Question 23M.3.HL.TZ2.13
| Date | May 2023 | Marks available | [Maximum mark: 4] | Reference code | 23M.3.HL.TZ2.13 |
| Level | HL | Paper | 3 | Time zone | TZ2 |
| Command term | Explain | Question number | 13 | Adapted from | N/A |
Biological pigments are coloured compounds.
The following structure is the β-carotene:
Explain in terms of its structure, why β-carotene appears orange in visible white light. Refer to section 17 of the data booklet.
[2]
contains many/multiple conjugated «carbon–carbon/C=C» double bonds
OR
extended system of delocalized electrons ✓
absorbs blue
OR
complementary to orange «light» ✓
M1 requires the concept of many or multiple conjugated double bonds in structure for mark.
Do not accept either “conjugation” OR “double bonds” alone for M1.
Anthocyanins can act as acid-base indicators. The two examples shown, are the flavylium cation and the quinoidal base.
Explain how these anthocyanins can act as acid-base indicators as pH increases.
[2]
Any two of:
equilibrium shifts right
OR
H+ ions lost ✓
red to blue ✓
loss of proton/H+ changes extent of conjugation ✓
affects frequency/wavelength of absorbed light ✓
complementary light transmitted ✓
Do not accept “cation red and base blue” alone.
Apply ECF from M1 to M2.