C2 2018

Question 1

Alkanes can be used in free-radical substitution reactions to produce
halogenoalkanes.
Give equations for the propagation steps in the reaction of butane to form
2-chlorobutane.

Answer 1

Cl. + CH3CH2CH2CH3 -> CH3CH2CH.CH3
+ HCl
CH3CH2CH.CH3 + Cl2 -> CH3CH2CHClCH3
+ Cl.

Question 2

Identify the radical produced from this CFC that is responsible for the depletion of
ozone in the atmosphere.
Explain, with the aid of equations, why a single radical can cause the decomposition
of many molecules of ozone.

Answer 2

Cl.
Cl. +O3 -> ClO. + O2
ClO. +O3 -> Cl. + 2O2
Cl. is regenerated

Question 3

Reaction 1 occurs via a nucleophilic substitution mechanism.
Explain why the halogenoalkane is attacked by the nucleophile in this reaction

Answer 3

Bromine is more electronegative than carbon
C is partially positive / electron deficient
Lone/electron pair (on the nucleophile) donated to the partially
positive carbon

Question 4

Give two ways of maximising the yield of propanal obtained by distillation of the
reaction mixture.

Answer 4

Keep the temperature of the reaction mixture below the boiling point
of propan-1-ol/below 97 °C
Cool the distillate / collecting vessel

Question 5

A student carried out an experiment to determine the enthalpy of combustion of
ethanol.
Combustion of 457 mg of ethanol increased the temperature of 150 g of water from
25.1 °C to 40.2 °C
Calculate a value, in kJ mol–1, for the enthalpy of combustion of ethanol in this
experiment.
Give your answer to the appropriate number of significant figures.
(The specific heat capacity of water is 4.18 J K–1 g–1)

Answer 5

(Temperature difference = 15.1 oC)
q = 150 × 4.18 × 15.1 or 9467.7 J or 9.4677kJ
amount ethanol burned = 0.457/46.0 = 9.93 × 10-3 mol
Heat change per mole = (M1/1000)/M2 = 952.99 kJ mol-1
ΔH = – 953 kJ mol–1
must be 3sfs and must be negative
(allow range -953 to -954)

Question 6

A mixture of isomeric alkenes is produced when pentan-2-ol is dehydrated in the
presence of hot concentrated sulfuric acid. Pent-1-ene is one of the isomers
produced.
Name and outline a mechanism for the reaction producing pent-1-ene.

Answer 6

Elimination
CHCH3OH lone pair -> H+
CHCH3OH2+ C-O bond to the O+
CH+CH2H C-H bond to C+-C

Question 7

Justify the statement that adding more water to the equilibrium mixture in
Question 04.3 will lower the amount of A in the mixture.

Answer 7

(All) conc fall: (ignore dilution)
Equm moves to side with more moles
To oppose the decrease in conc

Question 8

The enthalpy of hydrogenation of cyclohexa-1,3-diene is not exactly double that of
cyclohexene.
Suggest a value for the enthalpy of hydrogenation of cyclohexa-1,3-diene and justify
your value.

Answer 8

Value within range –239 to –121
Double bonds separated by one single bond / alternating (or shown in structure)
Allows some delocalisation/overlap of p orbitals

Question 9

A student dissolves a few drops of propylamine in 1 cm3 of water in a test tube.
Give an equation for the reaction that occurs.
Describe what is observed when Universal Indicator is added to this solution.

Answer 9

CH3CH2CH2NH2 + H2O ⇌ CH3CH2CH2NH3
+ + OH–
(green) turns blue

Question 10

Phenylamine can be prepared by a process involving the reduction of nitrobenzene
using tin and an excess of hydrochloric acid.
Give an equation for the reduction of nitrobenzene to form phenylamine. Use [H] to
represent the reducing agent.
Explain why an aqueous solution is obtained in this reduction even though
phenylamine is insoluble in water.

Answer 10

C6H5NO2 + 6[H] -> C6H5NH2 + 2H2O
C6H5NH2 present as ionic salt
phenyl ammonium (chloride)