Print version Updated: 29 April 2020 Lecture #49 Redox Chemistry: - PowerPoint PPT Presentation

Print version Updated: 29 April 2020 Lecture #49 Redox Chemistry: Predominance Diagrams; spanning the range of pe (Stumm & Morgan, Chapt.8 ) Benjamin; Chapter 9 David Reckhow CEE 680 #49 1

Chlorine Predominance Diagram  Features  Oxidation state  Higher oxidation states (HOCl/OCl-) in upper region  Middle oxidation state (Cl 2 ) in middle at low pH range  Chloride in lower region  pH divisions  Vertical lines at pK a values David Reckhow CEE 680 #48 2

Constants  Conversions [ ] 1 1 o ≡ ε o = = o pe p log K E ( volts ) H n 0 . 059 RT ln( 10 ) = 0 . 059 F David Reckhow CEE 680 #47 3

A highly oxidized system  Chlorine species  +I, 0 and -I oxidation states Stumm & Morgan, 1996; Fig. 8.11, pg. 463 David Reckhow CEE 680 #49 4

Chlorine Predominance Diagram  Features  Oxidation state  Higher oxidation states (HOCl/OCl-) in upper region  Middle oxidation state (Cl 2 ) in middle at low pH range  Chloride in lower region  pH divisions  Vertical lines at pK a values David Reckhow CEE 680 #49 5

Iron phases  From Soil Science Literature  Pyrite is FeS 2  Goethite is FeO(OH)  Jarosite is KFe 3+ 3 (OH) 6 (SO 4 ) 2 David Reckhow CEE 680 #49 6

Iron redox system  Ferrous – Ferric  hydroxides Stumm & Morgan, 1996; Fig. 8.8, pg. 461 David Reckhow CEE 680 #49 7

Iron (cont.)  Fe T = 10 -5 M  No carbonates From: Aquatic Chemistry Concepts, by Pankow, 1991 (pg 535) David Reckhow CEE 680 #49 8

Iron (cont.)  Same as previous, but pH axis limited to 14 From: Aquatic Chemistry Concepts, by Pankow, 1991 (pg. 536) David Reckhow CEE 680 #49 9

Iron (cont.)  Fe T = 10 -5 M  10 -3 M carbonates From: Aquatic Chemistry Concepts, by Pankow, 1991 David Reckhow CEE 680 #49 10

Multi-system  Fe T = 10 -5 M From: Aquatic Chemistry Concepts, by Pankow, 1991 (pg 543)  C T = 10 -3 M  S T = 10 -3 M David Reckhow CEE 680 #49 11

Fully oxygenated to anaerobic From: Aquatic Chemistry Concepts, by Pankow, 1991 David Reckhow CEE 680 #49 12

From: Aquatic Chemistry Concepts, by Pankow, 1991 David Reckhow CEE 680 #49 13

Multi-system  Fe T = 10 -5 M From: Aquatic Chemistry Concepts, by Pankow, 1991 (pg 543)  C T = 10 -3 M  S T = 10 -3 M David Reckhow CEE 680 #49 14

Other redox systems  Phosphorus Stumm & Morgan, 1996;  Nitrogen Fig. 8.9, pg. 461  Sulfur  carbon David Reckhow CEE 680 #49 15

 To next lecture DAR David Reckhow CEE 680 #49 16