CSES 2040- SG Exam 2 UPDATED ACTUAL Questions and CORRECT Answers
What is CEC? Sum total of exchangeable cation that a soil can absorb
In MOST soils, what is the overall charge in Negative
soils? Negative or positive?
K+
Potassium
39.09 g/mol
Na+
Sodium
22.98 g/mol
Al +3
Aluminum
26.98 g/mol
H+
Hydrogen
1.00 g/mol
Mg+2
Magnesium-
24.305 g/mol
NH+4
Ammonium
18.04 g/mol
Ca+2
Calcium
40.08 g/mol
Sand 1-5 typical 2
Know the range of CECs that can occur Smectite (clay) >30 typical 100
(from sand to organic matter) - what is a Vermiculite (clay) >30 typical 150
typical value? Kaolinite (clay) 3-5 typical 8
Organic 200-400 typical 200
, This is important in acid, humid soils (AL)
When we have pH dependent charge (variable charge).
What is the difference between CEC and -Al-OH + OH- <---→ Al-O-+ H2O
ECEC? In why kinds of climate is this Increasing pH ----------- →
important? The reaction shown above can happen when we add NH4- acetate at a pH of 7. It
creates more negative sites, so more NH4 gets adsorbed on those negative sites.
So, in acid soils we may overestimate the CEC of the soil.
We calculate the Effective CEC (ECEC)
Do the CEC determination as shown before, but don't measure the NH4 collected.
How do we fix the issue with CEC and
Instead, determine the individual amounts of Ca, Mg, K, Na collected from the first
ECEC? How does the lab procedure
filtering.
change?
Then, extracted with an unbuffered salt solution (KCl), and then analyze for the Al
and H content.
In acid weathered soils which will always ECEC
be lower? ECEC or CEC?
What are the acid cations? H+, Al+3
What are the nonacid cations? Ca+2, Mg+2, K+, Na+
How does base saturation change with soil As soil pH increases Base saturation increases
ph?
Be able to calculate base saturation Base saturation= (nonacid cations/ CEC (acid + nonacid cation)) X 100
Have soils high in 1:1 clays
Hydrous oxides of iron and aluminum
Which four types of soil have AEC?
Heavily weathered soils
Volcanic soils
Moles of positive charge adsorbed per unit of mass-this is centimoles of positive
What are the units by which we express
charge per kilogram soil -cmolc/kg
CEC? There are two types - how are they
Milliequivilant (meq), but the number is the same as a cmolc/kg. Meq is just an old
related?
system.
Layer silicate clays- crystalline silicate clays
What are the four major types of soil Iron and aluminum oxide clays (the minerals gibbsite and
colloids? Allophane- non-crystalline silicate clays (volcanic)
Humus (organic matter-well decomposed)
Planes of oxygen with mainly silicon (Si) in the spaces between the oxygens- called
What are the two main sheets of layer the Si tetrahedron.
silicate clays? Two planes of oxygen and hydroxyls (OH) with aluminum (Al) or magnesium (Mg) in
the spaces- called the Al octrahedron.
when cations of a similar size substitute for the Al and Si in the sheets- this occurs
What is isomorphic substitution? How does
during weathering.
it develop charge in layer silicate clays? Is
This is the part of CEC we call Permanent Charge.
this permanent or pH variable charge?
Can occur in the octahedral or tetrahedral sheets.
Which ions can sub in the tetrahedral sheet Si 4+, Al3+, Fe3+
Which ions can sub in the octahedral sheet Al3+, Fe3+, Mg+2, Fe+2
1:1, Sheets held tightly together by oxygen atoms. Fixed structure, only external
Kaolionte surface area. Little isomorphous substitution. Low plasticity. Low stickiness. Low
cohesion. Little shrink-swell, Low CEC.
What is CEC? Sum total of exchangeable cation that a soil can absorb
In MOST soils, what is the overall charge in Negative
soils? Negative or positive?
K+
Potassium
39.09 g/mol
Na+
Sodium
22.98 g/mol
Al +3
Aluminum
26.98 g/mol
H+
Hydrogen
1.00 g/mol
Mg+2
Magnesium-
24.305 g/mol
NH+4
Ammonium
18.04 g/mol
Ca+2
Calcium
40.08 g/mol
Sand 1-5 typical 2
Know the range of CECs that can occur Smectite (clay) >30 typical 100
(from sand to organic matter) - what is a Vermiculite (clay) >30 typical 150
typical value? Kaolinite (clay) 3-5 typical 8
Organic 200-400 typical 200
, This is important in acid, humid soils (AL)
When we have pH dependent charge (variable charge).
What is the difference between CEC and -Al-OH + OH- <---→ Al-O-+ H2O
ECEC? In why kinds of climate is this Increasing pH ----------- →
important? The reaction shown above can happen when we add NH4- acetate at a pH of 7. It
creates more negative sites, so more NH4 gets adsorbed on those negative sites.
So, in acid soils we may overestimate the CEC of the soil.
We calculate the Effective CEC (ECEC)
Do the CEC determination as shown before, but don't measure the NH4 collected.
How do we fix the issue with CEC and
Instead, determine the individual amounts of Ca, Mg, K, Na collected from the first
ECEC? How does the lab procedure
filtering.
change?
Then, extracted with an unbuffered salt solution (KCl), and then analyze for the Al
and H content.
In acid weathered soils which will always ECEC
be lower? ECEC or CEC?
What are the acid cations? H+, Al+3
What are the nonacid cations? Ca+2, Mg+2, K+, Na+
How does base saturation change with soil As soil pH increases Base saturation increases
ph?
Be able to calculate base saturation Base saturation= (nonacid cations/ CEC (acid + nonacid cation)) X 100
Have soils high in 1:1 clays
Hydrous oxides of iron and aluminum
Which four types of soil have AEC?
Heavily weathered soils
Volcanic soils
Moles of positive charge adsorbed per unit of mass-this is centimoles of positive
What are the units by which we express
charge per kilogram soil -cmolc/kg
CEC? There are two types - how are they
Milliequivilant (meq), but the number is the same as a cmolc/kg. Meq is just an old
related?
system.
Layer silicate clays- crystalline silicate clays
What are the four major types of soil Iron and aluminum oxide clays (the minerals gibbsite and
colloids? Allophane- non-crystalline silicate clays (volcanic)
Humus (organic matter-well decomposed)
Planes of oxygen with mainly silicon (Si) in the spaces between the oxygens- called
What are the two main sheets of layer the Si tetrahedron.
silicate clays? Two planes of oxygen and hydroxyls (OH) with aluminum (Al) or magnesium (Mg) in
the spaces- called the Al octrahedron.
when cations of a similar size substitute for the Al and Si in the sheets- this occurs
What is isomorphic substitution? How does
during weathering.
it develop charge in layer silicate clays? Is
This is the part of CEC we call Permanent Charge.
this permanent or pH variable charge?
Can occur in the octahedral or tetrahedral sheets.
Which ions can sub in the tetrahedral sheet Si 4+, Al3+, Fe3+
Which ions can sub in the octahedral sheet Al3+, Fe3+, Mg+2, Fe+2
1:1, Sheets held tightly together by oxygen atoms. Fixed structure, only external
Kaolionte surface area. Little isomorphous substitution. Low plasticity. Low stickiness. Low
cohesion. Little shrink-swell, Low CEC.
