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Lecture #49Redox Chemistry: Predominance Diagrams;
spanning the range of pe(Stumm & Morgan, Chapt.8 )
Benjamin; Chapter 9
David Reckhow CEE 680 #49 1
Updated: 29 April 2020 Print version
Chlorine Predominance Diagram Features
Oxidation state Higher oxidation states (HOCl/OCl-) in upper region Middle oxidation state (Cl2) in middle at low pH range Chloride in lower region
pH divisions Vertical lines at pKa values
David Reckhow CEE 680 #48 2
Constants
Conversions
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[ ] )(059.01log1 voltsEK
nppe o
Hoo ==≡ ε
FRT )10ln(059.0 =
Chlorine species +I, 0 and -I
oxidation states
David Reckhow CEE 680 #49 4
Stumm & Morgan, 1996; Fig. 8.11, pg. 463
A highly oxidized system
Chlorine Predominance Diagram Features
Oxidation state Higher oxidation states (HOCl/OCl-) in upper region Middle oxidation state (Cl2) in middle at low pH range Chloride in lower region
pH divisions Vertical lines at pKa values
David Reckhow CEE 680 #49 5
David Reckhow CEE 680 #49 6
From Soil Science Literature Pyrite is FeS2
Goethite is FeO(OH)
Jarosite is KFe3+
3(OH)6(SO4)2
Iron phases
Iron redox system Ferrous – Ferric
hydroxides
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Stumm & Morgan, 1996; Fig. 8.8, pg. 461
Iron (cont.)
FeT = 10-5 M No carbonates
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From: Aquatic Chemistry Concepts, by Pankow, 1991 (pg 535)
Iron (cont.)
Same as previous, but pH axis limited to 14
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From: Aquatic Chemistry Concepts, by Pankow, 1991 (pg. 536)
Iron (cont.)
FeT = 10-5 M 10-3 M carbonates
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From: Aquatic Chemistry Concepts, by Pankow, 1991
Multi-system
ST = 10-3 M
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From: Aquatic Chemistry Concepts, by Pankow, 1991 (pg 543) FeT = 10-5 MCT = 10-3 M
Fully oxygenated to anaerobic
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From: Aquatic Chemistry Concepts, by Pankow, 1991
David Reckhow CEE 680 #49 13
From: Aquatic Chemistry Concepts, by Pankow, 1991
Multi-system
ST = 10-3 M
David Reckhow CEE 680 #49 14
From: Aquatic Chemistry Concepts, by Pankow, 1991 (pg 543) FeT = 10-5 MCT = 10-3 M
Other redox systems Phosphorus Nitrogen Sulfur carbon
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Stumm & Morgan, 1996; Fig. 8.9, pg. 461
To next lecture
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DAR