Question 1

Soil colloids are too small to be seen with an ordinary light microscope.

Accepted Answer

A) True 
 B)False  True

Question 2

A tetrahedral sheet is characterized by a plane of aluminum atoms surrounded by oxygen and hydroxyl groups.

Accepted Answer

A) True 
 B)False  False

Question 3

You find that the CEC of a sandy loam soil at pH 5.0 is 8 cmolc/kg and at pH 8.2 it is 14 cmolc/kg.What is the most likely reason for this difference?

Accepted Answer

A) increase in the pH-dependent charges on 2:1 type silicate clays 
B) removal of Al3+ ions from the exchange complex at higher pH. 
C) ionization of carboxyl and phenolic groups to release H+ ions 
D) removal of Al atoms from tetrahedral layers at low pH. 
E) replacement of trivalent Al3+ ions with divalent Ca2+ ions at high pH. 
A) increase in the pH-dependent charges on 2:1 type silicate clays 
B) removal of Al3+ ions from the exchange complex at higher pH. 
C) ionization of carboxyl and phenolic groups to release H+ ions 
D) removal of Al atoms from tetrahedral layers at low pH. 
E) replacement of trivalent Al3+ ions with divalent Ca2+ ions at high pH. C

Question 4

Soils rich in which type of clay would provide the most troublesome site on which to build a home?

Accepted Answer

A) Fe,Al oxides 
B) kaolinite 
C) fine-grained micas 
D) chlorite 
E) smectite 
A) Fe,Al oxides 
B) kaolinite 
C) fine-grained micas 
D) chlorite 
E) smectite

Question 5

The primary source of charge for 2:1 type clay minerals is ionization of the surface hydroxyl groups on the tetrahedral sheets.

Accepted Answer

A) True 
 B)False

Question 6

While 2:1 type clays have significant internal surfaces,their external surfaces are generally much more extensive.

Accepted Answer

A) True 
 B)False

Question 7

A 1 kg soil sample has 2 cmolc of Al3+ on the exchange complex.Addition of which of the following would most effectively replace about half of this Al?

Accepted Answer

A) 1 cmolc K+ 
B) 10 cmolc OH- 
C) 4 cmolc Ca2+ 
D) 4 cmolc Na+ 
E) 2 cmolc Na+ 
A) 1 cmolc K+ 
B) 10 cmolc OH- 
C) 4 cmolc Ca2+ 
D) 4 cmolc Na+ 
E) 2 cmolc Na+

Question 8

The cation exchange capacity of a soil is determined primarily by the amount and kind of colloids in the soil and by the pH.

Accepted Answer

A) True 
 B)False

Question 9

Which of the following silicate clays would be least apt to be formed from the mere alteration of primary minerals?

Accepted Answer

A) smectite 
B) vermiculite 
C) chlorite 
D) fine-grained micas 
E) iron or aluminum oxides 
A) smectite 
B) vermiculite 
C) chlorite 
D) fine-grained micas 
E) iron or aluminum oxides

Question 10

Humus has a much higher cation adsorption capacity at pH 5.5 than at pH 8.0.

Accepted Answer

A) True 
 B)False

Question 11

Humus is an important soil colloid.It differs from 2:1 type minerals in all but one of the following characteristics (select the one).

Accepted Answer

A) structural framework of the particles 
B) CEC dependence on soil pH 
C) influence of isomorphous substitution 
D) capable of adsorbing cations 
E) influence on soil aggregate stability 
A) structural framework of the particles 
B) CEC dependence on soil pH 
C) influence of isomorphous substitution 
D) capable of adsorbing cations 
E) influence on soil aggregate stability

Question 12

The swelling/shrinking tendency of some silicate clay minerals is due primarily to _____.

Accepted Answer

A) the presence of cations attracted by the negative charges on the internal surfaces 
B) the movement of water molecules in and out of the interlayers of the crystal 
C) varying thickness of the film of water covering the external surface of the particles 
D) expansion in the width of the interlayers due to movement of larger ions such as K+ 
E) the high Mg2+ contents in the octahedral layers 
A) the presence of cations attracted by the negative charges on the internal surfaces 
B) the movement of water molecules in and out of the interlayers of the crystal 
C) varying thickness of the film of water covering the external surface of the particles 
D) expansion in the width of the interlayers due to movement of larger ions such as K+ 
E) the high Mg2+ contents in the octahedral layers

Question 13

The electronegative charge on 2:1 type silicate clays is due primarily to _____.

Accepted Answer

A) ionization of surface OH groups 
B) substitution of one metallic atom for another in the crystal structure of the clay 
C) extremely small size of the individual colloid particles 
D) the effect of pH on the presence of H+ ions in the exchange complex 
E) the preponderance of tetrahedral sheets compared to octahedral sheets 
A) ionization of surface OH groups 
B) substitution of one metallic atom for another in the crystal structure of the clay 
C) extremely small size of the individual colloid particles 
D) the effect of pH on the presence of H+ ions in the exchange complex 
E) the preponderance of tetrahedral sheets compared to octahedral sheets

Question 14

A well drained soil under a rain forest in Brazil contains significant amounts of a silicate clay.Which of the following is it most apt to be?

Accepted Answer

A) chlorite 
B) fine-grained mica 
C) smectite 
D) kaolinite 
E) vermiculite 
A) chlorite 
B) fine-grained mica 
C) smectite 
D) kaolinite 
E) vermiculite

Question 15

Which of the following is not a characteristic of soil colloids?

Accepted Answer

A) very small size 
B) high external surfaces 
C) electronegative charges 
D) ability to exchange ions with the soil solution 
E) low water holding capacity 
A) very small size 
B) high external surfaces 
C) electronegative charges 
D) ability to exchange ions with the soil solution 
E) low water holding capacity

Question 16

Some soil colloids exhibit positive charges under highly acid conditions.To what are these charges likely due?

Accepted Answer

A) protonation of some hydroxy groups by excess H+ ions 
B) the adsorption of Al3+ ions on the colloid 
C) the release of some OH- ions leaving an unsatisfied positive charge on the colloid 
D) substitution of lower valent atoms for higher valent atoms in the octahedral sheet 
E) increase in the level of H+ ions on the exchange complex 
A) protonation of some hydroxy groups by excess H+ ions 
B) the adsorption of Al3+ ions on the colloid 
C) the release of some OH- ions leaving an unsatisfied positive charge on the colloid 
D) substitution of lower valent atoms for higher valent atoms in the octahedral sheet 
E) increase in the level of H+ ions on the exchange complex

Question 17

An alkaline soil contains 20% clay and 3% humus.If the pure clay has a CEC of 40 cmolc/kg and the humus 200 cmolc/kg,calculate the CEC/kg of the soil.

Accepted Answer

A) 8 
B) 30 
C) 12 
D) 16 
E) 14 
A) 8 
B) 30 
C) 12 
D) 16 
E) 14

Question 18

Kaolinite is most prevalent in soils developed from volcanic ejecta (Andisols).

Accepted Answer

A) True 
 B)False

Question 19

If you were seeking a soil colloid with a high capacity to adsorb cationic pollutants,but also with a consistent capacity to do so even as the pH varied from 4.0 to 7.5,which of the following would you choose?

Accepted Answer

A) montmorillonite 
B) kaolinite 
C) fine-grained mica 
D) humus 
E) chlorite 
A) montmorillonite 
B) kaolinite 
C) fine-grained mica 
D) humus 
E) chlorite

Question 20

Vermiculite and associated silicate clays have a net electropositive charge in slightly acid soils.

Accepted Answer

A) True 
 B)False

Soil colloids are too small to be seen with an ordinary light microscope.

A tetrahedral sheet is characterized by a plane of aluminum atoms surrounded by oxygen and hydroxyl groups.

You find that the CEC of a sandy loam soil at pH 5.0 is 8 cmol_c/kg and at pH 8.2 it is 14 cmol_c/kg.What is the most likely reason for this difference?

Soils rich in which type of clay would provide the most troublesome site on which to build a home?

The primary source of charge for 2:1 type clay minerals is ionization of the surface hydroxyl groups on the tetrahedral sheets.

While 2:1 type clays have significant internal surfaces,their external surfaces are generally much more extensive.

A 1 kg soil sample has 2 cmol_c of Al³⁺ on the exchange complex.Addition of which of the following would most effectively replace about half of this Al?

The cation exchange capacity of a soil is determined primarily by the amount and kind of colloids in the soil and by the pH.

Which of the following silicate clays would be least apt to be formed from the mere alteration of primary minerals?

Humus has a much higher cation adsorption capacity at pH 5.5 than at pH 8.0.

Humus is an important soil colloid.It differs from 2:1 type minerals in all but one of the following characteristics (select the one).

The swelling/shrinking tendency of some silicate clay minerals is due primarily to _____.

The electronegative charge on 2:1 type silicate clays is due primarily to _____.

A well drained soil under a rain forest in Brazil contains significant amounts of a silicate clay.Which of the following is it most apt to be?

Which of the following is not a characteristic of soil colloids?

Some soil colloids exhibit positive charges under highly acid conditions.To what are these charges likely due?

An alkaline soil contains 20% clay and 3% humus.If the pure clay has a CEC of 40 cmol_c/kg and the humus 200 cmol_c/kg,calculate the CEC/kg of the soil.

Kaolinite is most prevalent in soils developed from volcanic ejecta (Andisols).

If you were seeking a soil colloid with a high capacity to adsorb cationic pollutants,but also with a consistent capacity to do so even as the pH varied from 4.0 to 7.5,which of the following would you choose?

Vermiculite and associated silicate clays have a net electropositive charge in slightly acid soils.

The Soils Around Us

Formation of Soils From Parent Materials

Soil Classification

Soil Architecture and Physical Properties

Soil Water: Characteristics and Behavior

Soil and the Hydrologic Cycle

Soil Aeration and Temperature

Soil Acidity

Soils of Dry Regionsalkalinity,salinity and Sodicity

Organisms and Ecology of the Soil

Soil Organic Matter

Nitrogen and Sulfur Economy of Soils

Soil Phosphorus and Potassium

Calcium,magnesium and Trace Elements

Practical Nutrient Management

Soil Erosion and Its Control

Soils and Chemical Pollution

Geographic Information About Soils

Prospects for Global Soil Quality As Affected by Human Activities

Filters

Exam 8: The Colloidal Fraction: Seat of Soil Chemical and Physical Activity

Soil colloids are too small to be seen with an ordinary light microscope.

A tetrahedral sheet is characterized by a plane of aluminum atoms surrounded by oxygen and hydroxyl groups.

You find that the CEC of a sandy loam soil at pH 5.0 is 8 cmolc/kg and at pH 8.2 it is 14 cmolc/kg.What is the most likely reason for this difference?

Soils rich in which type of clay would provide the most troublesome site on which to build a home?

The primary source of charge for 2:1 type clay minerals is ionization of the surface hydroxyl groups on the tetrahedral sheets.

While 2:1 type clays have significant internal surfaces,their external surfaces are generally much more extensive.

A 1 kg soil sample has 2 cmolc of Al3+ on the exchange complex.Addition of which of the following would most effectively replace about half of this Al?

The cation exchange capacity of a soil is determined primarily by the amount and kind of colloids in the soil and by the pH.

Which of the following silicate clays would be least apt to be formed from the mere alteration of primary minerals?

Humus has a much higher cation adsorption capacity at pH 5.5 than at pH 8.0.

Humus is an important soil colloid.It differs from 2:1 type minerals in all but one of the following characteristics (select the one).

The swelling/shrinking tendency of some silicate clay minerals is due primarily to _____.

The electronegative charge on 2:1 type silicate clays is due primarily to _____.

A well drained soil under a rain forest in Brazil contains significant amounts of a silicate clay.Which of the following is it most apt to be?

Which of the following is not a characteristic of soil colloids?

Some soil colloids exhibit positive charges under highly acid conditions.To what are these charges likely due?

An alkaline soil contains 20% clay and 3% humus.If the pure clay has a CEC of 40 cmolc/kg and the humus 200 cmolc/kg,calculate the CEC/kg of the soil.

Kaolinite is most prevalent in soils developed from volcanic ejecta (Andisols).

If you were seeking a soil colloid with a high capacity to adsorb cationic pollutants,but also with a consistent capacity to do so even as the pH varied from 4.0 to 7.5,which of the following would you choose?

Vermiculite and associated silicate clays have a net electropositive charge in slightly acid soils.

The Soils Around Us

Formation of Soils From Parent Materials

Soil Classification

Soil Architecture and Physical Properties

Soil Water: Characteristics and Behavior

Soil and the Hydrologic Cycle

Soil Aeration and Temperature

Soil Acidity

Soils of Dry Regionsalkalinity,salinity and Sodicity

Organisms and Ecology of the Soil

Soil Organic Matter

Nitrogen and Sulfur Economy of Soils

Soil Phosphorus and Potassium

Calcium,magnesium and Trace Elements

Practical Nutrient Management

Soil Erosion and Its Control

Soils and Chemical Pollution

Geographic Information About Soils

Prospects for Global Soil Quality As Affected by Human Activities

Filters

You find that the CEC of a sandy loam soil at pH 5.0 is 8 cmol_c/kg and at pH 8.2 it is 14 cmol_c/kg.What is the most likely reason for this difference?

A 1 kg soil sample has 2 cmol_c of Al³⁺ on the exchange complex.Addition of which of the following would most effectively replace about half of this Al?

An alkaline soil contains 20% clay and 3% humus.If the pure clay has a CEC of 40 cmol_c/kg and the humus 200 cmol_c/kg,calculate the CEC/kg of the soil.