ECS - Exam 2.docx

Sorption - correct answer The retention of a species without the implications to its retention mechanism Adsorption - correct answer The binding of an ion or small molecule to a surface at an isolated site (2d-surface complex). Not including surface precipitation and/or polymerization. One of the most important chemical processes in soils - nutrients, metals, pesticides, and other organic chemicals retained on soil surfaces; affects transport of nutrients and contaminants in soils Absorption - correct answer The uptake of a species WITHIN another material Surface Precipitation - correct answer A 3D growth mechanism of a species on a surface. This mechanism differs from Adsorb. in that the retained species directly interacts with each other on the surface and can eve have the solid structure grow away from the original substrate Precipitation - correct answer The formation of a 3D structure without the association of a substrate (sorbent) material Sorptive - correct answer A species in solution that may undergo sorption Sorbate - correct answer A species retain on another material Sorbent - correct answer The substrate material responsible for the retention of a solution species Fate of Pesticides - correct answer Drift, photodecomposition, runoff, volatilization, absorption, soil decomposition - adsorption, residues, leaching Inorganic Surface Function Groups - correct answer Oxygen atoms of the silica tetrahedral layer (siloxane surface) in the interlayer region of phyllosilicates. OH groups associate with edges of minerals Surface Functional Groups - correct answer Hydroxyl, Carbonyl (organic), Carboxyl (organic), and Amino Group. Phenolic - consists of phenyl and hydroxyl groups (organic) Forces involved in Adsorption - correct answer Physical (distance and valence) - Van der waals (weak electrostatic forces) and Electrostatic complexes (ion exchange) Chemical (electron reconfiguration, breaking/making bonds)- Inner-sphere and outer-sphere complexation Surface Complex - correct answer Surface Function Group + ion or molecule in solution = stable molecular entity, called SURFACE COMPLEX Surface Complexes - correct answer Outer-sphere - water molecule is present between the SFG and bound (adsorbed) ion or molecule. Inner-sphere complex - no water molecule present between the SFG and bound ion or molecule Inner and outer-sphere complexation occurs simultaneously (not mutually exclusive) Inner-sphere Complex - correct answer Strong (covalent and ionic bonding), May be slower than outer sphere complexation, Often irreversible or "fixed" depending upon environmental conditions, weakly affected by solution ionic strength, surface charge can be changed by complexation, charged surface is not required for complexation Outer-sphere Complex - correct answer Weak (H-bonding), Electrostatic interaction, thus surface must be charged, rapid, reversible (exchangeable), affected by ionic strength of the solution Adsorption Isotherm - correct answer Describes the relation between the activity or equilibrium concentration of the adsorptive and the quantity of adsorbate on the surface at constant temperature, is usually employed to describe adsorption Four General Adsorption Isotherms - correct answer S-curve, L-curve, H-curve, and C-curve Lewis Acid - correct answer A species that accepts an electron pair and will have vacant orbitals Lewis Base - correct answer A species that donates an electron pair and will have long-pair electrons Adsorption Models - correct answer Freundlich, Langmuir Disadvantages of Freundlich's isotherm - correct answer Purely empirical and no theoretical basis, constants vary with temperature, fails when concentration of adsorbate Disadvantages of Langmuir's isotherm - correct answer Not valid in the real situations Mineral Surfaces - correct answer Can also interact with other molecules and ions at the surface Attraction mechanisms between a particular mineral surface and an ion or molecule - correct answer -Electrostatic interaction -Hydrophobic/hydrophilic -Specific bonding reactions at the surface Toxic Metals to mammalian life - correct answer Pb (lead), Hg (mercury), Cd (cadmium) Mobility of heavy metals in soils and aqueous environments - correct answer -Solubility of Metal - M 2+