SWS3022 Exam 3 Questions and
Answers 100% Pass
What is mineral formation? - ✔✔When aluminosilicates dervive charge from
substitution of lower-charged cations for higher charged cations in the crystal matrix
What charge results from mineral formation? - ✔✔permanent negative charge
What substitution happens during mineral formation? - ✔✔- Al3+ for Si4+
- Mg2+ for Al3+
What do charges on silicate crystal edges and on Al/Fe oxides depend on? -
✔✔protonation and deprotonation (results in variable, pH-dependent charge
What do organic colloids derive their charge from? - ✔✔protonation/deprotonation of
hydrogen ions from acidic functional groups on humic organic materials
What is an acid? - ✔✔any substance which increases the hydrogen ion concentration in
solution
pH of 0-7
high H+ concentration
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,What are sources of acids? - ✔✔- atmosphere: respiration from microorganisms
- acid functional groups on organic matter
ammonium oxidation: nitrification and fertilizers
T/F charge balance must be maintained when plants uptake cations - ✔✔true
Which side of the US has acidic vs basic rain? - ✔✔- eastern US has acidic rain
- western US has basic rain
What is a base? - ✔✔any substance that decreases the hydrogen ion concentration in
solution
OH- and CO3 ^2-
pH of 4-14
low H+ concentration
What are the two ions considered acidic in soils? - ✔✔H+ and Al
- both are cationic
- Al participates in hydrolysis reactions with water
What is the hydrolysis of water? - ✔✔- self-ionization of water
- H2O -> OH- + H+
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,H+ is the acid
OH- is the base
- in pure water, H+ and OH- amounts are equal
What is hydrolysis by aluminum? - ✔✔- Al splits water and reacts with resulting OH-
H2O -> OH- + H+
Al3+ + H2O = Al(OH)2+ + H+
Al(OH)2+ + H2O = Al(OH)2+ + H+
What is active acidity? - ✔✔- acidity associated with soil solution
- this is what is measured when you take the pH of the soil (measure with a pH meter)
- cations held in solution
How do you measure active acidity? - ✔✔- 1:1 or 2:1 extract (10g soil and 10 mL water
or 10g soil and 20 mL water)
What is the pH formula concerning log? - ✔✔pH = -log(H+)
-pH = log(H+)
10^-pH = 10^log(H+)
10^-pH = (H+)mol/L
What is exchangeable acidity? - ✔✔- H+, Al3+Al(OH)2+, and Al(OH)2+ are all cations
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, - acidity associated with cation exchange sites on mineral or organic colloids
- aka salt-replaceable acidity
- 100-1,000x more than in active acidity
- allows it to contribute to the pH of soil
- cations held near minerals and materials
What is residual acidity? - ✔✔tightly bound to clay minerals and humic organic
materials
What is the formula for total acidity? - ✔✔total acidity = active + exchangeable +
residual
T/F Acids increase the H+ concentrations in solution - ✔✔true
Acidity associated with the soil solution is called: - ✔✔active acidity
Identify one source of H+ ions to soil - ✔✔atmosphere (respiration from
microorganisms)
T/F Rainfall is naturally acidic - ✔✔true
The two ions considered acids in soils are: - ✔✔H+ and Al
Is CEC a good indication of fertility? - ✔✔no
- CEC suggests ability of soil to store plant nutrients
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Answers 100% Pass
What is mineral formation? - ✔✔When aluminosilicates dervive charge from
substitution of lower-charged cations for higher charged cations in the crystal matrix
What charge results from mineral formation? - ✔✔permanent negative charge
What substitution happens during mineral formation? - ✔✔- Al3+ for Si4+
- Mg2+ for Al3+
What do charges on silicate crystal edges and on Al/Fe oxides depend on? -
✔✔protonation and deprotonation (results in variable, pH-dependent charge
What do organic colloids derive their charge from? - ✔✔protonation/deprotonation of
hydrogen ions from acidic functional groups on humic organic materials
What is an acid? - ✔✔any substance which increases the hydrogen ion concentration in
solution
pH of 0-7
high H+ concentration
Katelyn Whitman, All Rights Reserved © 2025 1
,What are sources of acids? - ✔✔- atmosphere: respiration from microorganisms
- acid functional groups on organic matter
ammonium oxidation: nitrification and fertilizers
T/F charge balance must be maintained when plants uptake cations - ✔✔true
Which side of the US has acidic vs basic rain? - ✔✔- eastern US has acidic rain
- western US has basic rain
What is a base? - ✔✔any substance that decreases the hydrogen ion concentration in
solution
OH- and CO3 ^2-
pH of 4-14
low H+ concentration
What are the two ions considered acidic in soils? - ✔✔H+ and Al
- both are cationic
- Al participates in hydrolysis reactions with water
What is the hydrolysis of water? - ✔✔- self-ionization of water
- H2O -> OH- + H+
Katelyn Whitman, All Rights Reserved © 2025 2
,H+ is the acid
OH- is the base
- in pure water, H+ and OH- amounts are equal
What is hydrolysis by aluminum? - ✔✔- Al splits water and reacts with resulting OH-
H2O -> OH- + H+
Al3+ + H2O = Al(OH)2+ + H+
Al(OH)2+ + H2O = Al(OH)2+ + H+
What is active acidity? - ✔✔- acidity associated with soil solution
- this is what is measured when you take the pH of the soil (measure with a pH meter)
- cations held in solution
How do you measure active acidity? - ✔✔- 1:1 or 2:1 extract (10g soil and 10 mL water
or 10g soil and 20 mL water)
What is the pH formula concerning log? - ✔✔pH = -log(H+)
-pH = log(H+)
10^-pH = 10^log(H+)
10^-pH = (H+)mol/L
What is exchangeable acidity? - ✔✔- H+, Al3+Al(OH)2+, and Al(OH)2+ are all cations
Katelyn Whitman, All Rights Reserved © 2025 3
, - acidity associated with cation exchange sites on mineral or organic colloids
- aka salt-replaceable acidity
- 100-1,000x more than in active acidity
- allows it to contribute to the pH of soil
- cations held near minerals and materials
What is residual acidity? - ✔✔tightly bound to clay minerals and humic organic
materials
What is the formula for total acidity? - ✔✔total acidity = active + exchangeable +
residual
T/F Acids increase the H+ concentrations in solution - ✔✔true
Acidity associated with the soil solution is called: - ✔✔active acidity
Identify one source of H+ ions to soil - ✔✔atmosphere (respiration from
microorganisms)
T/F Rainfall is naturally acidic - ✔✔true
The two ions considered acids in soils are: - ✔✔H+ and Al
Is CEC a good indication of fertility? - ✔✔no
- CEC suggests ability of soil to store plant nutrients
Katelyn Whitman, All Rights Reserved © 2025 4
