| Date | May 2013 | Marks available | 1 | Reference code | 13M.3.hl.TZ2.A3 |
| Level | HL | Paper | 3 | Time zone | TZ2 |
| Command term | Explain | Question number | A3 | Adapted from | N/A |
Question
The structures of some natural pigments and three preservatives are given in Table 22 of the Data Booklet.
When the flavylium cation is placed in alkaline solution the structure changes to the quinoidal base. Explain why the colour changes from red to blue.
Markscheme
increased conjugation/delocalization (due to removal of \({{\text{H}}^ + }\) from OH group on benzene ring) / light of lower frequency/longer wavelength absorbed;
Examiners report
Most candidates recognised that there was a change in the extent of conjugation but did not elaborate on whether conjugation had increased or decreased.
