(#) Soil colloids

Question 1

True or false, soil colloids are the most chemically active portion of the soil

Answer 1

True

Question 2

Average soil colloid diameter

Answer 2

<1μ or 0.001mm

Question 3

What are the types of soil colloids?

Answer 3

Organic
Inorganic

Question 4

What are the types of Organic soil colloids?

Answer 4

Humus

Question 5

What are the types of Inorganic soil colloids?

Answer 5

Silicate clays
Allophanes
Fe and Al oxides

Question 6

what is Micelle?

Answer 6

a silicate clay crystal

Question 7

Shape of silicate clays

Answer 7

• flaky, laminated, usually hexagonal

Question 8

Surface area of silicate clays

Answer 8

internal and external

Question 9

name a silicate clay crystal

Answer 9

Micelle

Question 10

Name silicate clay’s electro negative charges

Answer 10

net negatively charged

Question 11

Types of Silicate clays

Answer 11

1:1 (One silica tetrahedon & one aluminum actahedron)
2:1 Expanding type
2:1 Non-expanding type
2:1:1 or 2:2

Question 12

The type of silicate clay that’s one tetrahedral sheet attached to one side of an octahedral sheet

Answer 12

1:1

Question 13

Name a 1:1 silicate clay

Answer 13

Kaolinite

Question 14

CEC of kaolinite

Answer 14

low

Question 15

True or false, kaolinite has high surface area

Answer 15

False

Question 16

True or false, kaolinite has low water holding capacity

Answer 16

True

Question 17

True or false, kaolinite has low shrink-swell capacity. Why?

Answer 17

True, due to strong hydrogen bonding

Question 18

Which silicate clay has a symmetrical arrangement of two tetrahedral sheets and a central octahedral sheet?

Answer 18

2:1 Expanding silicate clay

Question 19

Name a 2:1 expanding silicate clay

Answer 19

Montmorillonite

Question 20

True or false, montmorillonite has low CEC

Answer 20

False

Question 21

Montmorillonite is a major component in what kind of soil?

Answer 21

Vertisols

Question 22

What is the D spacing of montmorillonite?

Answer 22

10-17A

Question 23

True or false, 2:1 Non-expanding silicate clay has the different composition/structure than 2:1 expanding silicate clay

Answer 23

false, they have the same composition/structure, it’s just non-expanding doesn’t expand

Question 24

Why do 2:1 non-expanding silicate clays not expand?

Answer 24

presence of K+ ions

Question 25

Name a 2:1 Non-expanding silicate clay

Answer 25

muscovite

Question 26

Which silicate clay has two silica tetrahedral sheet and two Mg-dominated octahedral sheet

Answer 26

2:1:1 / 2:2 silicate clay

Question 27

Name a 2:2 silicate clay

Answer 27

chlorites

Question 28

What are the substitutions in a 2:1 silicate clay's tetrahedral sheet

Answer 28

Al^3+ & Si^4+ (negative charge)

Question 29

What does the octahedral interlayer of a chlorite contain?

Answer 29

Mg^2+ & Fe^2+ (positive charge)

Question 30

Hydrous oxide ore are hydrous oxides of Fe and Al commonly dominant in?

Answer 30

Highly weathered soils of tropics and subtropics

Question 31

Name hydrous oxides of Fe and Al

Answer 31

Gibbsite and Goethite

Question 32

True or false, some hydrous oxides of Fe and Al have definite crystaline structure whilst others are amorphus

Answer 32

True

Question 33

True or false, hydrous oxides of Fe and Al are sticky and plastic

Answer 33

false, non-sticky and plastic

Question 34

"short-range order minerals"

Answer 34

allophanes

Question 35

What soil are allophanes prevalent in?

Answer 35

Andisols

Question 36

True or false, Allophanes have low capacity to adsorb cations

Answer 36

false

Question 37

Name two allophanes

Answer 37

allophanes & imogolite

Question 38

What is humus composed of?

Answer 38

C, H, O (non crystaline

Question 39

What are the 3 sources of negative charges?

Answer 39

1) Isomorphous substitution 2) Dissociation of exposed OH groups at the broken edges of the mineral 3) Dissociation of functional groups in organic colloids

Question 40

The source of negative charge wherein centrally coordinated cations are replaced by another cation without alteration of crystal structure of the mineral

Answer 40

Isomorphous substitution

Question 41

In which silicate clay is isomorphous substitution most prevalent?

Answer 41

2:1

Question 42

In which source of negative charge does OH dissociate at a high pH?

Answer 42

Dissociation of exposed OH groups at the broken edges of the mineral

Question 43

In which source of negative charge, when at high pH, creates pH dependent negative charge?

Answer 43

Dissociation of functional groups in organic colloids

Question 44

The interchange between a cation in solution and another cation on the surface of any surface-active material such as clay or organic matter

Answer 44

cation exchange

Question 45

True or false, cation exchange is the result of positive charges in soil colloids, which attract positive ions (cations) from soil solution

Answer 45

False, it's the other way around

Question 46

What is cation exchange capacity (CEC)?

Answer 46

sum of exchangeable cations that a soil can adsorb

Question 47

What is base saturation?

Answer 47

Proportion of CEC that is made up of exchangeable bases

Question 48

The quantity of a substance that exactly reacts with, or is equal to the combining value of, an arbitrarily fixed quantity of another substance in a particular reaction.

Answer 48

Equivalent weight