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

Lecture #49 Redox 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

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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

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Constants

 Conversions

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[ ]

) ( 059 . 1 log 1 volts E K n p pe

• H
• =

= ≡ ε

F RT ) 10 ln( 059 . =

 Chlorine

species

 +I, 0 and -I

• xidation

states

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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

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 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 M CT = 10-3 M

Fully oxygenated to anaerobic

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From: Aquatic Chemistry Concepts, by Pankow, 1991

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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 M CT = 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