Soil Science Lab 7

Title for Laboratory Exercise 7

Cation Exchange

This refers to the replacement or exchange of ions between soil and solution

Ion Exchange

What are the types of ion exchange?

Cation Exchange and Anion exchange

This refers to the exchange of one positive ion for another positive ion

Cation Exchange

This refers to the exchange of one negative ion for another negative ion

Anion Exchnage

Characterizations of cation exchnage

Rapid, Reversible, Stoichiometric

This is a characterization of cation exchange because it occurs almost instantaneously on soil surfaces

Rapid

This is a characterization of cation exchange because cations can move back and forth between the soil solution and the exchange complex

Reversible

This is a characterization of cation exchange because the exchange follows a strict one-to-one equivalent basis where the total number of positive charges remains balanced.

Stoichiometric

Importance of Ion Exchange

Controls nutrient availability, reduces nutrient leaching, influences soil permeability, and helps prevent pollution

This is a reversible chemical process where positively charged ions in a solution are exchanged for different cations held on the surface of a solid

Cation Exchange

This is exchange is crucial for nutrient retention in soil, wastewater treatment, and chemical analysis

Cation Exchange

What binds cations, negatively-charged or positively-charged particles?

Negatively-charged Particles

This ranks ions based on their ability to affect the solubility, stability, and structure of macromolecules like proteins and colloids.

Lyotropic Series

Based on the Lyotropic Series, what has the highest adsorption strength?

Aluminum ions (Al³+)

Based on the Lyotropic Series, what has the lowest adsorption strength?

Sodium (Na+)

Sources of charge in soils

Clay minerals, organic matter, permanent charge, variable charge, and point of zero charge

A higher pH would result to what charge?

Negative

This measures the soil’s ability to hold nutrients, influencing soil fertility, and buffering capacity against acidification

Cation Exchange Capacity

This is the process by which the soil pH decreases over time as basic cations are leached away and replaced by acidic cations, primarily hydrogen (H+) and aluminum (Al³+).

Acidification

Soils with higher clay or organic material typically has (higher, lower) cation exchange capacity

higher

Unit of measure for cation exchange capacity

cmol/kg

What are the factors that affect CEC?

Types of Clay and Soil Texture/% Clay Content, Organic Matter Content, pH Levels, Point of Zero Charge

True/False

Kaolinite is non-expanding

True

True/False

Illite is non-expanding

True

True/False

Smectite is non-expanding

False

True/False

Montmorillonite is non-expanding

False

Which has a higher CEC, montmorillonite or kaolinite?

Montmorillonite

Structure of kaolinite

1:1

Structure of Illite

2:1

Structure of Montmorillonite

2:1

Structure of Smectite

2:1

Structure of Chlorite

2:1:1

Which has higher CEC, soil with high sand content or high clay content?

Soil with high clay content

True/False

A higher pH results to a higher CEC

True

True/False

A negatively-charged soil results to a higher CEC

True

This is the specific pH value at which the net electrical charge on a soil particle or mineral surface is exactly zero.

Point of Zero Charge

What was the name of the negatively-charged dye that was added to the soil?

Gentian Violet

What was the name of the positively-charged dye that was added to the soil?

Methyl Red

This is a specific substance or mixture applied to a sample to produce a visible change, such as a color shift, precipitation, or fluorescence, indicating the presence or concentration of a particular ion or compound.

Detection Reagent

This served as the detection reagent for the presence of barium ions

Potassium dichromate (K²Cr²O7)

This was added to provide barium ions that can be adsorbed into the soil

Barium chloride (BaCl²)

This forms as a precipitate when potassium dichromate is added to a rotation containing barium ions

Barium dichromate (BaCr²O7)

What was added to test CEC?

Barium

More precipitate means (high, low) CEC

low CEC

Less barium left in the solution means that there is (high, low) adsorption

high

High adsorption means what when it comes to CEC?

High CEC

These are used to remove or substitute cations

Extracting Agent

What serves as the extracting agent in the cation substitution of soils

Potassium chloride (KCl)

What was added to detect calcium filtrate?

Ammonium oxalate

Name of the cloudy precipitate in the experiment

Calcium oxalate