In an experiment to determine the humus in a soil sample the following results were obtained: Mass of dish – 20g, Mass of dry soil – 7.5g, Mass of dish + soil after burning = 25g; the percentage of humus in the given sample is…
The quantity of humus in a dry soil can be determined by firstly, burning the soil to remove the humus, then subtracting the mass of the remnant from the initial mass of the unburnt dry soil. It can then be expressed in percentage by dividing this difference in mass with the mass of the initial unburnt soil.
Percentage humus content =
Mass of dish = 20g
Mass of dry soil = 7.5g
Mass of dish and soil after burning = 25g
Percentage humus in the sample =???
From the above data,
Mass of burnt soil will be = mass of dish and soil after burning – mass of dish
= 25g – 20g = 5g
Now for the right answer to the above question:
- 9.1 is quite incorrect.
- 37.5 is also incorrect.
- 12.5 is incorrect.
- D is correct, the percentage humus in the soil sample is 33.3%
You may please note that:
- The mass of the dish must not be involved in your final calculations of the percentage humus in the soil sample, as doing so will result in option A (9.1%)
- The soil sample must be dry; if it is moist, it is usually dried and weighted, before burning off the humus.
Use the questions and answers session to raise further questions on this topic…
/ culled from 2017 JAMB-UTME biology question 21 /