SWS3022 Exam 2 Study Guide State
Questions and Answers
Know how to determine if water will flow between two points in a soil and the direction of
flow. - CORRECT ANSWER-Water flows from high potential to low potential
Know what a gradient is and how to calculate it. Know that the greater the gradient, the
stronger the driving force for water movement. - CORRECT ANSWER-Difference in
potential between two points divided by the distance between two points
Understand that water moves in response to differences in TOTAL potential, not just
one potential. - CORRECT ANSWER-Understand that water moves in response to
differences in TOTAL potential, not just one potential.
Understand hydraulic conductivity, what it is, how it is affected by soil physical
properties. - CORRECT ANSWER-Ease with which water moves through soil, anything
that shrinks pores reduces hydraulic conductivity
Know how to combine hydraulic conductivity and the gradient to determine overall flow
of water in soils. Note the units of flow - CORRECT ANSWER-Hydraulic conductivity
times the gradient = flow, centimeters per hour
Be able to identify important soil solution constituents, both organic and inorganic, and
understand the fundamental differences between them. - CORRECT ANSWER-
Inorganic (simple)- sodium, calcium, potassium, magnesium, zinc; organic(complex)-
folic acids, pesticides, industrial solvents
Know how ions differ from the elements in the periodic table. - CORRECT ANSWER-
Ions are stable forms of elements that have become charged by gaining or losing
electrons
Know the difference between cations and anions. Understand particularly how charge is
acquired. - CORRECT ANSWER-Elements that lose electrons and become positively
charged are called cations.
Elements that gain electrons and become negatively charged are called anions.
Understand ion hydration and how it can impact the size of cations in soil solution. -
CORRECT ANSWER-Water molecules are polar, so they will orient themselves with the
negative oxygen toward the positive cation, eventually the cation will be surrounded by
water molecules oriented this way. Makes the cation bigger
Know the 3 fundamental features of soil mineral colloids. - CORRECT ANSWER-Small,
large surface area, highly reactive
, Know the fundamental building blocks for aluminosilicate clays and the dominant ions
comprising them. - CORRECT ANSWER-Silicon tetrahedron (silicon surrounded by
oxygen)
Aluminum octahedron (aluminum surrounded by hydroxides)
Know the difference between a 1:1 and a 2:1 mineral. - CORRECT ANSWER-One
tetrahedral sheet to one octahedral sheet
Two tetrahedral sheets to one octahedral sheet
Know that mineral colloids are layered structures made of individual 1:1 or 2:1 layers. -
CORRECT ANSWER-Know that mineral colloids are layered structures made of
individual 1:1 or 2:1 layers.
Understand isomorphous substitution in silicate clay minerals. - CORRECT ANSWER-
Substitution of lower-charge cations for higher charge cations during mineral formation.
Al3+ for Si4+ in tetrahedra, Mg2+ for Al3+ in octahedra
The result is a deficit of positive charge or a surplus of negative charge in the mineral
structure
This dramatically increases the reactivity of clays
Know the type of net charge developed on aluminosilicate minerals and the implications
in terms of soil solution cations. - CORRECT ANSWER-Isomorphous substitution
creates a negative charge, cations adsorb to negative charge sites
Understand cation exchange and the three factors that determine cation preference at
negative sites. - CORRECT ANSWER-Cation preference is determined by
concentration in solution, charge (higher-charge cations are more strongly attracted to
surface), and cation size (smaller cations are preferred at negative sites)
Know what cation exchange capacity is, the units, and the range for various mineral
colloids. - CORRECT ANSWER-Total charge on a clay mineral is indicated by the
cation exchange capacity, CEC
Units are cmolc/kg
Mineral CEC ranges between 0 and 180 cmolc/kg
Understand the concept of cation charge density and how it impacts preference of
various cations for negatively charged sites on mineral colloids. - CORRECT ANSWER-
Charge density equals charge divided by size
An indication of how tightly cations are held at exchange sites (at equivalent
concentrations)
Understand why interlayer spaces in Kaolinite are unavailable for exchange reactions or
water entry. - CORRECT ANSWER-Layers are glued together by hydrogen bonds,
adsorption takes place on external surfaces and edges because a lack of interlayer
access limits surface area/reactivity
Questions and Answers
Know how to determine if water will flow between two points in a soil and the direction of
flow. - CORRECT ANSWER-Water flows from high potential to low potential
Know what a gradient is and how to calculate it. Know that the greater the gradient, the
stronger the driving force for water movement. - CORRECT ANSWER-Difference in
potential between two points divided by the distance between two points
Understand that water moves in response to differences in TOTAL potential, not just
one potential. - CORRECT ANSWER-Understand that water moves in response to
differences in TOTAL potential, not just one potential.
Understand hydraulic conductivity, what it is, how it is affected by soil physical
properties. - CORRECT ANSWER-Ease with which water moves through soil, anything
that shrinks pores reduces hydraulic conductivity
Know how to combine hydraulic conductivity and the gradient to determine overall flow
of water in soils. Note the units of flow - CORRECT ANSWER-Hydraulic conductivity
times the gradient = flow, centimeters per hour
Be able to identify important soil solution constituents, both organic and inorganic, and
understand the fundamental differences between them. - CORRECT ANSWER-
Inorganic (simple)- sodium, calcium, potassium, magnesium, zinc; organic(complex)-
folic acids, pesticides, industrial solvents
Know how ions differ from the elements in the periodic table. - CORRECT ANSWER-
Ions are stable forms of elements that have become charged by gaining or losing
electrons
Know the difference between cations and anions. Understand particularly how charge is
acquired. - CORRECT ANSWER-Elements that lose electrons and become positively
charged are called cations.
Elements that gain electrons and become negatively charged are called anions.
Understand ion hydration and how it can impact the size of cations in soil solution. -
CORRECT ANSWER-Water molecules are polar, so they will orient themselves with the
negative oxygen toward the positive cation, eventually the cation will be surrounded by
water molecules oriented this way. Makes the cation bigger
Know the 3 fundamental features of soil mineral colloids. - CORRECT ANSWER-Small,
large surface area, highly reactive
, Know the fundamental building blocks for aluminosilicate clays and the dominant ions
comprising them. - CORRECT ANSWER-Silicon tetrahedron (silicon surrounded by
oxygen)
Aluminum octahedron (aluminum surrounded by hydroxides)
Know the difference between a 1:1 and a 2:1 mineral. - CORRECT ANSWER-One
tetrahedral sheet to one octahedral sheet
Two tetrahedral sheets to one octahedral sheet
Know that mineral colloids are layered structures made of individual 1:1 or 2:1 layers. -
CORRECT ANSWER-Know that mineral colloids are layered structures made of
individual 1:1 or 2:1 layers.
Understand isomorphous substitution in silicate clay minerals. - CORRECT ANSWER-
Substitution of lower-charge cations for higher charge cations during mineral formation.
Al3+ for Si4+ in tetrahedra, Mg2+ for Al3+ in octahedra
The result is a deficit of positive charge or a surplus of negative charge in the mineral
structure
This dramatically increases the reactivity of clays
Know the type of net charge developed on aluminosilicate minerals and the implications
in terms of soil solution cations. - CORRECT ANSWER-Isomorphous substitution
creates a negative charge, cations adsorb to negative charge sites
Understand cation exchange and the three factors that determine cation preference at
negative sites. - CORRECT ANSWER-Cation preference is determined by
concentration in solution, charge (higher-charge cations are more strongly attracted to
surface), and cation size (smaller cations are preferred at negative sites)
Know what cation exchange capacity is, the units, and the range for various mineral
colloids. - CORRECT ANSWER-Total charge on a clay mineral is indicated by the
cation exchange capacity, CEC
Units are cmolc/kg
Mineral CEC ranges between 0 and 180 cmolc/kg
Understand the concept of cation charge density and how it impacts preference of
various cations for negatively charged sites on mineral colloids. - CORRECT ANSWER-
Charge density equals charge divided by size
An indication of how tightly cations are held at exchange sites (at equivalent
concentrations)
Understand why interlayer spaces in Kaolinite are unavailable for exchange reactions or
water entry. - CORRECT ANSWER-Layers are glued together by hydrogen bonds,
adsorption takes place on external surfaces and edges because a lack of interlayer
access limits surface area/reactivity
