DP Chemistry (last assessment 2024)
Question 17N.3.hl.TZ0.19b
| Date | November 2017 | Marks available | [Maximum mark: 3] | Reference code | 17N.3.hl.TZ0.19b |
| Level | hl | Paper | 3 | Time zone | TZ0 |
| Command term | Outline | Question number | b | Adapted from | N/A |
b.
[Maximum mark: 3]
17N.3.hl.TZ0.19b
Vegetable oils can be used as a source of energy.
(b)
The natural absorption of light by chlorophyll has been copied by those developing dye-sensitized solar cells (DSSCs). Outline how a DSSC works.
[3]
Markscheme
Any three of:
dye has conjugated system
dye absorbs a photon «and injects an electron into TiO2»
electrons transferred to semiconductor «and dye ionized»
dye oxidizes/takes electron from electrolyte
electron flows through external circuit «to reduce electrolyte»
M4 may also be scored from more detailed answers involving iodide species (eg “iodide/I– oxidized to I3–/triiodide” OR “I–/iodide reduces dye” OR “I–/iodide releases electron to dye” OR “I3–/triiodide reduced to I–/iodide”).
[Max 3 Marks]
