Unit 2.5 - Hydrocarbons Flashcards
1
Q
Give 2 examples of types of hydrocarbons and explain why they are hydrocarbons
A
Alkanes and alkenes
Contain hydrogen and carbon only
2
Q
What type of hydrocarbons are alkanes and alkenes?
A
Aliphatic hydrocarbons
3
Q
Aliphatic hydrocarbons
A
Straight chain
4
Q
What do alkanes and alkenes contain that makes them aliphatic (straight chain) hydrocarbons?
A
Carbon chains with C-C bonds
5
Q
Which is saturated - alkanes or alkenes? Why?
A
Alkanes are saturated (only form single covalent bonds, C-C and C-H)
6
Q
Are alkanes or alkenes unsaturated and why?
A
Alkenes are unsaturated
Have 1 C=C bond
7
Q
What’s the main source of alkanes?
A
Crude oil and natural gas
8
Q
What are alkanes primarily used as?
A
Fuels
9
Q
What’s another word for crude oil?
A
Petroleum
10
Q
What IS crude oil?
A
A complex mixture of saturated hydrocarbons, mainly alkanes
11
Q
Describe how crude oil is formed
A
Formed from the remains of marine animals that lived many years ago…
Over time, they died
Sank to the bottom of the sea
Got covered in mud
The remain were compressed over time until they turned into a liquid
Collected in porous rocks like sandstone
12
Q
How do we extract crude oil?
A
We require powerful oil rigs
13
Q
What is the purpose of fractional distillation?
A
The first step in the separation of the different hydrocarbons in petroleum
14
Q
What does fractional distillation separate substances according to?
A
According to their different boiling points
15
Q
What’s the first step of fractional distillation?
A
Heated petroleum passed into a distillation column
16
Q
Describe the hydrocarbons that collect at the top of the chamber during fractional distilllation
A
Low melting points
Short chain
More volatile (easily evaporated at normal temperatures)
17
Q
Which hydrocarbons following fractional distillation are most in demand? Why?
A
The ones that collect at the top of the column (short chain)
Low melting point and more volatile
18
Q
Place, in order, the different hydrocarbons that wold be extracted from crude oil upon fractional distillation
A
Gases
Gasoline
Naphtha
Kerosine
Gas oil
Residue
19
Q
Example of a gas extracted from crude oil
A
Methane
20
Q
What is gasoline?
A
Petrol
21
Q
What is naphtha?
A
Chemical feedstock
22
Q
Give 2 uses of kerosine
A
Jet fuel
Heating fuel
23
Q
What is gas oil used as?
A
Diesel
24
Q
Give 3 examples of residue from the fractional distillation of crude oil
A
Lubricating oil
Waxes
Bitumen
25
What is most of the product of the fractional distillation of crude oil?
Residue
26
Fractions
Mixtures of hydrocarbons of similar chain length and thus similar boiling points
27
Wha temperatures do fractions boil in the range of?
40 to 500 degrees Celsius
28
2 advantages of petrolium/crude oil
An important chemical feedstock to the chemical industry
(Many chemicals come from it and are used to prepare other organic compounds)
Relied on for the economy (used in cars and central heating systems)
29
2 disadvantages of crude oil/petroleum
Releases greenhouse gases
Is non-renewable
30
What type of bonds are the C-C and C-H bonds in alkanes?
Non-polar covalent bonds
31
What type of molecules are alkanes?
Non-polar
32
What type of forces are between alkane molecules?
Weak Van der Waal forces
33
Describe the melting and boiling points of alkanes
Low
34
What are alkanes soluble in? Why?
Non-polar solvents such as other hydrocarbons
(They’re non polar, and like dissolves with like)
35
What are alkanes insoluble in? Why?
Polar solvents like water
(Alkanes are non polar and like dissolves with like)
36
Are alkanes chemically reactive or unreactive? Why?
Unreactive
Strength of the C-C and C-H bonds
37
Which processes do alkanes undergo?
1. Combustion
2. Cracking - homolytic fission of the C-C bond
3. Photo chlorination - radical attack
38
What is a combustion reaction?
Reaction with oxygen
39
Draw a diagram of the apparatus that you would use for the identification of the products of the combustion of a hydrocarbon
(See notes)
40
What are 2 things you’d use to identify the products of the combustion of a hydrocarbon?
Cobalt chloride paper
Limewater
41
What does cobalt chloride paper do?
Test for the presence of water
42
What would a positive test of a cobalt chloride paper show and what would this represent?
Blue to pink
Water is present
43
What would a positive test in limewater be and what would this represent?
Turns cloudy
CO2 is present
44
What colour flame do alkanes burn with?
Yellow
45
Do alkanes burn with a lot or a small amount of smoke?
Little or no smoke
46
What are most fossil fuels that are burnt to provide energy?
Alkanes
47
Give some examples of fossil fuels burnt to provide energy that are alkanes
Natural gas (methane)
L.P.G (propane and butane)
Petrol
Diesel
Power station oil
Marine fuel
48
What has the combustion of alkanes contributed to?
The greenhouse effect
Acid rain
Photochemical smog
49
How has the combustion of alkane contributed to acid rain?
Combusting impurities in the fuels
50
Why are alternative fuels being sought from alkanes?
They contribute to things like the greenhouse effect, acid rain and photochemical smog
51
When would an alkane undergo incomplete combustion?
In a lack of oxygen
52
What does the incomplete combustion of an alkane produce?
Carbon monoxide (CO)
53
What’s the problem with carbon monoxide?
Highly toxic
54
Why is carbon monoxide toxic?
Binds to haemoglobin, effecting gas exchange
55
Why is it important to keep stoves in good condition?
So that they have enough oxygen so that incomplete combustion doesn’t occur and form carbon monoxide
56
Products of incomplete combustion
Carbon monoxide (CO)
Water (often present as steam - use state symbol ‘g’)
57
In what form is the water produced from combustion?
Often as steam
(Use state symbol ‘g’)
58
What is cracking?
The process where large, less useful hydrocarbon molecules are broken down into smaller, more useful molecules
59
What will the useful molecules of cracking be?
A mixture of saturated and unsaturated hydrocarbons
60
Why are smaller molecules from cracking more useful than larger ones?
They burn easier
61
Why do smaller molecules burn easier? What does this make them?
Lower boiling temperature = evaporate better, and it’s the vapour of a fuel that burns
= better fuels
62
What is an alternative thing that can occur during cracking?
Straight chain alkanes are converted into branched alkanes
63
What is one of the main fractions cracked?
Naphtha
64
What conditions are required for cracking?
Very high temperatures and pressure
65
How is naphtha cracked?
Feedstock is heated to around 800 degrees Celsius (very high temperature and pressure)
Steam is added to dilute the feedstock
66
What are some fractions obtained from naphtha?
Methane
Ethene
Propene
Petrol
Other alkenes
67
What does cracking always form?
A smaller chain hydrocarbon and an alkene
68
What does cracking involve the formation of?
Free radicals
69
Why does cracking involve the formation of free radicals?
The C-C bond is broken at the high temperatures used
70
What has happened to the C-C bond in a hydrocarbon when it’s been broken at the high temperatures of cracking?
The homolysis of the C-C bod
71
When does the homolysis of the C-C bond in a hydrocarbon occur?
When the C-C bond is broken at the high temperatures used
72
What are the 2 ways that covalent bonds in organic compounds can break?
Homolytic bond fission
Heterolytic bond fission
73
What are homolytic and heterolytic bond fission examples of?
Ways that the covalent bonds in organic compounds can break
74
Homolytic bond fission
The covalent bonds break in such a way that each atom forming the bond retains one electron
75
What is the species formed from homolytic bond fission and why?
A free radical (has an unpaired electron)
76
Describe free radicals
Very reactive
77
Describe and give examples of reactions involving free radicals
Very rapid
E.g - photo chlorination of methane and cracking
78
Heterolytic bond fission
The covalent bonds break in such a way that one atom takes both electrons in the bond
79
What’s the most common type of bond fission?
Heterolytic bond fission
80
How are reactions involving heterolytic bond fission different to those involving homolytic bond fission?
Much slower
81
What does heterolytic bond fission form?
An electrophile and a nucleophile
82
Fission
The breaking of a chemical bond
83
What type of property is boiling point?
Physical
84
What physical property of molecules is used to separate them during fractional distillation?
Boiling points
85
What does methane react with and how?
Chlorine, vigorously
86
Under which conditions does methane react vigorously with chlorine
In sunlight (UV light)
87
Under which conditions would methane not react with chlorine? Why?
In the dark
The photo chlorination of methane required UV light
88
What’s the name for methane reacting with chlorine?
Photo chlorination of methane
89
What type of reaction is the photo chlorination of methane?
Free radical substitution
90
Write the reaction to form chloromethane
CH4 + Cl2 —> CH3Cl + HCl
91
Write the reaction to form dichloromethane
CH3Cl + Cl2 —> CH2Cl2 + HCl
92
What can also be formed in the photo chlorination of methane as well as chloromethane and dichloromethane and how?
Trichloroethane and tetrachloromethane
The products of the reaction before can react with further chlorine molecules
93
Why is the photo chlorination of methane a free radical substitution reaction?
Hydrogen atoms in the alkanes are substituted for chlorine atoms
94
What are the three steps to a free radical substitution reaction?
Initiation
Propagation
Termination
95
What happens during the initiation stage for free radical substation during the photo chlorination of methane?
Chlorine molecules in UV light undergo homolytic fissio
Forms free radicals
96
How much energy is required for the formation of free radicals during the initiation stage of free radical substation for the photo chlorination of methane?
A considerable amount - equivalent to the bond enthalpy of chlorine molecules
97
What type of reaction is initiation during free radical substitution?
Endothermic
98
Write the equation for the initiation stage of the free radical substitution reaction during the photo chlorination of methane
Cl2 —> 2Cl•
99
What happens during the propagation stage for free radical substation during the photo chlorination of methane?
Involves the formation of products
Chlorine radicals reform in the course of the reaction and are able to react with more methane molecules
100
Describe the propagation stage (2 separate things) of free radical substitution. Why is this?
Very fast due to the presence of free radicals
Self-sustaining due to chlorine radicals reforming in the course of the reaction that are able to react with more methane molecules
101
Why is the propagation stage of the photo chlorination of methane self-sustaining?
Chlorine radicals reform in the course of the reaction and so are able to react with more methane molecules
102
What type of reaction is the propagation stage of free radical substitution?
Chain reaction
103
What does the fact that the propagation stage of free radical substitution is a chain reaction mean for it?
One chlorine radical can react with many thousand methane molecules in a fraction of a second
104
Write the equations for the formation of chloromethane
CH4 + Cl• —> CH3 • + HCl
CH3 • + Cl —> CH2Cl2 + Cl •
105
Write the equations for the formation of dichloromethane
CH3Cl + Cl • —> CH2Cl • + HCl
CH2Cl • + Cl2 —> CH2Cl2 + Cl •
106
What happens during the termination stage for free radical substation during the photo chlorination of methane?
All remaining free radicals combine and are destructed
107
Where do the remaining free radicals usually combine at the termination stage of free radical substitution?
On the walls of the reaction vessel
108
What does the termination stage of free radical substitution produce?
Stable products that are organic molecules
109
Show free radicals combining to form ethane
CH3 • + CH3 • —> CH3CH3
110
What do we need to be able to apply to multiple alkanes?
The reaction mechanism s for their photo chlorination reactions
111
What type of bonds do alkanes have?
C-C bonds and a single C=C bond
112
How many C=C bonds to alkenes have?
1
113
What word describes alkenes?
Unsaturated
114
What is the position of the double bond in alkenes initiated with?
A number
115
What does the number in the name of an alkene initiate?
The position of a double bond
116
Which alkenes does the numbering of the position of the double bond not apply for?
Ethene
Propene
117
Draw and label the structure of Ethene
(See notes)
118
What shape is an Ethene molecule?
Trigonal planar
119
What size bond angles does Ethene have?
120 degrees
120
What are the 2 types of bond that the double bond in Ethene contains?
Sigma bond
Pi bond
121
What’s a sigma bond?
A covalent bond formed by the direct overlap of orbitals (s and p)
122
What’s a pi bond?
Formed by the sideways overlap of 2 Px orbitals, with the electrons above and below the plane of the 2 carbon atoms
123
What can the pi bond be thought of as?
A negative charge cloud above and below the plane of the molecule
124
Which bond is weakest - the pi bond or the sigma bond?
Pi bond
125
Which bond is most reactive - the pi bond or the sigma bond?
The pi bond
126
What’s the region of negative charge in a molecule of Ethene?
The pi bond
127
Which part of an Ethene molecule attracts electrophils and why?
The pi bond as this is the region of negative charge
128
What does the pi bond of Ethene attract? Why?
Electrophils, as electrophils are positively charges and the pi bond is the region of negative charge
129
What do alkenes react through?
Electrophillic addition
130
Which part of an Ethene molecule takes part in reactions?
The pi electrons
131
Which part of Ethene seeks electrophiles and why?
The pi electrons as they’re negatively charged
132
What do pi bonds seek?
Electrophiles
133
How are alkenes prepared from halogenoalkanes?
Using elimination reactions
134
How can Ethene be prepared from bromoethane?
By the elimination of HBr
135
How is Ethene prepared from bromoethane by the elimination of HBr?
Bromoethane is refluxed with sodium hydroxide in ethanol
136
What are the most important reactions that Ethene undergoes?
Addition reactions
137
Which bond is broken during the addition reactions of Ethene?
Pi bond
138
What happens after the pi bond has broken in Ethene in its addition reactions?
Atoms or groups add onto the 2 carbon atoms in the double bond
139
Why is only one product available in the addition reactions of Ethene?
Its symmetry
140
How come Ethene is symmetrical?
It’s only made up of 2 atoms
141
List all of the addition reactions of Ethene
Catalytic hydrogenation (reduction)
Addition of bromine
Decolorisation of potassium manganate (VII)
Addition of hydrogen bromide
Addition of water
142
What is catalytic hydrogenation also known as and why?
Reduction
Gain of hydrogen
143
Write the equation for the catalytic hydrogenation of Ethene
CH2=CH2 + H2 —> CH3CH3
144
What does hydrogenation involve the addition of?
Hydrogen
145
What turns into what during hydrogenation?
Alkene into an alkane
146
What brings about the conversion of Ethene to ethane during its catalytic hydrogenation?
A nickel catalyst
147
At what termparture is Ethene converted into ethane during catalytic hydrogenation?
About 150 degrees Celsius
148
Which reaction does the production of margarine use and why?
Catalytic hydrogenation
Unsaturated oils are hardened by the conversion into saturated products
149
The production of what uses the process of catalytic hydrogenation?
Margarine
150
What type of reaction do alkenes undergo with halogens such as chlorine and bromine?
Electrophilic addition
151
What do alkenes undergo electrophilic addition reactions with?
Halogens such as chlorine and bromine
152
Under which conditions do alkenes undergo electrophilic addition reactions with halogens such as chlorine and bromine?
Room temperature
153
What type of bromine is used when reacting with alkenes?
Aqueous bromine water
154
What happens to bromine water when reacted with an alkene?
It’s decolorised
Turns from orange to colourless
155
What’s the colour change that makes bromine water become decolourised in an alkene?
Orange to colourless
156
Which 2 reactions are used to test for the presence of a C=C double bond?
Decolorisation of bromine water
Decolorisation of potassium manganate (VII)
157
What do both the decolorisation of bromine water and potassium manganate test for?
The presence of the C=C double bond
158
Write the equation for bromine water reacting with Ethene
CH2=CH2 + Br2 —> CH2BrCH2Br
159
Where is bromine added to Ethene when it reacts?
Across the 2 carbon atoms in the double bond
160
What’s the decolorisation that occurs with an alkene and potassium manganate (VII) in the presence of a C=C double bond?
Purple —> colourless
161
At what temperature does an addition of hydrogen bromide to an alkene occur at?
Room temperature
162
What’s used as a reagent in the addition of hydrogen bromide to an alkene?
Hydrobromic acid
163
Write the equation for hydrogen bromide reacting with Ethene
CH2=CH2 + HBr —> CH3CH2Br
164
How is ethanol produced industrially?
By the direct addition of water (as steam) to Ethene
165
What is produced by doing water (steam) to Ethene?
Ethanol
166
In what form i water added to Ethene to reduce ethanol?
Steam
167
Write the equation for water being added to ethene to produce ethanol
CH2=CH2 + H2O —> CH3CH2OH
168
What are the conditions for the addition of water to ethene?
Phosphoric acid catalyst/concentrated sulphuric acid
300 degrees
60 atm pressure
169
Catalyst for the addition of water to ethene
Phosphoric acid
OR
Concentrated sulfuric acid
170
Temperature for the reaction of addition of water to ethene
300 degrees
171
Pressure for the addition of water to ethene reaction
60 atm
172
How is Propene different to ethene?
Asymmetrical
173
Reagent, conditions and observations for the addition of bromine to Propene - what is the significance of these?
Bromine water
Room temperature
Decolorised bromine water (orange to colourless)
All the same as bromine with ethene
174
How many products form with the addition of bromine to Propene?
1 (same as ethene)
175
What is the addition of bromine to Propene an example of and why?
Electrophillic addition
Bromine acts as an electrophile
176
Equation for the reaction of Propene with bromine
CH3CH=CH2 + Br2 —> CH3CHBrCH2Br
177
What is the reaction of Propene with hydrogen bromide an example of?
Electrophillic addition
178
What does the fact that Propene is asymmetrical mean for it in a particular circumstance?
2 organic products can be formed in the addition reaction between Propene and hydrogen bromide
179
How many products would form in the reaction of an alkene with hydrogen bromide if it were symmetrical?
1
180
Conditions for the reaction of hydrogen bromide with Propene
Room temperature (same as with ethene)
181
Whats’t the reagent for the reaction between Propene and hydrogenbromide?
Aqueous solution of hydrogen bromide
182
2-bromopropane
CH3CHBrCH3
183
1-bromopropane
CH3CH2CH2Br
184
What’s the major product of the reaction of Propene with hydrogen bromide?
2-bromopropane
185
What’s the minor product for the reaction between hydrogen bromide and Propene?
1-bromopropane
186
What does it mean that 2-bromopropane is the major product of the reaction between Propene and hydrogen bromide?
Only a small amount of other product forms
187
Write the equation for the first step for the electrophilic addition of hydrogen bromide to Propene
CH3CH=CH2 + H+ —> CH3CH+CH3
188
What’s the equation for the second step of the Electrophillic addition of hydrogen bromide to Propene?
CH3CH+CH3 + Br- —> CH3CHBrCH3
189
What does a Curley arrow represent?
The movement of a pair of electrons, from negative to positive
190
In which direction does a pair of electrons always move to and from?
From negative to positive
191
What’s the electrophile in the electrophilic addition of hydrogen bromide to Propene?
The hydrogen ion, H+
192
What’s the source of electrons in the electrphillic addition of hydrogen bromide to Propene?
Pi bond
193
Why is the pi bond the source of electrons in the Electrophillic addition of hydrogen bromide to Propene?
A region of high electron density
194
Describe with the aid of diagrams the Electrophillic addition of hydrogen bromide to Propene
As the hydrogen ion approaches the C=C bond, the pi Bon begins to break
A new bond is formed between the carbon atom and the hydrogen
An intermediate is formed - a carbocation
The carbocation is a reactive species, and a bromide ion combines with it (has a lone pair of electrons) to give the final product
(See diagrams in notes)
195
What’s the name of the intermediate formed in the Electrophilic addition of hydrogen bromide to Propene?
Carbocatalyst
196
Why is 2-bromopropane the major product of the reaction between hydrogen bromide and Propene?
The carbocation formed is known as a secondary carbocation
(The other product, 1-bromopropane, is formed through a primary carbocation)
The secondary carbocation is more readily formed and is more stable
197
2 products of the electrophillic addition of hydrogen bromide to Propene
2-bromopropane
1-bromopropane
198
Secondary carbocation
The positive charge is on a carbon atom to which 2 carbons are attached to
199
Which carbocation forms 1-bromopropane?
A primary carbocation
CH3CH2CH2+
200
What’s different betweeen a secondary carbocation and a primary carbocation?
More readily formed
More stable
201
Equation for the primary carbocation formed in the production of 1-bromopropane via the electrophillic addition of hydrogen bromide to Propene
CH3CH2CH2+
202
Equation for the secondary carbocation formed in the production of 2-bromopropane via the electrophillic addition of hydrogen bromide to Propene
CH3CH+CH3
203
Secondary symbol
2°
204
Primary symbol
1°
205
Who discovered the rule which correctly predicts the major product formed in the addition of hydrogen bromide to an asymmetrical alkene?
Vladimir Markovnikoff
206
What did Vladimir Markovnikoff discover?
The rule which correctly predicts the major product formed in the addition of hydrogen bromide to an asymmetrical alkene
207
State what Vladimir Markovnikoff discovered
When hydrogen bromide adds to a double bond of an asymmetrical alkene, the hydrogen joins to the carbon that has the most hydrogen atoms bonded to it
208
How do polymers occur?
Naturally and synthetically
209
Name some natural polymers
Proteins such as the skin, hair, starch and cellulose
210
What are addition polymers formed from?
Alkenes
211
What do the alkenes that undergo addition polymerisation form?
Addition polymers
212
Which process must alkenes undergo to form addition polymers?
Addition polymerisation
213
What happens during addition polymerisation?
Alkene molecule adds on to the end of another alkene molecule to form a chain of thousands of alkene molecules
214
Starting molecule of a polymer
Monomer
215
Describe monomers
Unsaturated
216
End product of polymerisation
Polymer
217
Describe polymers
Saturated
218
What always has and what never has a double bond?
Always = monomers
Never = polymers
219
What are addition polymers formed from?
1 monomer as a repeating unit
220
What is required to start a polymerisation reaction?
Catalyst
High temperature
High pressure
221
Substituted alkenes
Not just hydrogen attached to the carbon
222
What are 4 important polymers to remember?
Polypropene
PTFE (Teflon)
PVC (polychloroethene)
Polystyrene
223
What’s the polymer PTFE also known as?
Teflon
224
What’s the polymer PVC also known as?
Polychloroethene
225
What’s polychloroethene also known as?
PVC
226
What’s the polymer Teflon also known as?
PTFE
227
What are all of the important polymers for us to remember examples of?
Thermoplastics
228
Polypropene polymer…
Monomer
Monomer equation
Repeat unit
Uses
Propen
CH3CH=CH2
(Notes)
Pipes, ropes
229
PTFE/Teflon polymer…
Monomer
Monomer equation
Repeat unit
Uses
Tetrafluroethene
CF2=CF2
(Notes)
Non stick pans
230
PVC/polychloroethene…
Monomer
Monomer equation
Repeat unit
Uses
Chloroethene
CHCl=CH2
(Notes)
Floor tiles, tubing, film windows, rain coats, vinyl records
231
Polystyrene..
Monomer
Monomer equation
Repeat unit
Uses
Phylethene (styrene)
C6H5CH=CH2
(Notes)
Packaging, mouldings
232
What’s the relationship between the repeating units and monomers of a polymer?
Equal number of them
233
What the styrene monomer also known as?
Phenylethene
234
Phenylethene monomer’s other name
Styrene
235
How to we identify a repeating unit in a polymer?
Take any 2 Ar on atoms in the main chain and draw any atoms above and below
Add square brackets and a value for “n”
236
How do we identify the monomer of a polymer?
Take any 2 carbon atoms, write the atoms above and below it
Add a double bond
237
Conditions for the polymerisation of ethene
2000atm
250 degrees
Trace of oxygen (initiator)
238
What does oxygen act as in the polymerisation of ethene?
Initiator
239
How does oxygen initiate the polymerisation of ethene?
Homolysis of the initiator results in the formation of radicals which react with ethene
240
What happens to oxygen, the initiator of the polymerisation of Ethene?
Homolysis
241
What does the homolysis of the initiator oxygen, result in for the polymerisation of ethene?
The formation of radicals which react with ethene
242
What does the polymerisation of ethene involve?
Free radicals
243
What does the fact that the polymerisation of ethene involves radicals mean for it?
The reaction is very rapid
244
What happens during the course of the polymerisation of ethene?
Ethene molecules add to the end of the chain until a termination reaction occurs
245
What dorms from the polymerisation of ethene?
Polymer chains of varying length
(Usually contain thousands of monomer units)
246
What stops the polymerisation of ethene?
A termination reaction
247
What are the 3 ways of classifying polymers?
Uses
Structure
Type of polymer
248
3 uses of polymers
Plastics, fibres, elastomers
249
2 structures of polymers
Thermoplastics
Thermosets
250
Thermoplastics
Soften when heated and adopt a new structure when cooled
251
Thermosets
Bonds between the polymer chains are more resistant to heat than thermoplastics
252
2 examples of thermoset polymers
Bakelite
Melamin
253
What’s the Bakelite thermoset in?
Light sockets
254
2 types of polymer
Addition
Condensation
255
What do the properties of a polymer depend on?
Structure
Method used to prepare
Whether other substances were added
Manufacturing technique
256
What are the environmental problems of synthetic polymers?
Do not biodegrade
End up in landfill
End up in soil for centuries
257
Why do a lot of polymers end up in landfill?
Poor tensile strength
Poor resistance to heat
258
Why are polymers so widespread?
They’re cheap
259
Which atoms does the sigma bond occur between?
C-C
and
C-H
260
Which atoms does the pi bond occur between?
C-C
261
Which type of bond do both alkanes and alkenes contain?
Sigma bonds
262
If an alkene reacts with x in a 1:3 ratio, what does this mean?
There are 3 double bonds
263
Which react most readily - alkanes or alkenes?
Alkenes
264
Why do alkenes react more readily than alkanes?
Pi bond is weaker than the sigma bond and so is easily broken
The pi bond has a high electron density
265
Bonds in alkanes and bonds in alkenes
Alkanes = only sigma bonds
Alkenes = pi bonds and sigma bonds
266
Alkanes method of reacting with halogens
Radical substitution
267
Alkenes method of reacting with halogens
Electrophillic addition
268
What can the pi bond in an alkene be described to have?
High electron density
269
What do we do if asked to draw 2 repeat units of a polymer?
Show what is repeated twice (see notes, it makes more sense)
270
What feature of a molecule gives rise to E-Z isomerism?
Carbon to carbon double bond
271
Where do we ALWAYS shows the movement of the line pair of electrons from when drawing reaction mechanisms?
From the lone pair of electrons
272
What should you always show as the bare minimum when showing the termination stages of the free radical substitution reaction of alkanes?
The reaction between the free radicals that forms the originally desired product
273
What must we not forget when drawing a product of addition polymerisation?
Square brackets
274
What’s the difference between the products of homolytic bond fission and heterolytic bond fission?
Homolytic - forms free radicals
Heterolytic - forms an electrophile and a nucleophile
