soils exam 2 study guide

Definition of CEC?

cation exchange capacity. sum total of exchangable cations a soil can adsorb

MOST soils have an overwhelming ___ charge

negative

K charge, name, weight

Potassium +1 39g

Ca charge, name, weight

Calcium 2+ 40g

Mg charge, name, weight

Magnesium 2+ 24g

Al charge, name, weight

Aluminum 3+ 27g

Na charge, name, weight

Sodium +1 23g

NH4 charge, name, weight

Ammonium +1 18g

H charge, name, weight

Hydrogen + 1g

NO3 charge and name

Nitrate -1

SO4 charge and name

Sulfate 2-

Lyotrophic series considers _____ radius and charge ___

Hydrated, density

CEC of organic material

high, 200

CEC of non-clay material ~

1-15

Smectite and vermiculite clay CEC range

High

CEC and ECEC differences?

Important in acid, humid soils. In acid soils CEC may be overestimated. Doesn’t measure NH4 collected

-Al-OH + OH- ---→ Al-O- + H2O

Reaction showing how variable charge develops when high pH ammonium acetate is added

What are the nonacid cations?

Na+

K+

Ca+2

Mg+2

What are the acid cations

H +

Al +3

Formula for base saturation?

Nonacid cations / CEC(total cations)

Do most soils have AEC?

Yes

What 4 things in soil have AEC?

1:1 clays

Hydrous oxides of iron and aluminum

Heavily weathered soils

Volcanic soils

What is CEC measured in? (both units)

centimole charge/kilogram and milliequivalent. They are the same numbers

What do you need to calculate CEC?

Mass of extracted soil

atomic weight and charge on each ion measuredH

How to find equivalent weight of ions?

Atomic weight/charge = equivalent

Characteristics of soil colloids?

Extremely small

Large surface area per unit of mass

Negative and positive surface charges

4 types of soil colloids?

Layer silicate clays - crystalline silicate clays

Iron and aluminum oxide clays

Allophane

Humus

Same sources as CEC

Tetrahedral sheets have what ion at the center?

Silicon

Octahedral sheets have what ion at the center?

Aluminum

What ions can substitute in a tetrahedral sheet?

Si, Fe, Al

What is isomorphous substitution?

Cations of similar size substitute for Al and Si in sheets. Occurs during weathering

Isomorphous substitution is the part of CEC we call ___?

Permanent charge

What ions can substitute in octahedral sheets?

Al, fe, mg, zn, na, ca, k

What is the only 1:1 clay we discuss?

Kaolinite

Properties of kaolinite?

Fixed structure, external surface area, little isomorphous substitution, low plasticity stickiness cohesion shrink swell, cec.

4 clays that are 2:1?

Smectite, vermiculite, micas, chlorite

Smectite

Montmorillonite. shrink swell. much isomorphous substitution

Vermiculite

Lots of Al substituting for Si - high negative charges. Less swelling than smectite

Illite

Moderate CEC Larger particles than smectite. Major source of charge is in tetrahedral sheet. K ions are strongly attracted. Non-expansive

Chlorite

Moderate. Non-expansive No water adsorption.

Do all colloids have a degree of variable charge?

Yes

Do all colloids have a degree of fixed charge?

NO

Iron and aluminum oxides

Colloids. Hematite, goethite, gibbsite, weathering of iron containing silicates

Humus CEC

High

Goethite

FeOOH. Iron aluiminum oxide

Hematite

Fe2O3. Iron aluminum oxide

Gibbsite

AlOH3. fe/al oxide

General genesis of layer silicate clays

Illite,vermiculite,chlorite

Smectite

kaolinite

fe al oxide

Isomorphous substitution is also known as ___ charge

Permanent

Only colloid that has isomorphous substitution?

layer silicate clays

How does ph dependent charge develop?

OH or other groups accept/releast H to create -/+. depends on soil PH

pH dependent negative charges kicks in when soil is less than ____

7

Total range of soil pH?

2-10.5

If a soil has 10-6 hydroxyls what is the ph?

8

2-4 ph controlling

Oxidation of S. pyrite feS2. acid mines

4-5.5 controlling ph

Hydrogen and al

5.5-6.8

Hydrogen

6.8-7.2

Dissolved co2

7.2-8.5

CaCO3

8.5-10.5

exchangeable/dissolution of sodium carbonate

How does acid mine drainage work

pyrite reacts with water and o2 to make sulfuric acid

Why soil becomes acidic over time

removal of bases

ammonium containing fertilizers

acid parent material

organic acids from roots/om decomp

acid rain

How does aluminum contribute to soil acidity

Combines with oh to release H ions

Pools of soil acidity

Active, salt replaceable, residual acidity

Residual acidity is also known as?

Reserve potential

Liming material must contain?

Ca/mg

carbonates/oxides to raise soil ph

Dolomite

40-50/ carbonate common in AL

Calcite

Standard for other liming materials

Marl

Shell soil and carbonate

Calcium oxide

Quicklime. caustic

Calcium hydroxide

Caustic. builders lime

Nixtamalization

Calcium hydroxide. releases nutrients. prevented pellagra

Wood ash

From industrial processes. oxides of ca and mg

Slag

Calcium silicate slag. si, mg, ca

How does liming work?

Forms calcium bicarb

ca repleaces h

H react with bicarb to form carbonic acid

carbonic acid break into water and co2

Pellagra

Niacin deficiency. people in the south suffered when no nixtimalization

2 factors in lime quality

Acid neutralizing value

fineness

How to calculate CCE?

Find g/mol of each and compare for unitless value

What is the standard of liming

CaCo3. 100g/mol

How to calculate fineness

% passing through sieve x fineness factor and then add up

How to get ECCE?

Fineness x CCE

Lime quality is regulated by who?

State

What type of soils are well buffered?

High CEC. clay finer

Which colloid has some AEC?

Allophane