SWS3022 Exam Questions
and Answers All Correct
What happens to phosphorus when the soil is basic (high pH)? - Answer-- insoluble
solids are formed (Calcium phosphates)
- Ca + HPO4 = CaHPO4
- CaHPO4 will crystallize overtime and become highly insoluble
What pH is preferred for plant availability/solubility? - Answer-6.5
What are the four types of phosphorus immobilization? - Answer-- low pH (Fe and Al
phosphate solids)
- high pH (Ca phosphate)
- fixation in crystalline Fe and Al oxides
- anion exchange
How can you neutralize an acid? - Answer-- bases react with hydrogen and remove it
from the soil
OH- + H+ -> H2O
CO3^2- + H+ -> HCO3-
What is a common base used to increase the pH of the soil? - Answer-Decrease the H+
concentration in solution
- prevents Al toxicity
CaCO3
This is called liming
CaCO3 -> Ca2+ + CO3^2-
CO3^2- + H+ -> HCO3-
What is Al toxicity? - Answer-- restricts cell wall expansion an damages membrane sites
where Ca comes in
- more common and hurtful at pH below 5.2
What is finite immobilization? - Answer-- only a certain amount of Phosphorus that soil
can handle
- can exceed phosphorus absorption capacity
- if this is exceeded, phosphorus become more mobile in the soil so it becomes more
plant available, but greatly impacts aquatic systems (eutrophication)
,What is an acid? - Answer-any substance which increases the hydrogen ion
concentration in solution
pH of 0-7
high H+ concentration
What are sources of acids? - Answer-- 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 - Answer-true
Which side of the US has acidic vs basic rain? - Answer-- eastern US has acidic rain
- western US has basic rain
What is a base? - Answer-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? - Answer-H+ and Al
- both are cationic
- Al participates in hydrolysis reactions with water
What is the hydrolysis of water? - Answer-- self-ionization of water
- H2O -> OH- + H+
H+ is the acid
OH- is the base
- in pure water, H+ and OH- amounts are equal
What is hydrolysis by aluminum? - Answer-- 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? - Answer-- 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
What is mineral formation? - Answer-When aluminosilicates dervive charge from
substitution of lower-charged cations for higher charged cations in the crystal matrix
What charge results from mineral formation? - Answer-permanent negative charge
What substitution happens during mineral formation? - Answer-- Al3+ for Si4+
, - Mg2+ for Al3+
What do charges on silicate crystal edges and on Al/Fe oxides depend on? - Answer-
protonation and deprotonation (results in variable, pH-dependent charge
What do organic colloids derive their charge from? - Answer-protonation/deprotonation
of hydrogen ions from acidic functional groups on humic organic materials
How do you measure active acidity? - Answer-- 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? - Answer-pH = -log(H+)
-pH = log(H+)
10^-pH = 10^log(H+)
10^-pH = (H+)mol/L
What is exchangeable acidity? - Answer-- H+, Al3+Al(OH)2+, and Al(OH)2+ are all
cations
- 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? - Answer-tightly bound to clay minerals and humic organic
materials
What is the formula for total acidity? - Answer-total acidity = active + exchangeable +
residual
T/F Acids increase the H+ concentrations in solution - Answer-true
Acidity associated with the soil solution is called: - Answer-active acidity
Identify one source of H+ ions to soil - Answer-atmosphere (respiration from
microorganisms)
T/F Rainfall is naturally acidic - Answer-true
The two ions considered acids in soils are: - Answer-H+ and Al
Is CEC a good indication of fertility? - Answer-no
- CEC suggests ability of soil to store plant nutrients
Describe an example of ion saturation with a CEC of 20 cmolc/kg - Answer-Ca = 10
cmolc/kg (50%)
and Answers All Correct
What happens to phosphorus when the soil is basic (high pH)? - Answer-- insoluble
solids are formed (Calcium phosphates)
- Ca + HPO4 = CaHPO4
- CaHPO4 will crystallize overtime and become highly insoluble
What pH is preferred for plant availability/solubility? - Answer-6.5
What are the four types of phosphorus immobilization? - Answer-- low pH (Fe and Al
phosphate solids)
- high pH (Ca phosphate)
- fixation in crystalline Fe and Al oxides
- anion exchange
How can you neutralize an acid? - Answer-- bases react with hydrogen and remove it
from the soil
OH- + H+ -> H2O
CO3^2- + H+ -> HCO3-
What is a common base used to increase the pH of the soil? - Answer-Decrease the H+
concentration in solution
- prevents Al toxicity
CaCO3
This is called liming
CaCO3 -> Ca2+ + CO3^2-
CO3^2- + H+ -> HCO3-
What is Al toxicity? - Answer-- restricts cell wall expansion an damages membrane sites
where Ca comes in
- more common and hurtful at pH below 5.2
What is finite immobilization? - Answer-- only a certain amount of Phosphorus that soil
can handle
- can exceed phosphorus absorption capacity
- if this is exceeded, phosphorus become more mobile in the soil so it becomes more
plant available, but greatly impacts aquatic systems (eutrophication)
,What is an acid? - Answer-any substance which increases the hydrogen ion
concentration in solution
pH of 0-7
high H+ concentration
What are sources of acids? - Answer-- 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 - Answer-true
Which side of the US has acidic vs basic rain? - Answer-- eastern US has acidic rain
- western US has basic rain
What is a base? - Answer-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? - Answer-H+ and Al
- both are cationic
- Al participates in hydrolysis reactions with water
What is the hydrolysis of water? - Answer-- self-ionization of water
- H2O -> OH- + H+
H+ is the acid
OH- is the base
- in pure water, H+ and OH- amounts are equal
What is hydrolysis by aluminum? - Answer-- 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? - Answer-- 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
What is mineral formation? - Answer-When aluminosilicates dervive charge from
substitution of lower-charged cations for higher charged cations in the crystal matrix
What charge results from mineral formation? - Answer-permanent negative charge
What substitution happens during mineral formation? - Answer-- Al3+ for Si4+
, - Mg2+ for Al3+
What do charges on silicate crystal edges and on Al/Fe oxides depend on? - Answer-
protonation and deprotonation (results in variable, pH-dependent charge
What do organic colloids derive their charge from? - Answer-protonation/deprotonation
of hydrogen ions from acidic functional groups on humic organic materials
How do you measure active acidity? - Answer-- 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? - Answer-pH = -log(H+)
-pH = log(H+)
10^-pH = 10^log(H+)
10^-pH = (H+)mol/L
What is exchangeable acidity? - Answer-- H+, Al3+Al(OH)2+, and Al(OH)2+ are all
cations
- 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? - Answer-tightly bound to clay minerals and humic organic
materials
What is the formula for total acidity? - Answer-total acidity = active + exchangeable +
residual
T/F Acids increase the H+ concentrations in solution - Answer-true
Acidity associated with the soil solution is called: - Answer-active acidity
Identify one source of H+ ions to soil - Answer-atmosphere (respiration from
microorganisms)
T/F Rainfall is naturally acidic - Answer-true
The two ions considered acids in soils are: - Answer-H+ and Al
Is CEC a good indication of fertility? - Answer-no
- CEC suggests ability of soil to store plant nutrients
Describe an example of ion saturation with a CEC of 20 cmolc/kg - Answer-Ca = 10
cmolc/kg (50%)
