Soil Chemistry: Colloids, Acidity, Alkalinity & Organic Matter is one of 9 topics in the Grade 11 Agricultural Sciences CAPS syllabus, covered across 3 lessons on Study Vault. Below are real practice questions from this topic with full worked answers.
Sample practice questions
Easy
1. What are the two main components that make up soil colloids?
Clay minerals and humus
Sand and silt
Water and air
Bedrock and gravel
Answer: Clay minerals and humus — Soil colloids are extremely small, chemically active particles mainly consisting of clay minerals and humus (stable, decomposed organic matter).
Easy
2. What type of electrical charge do most soil colloid surfaces carry?
Answer: negative — Most soil colloid surfaces carry a net negative electrical charge, which attracts and holds positively charged cations from the soil solution.
Medium
3. What is cation exchange capacity (CEC)?
The measure of the total quantity of exchangeable cations a soil can hold on its colloid surfaces
The total volume of macro pores in a soil
The percentage of sand in a soil sample
The rate at which water drains through soil
Answer: The measure of the total quantity of exchangeable cations a soil can hold on its colloid surfaces — Cation exchange capacity (CEC) measures the total quantity of exchangeable cations a soil can hold on its colloid surfaces, indicating its capacity to retain and later supply plant-nutrient cations.
