Soil Science Finals Modules 5-9

Soils rich in ___ have dispersed or weak structure

Na+

Soils with _______ favors fungi and antagonistic bacteria

Low pH

Most of the chemical properties of soil are associated with soil ______

colloids

These are mineral or organic particles in soil having a diameter less than .001 mm

Colloids

True/False

Colloids are less than 1 micron

True

True/False

Colloids diffuse quickly through a semi-permeable membrane

False

True/False

Most colloids are negatively charged

False

These colloids are represented by clays

Inorganic

These colloids are represented by humus

Organic

The chemistry of a soil mass is largely a function of the properties of what soil fraction?

Clay

These are clays that could be iron or aluminum oxides and hydroxides

Oxide Clays

What is Fe00H?

Geothite

This is the most stable iron oxide and the most dominant one in most soils

Geothite

This oxide give soil a yellow color

Geothite

What is Fe2O3?

Hematite

These are red-colored forms under drier, warmer and more oxidized conditions

Hematite

What is Al(OH)3?

Gibbsite

These are individual particles that are laminated and made up of layers, are crystalline and have ordered internal arrangement, expose a large amount of external surface, micelles are negatively-charged, and composed of silica tetrahedral sheets and aluminum octahedral units

Silicate Clays

These are minute silicate clay colloid particles

Micelles

This is the orderly arrangement of atoms in a crystalline material

Lattice Structure

This is a silica-dominated sheet which is composed of silicon cation and surrounded by 4 oxygen anions

Silicon Tetrahedron

This is a unit composed of aluminum or magnesium surrounded by oxygen or hydroxyl ions giving an 8-sided block

Aluminum Octahedron

These are the mineral fractions of the soil having a diameter of 0.002 mm or smaller

Clay Minerals

These clays are composed of silica, alumina, and iron that are not crystalline

Amorphous Clays

These types of clays are mostly crystalline

Structured Clays

When tetrahedral units connect to each other, what is formed?

Tetrahedral Sheet

When octahedral units connect to each other, what is formed?

Octahedral Sheet

Permanent charge of clays result from what?

Isomorphous Substitution

This is the replacement of one atom by another of similar size in a crystal structure

Isomorphous Substitution

This is the removal of a proton from a molecule, resulting in the formation of its conjugate base.

Deprotonation

Kaolinite sheet type

1:1

Other name for Mica

Illite

Mica/Illite sheet type

2:1

Vermiculite sheet type

2:1

Montmorillonite sheet type

2:1

Chlorite sheet type

2:1:1

What mineral has a hydroxide sheet?

Chlorite

High/Low Layer Charge

Kaolinite

Low Layer Charge

High/Low Layer Charge

Mica/Illite

High Layer Charge

High/Low Layer Charge

Vermiculite

High Layer Charge

High/Low Layer Charge

Montmorillonite

Low Layer Charge

What mineral has an interlayer filling?

Chlorite

A mineral with a specific surface of 7-30 m2/g

Kaolinite

A mineral with a specific surface of 40-100 m2/g

Mica/Illite

Minerals with a specific surface of 600-800 m2/g

Vermiculite and Montmorillonite

A mineral with a specific surface of 25-150 m2/g

Chlorite

Name the minerals that are non-expanding in water

Kaolinite, Mica/Illite, and Chlorite

This mineral expands by 0.4-0.5 nm when in water

Vermiculite

This mineral has an unlimited expansion when in water

Montmorillonite

This mineral is 70-100 layers thick

Kaolinite

Each sheet of this mineral ranges from 0.1-5 microns thick

Kaolinite

Interlayer bond of Kaolinite

Strong Hydrogen Bonds

CEC meaning

Cation Exchange Capacity

CEC of Kaolinite

7 cmol(+)/kg

The source of charge of this mineral is the isomorphic substitution that occurs only in the tetrahedral sheet

Mica/Illite

In Illite,_____ sit tightly in the interlayer spaces and act like a “glue” that holds the layers together.

Fixed K+

True/False

Water can enter the interlayer of illite easily?

False

Kaolinite net negative charge

0

Illite net negative charge

0.7-1

Size of Kaolinite

0.1-5 µm

Illite size

0.1 - 2 µm

Where does the isomorphous substitution occur in vermiculite?

Tetrahedral Sheet

In vermiculite, the octahedron emanates a degree of positivity which results to what?

Lower net negative charge

Size of Vermiculite

0.1 - 2 µm

True/False

Multiple cations are present in the interlayer bonding of vermiculite

True

CEC of montmorillonite

100 cmol(+)/kg

Where does isomorphic substitution occur in montmorillonite?

Octahedral Sheet

Montmorillonite expands because its ____________ allows water and exchangeable cations to enter the interlayer space, causing the layers to swell.

Low Layer Charge

In the succession of weathering, what are the primary minerals?

Muscovite/Biotite

In the succession of weathering, what comes after the primary minerals?

Illite

In the succession of weathering, what comes after Illite?

Montmorillonite

In the succession of weathering, what comes after montmorillonite?

Kaolinite

In the succession of weathering, what comes after kaolinite?

Iron Oxides

Where does isomorphic substitution occur in chlorite?

Both Tetrahedral and Octahedral Sheets

What cation is present in the interlayer of chlorite?

Mg2+

Other name for montmorillonite

Weakened Illite

Layer charge of vermiculite

0.6-0.9

Layer charge of montmorillonite

0.2-0.6

Layer charge of chlorite

Variable

These are known as the swelling clays

Vertisols

This refers to cracking-swelling soil

Montmorillonitic

These are highly weathered tropical soils composed of kaolinites and Fe/Al oxides that have low fertility

Oxisols

These are the exchange of cations in solutions of cations adsorbed onto soil surfaces/exchange site

Cation Exchange Process

Properties of cation exchange process

Rapid, Reversible, Stoichiometric

The ability or capacity of a soil colloid to “sorb” cations that can be exchanged with cations in the solution

Cation Exchange Capacity

This is a surface phenomenon that refers to the process of a substance being taken up by a solid

Sorption

The degree of adsorption depends on what factors?

Valences, Radii, and Hydration Properties

The smaller the hydrated radius and the greater the valency, what happens to the degree of adsorption?

The degree of adsorption increases

The relationship between particle size and surface area exposure

Inverse

This influences the surface area exposed

The amount of clay present

Highest CEC

Vermiculite and Montmorillonite

Lowest CEC

Kaolinite

These contain negative charges from exposed functional groups

Organic Matter and Sesquioxides

This refers to hydrous oxides of Fe and Al

Sesquioxides

This influences the possibility of protonation/deprotonation of functional groups

pH

This refers to the amount of cation a soil can hold

Cation Exchange Capacity

Unit for CEC

cmol(+)/kg

In the order of preference for cation adsorption of soil particles, what is at the topmost position?

Al3+

In the order of preference for cation adsorption of soil particles, what is at the lowest position?

Li+

1 mole of H+ equals how many ions?

6.022 × 10 ²³ H+ ions