土壤化學(xué)題庫(kù).doc

土壤化學(xué)題庫(kù)1. Explain how layer charge influences the following layer silicate properties: (a) Interlayer bonds (b) Crystal size (c) Swelling (d) Surface area (e) c spacing (f) Exchangeability of adsorbed cations2. Write the half-unit-cell formula for a montmorillonite mineral with a layer charge of 0.3, with 90% of the substitution in the octahedral layer ( Mg2+ for Al3+ ) and 10% of the substitution in the tetrahedral layer ( Al3+ for Si4+ ). The saturating cation is Na+. Draw a diagram of this mineral, indicating the position of Mg2+, Al3+, Si4+ and Na+ ?3. What is meant by the zero point of charge? What are the functional groups responsible for pH-dependent charge in soil?4. An acidic pesticide of pK 5 is being applied to soils of a given region. Would leaching be greatest for soils of (a) pH 5 ? (b) pH 6 to 8 ? (c) pH 5 ? Why?5. A soil of pH 5.5 retains 60 mmol(+) kg-1 of exchangeable bases and has a CEC at pH 7 of 80 mmol(+) kg-1 :(a) What is its percent base solution? (b) What is its approximate CEC at pH 5.5?6. An irrigation water contains 750 mg L-1 soluble salts. If used at an average leaching fraction of 0.15, what would be the average EC of the drainage water leaving the bottom of the crop root zone?7. A 30-cm depth of surface soil contains 28% exchangeable sodium and has a CEC of 150 mmol(+) kg-1. How many tonnes per hectare of sulfur will be required to lower its ESP to 5% ? 8. A vermiculite surface soil has the ability to fix 25 mmol kg-1 of K+ or NH4+. What rate of (NH4)2SO4 or KCl fertilizer (in kg ha-1) would be require to saturate this fixation capacity for a 30-cm depth of soil?9. For a CEC procedure that uses Na+ as the index cation, H2O/ethanol as the wash solvent, and Mg2+ as the displacing cation, discuss the effect of each of the following on CEC measurements: (a) Hydrolysis due to excess washing (b) Presence of large amounts of lime or gypsum in the soil (c) Incomplete index-cation saturation (d) Precipitation of an insoluble Na+ salt in the ethanol (e) Incomplete removal of the index cation by Mg2+10. To calculate b(maximum amount of adsorbate) and K(affinity constant) of a pesticide with Langmuir equation from the data : Each 25 mL 20, 40, 60, 80, 100 mg/L respectively add to each 0.5 gm soil, and final solution cocentration respectively is 0.4, 2, 20, 35, 50 mg/L. 11. What kinds of function groups or segments contribute to the hydrophobicity of soil organic matters? What are the hydrophilic function groups in soil organic matter? Which function groups are the hard Lewis bases and which ones are the soft Lewis bases?12. For Ca2+, Mg2+, K+, P5+, Si4+, or other selected chemical elements, trace all the possible pathways that the ion might follow from its state in igneous rock through soils to its most stable state at the earths surface?13. How are Fe(III) and Al(III) reactions both different and similar in soils? Which transition metals are essential to (a) Plants? (b) Animals? 14. If K+ is release both from “fixed” forms and by weathering during the growing season, why is exchangeable K+, as determined by a single extraction, well correlated with the soils K-supplying power?15. What are Gapon equation and Vanselow equation? Whats difference of their explaining cation exchange and exchange coefficient on the surface of soil colloids?16. A 10 gm Na+-saturated montmorillonite (CEC = 100 cmolc/kg) is mixed with 1.0 liter of water containing 10 ppm Na+ and 10 ppm K+ as the only cations. if the exchange equation K = ExK+Na+/ExNa+K+ = 2.0 can be accepted as valid for this system, calculate the equilibrium concentrations of Na+ and K+ in solution?17. Narrate the developed process of DDL theories from Helmholtz to Gouy-Chapman to Stern, and explain their differences and suitability on the adsorption of ions.18. A sample of pure goethite, FeOOH, with a PZC of 7.5, is suspended in 10-3 MNaCl. The pH is adjusted to 5.0 with acid. What would be the effect of increasing the NaCl concentration to 10-2 M on (a) solution pH (b) CEC and AEC (c) net surface charge?19. Explain the mechanisms of buffer reactions of soils with acids, and describe various forms of acid in the soils?20. A mineral soil with pH 5 retains 7 cmolc/kg of exchangeable bases and 1 cmolc/kg of exchangeable Al3+ . The CEC is 10 cmolc/kg at pH 7. Try to answer the questions: (a) What is the percent base saturation at pH 5.0? (b) What fraction of the total acidity at pH 5 is nonexchangeable? (c) What is the approximate lime requirement ( metric tons/ ha) of surface soil (15 cm depth and B.D. = 1.33 gm/cm3)?21. What is Jacksons “Frayed-edge” theory during the weathering of mica minerals? Describe the proposed K-release processes and explain the difference of released mechanism between native K and Fixed K?22. What are the kinetic considerations (limitations) in applying Lindsays phosphate-phase diagram? Make mathematical calculations of (H2PO4-) for dica-phosphate (CaHPO4) at pH 7, pK = 6.66 and (Ca2+) = 0.005.23. Describe reduction reaction sequence and Eh in waterlogged soils, explain the difference of electrode current for Fe3+-Fe2+ redox pair between Fe3+=Fe2+=10-3 M and Fe3+=Fe2+=10-4 M at pH 2 in water with measurement of the platinum electrode potential.24. Explain clearly chemisorption and precipitation of inorganic ions, and describe a bonding mechanism that would explain Cu2+, Cd2+ and Pb2+ showing enhanced adsorption on Al hydroxide after the surface has adsorbed phosphate?25. The logarithm of the association constants, logK1M, for selected trace metals with acetate and ethylenediamine at 25 are give below: Metal Acetate Ethylenediamine Ni2+ 1.43 7.32 Cu2+ 2.22 10.48 Zn2+ 1.57 5.66 Cd2+ 1.93 5.41(a) Why do all of these metals, regardless of electronic properties and size, complex much more strongly with ethylenediamine than with acetate?(b) Why does Cu2+ complex most strongly with both ligands, particularly in the case of ethylenediamine?(c) Which metal shows the largest relative preference for ethylenediamine over acetate? Why?26. Soils of arid climates commonly contain smectite minerals with Na+ as a predominant exchange cation, yet Ca2+ can be present in the form of CaCO3. Explain this separation of Ca2+ and Na+ into separate solid phases. Explain the pH change if Na+-saturated smectite is added to a suspension of CaCO3, the pH is observed to rise from about 8 to 10 or higher.27. Substitution of electron withdrawing groups such as Cl or NO2 on the aromatic ring of phenols has the effect of lowering the pKa. Explain how the sorption characteristics of pentachlorophenol(PCP) would differ from those of phenol (a) at low soil pH (b) at high soil pH. (PCP is much less soluble in water than phenol).28. Suppose that 1.0 gm of a clay is equilibrated with 100 mL of 10-4 M methylene blue. After equilibration, the solution concentration is only 0.610-4 M. The experiment is then repeated using 2.0 gm of clay in 100 mL of 10-4 M methylene blue, and this time the final concentration is 0.410-4 M. If the Langmuir equation describes methylene blue adsorption, calculate the specific surface area of the clay in square meters per gram. Assume that each adsorbate molecule occupies 65 2 on the surface.29. Why should hydrated alkali and alkali earth cations deprotonate at extremely high pH values in soil environment? Does the deprotonation of these cations occur in nature?30. What are the weathering mechanisms as the rocks exposed to water, O2, and CO2?31. The dissociation of H4SiO4 follows the equation described below, H4SiO4 + H2O = H3SiO4- + H3O-The pKa of H4SiO4 is around 9.71. What is the activity ration of H3SiO4- to H4SiO4 at pH of 5.71?32. Differentiate complex ion and ion pair in a soil solution system. 33. What is the ionic strength of a solution? Calculate the ionic strength of a reaction solution controlled by 0.01 M CaCl234. Prove that 1 mmho cm-1 = ds m-1. Convert the conductance limit of 750 mho cm-1 for the standard of irrigation water quality to the quantity expressed by SI unit.35. What are ionic potential and its usage o