1. Define the terms “cation exchange capacity” (CEC) and “anion exchange capacity” (AEC) of soil.
2. Why is ion exchange important in soils?
3. A soil is determined to have the following amounts (in cmolc) of exchangeable cations and anions:
exchangeable cations
(cmolc/Kg) Exchangeable Anions
(cmolc/Kg)
Ca+2 – 3 cmolc/Kg Cl- - 1 cmolc/Kg
Mg+2 – 1 cmolc/Kg NO3- - 0.5 cmolc/Kg
K+ - 1 cmolc/Kg SO4-2 – 0.5 cmolc/Kg
Na+ - 0.5 cmolc/Kg
Al+3 – 2 cmolc/Kg
Determine the CEC and CIA of this soil.
4. In order from smallest to largest, rank the following soil
components in terms of their contribution per unit mass to the
negative electrical charge of the soil: kaolinite, smectite,
organic matter, Fe and Al oxides. For each material, indicate if
the load provided is permanent or pH-dependent.
5. Using the simplified format of rectangles and parallelopipeds,
illustrate the structure of 2:1 and 1:1 clay minerals, indicating
the layers of Si tetrahedrons and layers of Al octahedrons.
Indicate which structure (2:1 or 1 :1) correspond to smectite,
vermiculite and kaolinite.
6. Name three drugs that have clay minerals as active ingredients, and indicate which is the clay mineral in each product.
7. Define what specific surface area is, and how a high specific
surface area is produced in a material.
8. A soil is 60 percent clay. Of this clay fraction, 40 percent is
kaolinite, 40 percent is Fe oxide, and 20 percent is smectite. In
addition, the soil has 3 percent organic matter (humus). Using the
CEC values ??for pure materials (see property summary table),
calculate the CEC of the soil.
9. For the same soil as above, calculate the specific surface area.
10. Under what environmental conditions do 1:1 clays and oxides of Fe and Al usually form, and under what conditions do minerals like smectite usually form?
11. Which clay minerals are more expandable when wet in water, 1:1 or 2:1? Why ?