Outline two differences between heterogeneous and homogeneous catalysts.

Suggest, giving a reason, how elastomers used for the tyre tread can increase the traction between the tyre and the road.

Tyre fires emit trace quantities of polychlorinated dibenzofurans and polychlorinated dibenzo-p-dioxin.

Outline, using section 31 of the data booklet, why polychlorinated dibenzofuran is not classed chemically as a dioxin but considered “dioxin-like”.

Classify polybutadiene as either an addition or condensation polymer, giving a reason.

State one factor considered when making green chemistry polymers.

Any two of:
heterogeneous catalyst is in different phase than reactants AND homogeneous catalyst in same phase   [✔]

homogeneous catalysts chemically change/react and reformed at end of reaction
OR
reactants adsorb onto heterogenous catalyst and products desorb    [✔]

heterogeneous catalysts are more easily removed than homogenous catalysts     [✔]

heterogeneous catalysts can function at higher temperatures     [✔]

homogeneous catalysts are «generally» more selective     [✔]

homogeneous catalysts offer a broader range of reactions     [✔]

Note: Accept “state” for “phase”.

Accept “heterogeneous catalyst provides a surface to activate reaction”.

elastomers bend under force «and return to original form when force is released»
OR
elastomers make tyre more flexible   [✔]

allows greater contact with road    [✔]

does not contain heterocyclic ring with 2 oxygen atoms
OR
middle ring has only 1 oxygen atom    [✔]

produces similar toxic effects to dioxins    [✔]

addition AND not two different functional groups reacting
OR
addition AND formed by breaking one bond of the carbon–carbon double bonds
OR
addition AND empirical formula of monomer equals empirical formula of polymer
OR
addition AND no atoms removed/all atoms accounted for/no loss of water/ammonia/inorganic by-product/small molecules
OR
addition AND atom economy/efficiency is 100 %
OR
addition AND there is only one «reaction» product   [✔]

Any one of:
high content of raw materials in product/high atom economy    [✔]

use of low toxic chemicals/catalysts/materials/solvents     [✔]

renewable feedstock/raw materials     [✔]

use of renewable/clean/low carbon energy source     [✔]

high safety standards     [✔]

increase energy efficiency     [✔]

waste recycling     [✔]

Note: Accept other reasonable answers.

Most candidates correctly stated one difference between heterogeneous and homogeneous catalysts. Few gave a second difference even though the question is worth 2 marks.

Most explained well how elastomers increase tyre traction.

But had difficulty applying their knowledge to outline why polychlorinated dibenzofuran is considered dioxin-like but is not classified as a dioxin.

Some candidates failed to score the mark as they did not give a reason for classifying polybutadiene as an addition polymer.

Most candidates were able to state a factor considered when making green chemistry polymers.