Section 3: Soil Solution Flashcards
sampling soil solution: collection of drainage water
soil must be saturated at the time of the sample collection (collects gravitational water that flows through soil MACROPORES)
considered diluted since only through macropores
sampling soil solution: vacuum extraction
collects gravitational water and water under tension – macro AND micro pores
affects water flow by producing an artificial sink
consistent of soil solution analysis
cation (inorganic), anions (inorganic), organics, pH, electrical conductivity, concentration of C and N
If there is only one measurement you can do what should it be?
pH
What does the concept of activity include?
concentration - quantity of solute present in a given quantity/volume of solution
activity – effective concentration - defines the reactivity of a solute in a given quantity of solution - can decrease with more overall concentration
ideal conditions
hypothetical situations which concentrations equal activities (open space, dilute solution)
reference state
condition where a system behaves as close to ideality as possible; for solutions: an infinitely dilute solution
ionic strength
measures the electrostatic environment (total. electric field strength that an ion “feels” in the solution) - the non-ideality that the solution imposes on any dissociated electrolyte
Types of ion-ion interactions: free ions
water coordination - salvation complex; ions would exhibit their full charge
Types of ion-ion interactions: ion pairs
associations between hydrated cations and anions
anion coordinates to a cation salvation complex (water) to form an electrostatic bond with the cation (fairly weak association)
Types of ion-ion interactions: ion soluble complexes (complexation)
associations between cations and anions that are not in a hydration sphere
can involve ionic or covalent bonding between the central cation and the ligand
inner-sphere complex - more stable, starts sharing elections
Types of ion-ion interactions: ion soluble complexes (complexation (chelation)
special case of an ion complex
cation is coordinated by multiple bonds to a single molecule
(Very stable)
what characteristic does your solution have to have in order to have ion pairing and complexation?
cation or anions have high charge >2 (more charge, more complexes
inorganic anions other than NO3- (and Cl-) are present
transition (heavy) metals and neutral or anionic organic molecules (ligands) are present
the complexing species (ligand) is present in high concentration
the pH is relatively high and polyvalent cations are present
what is the progression of ion pairs to chelates?
ion pairs – complexes – chelates
what is speciation of the soil solution?
the determination of the distribution of ions in their various chemical forms
stability or equilibrium constant K formula
products over reactants
what is the equilibrium constant used for?
to quantify the level of interaction or interaction strength
are association and dissociation constants equal?
no they are not equal in value
what can equilibrium constant k describe?
ion pairs, ion complexes, chelation, hydrolysis, acid/base reactions, the solubility of a solid, chemisorption, ion exchange
hydration and hydrolysis: ionic potential
measure of the charge density at the surface of the ion (usually denser the charge there stronger the bond the ion can form)
smaller and more charged ions have ___ ionic potential
higher
ions of ___ size and ___ charge hydrate the most strongly (strong electrical field)
small; high
hydrolysis
a step further than hydration; pull electrons from water resulting in the release of a proton, H+
what ionic potential favor hydrated cation?
small ionic potential
what ionic potential favors hydrolysis?
med to large potential
As hydrolysis constant (pK) increases and ionic potential increases what happens to the tendency to hydrolyze?
it increases; remember that pK is increasing in the small numbers, not big ones
if only electrostatic (ion-dipole) forces existed what would the pK and ionic potential relationship look like?
it would have a negative slope and all the elements would be on the solid line
speciation
determination of the distribution of ions in their various chemical forms
why do we care about metal mobility?
ground water contamination, pedogenic processes
what is the formation of Cd-Cl complexes supported by?
Cd2+ forms fairly strong soluble complexes with Cl-
same effect with other crops
SO4 2- salts form weaker complexes with Cd2+
rule out cation (Na+) competition for exchange sites
Metal Bioavailability: how speciation can impact uptake in biota?
there can be accidental transport because the metal can come along for the ride and the cell doesn’t know what it is up-taking and then it can have negative impacts
