Module 4.1 - Basic Concepts and Hydrocarbons Flashcards
1
Q
What is the empirical, molecular and structural formulae of methane?
A
-CH4
CH4
-CH4
2
Q
What is the empirical, molecular and structural formulae of ethane?
A
- CH3
- C2H6
- CH3CH3
3
Q
What is the empirical, molecular and structural formulae of propane?
A
- C3H8
- C3H8
- CH3CH2CH3
4
Q
What is the empirical, molecular and structural formulae of butane?
A
- C2H4
- C4H10
- CH3CH2CH2CH3
5
Q
What is the empirical, molecular and structural formulae of pentane?
A
- C5H12
- C5H12
- CH3CH2CH2CH2CH3
6
Q
What is the empirical, molecular and structural formulae of hexane?
A
- C3H7
- C4H14
- CH3CH2CH2CH2CH2CH3
7
Q
What is the empirical, molecular and structural formulae of heptane?
A
- C7H16
- C7H16
- CH3CH2CH2CH2CH2CH2CH3
8
Q
What is the empirical, molecular and structural formulae of octane?
A
- C4H9
- C8H18
- CH3CH2CH2CH2CH2CH2CH2CH3
9
Q
What is the empirical, molecular and structural formulae of nonane?
A
- C9H20
- C9H20
- CH3CH2CH2CH2CH2CH2CH2CH2CH3
10
Q
What is the empirical, molecular and structural formulae of decane?
A
- C5H11
- C10H22
- CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
11
Q
What is the functional group of alkanes?
A
C-C
12
Q
What is the naming ending of an alkane?
A
-ane
13
Q
What is the functional group of alkenes?
A
C=C
14
Q
What is the naming ending of an alkene?
A
-ene
15
Q
What is the functional group of an alcohol?
A
-OH
16
Q
What is the naming ending of an alcohol?
A
-ol
17
Q
What is the functional group of a halogenoalkane?
A
- F
- Cl
- Br
- I
18
Q
What is the naming rule of halogenoalkanes?
A
fluoro-
chloro-
bromo-
iodo-
19
Q
What are the rules for naming compounds?
A
- Decide if alkane or alkene (-ane or -ene)
- Find the longest chain
- Identify side chains starting with the smallest carbon number
- Place hyphens between numbers and words
- If there’s more than one side chain of the same type, separate any consecutive numbers with commas
- Use di-, tri-, tetra- etc for side chains of the same type
20
Q
How do you name molecules as Z/E isomers?
A
- Assign priority groups
- Identify which atom bonded to the carbon has the highest atomic number
- If they’re diagonally opposite it’s an E isomer
- If they’re not diagonally opposite it’s a Z isomer
- If 2 attached atoms have the same atomic number than look at the next bonded atom ie. CH3CH2CH2>CH3CH2>CH3
21
Q
What is the system of naming compounds called?
A
Nomenclature
22
Q
What is an aliphatic hydrocarbon?
A
Where the carbon atoms are joined together in either straight chains (unbranched) or branched chains
23
Q
What is an alicyclic hydrocarbon?
A
Where the carbon atoms are joined together in a structure but are not aromatic
24
Q
What is an aromatic compound?
A
Where there’s at least one benzene ring in a structure
25
What is an alkyl group with one carbon chain called?
Methyl
26
What is an alkyl group with two carbon chain called?
Ethyl
27
What is an alkyl group with three carbon chain called?
Propyl
28
What is an alkyl group with four carbon chain called?
Butyl
29
What is an alkyl group with five carbon chain called?
Pentyl
30
What is an alkyl group with six carbon chain called?
Hexyl
31
What is an alkyl group with seven carbon chain called?
Heptyl
32
What is an alkyl group with eight carbon chain called?
Octyl
33
What is an alkyl group with nine carbon chain called?
Nonyl
34
What is an alkyl group with ten carbon chain called?
Decyl
35
What is the formula of an aldehyde?
-CHO
36
What is the suffix of an aldehyde?
-al
37
What is the formula of a ketone?
C-CO-C
38
What is the suffix of a ketone?
-one
39
What is the general formula of an alkane?
CnH2n+2
40
What is the general formula of an alkene?
CnH2n
41
What is the general formula of an alcohol?
CnH2n+1OH
42
What is an empirical formula?
The smallest whole number ratio of atoms of the elements in a compound
43
How can you work out the empirical formula if you have the mass of each formula in a compound?
1. Calculate the number of moles of each element (n=m/Mr)
2. Divide by the smallest value
4. Change the ratio to whole numbers
5. Write the formula
44
What does the molecular formula show?
The numbers and types of atoms in a compound
45
If you have the empirical formula and the molecular mass, how do you work out the molecular formula?
1. Calculate the relative empirical mass using the empirical formula
2. Divide the relative molecular mass by the empirical formula
3. Multiply each atom in the empirical formula by the number calculated in step 2 and write the molecular formula
46
When might it be good to use a displayed formula?
Useful when considering the shape/size of a molecule but this is time consuming + easy to draw complex molecules incorrectly
47
When might it be useful to use a structural formula?
- give a feel for the arrangement of atoms in a molecule + can be drawn quickly
- physical properties often relate to chain length + branching, making this type of representation useful
48
Why might someone use a skeletal formula?
- the chemistry of organic compounds is often related to their functional groups
- skeletal formula focuses the attention on this part of the molecule
- often used in constructing mechanisms e.g. flow charts that model electron movement in chemical reactions
49
What is a skeletal formula?
Simplified structural formula drawn by removing hydrogen atoms from alkyl chains
50
What does unsaturated mean?
Organic chemicals containing at least one carbon-carbon double covalent bond
51
What is a hydrocarbon?
Compounds that contain only hydrogen and carbon
52
What does saturated mean?
An organic compound containing only single covalent bonds
53
What form a cyclic compounds commonly shown in?
Skeletal formula
54
What is the molecular formula of a benzene ring?
C6H6
55
Why is the benzene ring in aromatic compounds very stable?
- the electrons are shared across all the carbon atoms
| - this part of the molecule is rarely involved in the chemical reactions + is often represented using skeletal formula
56
Give one use of butan-2-ol.
Brake fluid
57
What is an isomer of Helene?
Cyclohexane
58
What can cause structural isomers?
- alkyl groups in different places
- functional groups bonded to different parts of parent chain (e.g. primary alcohol, secondary alcohol, tertiary alcohol)
- different functional groups e.g. aldehyde vs ketones
59
What is a structural isomer?
Compounds with the same molecular formula but a different structural formula
60
What is a functional group?
A group of atoms responsible for the chemical reactions of a compound
61
What are stereoisomers?
Organic compounds with the same molecular formula and structural formula but have a different arrangement of atoms in space
62
What is cis/trans isomerism?
A type of E/Z isomerism in which the two substituent groups attached to both carbon atoms of the C=C double bond are the same
63
What is E/Z isomerism?
A type of stereoisomerism caused by the restricted rotation around the double bond - the two different groups attached to both carbon atoms of the C=C double bond
64
How do you use the Cahn-Ingold-Prelog (CIP) rules to identify E/Z isomers?
1. Locate the C=C double bond in the molecule + redraw it to show the substituents
2. Focus on one carbon atom and assign the priority of each substituent based on its relative atomic mass - the highest is given the highest priority. Then assign the priority of the second carbon atom
3. If the highest priority groups are on the same side of the C=C double bond, then the isomer is Z. If the highest priority groups are on different sides of the C=C double bond, then the isomer is E
65
What is a covalent bond?
Electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
66
What does homolytic fission?
Two highly reactive, neutral species called radicals
67
When does homolytic fission occur?
When a covalent bond breaks + each electron from the covalent bond goes to different bonded atoms
68
What is the general equation that summarises homolytic fission?
X-Y --> X. + Y.
69
How does the homolytic fission of a chlorine molecule occur?
Cl-Cl --> 2Cl.
- UV radiation causes the covalent bond to break
- one electron from the covalent bond goes to each chlorine atom
70
When does heterolytic fission occur?
When a covalent bond breaks and both electrons go to one of the bonded atoms, resulting in a positive and a negative ion
X-Y --> X+ + Y-
E.g. The dipoles on the carbon and bromine on 2-bromopropane can cause heterolytic fission under certain circumstances and therefore leave a carbocation and a bromide ion
71
What happens when a positive and negative ion or two radicals collide?
A covalent bond forms
72
Why are carbocations very reactive intermediates?
Because they're unstable
73
What is the shape and bond angle in alkanes?
Tetrahedral, 109.5º
74
How do the C-C and C-H bonds form in alkanes?
Overlap of the electron clouds from each atom making a sigma bond
75
Why are alkanes non-polar?
Electronegativity of hydrogen and carbon is very similar so no significant dipoles form
76
What are the forces between alkane molecules and how do they arise?
- electrons moving around the shells occasionally causes lack of balance of charge distribution
- causes an instantaneous dipole
- induces dipoles on neighbouring molecules
- causes induced dipole-dipole interactions: London forces
77
What is the boiling point of a substance?
- precise temp that substance changes from gas to liquid or vice versa
- as bp changes with pressure, standard vales are given in K at 100kPa
78
How does the carbon chain length affect the boiling point of alkanes?
- as alkane chains get longer their relative molecular mass increases
- larger molecules have more areas of surface contact between adjacent molecules
- increases the number of induced dipole-dipole forces (more London forces)
- more energy needed to overcome the intermolecular attraction so it can change state
- positive correlation when chain length plotted against bp
79
How does branching affect the boiling point of alkanes?
- more branching = fewer areas of surface contact as molecules can't pack together as closely
- branched molecules have fewer London forces than the straight chain isomer with the same molecular formula
- branched molecules have a lower bp than the equivalent straight chain isomer
80
Why do alkanes have a low reactivity?
- all the covalent bonds in alkane molecules have high bond enthalpies (large amounts of energy required to break the bonds)
- the carbon-hydrogen sigma bonds have very low polarity because carbon + hydrogen's electronegativities are almost the same
81
What are alkanes often used for?
- fuels
| - undergo combustion transferring stored chemical energy to a usable form e.g. thermal energy
82
What is combustion?
Rapid oxidation reaction combining oxygen (usually from air) with another substance
83
When does complete combustion occur?
Plentiful supply of air (oxygen)
84
What colour flame does complete combustion produce on a Bunsen burner?
Clean, blue flame transferring max amount of thermal energy as fully oxidises carbon and hydrogen
85
What fuel do Bunsen burners usually burn?
Methane
86
What is the equation for the complete combustion of methane?
CH4 + 2O2 --> CO2 + 2H2O
87
When does incomplete combustion occur?
When there is a limited supply of air (oxygen)
88
What colour flame does a Bunsen burner produce during incomplete combustion?
Yellow
89
What are the equations for the incomplete combustion of methane?
2CH4 + 2 1/2O2 --> CO + C + 4H2O
2CH4 + 3 1/2O2 --> CO2 + CO + 4H2O
3CH4 + 4 1/2O2 --> CO2 + CO + C + 6H2O
90
What condition must be present for radical substitution to take place?
UV light
91
Briefly, what happens during radical substitution with halogens?
- homolytic fission of halogen molecules forming radicals
- hydrogen atom is substituted for a halogen atom
- if reaction conditions maintained, substitution can continue until all H atoms replaced in original alkane by halogen atoms
92
What are the three stages of radical substitution and what happens in each?
- initiation: homolytic fission causing the formation of 2 radicals
- propagation: two repeated steps that build up the desired product in a side reaction
- termination: two radicals collide to make a stable product
93
Why is radical substitution difficult to control and unpredictable?
Reactions are randomly caused by a v reactive radical colliding with another species
94
How must the end result of radical substitution be treated to get the desired produce and why?
- mixture of products is formed
| - chromatography or fractional distillation needed to separate products before they can be used
95
Describe the initiation step of the chlorination of methane produce chloromethane, including the conditions needed.
Cl2 --> 2Cl•
| -UV light or temps of about 300ºC needed
96
Describe the propagation step of the chlorination of methane to produce chloromethane.
CH4 + Cl• --> •CH3 + HCl
•CH3 + Cl2 --> CH3Cl + Cl•
-step 1 generates an alkyl radical and a hydrogen chloride
-step 2 generates the desired product + regenerates the chlorine radical
97
Describe the termination stage of the chlorination of methane to form chloromethane.
2Cl• --> Cl2
2•CH3 --> C2H6
•CH3 + •Cl --> CH3Cl
Mixture of products formed by the random collisions between radicals. Low atom economy as only one desired product (CH3Cl)
98
Why might there be more than 3 products formed from the chlorination of methane using radical substitution?
Chloromethane molecules molecules may collide agin with other chloride radicals causing further substitutions
99
What are the equations for each step of the bromination of ethane to produce bromoethane?
```
Initiation: Br2 --> 2Br•
Propagation: C2H6 + Br• --> •C2H5 + HBr
•C2H5 + Br2 --> C2H5Br + Br•
Termination: 2Br• --> Br2
2•C2H5 --> C4H10
•C2H5 + Br• --> C2H5Br
```
100
Describe the C=C double bond in alkenes.
- sigma bond formed between 2 carbon atoms using the direct overlap of electron clouds of two atoms (s or p orbitals)
- pi bonds formed by electrons in adjacent p-orbitals overlapping above and below the carbon atoms. Can only be made after a sigma bond has been formed
101
How do pi bonds affect the movement of the atoms in alkenes?
Holds atoms in position by restricting rotation around the double bond, hence alkenes have a flat shape in the region of the double bonds
102
Describe the shape and bond angle around the carbons in the C=C double bond.
Trigonal planar. 120º
103
Which part of the alkene molecules are reactive and why?
Pi bond because of the high electron density around it
104
What is the first member of the alkene homologous series?
Ethene
105
What are the 3 areas of electron density around the carbon atoms in ethene?
- 2 separate covalent bonds between C atoms + two different H atoms (sigma bond)
- covalent bond between the 2 C atoms, made from a sigma and a pi bond
106
What causes E/Z isomerism?
The restricted rotation around the double bond
107
Which are more reactive, alkanes or alkenes, and why?
- alkenes due to the double bond
- bond enthalpy for C-C is +347kJmol^-1 and for a C=C bond is +612kJmol^-1, meaning bond enthalpy of pi bonds is (612-347=265kJmol^-1)
- in chemical reactions the pi bonds break first as lower bond enthalpy and react leaving the sigma bond between the two carbon atoms
- double bond is an area of high electron density attracting electrophiles e.g. Br2, HBr + NO2+
108
What happens in addition reactions?
Two or more molecules become bonded to make one product
109
What happens in a hydrogenation reaction?
An addition in which hydrogen is added across the C=C bond of an alkene
110
What are the conditions and reagents needed for the hydrogenation of an alkene?
150ºC, nickel catalyst, hydrogen (alkene)
111
What happens in a halogenation reaction?
An addition reaction in which a halogen is added across the C=C double bond becoming a saturated dihaloalkane (can be used to test for saturation)
112
How can halogenation be used to test for saturation?
Bromine/iodine solution mixed w a saturated compound there's no reaction. When added to an unsaturated compound e.g. ethene, decolorisation occurs as an addition reaction occurs
113
Describe the reaction mechanism for the bromination of propene.
- bromine is non polar
- when the bromine molecule becomes close to the electron rich C=C bond a dipole is induced on the bromine molecule
- ∂+ side of the molecule is attracted to the electron density of the C=C bond
- electrons from π bond make bond w a bromine atom
- causes heterolytic fission of the bromine molecule
- +ve charge remains on second carbon atom
- leaves a v reactive species known as a carbocation
- 2 electrons from the bromide ion are shared with the carbocation, making a second bond and a stable product
114
What is an electrophile?
An electron pair acceptor
115
When is hydration used in industry?
To make alcohols
116
What is a reaction mechanism?
A model showing the movement of electrons in an organic reaction
117
What conditions are needed in hydration?
- phosphoric acid catalyst
- 300ºC
- 65 atm
- H2O reagent
118
What is produced by the addition of a hydrogen halide to an alkene?
A haloalkane
119
Describe the mechanism of the addition of hydrogen bromine to ethene.
- large difference in electronegativity between H and Br so a HBr molecule is polar. H (delta +) of HBr is attracted to the high electron density of C=C bond
- electrons in pi bond make a bond w the H causing heterolytic fission (electrons in HBr molecule given to Br atom making a Br- atom). Carbocation also made
- Br- ion + carbocation bond to make a stable product
120
What does Markownikoff's Rule state?
When H-X is added to an unsymmetrical alkene the H become attached to the C with the most H atoms to start with
121
Why does Markownikoff's Rule happen?
Carbocations that have alkyl groups attached are more stable than those with H atoms attached
122
Which are most stable, primary, secondary or tertiary carbocations?
Tertiary
123
What bonds are broken during polymerisation?
pi bonds
124
What is the polymer formed when the monomer is ethene and what are the uses of the polymer?
- poly(ethene)
| - plastic bags + bottles
125
What is the polymer of a propene monomer and what are its uses?
- poly(propene)
| - ropes + crates
126
What is the polymer of a chloroethene monomer and what are its uses?
- poly(chloroethene) (PVC)
| - electrical cable insulation
127
What is the polymer of the phenylethene monomer and what are its uses?
- poly(phenylethene) (polystyrene)
| - packaging
128
What is the polymer of the tetrafluoroethene monomer and what are its uses?
- poly(tetrafluoroethene) (Teflon)
| - non-stick coatings on cooking pans
129
How do you deduce the structure of a polymer?
1. Draw the monomer structure so the C=C bond is the focus of the diagram
2. Draw square brackets around the monomer
3. Change the C=C to C-C + draw 2 lines extending from each C atom through the square brackets
4. Add a subscript 'n'
130
Give some examples of uses of synthetic polymers.
- clothing
| - materials in cars
131
Why are synthetic polymers so important?
due to their versatility
132
What are addition polymers?
- saturated organic compounds + so are very stable
- don't get attacked by environmental conditions/microorganisms so remain chemically unchanged for hundreds of years
- made from compound made available from processing crude oil (non renewable resource, being used faster than planet's natural processes can make it so may come a time where we can't use it)
133
In what ways is polymer waste handled?
- landfill
- combustion
- combustion with electrical generation
- reusing
- recycling
- using them as organic feedstock
134
How is polymer waste handled in landfill?
- large holes dug into landscape, lined to stop contaminants seeping into water table. Rubbish put into holes + compacted. When site full its copped + landscape
- after buried conditions change from normal atmospheric to anaerobic + often limited supply of water. Reduces rate of biodegradable material's decomposition. As many plastics are non biodegradable the waste doesn't break down + can become a danger to wildlife
135
How is polymer waste handled through combustion?
- plastics: mainly organic + can be burnt. Contain large amounts of carbon so combustion releases CO2 (greenhouse gas linked to climate change)
- depending on plastic other toxin/polluting gases (e.g. HCl) can be made. Can be removed by using gas scrubbers, where a base (e.g. CaO) neutralises acidic gas
- plastics: high calorific value so can be burnt in power stations. Chemical energy transferred can be used to drive turbines + generate electricity
136
How is polymer waste handled through recycling?
- plastics have to be sorted into different types, expensive as either labour intensive or uses costly high technology to automate the process
- plastics cleaned, melted down + reshaped to new products. Limited market for recycled plastic companies concerned about quality + whether or not there could be contamination from its previous use
137
How is polymer waste handled through organic feedstock?
when plastics sorted into different types, a series of chemical reactions can be used to break down the plastic polymers into small organic molecules, allowing recovered chemicals to be used in other industrial reactions
138
How are biodegradable polymers used to combat polymer waste?
- e.g. plant starch
- research into plastics that can be broken down chemically by microorganisms + environmental factors into harmless (even useful) substances. Sometimes mixed w an addition polymer. Starch part breaks down so polymer chain smaller + the material biodegrades. Growing concern small pieces of addition polymers still cause hazards to ecosystem
- if only bio polymer used new material called bioplastic. Plant starch used to make bin bags. If starch derived from sustainable farming methods then material classified 'carbon neutral'
- to be fully decomposable plastic must decompose landfill about as quickly as compost forms from grass clipping + other green waste. Only products should be CO2, H2O, inorganic compounds + biomass
- substances e.g. poly(lactic acid) decompose in about 180 days + currently being used to make cold-drink cups + wrap fresh fruit + vegetables
139
How are photodegradable polymers used to combat polymer waste?
- break down chemically using energy w wavelengths similar to light. either adition polymers w bonds within their structures weakened by absorption of light or have an additive affected by light, which weakens bonds within the polymer. Once polymer exposed to light, begins to break down + not possible to stop process
- photodegradable plastics in landfill may not be exposed to sufficient light to degrade
