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Homework CEC KEY

# Homework CEC KEY - c 0.06 kg oxide clay x 2 cmol c/kg =...

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SS 121 Name _________________ Fall 2010 SHOW ALL WORK Component Average CEC in cmol(+)/kg material Humus 200 Vermiculite 115 Montmorillonite (smectites) 80 Hydrous mica (illite) 35 Kaolinite 10 Sesquioxides 2 0.75 pt 1. What is the CEC (cmol c /kg) of a soil containing 3.0% humus, 20% montmorillonite, 8%, vermiculite, and 10% illite? CEC = 34.7 cmol c /kg soil 0.03 kg humus x 200 cmol c /kg = 6 cmol c 0.2 kg montmorillonite x 80 cmol c /kg = 16 cmol c 0.08 kg vermiculite x 115 cmol c /kg = 9.2 cmol c 0.1 kg illite x 35 cmol c /kg = 3.5 cmol c 0.75 pt 2. What is the CEC (cmol c /kg) of a soil containing 3.0% humus, 6% oxide clay, and 69% kaolinite? CEC = 13 cmol c /kg soil 0.03 kg humus x 200 cmol c /kg = 6 cmol
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Unformatted text preview: c 0.06 kg oxide clay x 2 cmol c /kg = 0.12 cmol c 0.69 kg kaolinite x 10 cmol c /kg = 6.9 cmol c 1.25 pts (0.25, 0.25, 0.75) 3. The soil in problem 1 contains 38 % clay. The soil in problem 2 contains 75 % clay. Explain why the soil with the most clay has the lower CEC. Lower cation exchange capacity of the oxide clay and kaolinite 4. Define CEC. What are the two major sources of charges on soil colloids that result in CEC? 0.75 pts The amount of exchangeable cations per unit weight of dry soil 0.75 pts Ionizable H ions (pH dependent) 0.75 pts Isomorphous substitution (substitution of one ion for another of similar size and often lower positive valence)...
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