Topic 6 Flashcards
(78 cards)
1
Q
What is a hydrocarbon
A
A compound made of hydrogen and carbon only
2
Q
What is the difference between a saturated and a non-saturated hydrocarbon
A
- Saturated hydrocarbon contains as many hydrogens as possible, only single bonds
- unsaturated hydrocarbon contains a carbon double bond
3
Q
What are the different formulaes to refer to organic compounds
A
- Displayed
- Structural
- Skeletal
- Molecular
- Empirical
4
Q
What is meant by the term functional group
A
It is an atom or a group of atoms in a molecule that is responsible for its chemical reactions
5
Q
What is meant by the term homologous group
A
It is a family of compounds with the same functional group, which differ in formula by CH2, from the next member
6
Q
What is the general formula of an alkane
A
CnH2n+2
7
Q
What is the general formula of an alkene
A
CnH2n
8
Q
What are the products when alkanes are burned completely in air
A
Carbon dioxide and water
9
Q
What are the prefixes of the amount of carbon atoms, up to 5
A
1 - methyl
2- ethyl
3 - propyl
4 - butyl
5- pentyl
10
Q
How is the presence of an alcohol indicated
A
By the suffix -ol
11
Q
What is a structural isomer
A
Same molecular formula but different structural formulae
12
Q
What are the two types of structural isomerism
A
- Chain isomerism
- Position isomerism
13
Q
What is chain isomerism
A
Refers to molecules with different carbon chains
14
Q
What is position isomerism
A
Refers to molecules with the same functional group attached but in a different position on the same carbon chain
e.g. propan-1-ol and propan-2-ol
15
Q
What does ‘trans’ mean for a molecule
A
Two groups are positioned diagnoally opposite from eachother
16
Q
What does ‘cis’ mean for a molecule
A
Two groups are positioned next to each other, e.g. both attached upwards
17
Q
Why can geometric isomers, ‘cis’ and ‘trans’ not occur in alkanes
A
As a double carbon bond must exist, as the double carbon bond leads to restricted rotation so that the groups attached to the double carbon bond cannot move around
18
Q
How to use the E and Z notation on a structure
A
Use priority rules to decide which atom on each side has higher priority, whichever one has the higher atomic number has higher priority
- if the higher priority are diagonally opposite it is an E-isomer
- if the higher priority are next to each other it is a Z-isomer
19
Q
What are the main 3 ways to convert crude oil into fuel
A
- Fractional distillation
- Cracking
- Reforming
20
Q
What are most crude oils and natural gases
A
Alkanes
21
Q
What is the process of fractional distillation
A
- The crude oil is first heated in a furnace, so most of it turns into vapour and is then passed into a column near the bottom
- there is a temperature gradient in the column, hotter near the bottom cooler near the top
- as the vapour passes up through the column, different fractions condense at different heights, depending on the boiling temperature
22
Q
How are the fractions separated in fractional distillation, why are some at the bottom and some at the top
A
- Near the bottom, the fractions contain larger molecules with larger chains and high boiling temperatures
- Near the top, the fractions contain smaller molecules with shorter chains and lower boiling points
23
Q
What is the process of cracking
A
- done by passing the hydrocarbons in the heavier fractions through a heated catalyst
- this causes larger molecules to break into smaller molecules
24
Q
What is the product of cracking alkanes
A
one alkane and one alkene
25
What is the process of reforming
Used to convert straight chain alkanes into branched-chain alkanes and cyclic hydrocarbons by heating them with a catalyst
- this helps them burn more smoothly in the engine
26
Equation of propane complete combustion
C3H8 + 5O2 --> 3Co2 + 4H2O
27
Products of incomplete combustion
Water, gaseous carbon monoxide or solid carbon (can be seen as soot)
28
Why is carbon monoxide so harmful
toxic gas, prevents the transport of oxygen around the body
29
Oxides of sulfur
Some molecules of crude oil contain sulfur that may not have been removed
- During combustion sulfur forms sulfur dioxide which can react in the atmosphere to form sulfur trioxide
- both these gases are acidic oxides so when dissolved in water in the atmosphere form sulfuric acid and
- they contribute to acid rain which is responsible for a lot of environmental damage
30
Oxides of nitrogen
- Combustion of alkanes containing nitrogen happens at a very high temperatures
- nitrogen molecules react with oxygen to form oxides of nitrogen
- main ones nitrogen monoxide, nitrogen dioxide
- nitrogen dioxide is acidic and when dissolved in water forms nitric acid
- contributes to environmental damage
31
What is a three way catalyst
It can remove 3 different pollutants,
carbon monoxide, unburned hydrocarbons and oxides of nitrogen
32
What are the need for alternative fuels
- Depletion of natural resources
- Climate change, global warming
- Pollution caused by combustion of alkanes
33
What is biofuel
Obtained from living matter that has died recently, rather than having died millions of years ago
34
Examples of renewable energy
Biofuel, sunlight, wind, waves and tides, geothermal
35
Two types of biofuels
Biodiesel
Bioalcohols
36
What to consider when comparing alternative fuels
Land use - how much land is used to grow the crop, could it be used for food for people?
Yield - How quickly does it grow, what percentage of the hydrogen and carbon atoms end up in the fuel?
Manufacture and transport -How much energy is used in growing, processing and transporting the crop?
Carbon neutrality - How close is it to being carbon neutral?
37
What is a radical
A species with an unpaired electron, it is represented in mechanism by a dot
38
How is a radical formed
By homolytic fission of a covalent bond and results in the formation of radicals
39
What is halogenation (may be called chlorination, bromination)
A reaction, where one of the hydrogen atoms in methane has been replaced (or substituted) by an atom of chlorine
40
What are the three stages of free radical substitution
1. Initiation
2. Propagation
3. Termination
41
What happens in step one, initiation, to a chlorine molecule
With the help of UV light, the chlorine molecule is broken down into two chlorine radicals 'homolytic fission'
42
What happens in step two, propagation, to a chlorine radical and methane, and then what can happen after
Methane loses a hydrogen and becomes a radical CH3.
Chlorine gains a hydrogen to become HCl and is no longer a radical.
CH3. radical can then react with Cl2, CH3. gains a Cl to form CH3Cl and then Cl2 forms a Cl. radical
43
What happens in step three, termination
Two radicals must react together
Cl. + Cl. --> Cl2
CH3. + CH3. --> C2H6
Cl. + CH3. --> CH3Cl
44
Why is free radical substitution not a good method to use
The likelihood of further reactions occurring is high, so the yield is low for the product which is needed, and the products will have to be separated
45
What is homolytic fission
The breaking of a covalent bond where each of the bonding electrons leaves with one species, forming a radical
46
What is an alkene
Contains a double carbon bond, they are unsaturated
47
What bonds make up an alkenes double carbon bond
Sigma bond and pi bonds
48
What is the test for a double carbon bond
Bromine water
The water becomes discoloured
The bromine water goes from orange to colourless due to the addition reaction breaking the double carbon bond
49
What is hydrogenation
When hydrogen is added to an alkene
50
How do you convert alkenes into an alkane
H2, heat and a nickel catalyst
51
How do you form dihalogenoalkanes from alkenes
Alkene + (Br2, Cl2)
52
How do you form an alcohol from an alkene
H2O (steam)
H3PO4
53
How do you form a halogenoalkane from an alkene
By the addition of a halogen halide e.g. HBr, HCl
54
How do you form a diol from an alkene
KMnO4, dilute H2SO4
55
What do curly arrows represent in mechanism
The movement of a pair of electrons
56
What is created in step one of electrophilic addition of hydrogen halides
A carbocation intermediate
57
Why is there two products when the alkene and the attacking molecule are both unsymmetrical in electrophilic addition of hydrogen halides
There are two products because the attacking molecules can attach in two different places
- Major product and Minor product
58
What is an unsymmetrical attacking molecule
Where the two atoms are different e.g. HBr
59
How is the major and minor product determined
The carbocation intermediates produced can be, primary, secondary, or tertiary
- Tertiary > secondary > primary in stability
- the most stable is the major product produced
60
Which carbocation intermediate is the most stable
Tertiary
61
What is an electrophile
A species that is attracted to a region of high electron density
62
Explain the trend in boiling points of alkanes
As the carbon chain length increases the boiling point increases, this is because the points of contact between molecules increase, therefore more london forces increasing the overall intermolecular forces of attraction so more energy is needed to separate the molecules
63
What are the conditions needed for the reaction of ethene and steam to produce ethanol
350 degrees
60 to 70 atm pressure
Phosphoric (V) acid pressure
64
Why is reforming used in the production of petrol
To produce more efficient burning petrol
65
Why are substitution reactions faster with 1-bromobutane than with 1-chlorobutane
The C-Br bond is weaker as bromine is a larger atom than chlorine, therefore the activation energy is lower with 1-bromobutane with more collisions per second
66
Write the balanced equation for the reforming of heptane into methylcyclohexane
C7H16 --> C7H14 + H2
67
What does the addition of ethanol do to halogenoalkanes
Increases their solubility
68
Why is the cracking of larger alkane molecules important in industry
- The demand is greater for shorter molecules
- Short chain alkanes are more useful products
69
Why is a sigma bond stronger than a pie bond
-Overlap of orbitals in sigma bonds is along the lines between the 2 nuclei
- whereas pie bonds there is sideways overlap
70
Which bond is stronger C-Br or C-I?
C-Br is stronger than C-I, this is because the Br atom is smaller
71
Why does the termination stage in radical substitution result in the reaction ending
Two radicals reacting together creates a stable product
72
What bond type is broken when Cl2 is converted into 2Cl. radical
Sigma bond
73
Why sometimes when naming a compound it has to be E/Z not cis/trans
As the groups on the carbon aren't the same
74
Why is sodium hydrogencarbonate solution added to the organic layer when preparing 2-chloro-2-methylpropane, and once it is added why is it important to open the tap
It is added to neutralise any excess HCl
it is important to open the tap to relieve the built up pressure
75
What is an example of a common drying agent
sodium sulfate
76
Why should the bulb of the thermometer be opposite the opening to the condenser
So the temperature measured of the water vapour is just as it is about to enter the condenser
77
Why is it important that water goes in at the bottom of the condenser and out at the top
If water goes in at the top is means the condenser doesn't fully fill, and it will have inefficient condensation
78
How to prepare a volume of solution
1. Flask - use a volumetric flask or graduated flask
2. Weighing - weigh the acid in a weighted container and record the exact mass
3. Dissolve, transfer and washings
4. Mark and mix - make up the the correct volume mark and then mix
