| Date | May 2010 | Marks available | 2 | Reference code | 10M.3.hl.TZ2.D3 |
| Level | HL | Paper | 3 | Time zone | TZ2 |
| Command term | Explain | Question number | D3 | Adapted from | N/A |
Question
Mild analgesics such as aspirin, and strong analgesics such as opiates, differ not only in their potency but also in the ways they act on the central nervous system.
Explain why heroin is a more potent drug than morphine.
Markscheme
molecule of heroin is less polar / molecule of morphine is more polar / polar OH groups in morphine are replaced with less polar/non-polar groups in heroin;
(less polar molecules) cross the blood-brain barrier faster/more easily / (heroin) is more soluble in non-polar environment of the CNS/central nervous system than morphine / OWTTE;
Examiners report
Candidates struggled to explain why heroin is a more potent drug than morphine. An explanation based on differences of the polarity of the molecules was expected.
