| Date | November 2012 | Marks available | 3 | Reference code | 12N.3.sl.TZ0.C3 |
| Level | SL | Paper | 3 | Time zone | TZ0 |
| Command term | Explain | Question number | C3 | Adapted from | N/A |
Question
The two diagrams below show the arrangement of molecules in two different types of polyethene, labelled A and B.
Predict which type of polyethene (A or B) has the strongest intermolecular forces, highest density and greatest flexibility.
(i) Strongest intermolecular forces:
(ii) Highest density:
(iii) Greatest flexibility:
The polymer polyvinyl chloride (PVC), also known as poly(chloroethene), is hard and brittle when pure. Explain, in terms of intermolecular forces, how adding a plasticizer to PVC modifies the properties of the polymer.
Markscheme
(i) A;
(ii) A;
(iii) B;
closely packed molecules with crystalline structure;
(plasticizers) separate the PVC molecules/polymer chains / disrupt crystalline structure;
decrease/weaken intermolecular forces/intermolecular dipole-dipole interactions/van der Waals’/London Dispersion;
Do not accept mention of H-bonding
makes it (PVC) softer/more flexible/more easily moulded;
Examiners report
Many candidates were able to score three marks in (a) and most gave a good account of (b). Many, however, neglected to mention intermolecular forces, specifically requested in the question.
Many candidates were able to score three marks in (a) and most gave a good account of (b). Many, however, neglected to mention intermolecular forces, specifically requested in the question.
