Chapter 3

Question 1

The most reactive component of the soil.

Answer 1

soil colloid

Question 2

What are the two types of the soil colloids?

Answer 2

organic colloids
inorganic colloids

Question 3

The highly decomposed organic matter?

Answer 3

Humus

Question 4

The type of colloid that is composed of highly decomposed organic matter?

Answer 4

Organic colloid

Question 5

More reactive type of colloid?

Answer 5

organic colloid

Question 6

_____ are more reactive chemically and generally have a greater influence on soil properties per unit weight than the inorganic colloids.

Answer 6

Organic colloids

Question 7

Inorganic colloids include what?

Answer 7

silicate clays
oxides
hydrous oxides
amorphous clays

Question 8

The size of soil colloid

Answer 8

0.001 mm

Question 9

The charge of colloids in very acid soils

Answer 9

net positive charge

Question 10

Exhibit positive as well as negative charge.

Answer 10

amphoteric

Question 11

The pH at which the surface charge is neutral.

Answer 11

Zero point of Charge

Question 12

The dissociation of H from hydroxyl group also decreases CEC.

Answer 12

increases CEC

Question 13

Fe/Al oxide minerals are stable at what pH?

Answer 13

pH 5

Question 14

Variable charge soils can be limed up to what pH.

Answer 14

pH 5.5

Question 15

Is it viable to increase the pH of variable charge soils up to pH 6?

Answer 15

no, it is costly because variable charge soils are buffered below or above pH0

Question 16

What are the effects of lime?

Answer 16

increase pH
precipitate Al to Al(OH)3
replace precipitated Al with Ca

Question 17

The reaction involved in reacting H+ with OH- with the release of H2O.

Answer 17

neutralization

Question 18

What is the main value of lime?

Answer 18

provide hydroxyl ions

Question 19

What is the surface charge if pH0-pH is (-)?

Answer 19

net negative charge

Question 20

What is the net surface charge if pH0-pH is (+)?

Answer 20

net positive charge

Question 21

Which has lower pH0:
surface soil vs subsoil

Answer 21

surface soil due to higher OM

Question 22

soils that have low pH0?

Answer 22

silica
OM

Question 23

This is the point at which net surface charge is independent of salt concentration so the titration curves should intersect at this point.

Answer 23

Zero Net Charge

Question 24

The pH0 value of Fe/Al oxides

Answer 24

7-9 ( high AEC)

Question 25

Parameters that affect the sign and magnitude of charge on variable charge colloids

Answer 25

pH0 soil pH electrolyte concentration valence counterion Dielectric constant

Question 26

Enumerate the theories of Electrical Double Layer

Answer 26

Helmholtz Double Layer Theory Gouy-Chapman Diffuse DL Theory Stern DL Theory

Question 27

consist of an inner layer of strongly adsorbed counterions and an outer layer of ion swarm.

Answer 27

Stern DL

Question 28

2 fundamental equations to describe ionic concentration near the surface and potential distribution with distance from the surface:

Answer 28

Poisson equation Boltzman distribution

Question 29

Describes the coulombic interaction between charges.

Answer 29

Poisson equation

Question 30

Describes the change in concentration of counterions near a charged surface.

Answer 30

Boltzman distribution

Question 31

What happens to DDL at increasing concentration?

Answer 31

decrease thickness

Question 32

What happens to DDL in monovalent cations?

Answer 32

thicker

Question 33

What happens to DDL in divalent cations?

Answer 33

thinner

Question 34

It accounts for the thermal motion of counterions at the charged surface.

Answer 34

Gouy-Chapman Diffuse Double Layer Theory

Question 35

Gouy-Chapman Diffuse DL theory was developed by Gouy in what year?

Answer 35

1910

Question 36

What are the sources of Negative Charge in Colloidal Surfaces

Answer 36

Isomorphous substitution Ionization of exposed hydroxyl group broken bonds at edges of silica-alumina units

Question 37

What are the sources of Positive Charge in Colloidal surface

Answer 37

Isomorphous substitution Protonation of exposed hydroxyl group

Question 38

if Al3+ is being replaced with Mg2+, what will happen to the charge?

Answer 38

leads to increase in negative

Question 39

Source of the positive charge of organic colloid at low pH?

Answer 39

protonation of hydroxyl group and NH group

Question 40

What will happen to the charge if there is IS of Al3+ to Mg2+

Answer 40

gain positive charge

Question 41

Examples of minerals with permanent charge

Answer 41

2:1 clay minerals 2:2 intergrades

Question 42

Enumerate minerals with pH-dependent or variable charge

Answer 42

1:1 clay minerals Fe and Al oxides or sesquioxides Amorphous aluminosilicate Amorphous Fe/Al hydrous oxides Organic colloids

Question 43

They balance or neutralize the net negative charge generated by clay particles

Answer 43

Adsorbing cations

Question 44

It refers to the amount of charge associated per unit area of the clay colloid.

Answer 44

surface charge density

Question 45

if the change in pH is positive, what is the charge of the colloid

Answer 45

negative

Question 46

If the change in pH is negative, what is the charge of the colloid?

Answer 46

positive

Question 47

Implications of charge colloids to soil management

Answer 47

increasing cation retention liming acid soil

Question 48

What will happen to phosphate applied to an oxisol decreased pH0?

Answer 48

increase CEC

Question 49

Mg-dominated octahedral sheets minerals

Answer 49

vermiculite chlorite