Question 20N.3.HL.TZ0.10
| Date | November 2020 | Marks available | [Maximum mark: 5] | Reference code | 20N.3.HL.TZ0.10 |
| Level | HL | Paper | 3 | Time zone | TZ0 |
| Command term | Explain, State, Suggest | Question number | 10 | Adapted from | N/A |
Citric acid was produced in a fermenter using the pulp of cassava (Manihot esculenta) and the fungus Aspergillus niger. This process was carried out at room temperature for 6 days and citric acid was then collected. The apparatus was cleaned and set up for a new fermentation. The process is shown in the diagram.
[Source: Prado, F.C., Vandenberghe, L.P.S., Woiciechowski, A.L., Rodrígues-León, J.A. and Soccol,
C.R., 2005. Citric acid production by solid-state fermentation on a semi-pilot scale using different percentages of
treated cassava bagasse. Brazilian Journal of Chemical Engineering, 22(4), pp.547–555.]
State in which numbered part of the process you would find the probes to detect changes in pH.
[1]
2
Most could correctly identify part 2, others wrote part 1.
Explain the possible causes of these changes in pH.
[2]
a. pH decreased by citric acid;
b. (pH lowered by) production of CO2 produced (by the fungus) in respiration;
c. (pH lowered by) production of carbonic acid by CO2 dissolving in water;
Most stated that the pH changes were due to acidic conditions, but fewer could explain how the acidic conditions were generated.
Suggest, with a reason, whether this is a batch or a continuous fermentation.
[1]
batch fermentation because the citric acid is collected at the end of the fermentation
OR
batch fermentation because the process was carried out over 6 days then re-set up
OR
diagram does not show constant supply of nutrients so it must be a batch;
Most suggested that it was a batch fermentation, but some omitted to provide a reason; a few others had incorrect answers.
State one use of the citric acid produced.
[1]
preservative/flavour
Accept other verified use, e.g. buffering.
Good candidates correctly stated flavour enhancer, others didn't know.