WASSCE FOR PRIVATE CANDIDATES 2019 FIRST SERIES PAPER3

DETAILED COMMENTS ON EACH QUESTION


Question 1


The diagram below illustrates an experimental set-up on soil. Study it and answer the questions that follow.

    1. State the aim of the experiment.

      (1 mark)


    2. Name the parts labelled I and II in the diagram.
    3. (2 mark)


  1. Describe how the experiment is carried out.
  2. (4 mark)


  3. State four properties of sandy soils.
  4. (4 mark)


  5. Describe a test for soil acidity using litmus paper

    (4 mark)


Observation

 

  1. Most candidates were unable to state the aim of the experiment as many erroneously
    described it as a soil profile; thus mislabelling its parts.

  2. Candidates were however able to state the properties of sandy soil as well as describe a
    test for soil acidity using litmus paper.

The expected answers include:


    1. Aim of the experiment

    2. -Separation of soil into its fractions/determination of soil texture by sedimentation


    3. Naming of the parts labelled I and II

    4. I Clay in suspension/Clay


      II Silt


  1. Description of the experiment

  2. - Place a glass jar on a surface


    - Weigh about 70 – 100g of the soil


    - Add the weighed soil into an equivalent quantity of water in a glass jar


    - Add suitable dispersing agent e,g, NaOH, NaHCO3


    - Shake the glass jar vigorously to disperse any soil clods


    - Allow the glass jar to settle for an hour


    - Observe the result


  3. Properties of sandy soils

  4. -Low cation exchange capacity


    -Gritty/rough/coarse in nature


    -Diameter is between 0.02mm – 2m2


    -High percolation rate


    -Well drained, loose and highly aerated


    -Low capillary action


    -Low plant nutrients


    -Cannot be moulded


    - Low buffering capacity


    - Leaching of nutrients is high/supports leaching .


    -Easily gets hot and cold


    - Low water holding capacity


    - Particles are light and easy to till


  5. Testing soil acidity using litmus paper

  6. - Mix the soil very well


    - Moisten with distilled water


    - Dip red and blue litmus paper into moistened soil.


    - If blue litmus paper changes pink/red, the soil is acidic


    - If red litmus paper changes blue, the soil is basic/alkaline


    - If there is no colour change, the soil is neutral