organic paper 1

Question 1

explain why there is an attraction between c=c double bond and br2

Answer 1

M1 C=C electron rich / area of high electron density
M2 Br-Br becomes polarised
M3 δ+ Br attracted to C=C

Question 2

problem of distillation

Answer 2

Anti-bumping granules
1a no anti-bumping granules / add anti-bumping
granules
1b to create smaller bubbles / to prevent large
bubbles / to prevent mixture jumping into
condenser
Stage 2
Open system with no thermometer
2a system should be closed (above flask) to
prevent gases escaping
2b should be closed with (bung +) thermometer
2c to allow collection of propanone (only) / to
prevent distillation of other components / to
stay in suitable temperature range
Stage 3
The water direction in the condenser
3a water flows in wrong direction through
condenser / change water direction
3b condenser not cool enough / not full of water
3c product may not condense / comes through as
gas

Question 3

explain why propanone has a lower bp than propan2ol

Answer 3

M1 propan-2-ol has stronger intermolecular forces
M2 propan-2-ol has hydrogen bonds between molecules
M3 propanone has dipole-dipole forces and/or van der
Waals’ forces

Question 4

state the benefit to life on earth of ozone in the upper atmosphere

Answer 4

Absorbs (harmful) ultraviolet / uv (light / radiation)

Question 5

suggest one reason why use of fcfs were not restricted for several years

Answer 5

• lack of evidence that ozone was being depleted
• lack of alternatives to CFCs
• commercial interest to continue to use CFCs
• hard to obtain international agreement

Question 6

state and explain how cdc-11 is able to contribute to global warming

Answer 6

M1 absorbs infrared radiation
M2 molecule has polar bonds

Question 7

naphtha to propene

Answer 7

M3 (thermal) cracking
M4 to make alkenes / propene / shorter molecules

Question 7

crude oil to naphtha

Answer 7

M1 fractional distillation
M2 separated into mixtures of compounds with similar boiling
points / similar sized molecules

Question 8

propene to polypropylene

Answer 8

M5 (addition) polymerisation
M6 molecules joined together or to produce long chain molecule

Question 9

why poly(propene) is unreactive

Answer 9

no polar bonds (in chain) / non-polar

Question 10

suggest why it’d benenfiial for some polymers to be biodegradable

Answer 10

to prevent build-up of waste (in landfill) OR
they can be broken down by natural processes

Question 11

define the term enthalpy change

Answer 11

Heat (energy) change at constant pressure

Question 12

explain why the value given for the o=o bond enthalpy is not a mean value

Answer 12

Oxygen / O2 is the only substance that has O=O bond

Question 13

A student has samples of these four compounds but does not know which is which:
* butanoic acid
* 2-methylpropanal
* 2-methylpropanoic acid
* 2-methylpropan-1-ol
Step 1: Two of these compounds can be identified by simple chemical tests.
Step 2: The other two compounds, that contain the same functional group as each
other, can then be distinguished using a spectroscopic technique.
Describe how these two steps could be used to identify which compound is which.

Answer 13

Stage 1
Identifying aldehyde / 2-methylpropanal
1a Tollens’ or Fehling’s
1b silver mirror or orange-red precipitate
Stage 2
Identifying alcohol / 2-methylpropan-1-ol
2a acidified potassium dichromate
2b (orange to) green
2c tests done in suitable sequence to distinguish
aldehyde from alcohol,
Stage 3
Distinguishing the acids
3a using IR spectroscopy to distinguish the two
acids (or other suitable technique)
3b use finger-print region of IR spectrum (feature
of spectrum to use)
3c look for exact match to spectra of known
compounds (what the difference is)

Question 14

Analysis of the products of this reaction shows the formation of a compound with the
empirical formula CCl2F
Give an equation to represent a termination step forming this compound.
Show the structural formula of the product in the equation.

Answer 14

*CCl2F → CCl2FCCl2F

Question 15

The ethanol produced by fermentation of glucose may be regarded as a
carbon-neutral fuel.
Justify this statement. Include the relevant chemical equations in your answer.

Answer 15

M1 6CO2 + 6H2O → C6H12O6 + 6O2
M2 C6H12O6 → 2C2H5OH + 2CO2
M3 2C2H5OH + 6O2 → 4CO2 + 6H2O
M4 explains with reference to relevant equations that formation of
C6H12O6 takes in 6CO2 and fermentation and combustion of
ethanol gives out 6CO2

Question 16

Coffee beans from South America are exported to Europe in an outer layer called
silverskin.
The waste silverskin can be fermented to produce a solution containing propanone,
ethanol and butan-1-ol

Suggest why ethanol produced in Europe using silverskin from South America is less
likely to be carbon-neutral than ethanol produced from crops grown in Europe

Answer 16

transport (from South America to Europe) produces CO2 /
has C emissions / has larger C footprint

Question 17

There is a very low yield of butan-1-ol from but-1-ene in this manufacturing process.
Explain why

Answer 17

M1 formed from/on/via less stable carbocation
M2 (formed from) primary rather than secondary carbocation

Question 18

A data book value for the enthalpy of combustion of cyclohexane is –3920 kJ mol−1
The student concluded that the temperature rise recorded in the experiment
was smaller than it should have been.
Suggest a practical reason for this

Answer 18

thermal energy / heat loss or
incomplete combustion or
evaporation

Question 19

Give an equation for the complete combustion of octane

Answer 19

C8H18 + 12.5 O2 → 8 CO2 + 9 H2O

Question 20

Give an equation for a reaction that removes nitrogen monoxide in
a catalytic converter.

Answer 20

2 NO + 2 CO → N2 + 2 CO2

Question 21

The bond angle around the oxygen atom in methanol is slightly smaller than the
regular tetrahedral angle of 109.5°
Explain why this bond angle is smaller than 109.5°

Answer 21

Idea that lone pairs have greater repulsion than bonding pairs

Question 22

Describe how to prepare 250 cm3 of an aqueous standard solution of
propanedioic acid containing an accurately measured mass of the acid.
Include essential practical details in your answer.

Answer 22

M1 weigh out sample in bottle / boat / container
M2 transfer to (conical) flask / beaker (or suitable container) and
wash all sample in or re-weigh bottle / boat / container or re
weigh bottle / boat / container
M3 dissolve sample in (deionised / distilled ) water (if volume of
water is specified, must be less than 250 cm3)
M4 add into volumetric flask with washings
M5 make up to mark / 250 cm3 in volumetric flask
M6 shake / invert (this should be to give a homogenous solution
rather than to dissolve

Question 23

Give an equation to show the breakdown of one molecule of
1,2-dichlorotetrafluoroethane to form one chlorine radical and one other species.

Answer 23

CF2ClCF2Cl → *CF2CF2Cl + *Cl

Question 24

Give two equations to show how chlorine radicals catalyse the decomposition of ozone

Answer 24

M1 Cl* + O3 ⟶ ClO* + O2 M2 ClO* + O3 ⟶ Cl* + 2 O2

Question 25

Why ultraviolet light is needed

Answer 25

provides energy to break (covalent) bond in chlorine / Cl2 or to form chlorine free radicals

Question 26

Suggest why the student chose not to carry out experiments at temperatures in the experiment

Answer 26

reaction would take too long / too slow / take a long time / very slow

Question 27

mportance of percentage yield

Answer 27

idea of getting as much product as possible in the reaction / idea of efficient conversion of reactants to products

Question 28

Importance of percentage atom economy

Answer 28

idea of maximising the mass of reactants / atoms that ends up in desired product or idea of minimising the amount of by-products

Question 29

Explain why pentan-2-ol has a higher boiling point than pent-1-ene.

Answer 29

M1 idea that pentan-2-ol has stronger intermolecular forces M2 pent-1-ene has van der Waals’ forces (only) M3 pentan-2-ol (also) has hydrogen bonds

Question 30

Explain the differences between structural isomerism and stereoisomerism. Use examples to show how compounds with the molecular formula C4H8 exhibit stereoisomerism and the three types of structural isomerism.

Answer 30

1a structural isomers = molecules with same molecular formula but different structure 1b stereoisomers = molecules with same structural formula but different arrangement of atoms in space 2a lack of rotation around C=C 2b structures of E- and Z-but-2-ene 2c correct identity of E and Z isomers 3a different C chain, e.g. methylpropene & but-1-ene / but-2-ene 3b different position of functional group e.g. but-1-ene & but-2-ene 3c different functional group, e.g. cyclobutane & but-1-ene / but-2-ene / methylpropene

Question 31

State what you would observe if bromine water was added to poly(chloroethene). poly(chloroethene). [3 marks] Explain this observation.

Answer 31

M1 no reaction / yellow-orange M2 polymer is saturated / does not contain double bond(s)

Question 32

Ethanedioic acid is formed by the oxidation of ethane-1,2-diol (HOCH2CH2OH). State suitable reagent(s) and a condition for this reaction.

Answer 32

M1 acidified potassium dichromate(VI) or sulfuric acid & potassium dichromate(VI) M2 reflux

Question 33

Explain why nonane has a higher boiling point than 2,4-dimethylheptane.

Answer 33

M1 nonane has stronger / greater / more van der Waals’ forces between molecules M2 nonane molecules pack closer together / more (surface) contact

Question 34

Four compounds, all colourless liquids, are * butan-2-ol * butanal * butanone * 2-methylpropan-2-ol Two of these compounds can be identified using different test-tube reactions. Describe these two test-tube reactions by giving reagents and observations in each case. Suggest how the results of a spectroscopic technique could be used to distinguish between the other two compounds

Answer 34

Tollens’ reagent [or Fehling’s / Benedict’s] Identifies butanal – silver mirror (or black ppt) [or orange/brick/red ppt with Fehling’s] (No reaction with other compounds) Acidified potassium dichromate Reacts with butanal and butan-2-ol – goes green (No reaction with other compounds) Sodium (not on specification but may be mentioned) Reacts with butan-2-ol and 2-methylpropan-2-ol – fizzes (No reaction with other compounds) IR (infra-red) spectroscopy If different functional groups: need to identify wavenumber and bond of key functional group signal (e.g. (alcohol) O-H 3230-3550 or C=O 1680-1750 (cm–1)). If same functional group, need idea of using fingerprint region to look for match to known compounds / comparing region to samples in a database Mass spectrometry If different, can use different Mr values with values of Mr given butanone 72(.0), 2-methylpropan-2-ol = 74(.0), butan-2-ol = 74(.0), butanal = 72(.0)