台大-土壤化学题库.pdf

土壤化學題庫 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 cations 2 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 earth s 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 soil s K supplying power 15 What are Gapon equation and Vanselow equation What s 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 Jackson s 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 Lindsay s 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 6 10 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 4 10 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 CaCl2 34 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 of a