| Date | November 2011 | Marks available | 4 | Reference code | 11N.3.sl.TZ0.C2 |
| Level | SL | Paper | 3 | Time zone | TZ0 |
| Command term | Describe | Question number | C2 | Adapted from | N/A |
Question
Since the accidental discovery of polyethene in the 1930s, polymers have played an essential role in daily life because of their wide range of properties and uses.
Titanium compounds are used as catalysts in the manufacture of high-density polyethene (HDPE). Discuss two factors scientists would have considered in choosing these catalysts.
Describe a structural feature of low-density polyethene (LDPE) that explains why LDPE has a different melting point from that of HDPE.
State one environmental impact of the disposal of these polyethenes by using incineration.
Markscheme
no other product formed (except HDPE);
expensive but effective;
little or no environmental/health impact;
not easily poisoned by impurities;
cause (considerable) increase in rate;
ability to work under mild/severe conditions;
side-chains / branching present (in LDPE);
limits closer packing / chains further apart / OWTTE;
less van der Waals’/dispersion/London forces / OWTTE;
Award mark for less intermolecular forces. Do not accept weaker.
low(er) melting point (than HDPE);
No mark for different melting point.
Accept reverse argument for HDPE.
\({\text{C}}{{\text{O}}_2}\) is a greenhouse gas / causes climate change / global warming / formation of soot/particulates / melting of polar ice caps / rising sea levels / OWTTE;
Accept CO produced is toxic/poisonous.
Examiners report
(a) was surprisingly poorly answered, with very few candidates understanding how to discuss two factors in choosing catalysts, although they should have studied several factors.
(b) was answered well.
(c) was answered well.
