Question 1
The diagrams below illustrate an experimental set up to determine a soil property. Study them carefully and answer the questions that follow.
- (a) Suggest a suitable title for the experiment. [ 1 mark ]
- (b) Outline the procedure for carrying out the experiment. [ 7 marks ]
- (c) Identify the soil samples in diagrams I, II and III. [ 3 marks ]
- (d) State two precautions to be taken when carrying out the experiment.
[ 2 marks ]
- (e) (i) Which of the soil samples is prone to waterlogging? [ 1 mark ]
(ii) Give one reason for your answer in 1(e)(i). [ 1 mark ]
Observation
This question was fairly attempted by the candidates. Most of the candidates were able to suggest a suitable title for the diagram but were unable to outline the procedure for carrying out the experiment as required in 1(a) and (b) respectively. Also, most of the candidates were able to identify the soil samples in diagrams I, II and III but they could not state the precautions to be taken when carrying out the experiment as required in 1(c-d). Further to this, most of the candidates were able to state with reason, which of the soil samples is prone to waterlogging as required in 1(e)(i-ii).
The expected answers include:
1(b) Procedure for carrying out the experiment
- Obtain samples of sandy, clayey and loamy soils.
- Dry them under the sun.
- Grind loamy and clayey soils.
- Plug the necks of three funnels with cotton wool.
- Put equal volumes of sandy, clayey and loamy soils separately into
three funnels plugged with cotton wool.
- Tap the funnels carefully on the bench until all air spaces are filled with
soil.
- Stand each funnel in the open end of a measuring cylinder.
- Pour 50cm3 of water into the funnel containing each soil sample.
- Allow the set up to settle for at least 1 hour.
- Measure the amount of water that dripped through each soil sample.
- By subtracting the amount of water that dripped through each soil sample, obtain the amount of water retained in each soil sample.
(d) Precautions to be taken when carrying out the experiment
- Soil samples should be dried under the sun.
- Loam and clay should be ground before use.
- The funnels should be properly plugged with cotton wool to
prevent soil samples from dripping into the measuring cylinders.
- The funnels should be properly tapped to close all air spaces that
could distort the experiment.
- Cylinders should be placed on flat and level surface.
- Water should be poured into the cylinder at the same time