| Date | May 2013 | Marks available | 1 | Reference code | 13M.3.sl.TZ2.C3 |
| Level | SL | Paper | 3 | Time zone | TZ2 |
| Command term | Describe | Question number | C3 | Adapted from | N/A |
Question
Poly(ethene) can be produced in a low density (LDPE) or a high density (HDPE) form.
Describe how the two forms differ in their chemical structure.
Explain in terms of their structures how the flexibility of the two forms of poly(ethene) differ.
Describe why pentane is sometimes added during the formation ofpoly(phenylethene), also known as polystyrene.
State one use for the product formed from this process.
Markscheme
HDPE/high density polyethene has little/no branching/side chains and low density has (many) branches/side chains;
branching in LDPE/ low density polyethene prevents chains fitting closely together;
weaker intermolecular/van der Waals’/London/dispersion forces so more flexible;
Accept opposite statements for HDPE/high density polyethene.
vaporizes causing it to expand/form expanded polystyrene / OWTTE;
(thermal) insulator / packaging material / absorb shock;
Do not accept just cups.
Examiners report
The answers to this often betrayed a confusion between isotactic and atactic polypropene. That being said the link between packing and the strength of the dispersion forces was relatively well understood at least to the extent of gaining one of the marks. Most candidates were aware of the role of pentane and even the weakest were scoring the mark for a use of expanded polystyrene.
The answers to this often betrayed a confusion between isotactic and atactic polypropene. That being said the link between packing and the strength of the dispersion forces was relatively well understood at least to the extent of gaining one of the marks. Most candidates were aware of the role of pentane and even the weakest were scoring the mark for a use of expanded polystyrene.
The answers to this often betrayed a confusion between isotactic and atactic polypropene. That being said the link between packing and the strength of the dispersion forces was relatively well understood at least to the extent of gaining one of the marks. Most candidates were aware of the role of pentane and even the weakest were scoring the mark for a use of expanded polystyrene.
The answers to this often betrayed a confusion between isotactic and atactic polypropene. That being said the link between packing and the strength of the dispersion forces was relatively well understood at least to the extent of gaining one of the marks. Most candidates were aware of the role of pentane and even the weakest were scoring the mark for a use of expanded polystyrene.
