Soil Chem Topic 2,3,4,5

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Cation Exchange

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Is the reaction of cations with the negative charge in soil in order to maintain electrical neutrality in the system.

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Cation Exchange Capacity

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Is the magnitude of the negative charge in soils. It is usually expressed in milliequivalents per 100 grams of soil or centimoles of positive charge per
kilogram.

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Coordination Number

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The number of ligand atoms arranged in definite geometry and directly bonded to a central ion.

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Clay Mineral

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Naturally occurring inorganic crystalline material found in soils and other earthy deposits, the particles being of clay size; that is, <0.002 mm in diameter.

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Clay sized Fraction

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Refers to soil particles that are less than or equal to two microns in diameter.

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Fulvic Acid Fraction

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Fraction of soil organic matter that is soluble in both alkali and acid.

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Humic Substances

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a series of relatively high-molecular-weight, yellow to black colored substances formed by secondary synthesis reactions. The term is used as a generic name to describe the colored material or its fractions obtained on the basis of solubility characteristics. These materials are distinctive to the soil (or sediment) environment in that they are dissimilar to the biopolymers of microorganisms and higher plant (including lignin).

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Humin

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The alkali insoluble fraction of soil organic mater or humus.

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Humin Acid

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The dark-colored organic material that can be extracted from soil by dilute alkali and other reagents and that is insoluble in dilute acid.

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Humus

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Total of the organic compounds in soil exclusive of undecayed plant and animal tissues, their “partial decomposition” products, and the soil biomass.

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Hymatonelanic Acid

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alcohol-soluble portion of humic acid.

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Interlayer

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Materials between layers, including cations, hydrated cations, organic molecules, and hydroxide groups or sheets.

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Isomorphous substitution

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The replacement of one atom by another of similar size in a crystal lattice without disrupting or changing the crystal structure of the mineral.

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Kaolinite

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An aluminosilicate mineral of the 1:1 crystal lattice group, which consists of one silicon tetrahedral layer and one aluminum oxide-hydroxide octahedral layer, and (ii) The 1:1 group or family of aluminosilicates.

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Lattice

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A three-dimensional grid of lines connecting the points representing the centers of structural elements (atoms or ions) in a crystal.

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Layer or platelet

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A combination of sheets in a 1:1 or 2:1 combination.

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Litter

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Macroorganic matter (e.g., plant residues) that lies on the soil surface.

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Light Fraction

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Undecayed plant and animal tissues and their partial decomposition products that occur within the soil proper and that can be recovered by flotation with a
liquid of high density (see Chapter 1).

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Mineral

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A natural inorganic compound with definite physical, chemical, and crystalline properties.

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Montmorillionite

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An aluminosilicate clay mineral with a 2:1 expanding crystal structure; that is, with two silicon tetrahedral layers enclosing an aluminum octahedral layer. Considerable expansion may be caused along the C axis by water moving between
silica layers of continuous units.

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Montmorillionite-saponite group

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Clay minerals with 2:1 crystal lattice structure; that is,
two silicon tetrahedral layers enclosing an aluminum octahedral layer. It consists of montmorillonite, beidellite, nontronite, saponite, etc.

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Nonhumic Substance

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Compounds belonging to known classes of biochemistry, such as amino acids, carbohydrates, fats, waxes, resins, organic acids, etc. Humus probably contains most, if not all, of the biochemical compounds synthesized by living organisms.

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Permanent Cation Exchange Capacity

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Is that which does not vary with a change in soil
pH.

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pH Dependent Cation Exchange Capacity

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Is that which increases with an increase in soil
pH.

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Polymerization

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Is a union of two or more molecules of the same kind into another compound.

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Primary Mineral

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A mineral that has not been altered chemically since deposition and crystallization from molten lava.

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Radius Ratio

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Diameter of the cation divided by the diameter of the anion.

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Secondary Mineral

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A mineral resulting from the decomposition of a primary mineral or from the reprecipitation of the products of decomposition of a primary mineral.

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Sheet of Atoms

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Flat array of more than one atomic thickness and composed of one or more levels of linked coordination polyhedra. A sheet is thicker than a plane and thinner than a layer. Example: tetrahedral sheet, octahedral sheet.

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Soil Biomass

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Organic matter present as live microbial tissue.

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Soil mineral

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Any mineral that occurs as part of or in the soil, and (ii) A natural inorganic compound with definite physical, chemical, and crystalline properties (within
the limits of isomorphism), that occurs in the soil.

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Soil organic matter

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Same as humus

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Unit Cell

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repeat unit by which the crystal lattice can be built.

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Alteration

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part of the mineral structure is inherited by the weathering product.

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Bowen reaction Series

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sequence of crystallization of the common minerals forming igneous rocks.

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Congruent (stoichiometric) dissolution

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elements released into solution in proportion to
their mole fractions in the structure.

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Exfoliation

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when surface layers of a primary mineral peal away from the parent mass.

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Ferromagnesium minerals

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primary minerals made up of Fe and Mg (e.g. Pyroxene, olivine)

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Heterogenous Nucleation

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is the formation of crystal nuclei at surfaces of a different solid that is present before initiation of precipitation.

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Homogenous Nucleation

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formation of crystal nuclei from ions in solution when
solutions are supersaturated with respect to a solid phase.

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Hydration

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the binding of an ion or a molecule to one or more water molecules.

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Hydrolysis

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a reaction between an ion and water in which an oxygen-hydrogen bond is broken.

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Incongruent (nonstoichiometric) dissolution

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meaning that a portion of the mineral structure is dissolving selectively.

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Neoformation

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elements that are dissolved from primary minerals precipitate as new low-temperature minerals.

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Oxidation

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the loss of an electron by an atom, ion, or molecule leading to an increase in oxidation number.

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Primary Mineral

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a mineral that has not been altered chemically since deposition and crystallization from molten lava.

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Reduction

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the gain of electrons by an atom, ion, or molecule leading to a decrease in oxidation state

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Secondary Mineral

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a mineral resulting from the decomposition of a primary mineral or from the reprecipitation of the products of decomposition of a primary mineral.

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Chelate

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a coordination complex in which more than one atom of a ligand binds to the metal.

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Chemical Kinetics

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the investigation of chemical reaction rates and the molecular processes by which reactions occur where transport is not limiting.

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Compatible Pairs

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minerals that can coexist in equilibrium.

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Enthalpy of formation

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the enthalpy change occurring when a compound is formed from its elements, ∆H˚ƒ. Elements in their standard states have ∆H˚ƒ= 0.

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Endothermic

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heat transfer is in the direction surroundings -----> system.

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Enthalpy

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(H) heat transferred into or out of a system at constant pressure.

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Enthalpy Change

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the heat energy transferred at constant pressure.

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Entropy

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(S) measure of the disorder of a system.

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Exothermic

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heat transfer is in the direction system ----> surroundings.

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Extensive properties

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dependent on the magnitude of the system (i.e. vol., mass)

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First law of Thermodynamics

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the law of conservation of energy. ∆E = q + w. The
change in the energy of a system is equal to the heat transferred to the system plus the work dine on the system.

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Free Energy

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(G) thermodynamic state function relating enthalpy, temperature, and entropy.

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Ionic Strength

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is a measure of the total electrolyte concentration.

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Intensive Properties

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dependent on the magnitude of the system (i.e. pressure, temp)

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Kinetics

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is the study of time-dependent processes.

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Second Law of Thermodynamics

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states that the combined entropy of the system and its surroundings (the entropy of the universe) always increases in a spontaneous process.

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Third Law of Thermodynamics

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the entropy of a pure, perfectly ordered crystalline
substance is 0 at zero kelvin

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State Function

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a quantity for which the change in value is determined only by the initial and final states of the system.

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Surrondings

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the rest of the universe exclusive of the system.

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System

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the part of the universe (the specific atoms, molecules, or ions) under study.

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Ion Exchange

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the interchange between an ion in solution and another on a charged surface.

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Ion Exchange Capacity

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the sum of the CEC and AEC.

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Exchanger Phase

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solid phase on which ions adsorb.

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Base Saturation

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the extent to which the adsorption complex of a soil is saturated with exchangeable cations other than hydrogen and Al. It is expressed as a percentage of the total cation exchange capacity.

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Isomorphous substitution

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substitution of one atom by another of similar size in the crystal lattice without disrupting the crystal structure

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CEC

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(cation exchange capacity) sum total of exchangeable cations that a soil can hold

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AEC

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(abion exchange capacity) sum total of exchangeable anions that a soil can hold

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Permanent Change

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(-) charge due to isomorphous substitution

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pH-Dependent Charge

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(+) or (-) charge generated by protonation/deprotonation of functional groups

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electric-Double Layer

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ionic distribution adjacent to a charged surface

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Counter ions

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ions of opposite charge to the surface charge

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PZNC

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(point of zero net charge) where surface neg charge (CEC) equals surface pos charge (AEC)

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PZSE

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(point of zero salt effect) is the pH at which two or more potentiometric titration curves intersect

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PZC

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(point of zero charge) pH value at which there is no net movement of particles or the point at which flocculation occurs

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sesquioxides

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Al and Fe oxides

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Distribution coefficient

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measure of the affinity of a surface for an element or compound.