AS Level
TOPIC 15 ANSWERS & MARK SCHEMES
QUESTIONSHEET 1
DISTILLATION OF PETROLEUM
a) (i)
Mixture of alkanes with a wide range of Mr (1)
(ii) Middle East crude has a relatively high proportion of alkanes of high Mr (1)
b) (i)
Mixture of alkanes / compounds (1)
of similar boiling point (1)
(ii) Boiling point (1)
c) Sketch to show:
furnace for partial vaporisation of crude oil (1)
fractionating column (1)
any indication of trays and bubble caps (1)
injection of feedstock (1)
(superheated) steam injected at base of column (1)
Maximum 3 marks
d) (i)
Cool / 110 ºC at top to hot / 340 ºC at bottom (1)
(ii) Petroleum gases from top of column (1)
Light gasoline / petrol from top or near top (1)
Then, in decreasing order:
heavy gasoline / naphtha (1)
Half marks if shown at
kerosene / paraffin (1)
incorrect levels
diesel fuel / DERV (1)
lubricating oil (1)
Maximum 4 marks
e) Material
Use
Bitumen (1)
Road surfacing / for making fuel oil (1)
f) Industrial operation is continuous (1)
Laboratory operation is a batch process (1)
AS Level
TOPIC 15 ANSWERS & MARK SCHEMES
QUESTIONSHEET 2
CRACKING
a) (i)
Insufficiently volatile / does not fully vaporise in the cylinder (1)
(ii) CH3(CH2)8CH3 → CH3(CH2)6CH3 + CH2 = CH2 (1)
CH3(CH2)8CH3 → CH3(CH2)5CH3 + CH3CH = CH2 (1)
(iii) Lower alkanes are useful as petrol (1)
Lower alkenes can be polymerised (1)
Or one example of polymerisation (1)
Alkenes are used as feedstock for the petrochemical industry (1)
Or one example of this (1)
b)
Thermal cracking
Catalytic cracking
Conditions
High temperature (½)
High pressure (½)
High temperature (½)
Slight pressure (½)
Zeolite / alumino-silicate catalyst (1)
Type of bond breaking
Homolytic (1)
Heterolytic (1)
Type of reaction intermediate
Free radicals (1)
Carbonium ions / carbocations (1)
Principal products
Alkenes (1)
Motor fuels / arenes (1)
c) Reaction occurs on the surface of a catalyst (1)
With prolonged use the surface becomes coated / inefficient / will not properly adsorb reactants (1)
so the catalyst must be replaced (1)
Maximum 2 marks
AS Level
TOPIC 15 ANSWERS & MARK SCHEMES
QUESTIONSHEET 3
FUELS
a) (i)
Methane -882/16 = - 55.1 kJ g-1 (1)
Octane -5512/114 = - 48.4 kJ g-1 (1)
(ii) Volume problem if CH4 is gaseous (1)
Cost / weight / escape problem if CH4 is liquid (1)
Transfer / refuelling problem for gaseous fuels (1)
Maximum 2 marks
b) Disadvantage :
Advantage :
c) (i)
too great a volume/bulky or usable volume would require high pressure so eg reinforced
dense containers (1)
non-polluting/only forms water/renewable (1)
Benzene
Carcinogenic / causes cancer (1)
Tetraethyllead
Exhaust emissions are poisonous / cause brain damage in children (1)
(ii) Carbon monoxide (1) CO (1)
(iii) Carbon dioxide (1) Global warming (1)
Nitrogen dioxide (1) Acid rain (1)
d) (i)
Compression ignition / no spark plug (1)
(ii) Higher alkanes / higher Mr / higher b.p. / greater chain length (1)
(iii) Particulate carbon (1)
e) C neutral : absorbs as much carbon dioxide during growth as during combustion (1)
C footprint : only gives out carbon dioxide/net producer of carbon dioxide (1)
AS Level
TOPIC 15 ANSWERS & MARK SCHEMES
QUESTIONSHEET 4
EPOXYETHANE AND ETHANE-1,2-DIOL
a) (i)
O
2CH2 = CH2(g) + O2(g) → 2CH2 – CH2(g) (1)
(ii) Silver (1)
(iii) To relieve the pressure / by Le Chatelier’s principle (1)
equilibrium is disturbed to the side with fewer gas molecules (1)
(iv) Risk of explosive oxidation if too much ethene is present (1)
b) (i)
The C ⎯ O ⎯ C bond angle is only 60º (1)
∴ the ring is strained / strain is relieved when the ring opens up (1)
(ii) CH2
O + CH3OH →
CH2
CH2OH
(1)
CH2OCH3
(iii) CH2
O + CH3O(CH2) 2OH → CH3O(CH2)2O(CH2)2OH (1)
CH2
c) The molecule hydrogen bonds with water through two OH groups (1)
∴ there is little loss through vaporisation (1)
d) (i)
A chemical reaction in which two reactants undergo addition (1)
with subsequent elimination of a small molecule, such as H2O (1)
(ii)
C
O
O
H
(1)
C
O
O
H
(iii) Instead of one molecule of acid reacting with one molecule of the diol, one acid molecule reacts with the –OH
groups of two diol molecules (1)
Or explained by formulae (1)
e) Hydraulic fluid / brake fluid (1)
AS Level
TOPIC 15 ANSWERS & MARK SCHEMES
QUESTIONSHEET 5
ADDITION POLYMERS
a) Monomer
Addition polymer
b) (i)
A simple molecule which is used in forming a polymer (1)
A large molecule formed by combination of unsaturated molecules without loss of atoms (1)
LDPE random overlap of chains with chain-branching (1)
HDPE relatively parallel chains with little chain-branching (1)
(ii) Greater impact strength
Higher melting-point
Increased transparency
Softens less easily when hot
c) (i)
any two = (2)
CH 3
CH 2 C
COOCH3
(1)
(ii)
H
CH 3
C
C
(2) deduct 1 mark per error bonds must project through brackets
CH 3 CH 3 n
d) PVC /polyvinyl chloride/poly(chloroethene) (1)
e) Polar C-Cl bonds (1)
Gives dipole attraction between chains (1)
Stronger than (1) van der Waals attraction with poly(ethane) (1)
f) Poly(ethene) (1)
OH- nucleophile attacks (1) polar C-Cl bond (1)
Poly(ethene) non-polar (1)
g) Combustion gives carcinogenic dioxins/HCl (1)
Do not biodegrade (1)
any 3
AS Level
TOPIC 15 ANSWERS & MARK SCHEMES
QUESTIONSHEET 6
HALOALKANES AS SYNTHETIC INTERMEDIATES
a) B = Ethene (1)
C = Ethyl hydrogen sulfate (1)
D = Ethanol (1)
E = Ethanoic acid (1)
F = Propanenitrile (1)
G = Propanoic acid (1)
b)
C
C2H6SO4
Reagent(s)
Concentrated H2SO4
(1)
Reagent(s)
Water
(1)
Conditions
Room temp. / 10-30 0C
(1)
Conditions
Warm / 30 - 40 0C
(1)
B
Concentrated H2SO4
Reagent(s)
C2H4
Conditions
(1)
0
170 - 180 C
D
C2H6O
(1)
Reagent(s)
Alcoholic KOH / NaOH
(1)
Reagent(s)
Aqueous NaOH / KOH
(1)
Conditions
Heat / boil
(1)
Conditions
Heat / boil under reflux
(1)
A C2H5Br
Reagent(s)
KCN / NaCN
(1)
Conditions
Heat / boil in aq. ethanol
(1)
Reagent(s)
F C3H5N
Conditions
Reagent(s)
Na2Cr2O7 + dil. H2SO4
(1)
Conditions
Heat / boil under reflux
(1)
Dilute H2SO4 / HCl(aq)
(1)
Heat / boil under reflux
(1)
E
C2H4O2
G
C3H6O2
AS Level
TOPIC 15 ANSWERS & MARK SCHEMES
QUESTIONSHEET 7
CFCs
a) (i)
(ii)
Chlorofluorocarbon (1)
Cl F
Cl C
C
F (1) (Accept CHCl2CHF2)
H H
(iii) In refrigerators / air conditioning units (1)
In the manufacture of expanded polystyrene (1)
Sprays for muscular sports injuries (1)
As cleaners (1)
Maximum 2 marks
b) (i)
An atom or group of atoms with an unpaired electron (1)
(ii) C⎯F bond is stronger than the C⎯Cl bond (1)
because the F atom is smaller than the Cl atom / the C⎯F bond is shorter than the C ⎯Cl bond (1)
(iii) Reaction 1
·
Cl + O3 → ·ClO + O2 (1)
Reaction 2
·
ClO + O → ·Cl + O2 (1)
(iv) The Cl free radical is catalyst (1)
and is not used up (1)
The Cl free radical which is used in Reaction 1 reappears as a product in Reaction 2 (1)
Because Cl free radicals are regenerated, they are available to bring about further change (1)
Maximum 2 marks
(v) At high altitudes the concentrations of the gaseous reactants are very low (1)
c) (i)
Greater intensity of ultraviolet light reaching the Earth’s surface (1)
can lead to skin cancer (1)
(ii) Contribute to the greenhouse effect (1)
(iii) Butane / ammonia / dinitrogen monoxide (1)
AS Level
TOPIC 15 ANSWERS & MARK SCHEMES
QUESTIONSHEET 8
USES OF OTHER ORGANIC HALOGENOCOMPOUNDS
a) (i)
Paint / electrodeposited metals will not adhere to a greasy surface (1)
(ii) Precaution
Reason
Efficient fume extraction (1)
Vapour is highly toxic / causes liver damage (1)
(iii) Dry cleaning (1)
b) (i)
Durability / resistance to weathering (1)
Low maintenance costs / does not need painting (1)
Fire resistance (1)
(ii) Name
Use
c) (i)
Poly(tetrafluoroethene) / PTFE (1)
Non-stick pans (1)
Slow to break down in the environment / effective for a long time (1)
(ii) Can enter the food chain (1)
d) (i)
Forms a blanket of non-flammable vapour (1)
which excludes air / oxygen (1)
(ii) Foam extinguishers may cause a short circuit / BCF cannot do so (1)
AS Level
TOPIC 15 ANSWERS & MARK SCHEMES
QUESTIONSHEET 9
FERMENTATION
a) (i)
Glucose / fructose (1)
(ii) In the absence of air / oxygen (1)
(iii) C6H12O6 → 2C2H5OH + 2CO2 (2)
Award (1) for reactant and (1) for products if balance is correct.
(iv) Catalyst (1)
b) (i)
Flexible tube
Gas syringe (1)
Thermostaically controlled water bath (1)
Sugar solution + yeast
(ii)
Rate
(1)
Temperature
(iii) Rate of reaction / fermentation increases with temperature (1)
until higher temperatures denature the enzyme (1)
c) Brazil has a warm climate (½)
with a high intensity of sunlight for long periods (½)
Therefore sugar cane (accept ‘plants’) grows quickly (½)
Brazil has little reserves of mineral oil (½)
and cannot afford using scarce foreign currency to purchase oil (½)
Maximum 2 marks
d) Rapid (1)
Synthetic ethanol contains fewer impurities (1)
AS Level
TOPIC 15 ANSWERS & MARK SCHEMES
QUESTIONSHEET 10
SYNTHETIC ETHANOL PROCESS
a) (i)
CH2 = CH2(g) + H2O(g) ¾ CH3CH2OH(g) (1)
(ii) Electrophilic (½) addition (½)
b) (i)
Carbocation / carbonium ion (1)
(ii) Arrow bottom left (should be encircled) should point from the bond to the O atom (1)
c) Advantage
Disadvantage
d) (i)
Increased rate of reaction / attaining equilibrium (1)
Lower yield of ethanol at equilibrium (1)
Higher yield of ethanol at equilibrium (1)
Equilibrium is disturbed to the side with fewer gas molecules (1)
so as to relieve the pressure / in accordance with Le Chatelier’s principle (1)
(ii) Higher power costs for the compressor (1)
High cost of constructing / maintaining thick-walled pressure vessels (1)
e) (i)
So that it presents a larger surface area to the reactants (1)
(ii) No effect (1)
f) Cool / condense to give aqueous ethanol (1)
Concentrate by fractional distillation (1)
Add methanol (1)
AS Level
TOPIC 15 ANSWERS & MARK SCHEMES
QUESTIONSHEET 11
ETHANOL AS A FUEL
a) (i)
C8H18(l) + 12½O2(g) → 8CO2(g) + 9H2O(l) (1)
(ii) C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l) (1)
b) (i)
m (C8H18) = 1000 x 0.72 = 720 g (½)
∴ n (C8H18) = 720/114 = 6.316 mol (½)
∴ enthalpy change = -5512 x 6.316 ≈ 34,800 kJ (1)
(ii) m (C2H5OH) = 1000 x 0.79 = 790 g (½)
∴ n (C2H5OH) = 790/46 = 17.17 mol (½)
∴enthalpy change = -1371 x 17.17 ≈ 23,500 kJ mol-1 (1)
c) (i)
6.316 mol C8H18 → 6.316 x 8 = 50.53 mol CO2 (1)
∴ m (CO2) = 50.53 x 44 = 2223 g CO2 (1)
(ii) 17.17 mol C2H5OH → 17.17 x 2 = 34.34 mol CO2 (1)
∴ m (CO2) = 34.34 x 44 = 1511 g CO2 (1)
d) (i)
2223/34800 = 0.0639 g kJ-1 (1)
(ii) 1511/23500 = 0.0643 g kJ-1 (1)
Comment
Similar masses of CO2 in both cases, therefore a similar impact on the environment (1)
e) Ethene originates from crude oil / fossil fuel / petroleum (1)
∴ on combustion ethanol releases additional CO2 to the atmosphere (1)
Using ethanol made by fermentation recycles CO2 (1)
(No marks for ‘greenhouse effect’ unless related to CO2 in the atmosphere)
AS Level
TOPIC 15 ANSWERS & MARK SCHEMES
QUESTIONSHEET 12
DISPOSAL OF ORGANIC WASTE
a) (i)
A huge range of plastics is in common use (1)
Separation is virtually impossible (1)
(ii) Paper can be pulped (1)
Vegetable waste can be composted (1)
b) Detrimental to the environment because of the large quantity of waste involved (1)
Toxic substances from industrial waste may contaminate surrounding land / enter the water table (1)
Microbiological reactions in the waste may produce toxic substances (1)
Maximum 2 marks
c) Domestic heating projects (1)
Generating electricity, using a steam turbine (1)
d) (i)
Chlorinated materials (1)
produce toxic compounds / dioxins (1)
(ii) Incomplete combustion (1)
leading to carbon monoxide / soot (1)
e) Sulfur-containing materials produce SO2 / SO3 / oxides of sulfur (1)
Nitrogen-containing materials produce NO2 / oxides of nitrogen (1)
These gases cause acid rain (1)
f) Most noxious gases / named examples are acidic (1)
∴ they can be removed by passing over a base / scrubbing with an alkaline solution (1)