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SOIL 140 > Chapter 3 > Flashcards

Chapter 3 Flashcards

1
Q

The most reactive component of the soil.

A

soil colloid

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2
Q

What are the two types of the soil colloids?

A

organic colloids
inorganic colloids

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3
Q

The highly decomposed organic matter?

A

Humus

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4
Q

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

A

Organic colloid

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5
Q

More reactive type of colloid?

A

organic colloid

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6
Q

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

A

Organic colloids

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7
Q

Inorganic colloids include what?

A

silicate clays
oxides
hydrous oxides
amorphous clays

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8
Q

The size of soil colloid

A

0.001 mm

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9
Q

The charge of colloids in very acid soils

A

net positive charge

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10
Q

Exhibit positive as well as negative charge.

A

amphoteric

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11
Q

The pH at which the surface charge is neutral.

A

Zero point of Charge

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12
Q

The dissociation of H from hydroxyl group also decreases CEC.

A

increases CEC

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13
Q

Fe/Al oxide minerals are stable at what pH?

A

pH 5

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14
Q

Variable charge soils can be limed up to what pH.

A

pH 5.5

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15
Q

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

A

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

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16
Q

What are the effects of lime?

A

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

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17
Q

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

A

neutralization

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18
Q

What is the main value of lime?

A

provide hydroxyl ions

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19
Q

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

A

net negative charge

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20
Q

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

A

net positive charge

21
Q

Which has lower pH0:
surface soil vs subsoil

A

surface soil due to higher OM

22
Q

soils that have low pH0?

A

silica
OM

23
Q

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

A

Zero Net Charge

24
Q

The pH0 value of Fe/Al oxides

A

7-9 ( high AEC)

25
Q

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

A

pH0
soil pH
electrolyte concentration
valence counterion
Dielectric constant

26
Q

Enumerate the theories of Electrical Double Layer

A

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

27
Q

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

A

Stern DL

28
Q

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

A

Poisson equation
Boltzman distribution

29
Q

Describes the coulombic interaction between charges.

A

Poisson equation

30
Q

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

A

Boltzman distribution

31
Q

What happens to DDL at increasing concentration?

A

decrease thickness

32
Q

What happens to DDL in monovalent cations?

A

thicker

33
Q

What happens to DDL in divalent cations?

A

thinner

34
Q

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

A

Gouy-Chapman Diffuse Double Layer Theory

35
Q

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

A

1910

36
Q

What are the sources of Negative Charge in Colloidal Surfaces

A

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

37
Q

What are the sources of Positive Charge in Colloidal surface

A

Isomorphous substitution
Protonation of exposed hydroxyl group

38
Q

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

A

leads to increase in negative

39
Q

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

A

protonation of hydroxyl group and NH group

40
Q

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

A

gain positive charge

41
Q

Examples of minerals with permanent charge

A

2:1 clay minerals
2:2
intergrades

42
Q

Enumerate minerals with pH-dependent or variable charge

A

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

43
Q

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

A

Adsorbing cations

44
Q

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

A

surface charge density

45
Q

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

A

negative

46
Q

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

A

positive

47
Q

Implications of charge colloids to soil management

A

increasing cation retention
liming acid soil

48
Q

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

A

increase CEC

49
Q

Mg-dominated octahedral sheets minerals

A

vermiculite
chlorite

SOIL 140 (3 decks)

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