic products of chlorine (e.g. HCl)
139
Q

What polymer does ethene produce?

A

Polyethene (also known as polythene or polyethylene)

140
Q

What polymer does propene produce?

A

Polypropene (also known as polypropylene) - stronger than polyethene

141
Q

What polymer does vinyl chloride (C2H3Cl) produce?

A

Polychloroethene (also known as polyvinyl chlorine/ PVC)

142
Q

What polymer does tetrafluoroethylene (C2F4) produce?

A

Polytetrafluoroethene (also known as PTFE, fluon or teflon)

143
Q

What polymer does CH2CHC6H5 produce?

A

Polyphenylethene (also known as polystyrene)

144
Q

What environmental problems are associated with polymer production and use?

A

Carbon dioxide is released into the atmosphere from burning fossil fuels to provide energy for production and transportation and incineration of polymers.
There can be atmospheric pollution when incineration hasn’t been carried out under the correct conditions. There are also landfill issues as most polymer products do not biodegrade so have to be disposed of in landfill. There can also be plastic pollution, and polymers can be found all over the world and have an environmental impact

145
Q

What is an advantage of the resilience of polymers?

A

Resistance to corrosion and chemical attack are useful properties, so give plastic products a long life

146
Q

What is a disadvantage of the resilience of polymers?

A

Discarded plastics can litter the environment (particularly smaller objects like plastic bags) and can fill waste disposal (more bulky plastic). If disposed of by incineration, especially of halogenated polymers, toxic fumes may be produced

147
Q

How can wasted polymers be minimised?

A
  • Not using them unnecessarily
  • Putting it to other uses
    > Recycling
    > Incineration
    > Use as chemical feedstock (raw materials)
148
Q

Recycling polymers

A

Converting the polymer into other materials - e.g. PET/PETE from plastic bottles into carpet

149
Q

What are the stages of polymer recycling?

A

1) Sorting - polymers cannot effectively be processed together, so there are codes that allow different polymers to be separated and sorted
2) Processing - Chopping the waste into small pieces and washing it. It can then be used to make new materials using melting, moulding and fibre production

150
Q

Incinerating polymers

A

Elements present in polymers are mostly H and C, so they can be used as fuels. There is very little solid waste left as most products of combustion are gases, and the energy produced can be used domestically and industrially.

151
Q

Why are there problems with incinerating polymers?

A

As well as hydrogen and carbon, there are sometimes other elements, such as in colouring or small amounts of toxic heavy metals, which can cause air pollution as they are difficult to remove from waste gases released into the atmosphere

152
Q

Use of polymers as a chemical feedstock

A

This is a process similar to cracking which is used to break polymer waste into gases (mainly carbon monoxide and hydrogen), which creates a chemical feedstock to use in other chemical reactions, often to make new polymers

153
Q

What are the key features of a life cycle assessment of a polymer?

A
  • Main requirements for energy input
  • Environmental impact and sustainability of making materials from natural resources
  • Environmental impact of making the product from the material
  • Environmental impact of using the product
  • Environmental impact of disposing the product by incineration, landfill or recycling
154
Q

How are decisions made about the management of polymer waste?

A

To reduce the long term impact of a polymer on the environment and to compare different polymer uses, a life cycle analysis is drawn out

155
Q

What are biodegradable polymers?

A

Biodegradable polymers are ones which are allowed to be broken down by microbes in the environment and are used on a small scale in medicine for stitches and drug delivery

156
Q

What are the disadvantages of biodegradable polymers?

A

They are often made from plant material, so land is required to grow the plants, and because they are designed to break down in the environment, the hydrogen and carbon atoms they contain cannot be directly used.

157
Q

What is a monomer?

A

Small chains that join together in long chains to make polymers

158
Q

What is a polymer?

A

Long chain molecules that are formed of many small molecules joined together

159
Q

What are examples of natural polymers?

A

Proteins, polysaccharides, nucleic acids

160
Q

What are examples of synthetic polymers?

A

Poly(eth)ene, polypropene, polystyrene, nylon, polyester

161
Q

What is polymerisation?

A

A process in which many small molecules (monomers) join up in long chains

162
Q

What does it mean if a material is biodegradable?

A

It is able to break down in the environment due to the action of bacteria or microorganisms

163
Q

What is recycling?

A

A method of dealing with waste where a material is processed and reformed into new products

164
Q

What is landfill?

A

A waste management method where waste is dumped into large pits and covered with soil

165
Q

What is the definition of environmental?

A

The influence of any activity on the environment (atmosphere, sea, rivers, plants, animals)

166
Q

What is a nucleophile?

A

Molecules or ions with a lone pair of electrons that they can donate to form new covalent bonds

167
Q

Alkaline hydrolysis of halogenoalkanes

A

Nucleophilic substitution, heat with aqueous KOH to form an alcohol (OH^- substitutes for the halogen ion)

168
Q

Silver nitrate test for halogenoalkanes

A

Heat the halogenoalkane with aqueous AgNO3). Water replaces the halogen to form an alcohol and the halide ion is lost, and the halide ion will react with the silver nitrate to form a coloured ppt depending on the ion. Used to identify the halogenoalkane, not to produce alcohols

169
Q

Nitrile formation with halogenoalkanes

A

Heat the halogenoalkane under reflux with potassium cyanide in ethanol. This replaces the halogen with CN, adding an extra carbon to the chain

170
Q

Primary amine formation using halogenoalkanes

A

Heat the halogenoalkane in a high pressure sealed apparatus with concentrated ammonia in ethanol. The mechanism happens in 2 steps, first with NH3 joining onto the carbon that the halide ion was attached to, then because the N has too many bonds, then the lone pair on another NH3 removing the extra hydrogen, forming the primary amine and NH4^+

171
Q

Elimination reaction of halogenoalkanes

A

KOH in ethanol. Heat under reflux to form an alkene, the halide ion and water

172
Q

Hydrolysis of halogenoalkanes

A

Different halogenoalkanes undergo hydrolysis at different rates. The experiment is carried out by reacting different halogenoalkanes with aqueous silver nitrate in ethanol while heating in a water bath

173
Q

What are the results of hydrolysis of halogenoalkanes?

A

Iodo reacts faster than bromo which reacts faster than chloro
Tertiary reacts faster than secondary which reacts faster than primary

174
Q

Explain the trend in the rate of hydrolysis of halogenoalkanes (comparing between different halides)

A

It has the longest bond (because of iodine’s large atomic radius) so it has the weakest bond enthalpy and breaks the most easily of the halogenoalkanes. As bond lengths get shorter, bond enthalpy increases and they require more energy to break, which is why rate of hydrolysis decreases up the group

175
Q

Mechanism for nucleophilic substitution of primary halogenoalkanes

A

React via SN2.
There are 2 species in the slow step (the nucleophile and the halogenoalkane)
There is a 5-bonded transition state which has a negative charge.
No carbocation is formed as the primary carbocations do not have sufficient inductive effects to stabilise the positive charge.
The second step (kicking out the halide ion) is fast

176
Q

Mechanism for nucleophilic substitution of secondary and tertiary halogenoalkanes

A

React via SN1
There is 1 species in the slow step (the halogenoalkane)
There is a carbocation intermediate
A carbocation can be formed as the secondary and tertiary carbocations are made more stable by the inductive effects.
The first step is slow and the second step is fast.

177
Q

Complete combustion of alcohols

A

Clean blue flame when they burn in plentiful oxygen, carbon dioxide and water are formed

178
Q

Chlorination of alcohols

A

Vigorous reaction with PCl5 that forms steamy fumes (of HCl), POCl3 and a chloroalkane
e.g. C2H5OH + PCl5 -> C2H5Cl + POCl3 + HCl
This acts as a test for the hydroxyl group. The positive result of steamy is given when the HCl produced is exposed to ammonia

179
Q

Bromination of alcohols

A

Heat under reflux with 50% (concentrated) sulfuric acid and KBr to produce a bromoalkane and water
2 stages, e.g.
H2SO4 + 2KBr -> K2SO4 + 2HBr
C2H5OH + HBr -> C2H5Br +H2O
Halogenoalkane needs to be separated from reaction mixture

180
Q

Iodination of alcohols

A

Heat under reflux with red phosphorus and iodine to produce an iodoalkane and H3PO4
2 stages, e.g.
2P + 3I2 -> 2PI3
3C2H5OH + PI3 -> 3C2H5I + H3PO4
Distill to separate halogenoalkane from reaction mixture as it has a low bp

181
Q

Oxidation of primary alcohols in distillation apparatus

A

Heat with potassium dichromate (VI) and dilute sulfuric acid

Product collected is an aldehyde as it has a low bp. A colour change from orange to dark green is seen (Cr^6+ to Cr^3+)

182
Q

Oxidation of primary alcohols in reflux apparatus

A

Heat with potassium dichromate (VI) and dilute sulfuric acid
Product is fully oxidised to a carboxylic acid (aldehyde is formed first but it continues to be oxidised to a carboxylic acid). A colour change from orange to dark green is seen (Cr^6+ to Cr^3+).
Carboxylic acid is purified using distillation as it has a much higher bp than the alcohol and alcohol

183
Q

Oxidation of secondary alcohols

A

Heat under reflux with potassium dichromate (VI) and dilute sulfuric acid.
Ketone produced.
Orange to green colour change seen. Heating under reflux gives the best possible yield of the ketone, and the product is then purified and collected by distillation

184
Q

Oxidation of tertiary alcohols

A

No reaction with potassium dichromate (VI), so no colour change is seen

185
Q

How can the products produced by the oxidation of primary and secondary alcohols be distinguished?

A

Use of Benedict’s and Fehling’s solution. They are both initially blue (due to Cu^2+ ions), and there is no reaction when added to a ketone, but a brick red ppt of copper (I) oxide is formed when added to an aldehyde

A Level Chemistry (25 decks)

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