課程名稱︰土壤化學
課程性質︰農化系必修
課程教師︰李達源
開課學院：生農學院
開課系所︰農化系
考試日期（年月日）︰2013.11.06
考試時限（分鐘）：10:20~12:10, 110 min
是否需發放獎勵金：是
試題 :
1.What are complex ions? What are ion pairs? Which are inner-sphere complexes
and which are outer-sphere complexes? Give an example of complex ions and ion
pairs respectively in soil solutions and write the equations for expressing
the stability constant of complex ions and ion pairs. Please also answer whi-
ch one (inner-sphere complex or outer-sphere complex) has larger stability
constant in general and explain why.(10%)
2.What is the ionic strength of a solution containing 0.01M Ca2+, 0.05M Na+,
0.030M Cl-, 0.02M SO42-, and 0.01M HCO3-? Please calculate the activity coef-
ficients of Ca2+, and SO42- based on the Davies equation in the solution. In
addition, please answer if the precipitation of CaSO4 can occur in the solut-
ion or not.(10%)
(Ksp=10^-4.6 for CaSO4)
(Davies equation:log10γi=-AZi^2｛〔I^0.5/(1+I)0.5〕-0.3I｝,A=0.511)
3.Please give an example of 1:1, 2:1, and 2:1:1 of layer silicates respectivel-
y. Discuss the difference in CEC, specific surface area, expanding, c-spacin-
g among them and explain why based on their structure.(10%)
4.Write the half-unit-cell formula for a montmorillonite mineral with a layer
charge of 0.3, with 90% of the isomorphic substition in the octahedral layer
(Mg2+ for Al3+) and 10% of the isomorphic substition in the tetrahedral layer
(Al3+ for Si4+). The saturating cation is Na+. Draw a diagram of this minera-
l, indicating the position of Mg2+, Al3+, Si4+, and Na+. Calculate the CEC of
the mineral.(10%)
5.What is X-ray diffraction method? Explain how it can be used for soil layer
silicate identification and determination.(10%)
6.Please describe the procedure for extracting fulvic acids and humic acids fr-
om soils and illustrate the difference of properties between fulvic acids and
humic acids. In addition, explain why they can buffer soil pH, affect soil s-
tructure, and influence the mobility of heavy metal and trace elements in so-
ils.(10%)
7.Compare the affinity of soil colloids for different cations (Ca2+, Mg2+, K+,
Na+, and Al3+) and explain why.(10%)
8.Please write the Gapon equation for Na+ to exchange Ca2+ from soil colloids,
indicating the units for each term in the equation. If a soil, with Gapon ex-
change coefficient (KG)=0.015 (L mmole^-1)^0.5, is irrigated with irrigation
water of SAR=40 (mmole L^-1)^0.5, what would be its equilibrium ESR (exchang-
eable sodium ratio)?(10%)
9.What is the diffuse double layer(DDL)? Please draw a diagram to show and exp-
lain why the thickness of DDL as influenced by salt concentration of balk so-
lutions and the valence of cations. In addition, please describe how the thi-
ckness of DDL can affect the flocculation and dispersion of clay particles.
(10%)
10.Please illustrate the importance of obtaining the equilibrium coefficient(K)
of the reactions of solutions in soil solutions and also K of interactions of
solutes with soil solids on the evaluating the deficiency and unbalance of p-
lant nutrients and mobility of toxic metals on soils.(10%)
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