SWS3022 Exam 3 Questions and Answers All Correct
Define an acid - Answer-Any substance which increases the hydrogen ion concentration in a solution.
Know the two ions considered acids in soils` - Answer-Hydrogen & Aluminum
Understand how aluminum contributes to soil acidity - Answer-Aluminum...
SWS3022 Exam 3 Questions and
Answers All Correct
Define an acid - Answer-Any substance which increases the hydrogen ion concentration
in a solution.
Know the two ions considered acids in soils` - Answer-Hydrogen & Aluminum
Understand how aluminum contributes to soil acidity - Answer-Aluminum has the ability
to facilitate the splitting of water and react with the resulting H+. Aluminum reacts with
water to bind to the hydroxide, leaving the hydrogen ion not neutralized (so lots of H+'s).
Understand the two basic types of soil acidity discussed in class. - Answer-a. Active
acidity: acidity associated with soil solution. Measured with a pH meter. Typically a 1:1
or 2:1 extract.
b. Exchangeable acidity: H+, Al3+Al(OH)2+, Al(OH)2+ are all cations. Acidity associated
with cation exchange sites on mineral or organic colloids.
i. Exchangeable cations: exchange sites often are dominated by 4 cations: Ca, Mg, K,
Na. called "base cations" and calcium usually dominates.
ii. CEC suggests the ability of a soil to store important plant nutrients (K, Mg, Ca, Fe).
However, CEC is not always a good indicator of fertility.
Know the relationship between pH and H+ concentration in solution. - Answer-a. pH= -
log[H+]
b. For each 1 unit change in pH there is a 10 fold change in Hydrogen concentration
Know how soil salinity is typically measured and the threshold for what are considered
saline soils. - Answer-a. Electrical conductivity: pure water conducts electricity poorly;
conductivity increase with salt content.
b. Conductance= 1/resistance
c. Saline soil: E.C. > 4 dS/m.
Know the principle method by which saline soils are reclaimed. - Answer-a. Leaching
with high quality irrigation water with adequate drainage. (he won't ask us to calculate
the leaching requirements).
Know the two most common ways that soil alkalinity is mitigated. (how to decrease pH)
- Answer-a. Use iron sulfate; iron like aluminum can undergo hydrolysis.
b. Add elemental sulfur. (slow solution; it converts to sulfate, releasing)
c. "Acidification can be accomplished by Fe, Al, or S.
O Horizon - Answer-Organic horizon formed above the mineral soil.
Derived from decomposition of plant and animal residues
, Range in thickness from absent to meters thick.
Common in forested soils
Thickness: 0 to deep
Subordinate distinctions
Oa- highly decomposed
Oe- moderately decomposed
Oi- slightly decomposed
(>20%), dark
Know the two principal chemical elements in organic chemical compounds - Answer-
Carbon & Hydrogen (maybe Oxygen)
Know the two properties that make certain types of organic chemicals highly water
soluble. - Answer-Polarity & Electrical Charge
Understand basically the impediments to water solubility for non-ionic hydrophobic
organic compounds. - Answer-a. Solubility: The ease with which substances dissolve in
water; the degree to which organic contaminants impact soil and water quality often is
related to their water solubility.
b. Non-ionic, non-polar organic chemicals do not possess an electrical charge, nor are
the polar. So they don't share any compatibility with water. Example: Dioxin
Given the relative insolubility of hydrophobic organic compounds, in what type of
substances are they soluble and why? - Answer-a. These types of chemicals are
compatible with carbon-based environments (similar chemically). They are soluble in
environments that are chemically similar to their chemical properties. Carbon-based
compounds dissolve more easily in carbon-based solvents.
Understand how hydrophobic organic chemicals interact with organic colloids in soils. -
Answer-a. An organic colloid has a dense carbon, non-polar uncharged center and
carboxylic, phenolic, and enolic (charged, polar) moleculres surrounding it. They provide
an organic domain/matrix, in which they move into that organic environment because it
is much more compatible with them.
b. In regards to synthetic organics: chemicals interact with soil organic matter and slow
or arrest their movement.
i. The lower the water solubility, usually the stronger the interaction, the slower the
chemical movement.
What is partitioning? - Answer-When the chemical will distribute between the organic
and aqueous phases.; The organic colloid behaves like an organic solvent.
Understand the basic relationship between the water solubility of organic chemicals and
the strength of interaction with organic colloids. - Answer-Organic chemicals tend to
partition into the organic domain/sediments. Examples of this are pesticides, DDT, and
Toxaphene. (Persistence).
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