Section 3: Soil Solution

Question 1

sampling soil solution: collection of drainage water

Answer 1

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

Question 2

sampling soil solution: vacuum extraction

Answer 2

collects gravitational water and water under tension – macro AND micro pores

affects water flow by producing an artificial sink

Question 3

consistent of soil solution analysis

Answer 3

cation (inorganic), anions (inorganic), organics, pH, electrical conductivity, concentration of C and N

Question 4

If there is only one measurement you can do what should it be?

Answer 4

pH

Question 5

What does the concept of activity include?

Answer 5

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

Question 6

ideal conditions

Answer 6

hypothetical situations which concentrations equal activities (open space, dilute solution)

Question 7

reference state

Answer 7

condition where a system behaves as close to ideality as possible; for solutions: an infinitely dilute solution

Question 8

ionic strength

Answer 8

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

Question 9

Types of ion-ion interactions: free ions

Answer 9

water coordination - salvation complex; ions would exhibit their full charge

Question 10

Types of ion-ion interactions: ion pairs

Answer 10

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)

Question 11

Types of ion-ion interactions: ion soluble complexes (complexation)

Answer 11

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

Question 12

Types of ion-ion interactions: ion soluble complexes (complexation (chelation)

Answer 12

special case of an ion complex
cation is coordinated by multiple bonds to a single molecule
(Very stable)

Question 13

what characteristic does your solution have to have in order to have ion pairing and complexation?

Answer 13

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

Question 14

what is the progression of ion pairs to chelates?

Answer 14

ion pairs – complexes – chelates

Question 15

what is speciation of the soil solution?

Answer 15

the determination of the distribution of ions in their various chemical forms

Question 16

stability or equilibrium constant K formula

Answer 16

products over reactants

Question 17

what is the equilibrium constant used for?

Answer 17

to quantify the level of interaction or interaction strength

Question 18

are association and dissociation constants equal?

Answer 18

no they are not equal in value

Question 19

what can equilibrium constant k describe?

Answer 19

ion pairs, ion complexes, chelation, hydrolysis, acid/base reactions, the solubility of a solid, chemisorption, ion exchange

Question 20

hydration and hydrolysis: ionic potential

Answer 20

measure of the charge density at the surface of the ion (usually denser the charge there stronger the bond the ion can form)

Question 21

smaller and more charged ions have ___ ionic potential

Answer 21

higher

Question 22

ions of ___ size and ___ charge hydrate the most strongly (strong electrical field)

Answer 22

small; high

Question 23

hydrolysis

Answer 23

a step further than hydration; pull electrons from water resulting in the release of a proton, H+

Question 24

what ionic potential favor hydrated cation?

Answer 24

small ionic potential

Question 25

what ionic potential favors hydrolysis?

Answer 25

med to large potential

Question 26

As hydrolysis constant (pK) increases and ionic potential increases what happens to the tendency to hydrolyze?

Answer 26

it increases; remember that pK is increasing in the small numbers, not big ones

Question 27

if only electrostatic (ion-dipole) forces existed what would the pK and ionic potential relationship look like?

Answer 27

it would have a negative slope and all the elements would be on the solid line

Question 28

speciation

Answer 28

determination of the distribution of ions in their various chemical forms

Question 29

why do we care about metal mobility?

Answer 29

ground water contamination, pedogenic processes

Question 30

what is the formation of Cd-Cl complexes supported by?

Answer 30

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

Question 31

Metal Bioavailability: how speciation can impact uptake in biota?

Answer 31

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