| Date | May 2013 | Marks available | 1 | Reference code | 13M.3.sl.TZ2.F2 |
| Level | SL | Paper | 3 | Time zone | TZ2 |
| Command term | Describe | Question number | F2 | Adapted from | N/A |
Question
Naturally occurring pigments give many foods their distinctive colours.
Chlorophyll is a pigment found in green vegetables.
A student decided to investigate the effect of sodium hydrogencarbonate, \({\text{NaHC}}{{\text{O}}_{\text{3}}}\), and vinegar on the colour of cooked green peas. Her results are shown below:
List two factors which may affect the colour stability of a pigment.
State how the sodium hydrogencarbonate maintains the green colour of the peas.
The structure of chlorophyll is shown in Table 22 of the Data Booklet. Describe what happens to the structure of chlorophyll when the peas are heated in water containing vinegar.
Markscheme
temperature (changes);
light;
pH (change);
presence of metal ions;
oxidation/reduction;
\({\text{HCO}}_3^ - \) produces a (slightly) alkaline/basic pH / pH range 7.5–9 / OWTTE;
Accept “buffers the solution”.
Mg2+/magnesium (ion) displaced by (two) H+/hydrogen (ions);
Accept Mg2+/magnesium (ion) is released.
Examiners report
This question was very poorly answered. Whilst many candidates correctly identified factors affecting the stability of pigments, hardly any displayed the detailed knowledge required regarding the degradation of chlorophyll and the way that sodium hydrogencarbonate and vinegar affect the process. The Maillard reaction was even less well understood with only a handful of candidates gaining any marks.
This question was very poorly answered. Whilst many candidates correctly identified factors affecting the stability of pigments, hardly any displayed the detailed knowledge required regarding the degradation of chlorophyll and the way that sodium hydrogencarbonate and vinegar affect the process. The Maillard reaction was even less well understood with only a handful of candidates gaining any marks.
This question was very poorly answered. Whilst many candidates correctly identified factors affecting the stability of pigments, hardly any displayed the detailed knowledge required regarding the degradation of chlorophyll and the way that sodium hydrogencarbonate and vinegar affect the process. The Maillard reaction was even less well understood with only a handful of candidates gaining any marks.
