Question 1

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  False

Question 2

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

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.
21) 
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.
21) C

Question 4

You would expect the cation exchange capacities of Ultisols to be lower than those of Aridisols if the soil textures are about the same.

Accepted Answer

A) True 
 B)False

Question 5

Allophane differs from other silicate clays in all ways but one of the following (select the one).

Accepted Answer

A) nature of parent materials from which it forms 
B) degree of crystallization of the particles 
C) the presence of negative charges on the colloidal particles 
D) widespread occurrence around the world 
E) the period of time it has been subject to weathering 
A) nature of parent materials from which it forms 
B) degree of crystallization of the particles 
C) the presence of negative charges on the colloidal particles 
D) widespread occurrence around the world 
E) the period of time it has been subject to weathering

Question 6

The leaf-like structure of silicate clays involves two kinds of horizontal sheets, one dominated by a plane of silicon atoms, the other by a plane of aluminum and/or magnesium.

Accepted Answer

A) True 
 B)False

Question 7

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 8

The negative charges associated with smectite clay crystals are due mostly to _____.

Accepted Answer

A) isomorphous substitution of Mg for Al in the octahedral sheet 
B) substitution of Al for Mg in the tetrahedral sheet 
C) high pH associated with the formation of the mineral 
D) substitution of Si for Al in the tetrahedral sheet 
E) OH groups on the external surface of the crystal 
A) isomorphous substitution of Mg for Al in the octahedral sheet 
B) substitution of Al for Mg in the tetrahedral sheet 
C) high pH associated with the formation of the mineral 
D) substitution of Si for Al in the tetrahedral sheet 
E) OH groups on the external surface of the crystal

Question 9

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

Accepted Answer

A) True 
 B)False

Question 10

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

Accepted Answer

A) True 
 B)False

Question 11

You are working with a soil colloid known to have a reasonably high potassium level, a cation exchange capacity of about 20 cmolc/kg of clay and little tendency to swell when wetted.Which of the following is it most apt to be the dominant clay mineral in this soil?

Accepted Answer

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

Question 12

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 13

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 14

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 15

Of the silicate clays, smectite has the least tendency to expand upon wetting and shrink upon drying.

Accepted Answer

A) True 
 B)False

Question 16

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 17

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 18

Which of the silicate clays would likely have the highest level of potassium in the crystal structure?

Accepted Answer

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

Question 19

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 20

Smectite and vermiculite are more prominent in extremely weathered soils than in soils where only modest weathering has occurred.

Accepted Answer

A) True 
 B)False

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.

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?

You would expect the cation exchange capacities of Ultisols to be lower than those of Aridisols if the soil textures are about the same.

Allophane differs from other silicate clays in all ways but one of the following (select the one).

The leaf-like structure of silicate clays involves two kinds of horizontal sheets, one dominated by a plane of silicon atoms, the other by a plane of aluminum and/or magnesium.

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

The negative charges associated with smectite clay crystals are due mostly to _____.

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

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

You are working with a soil colloid known to have a reasonably high potassium level, a cation exchange capacity of about 20 cmol_c/kg of clay and little tendency to swell when wetted.Which of the following is it most apt to be the dominant clay mineral in this soil?

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

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.

Of the silicate clays, smectite has the least tendency to expand upon wetting and shrink upon drying.

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

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

Which of the silicate clays would likely have the highest level of potassium in the crystal structure?

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

Smectite and vermiculite are more prominent in extremely weathered soils than in soils where only modest weathering has occurred.

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 Regions: Alkalinity, Salinity, and Sodicity

Organisms and Ecology of the Soil

Soil Organic Matter

Nitrogen and Sulfur Economy of Soils

Soil Phosphorus and Potassium

Micronutrients and Other Trace Elements

Practical Nutrient Management

Soil Erosion and Its Control

Soils and Chemical Pollution

Geographic Soils Information

Prospects for Global Soil Quality

Filters

Exam 8: Soil Colloids: Seat of Soil Chemical and Physical Activity

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.

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?

You would expect the cation exchange capacities of Ultisols to be lower than those of Aridisols if the soil textures are about the same.

Allophane differs from other silicate clays in all ways but one of the following (select the one).

The leaf-like structure of silicate clays involves two kinds of horizontal sheets, one dominated by a plane of silicon atoms, the other by a plane of aluminum and/or magnesium.

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

The negative charges associated with smectite clay crystals are due mostly to _____.

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

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

You are working with a soil colloid known to have a reasonably high potassium level, a cation exchange capacity of about 20 cmolc/kg of clay and little tendency to swell when wetted.Which of the following is it most apt to be the dominant clay mineral in this soil?

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

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?

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.

Of the silicate clays, smectite has the least tendency to expand upon wetting and shrink upon drying.

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

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

Which of the silicate clays would likely have the highest level of potassium in the crystal structure?

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

Smectite and vermiculite are more prominent in extremely weathered soils than in soils where only modest weathering has occurred.

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 Regions: Alkalinity, Salinity, and Sodicity

Organisms and Ecology of the Soil

Soil Organic Matter

Nitrogen and Sulfur Economy of Soils

Soil Phosphorus and Potassium

Micronutrients and Other Trace Elements

Practical Nutrient Management

Soil Erosion and Its Control

Soils and Chemical Pollution

Geographic Soils Information

Prospects for Global Soil Quality

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?

You are working with a soil colloid known to have a reasonably high potassium level, a cation exchange capacity of about 20 cmol_c/kg of clay and little tendency to swell when wetted.Which of the following is it most apt to be the dominant clay mineral in this soil?

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.