Question 20N.3.HL.TZ0.c
| Date | November 2020 | Marks available | [Maximum mark: 1] | Reference code | 20N.3.HL.TZ0.c |
| Level | HL | Paper | 3 | Time zone | TZ0 |
| Command term | Suggest | Question number | c | Adapted from | N/A |
Sodium alginate beads were prepared containing a suspension of Chlorella algae. These beads were placed in nine small jars containing hydrogencarbonate indicator solution. Hydrogencarbonate indicator is commonly used to detect changes in pH.
The jars were placed at different distances from a lamp, which was the only light source. The distances ranged from 40 to 130 centimetres. Jars were placed one at a time to avoid the jars from shading each other. Colour changes were observed.
[Source: © International Baccalaureate Organization 2020.]
Suggest one other factor that has to be kept constant in all the jars during the experiment.
[1]
temperature/volume of indicator/identical jars/number of beads/size of beads / density of Chlorella / other reasonable answer
Do not accept light/pH/humidity.
A very large number of candidates suggested a valid factor that should be kept constant.
