1 / 17

Processes of horizon development

Processes of horizon development. Redox processes Environmental Pedology. What is an oxidant?. What is an oxidant? Oxidants oxidize other compounds and in the process they accept electrons and are converted into reductants Oxidants electron acceptors

jadzia
Télécharger la présentation

Processes of horizon development

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Processes of horizon development Redox processes Environmental Pedology

  2. What is an oxidant?

  3. What is an oxidant? Oxidants oxidize other compounds and in the process they accept electrons and are converted into reductants Oxidants electron acceptors Oxidant + e- Reductant

  4. What is a reductant?

  5. What is a reductant? • Reductants reduce other compounds and in the process they give away their electrons • Reductants electron donors • Reductant Oxidant + e-

  6. Name some oxidants • O2 • NO3- • Mn4+ • Fe3+ • SO42- • CO2

  7. Name some reductants • OH- • NO-2, NO, N2O, N2 • Mn2+ • Fe2+ • SO2, S2- • C

  8. Cell potential for a redox reaction can be expressed as (Nernst Equation): a Oxidant + b H+ + ne c Reductant Eh=Eo – RT ln [Reductant]c nF [Oxidant]a [H+]b Eh=Eo - 0.059 log [Reductant]c n [Oxidant]a [H+]b

  9. Eh - Electrode potential (volts) • Eo - standard electrode potential (volts) • R - Gas constant • T - Temperature (K) • F - Faraday’s constant • n - Number of electrons involved • [ ] - Concentration of the reductants and oxidants (mol/L).

  10. Fe3+ +e- Fe2+ Write the Nernst equation for the reaction • [Oxidant] = x mol/L • [Reductant] = y mol/L • Eo of Fe3+/Fe2+ = 0.77v • E = 0.77 – 0.059 log (y/x)

  11. Name an oxidation and reduction reaction that occurs in nature • Photosynthesis (Reduction) 6CO2 + 6H2O + energy C6H12O6 + 6O2 • Respiration (Oxidation) C6H12O6 + 6O2 6CO2 + 6H2O + energy

  12. Oxidation of organic matter • What happens when oxygen present is consumed? • Is there no more oxidation of organic matter? oxidant CO2 + H2O + energy Organic Matter

  13. Other electron acceptors are utilized in the order • NO3- • Mn4+ • Fe3+ • SO42- • CO2 But the energy yield decreases

  14. O2 + 4H+ 4e- 2H2O     • Eh about +350v • 2NO3 + 12H+ +12e- N2 +6H2O   • Eh about +220v • MnO2 + 4H+ 2e- Mn+2 + 2H2O       • Eh about +200v

  15. Fe(OH)3 + 3H+ + e- Fe 2+ + 3H2O  • Eh about +120v • SO42- + 10H+ + 8e- H2S + 4H2O       • Eh about -150v • CO2 + 8H+ 8e- CH4 +H2O • Eh about -250v

  16. Importance of studying oxidation – reduction processes in pedology • Influences soil color • Redoximorphic features • Organic matter content • Influences the forms of N2, Mn, Fe and S species

  17. Assignment: • Write the Nernst equations of the equations given in slides 14 and 15

More Related