Question 1

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?

Accepted Answer

The fact that the soil has little tendency to swell when wetted indicates that it does not contain a large amount of expandable clay minerals such as vermiculite or smectite. The cation exchange capacity (CEC) of 20 cmol_c/kg of clay suggests a relatively high clay content, which is characteristic of some types of fine-grained mica. Additionally, micas are known to have a high level of potassium, which is also a characteristic of this soil.

Question 2

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

Accepted Answer

The swelling/shrinking tendency of some silicate clay minerals is primarily due to the movement of water molecules in and out of the interlayers of the crystal. This causes the interlayers to expand or contract, leading to the clay mineral's swelling or shrinking behavior.

Question 3

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

Accepted Answer

A

Question 4

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

Accepted Answer

The electronegative charge on 2:1 type silicate clays primarily arises from the substitution of one metallic atom for another in the crystal structure of the clay, leading to a net negative charge that attracts cations.

Question 5

Anion exchange by formation of outer sphere complexes is of least importance in the plant absorption of _____.

Accepted Answer

Phosphate (H2PO4-) is typically absorbed by plants through inner sphere complexation rather than outer sphere complexation, making anion exchange less important for its absorption.

Question 6

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

Accepted Answer

Allophane is similar to other silicate clays in that it also has negative charges on its colloidal particles. The differences lie in its parent materials, degree of crystallization, distribution, and weathering period.

Question 7

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

Humus and 2:1 type minerals both have the capability to adsorb cations, which is a common characteristic between them. The other options (A, B, C, E) highlight differences between humus and 2:1 type minerals in terms of structure, CEC pH dependence, isomorphous substitution, and influence on soil aggregate stability.

Question 8

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?

Accepted Answer

The answer of You find that the CEC of a...

Question 9

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

Kaolinite is the most likely type of silicate clay found in well-drained soils under rainforests in Brazil. This is because kaolinite forms in warm, moist climates through the intense weathering of rocks, a process common in rainforest environments.

Question 10

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

Accepted Answer

Smectite is a highly expandable clay that swells significantly when exposed to water and contracts when dried out. This property leads to significant soil movement, which can cause damage to foundations and structures built on top of it. Thus, soils rich in smectite can provide the most troublesome site on which to build a home.

Question 11

Which cation would you expect to be mostly tightly held in a soil at pH 4.5?

Accepted Answer

At pH 4.5, the soil is acidic and positively charged cations like Al3+ are strongly held by negatively charged soil particles. The larger ionic radius of Al3+ compared to cations like K+ or Na+ further increases its sorption potential. Calcium (Ca2+) and magnesium (Mg2+) are also two other cations that are commonly present in soil, but they are not as strongly held as Al3+ at pH 4.5. Therefore, option C - Al³⁺, is the best choice.

Question 12

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

Accepted Answer

The answer of The negative charges associated with smectite clay...

Question 13

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

Accepted Answer

Fine-grained micas, such as illite, have the highest level of potassium in the crystal structure.

Question 14

Which of the following silicate clays would be least apt to be formed from the mere alteration of 70 primary minerals?

Accepted Answer

Iron and aluminum oxides are not primary minerals, and therefore cannot be formed from the alteration of other primary minerals. The other options are all silicate clays that can be formed from the alteration of primary minerals, with varying degrees of likelihood depending on the specific conditions of the alteration.

Question 15

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 form 4.0 to 7.5, which of the following would you choose?

Accepted Answer

Montmorillonite is a type of clay mineral that has a high cation exchange capacity (CEC), which means it can adsorb cationic pollutants. It also has a consistent CEC even as the pH varies, making it a good choice for this scenario. Kaolinite, fine-grained mica, and chlorite also have high CECs but their capacities can vary with pH. Humus is an organic matter and does not have a consistent CEC.

Question 16

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.

Accepted Answer

The CEC (Cation Exchange Capacity) of the soil can be calculated by taking into account the contributions from both the clay and the humus. The calculation is as follows:- For clay: 20% of the soil is clay, and its CEC is 40 cmol(+)/kg. Therefore, its contribution is 0.20 * 40 = 8 cmol(+)/kg.- For humus: 3% of the soil is humus, and its CEC is 200 cmol(+)/kg. Therefore, its contribution is 0.03 * 200 = 6 cmol(+)/kg.Adding these contributions together gives a total CEC for the soil of 8 + 6 = 14 cmol(+)/kg.

Question 17

As biotite weathers in soils, which of the following would not likely develop by mere alteration of this mineral?

Accepted Answer

The answer of As biotite weathers in soils, which of...

Question 18

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

Accepted Answer

Soil colloids typically have a high water holding capacity due to their ability to attract and hold onto water molecules through various forces, such as hydrogen bonding. Therefore, the option that is not a characteristic of soil colloids is E, which states a "low water holding capacity."

Question 19

If you were looking for a soil with high cation exchange capacity and were not concerned with the soil's physical properties, which of the following would most likely fit your needs?

Accepted Answer

Vertisols have a high cation exchange capacity due to their high clay content, which allows them to hold onto cations (positively charged ions) more effectively than other soil types.

Question 20

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?

Accepted Answer

Ca²⁺ has a higher charge than Na⁺ or K⁺, making it more effective at displacing Al³⁺ from the exchange complex. 4 cmol_c of Ca²⁺ can replace about half of the 2 cmol_c of Al³⁺ due to its divalent nature.

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

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

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

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

Anion exchange by formation of outer sphere complexes is of least importance in the plant absorption of _____.

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

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

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 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?

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

Which cation would you expect to be mostly tightly held in a soil at pH 4.5?

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

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

Which of the following silicate clays would be least apt to be formed from the mere alteration of 70 primary minerals?

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 form 4.0 to 7.5, which of the following would you choose?

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.

As biotite weathers in soils, which of the following would not likely develop by mere alteration of this mineral?

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

If you were looking for a soil with high cation exchange capacity and were not concerned with the soil's physical properties, which of the following would most likely fit your needs?

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?

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

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

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

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

Anion exchange by formation of outer sphere complexes is of least importance in the plant absorption of _____.

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

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

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?

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?

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

Which cation would you expect to be mostly tightly held in a soil at pH 4.5?

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

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

Which of the following silicate clays would be least apt to be formed from the mere alteration of 70 primary minerals?

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 form 4.0 to 7.5, which of the following would you choose?

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.

As biotite weathers in soils, which of the following would not likely develop by mere alteration of this mineral?

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

If you were looking for a soil with high cation exchange capacity and were not concerned with the soil's physical properties, which of the following would most likely fit your needs?

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?

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?

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?

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.

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?