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Biogeochem - Ernest > Biogeochem - Redox Sensitive Metals > Flashcards

Biogeochem - Redox Sensitive Metals Flashcards

1
Q

What is the product if Fe(II) is oxidised

A

Fe(III)

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2
Q

What is the product if Fe(III) is reduced?

A

Fe(II)

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3
Q

What are some redox sensitive elements?

A

Iron, Manganese and nickel

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4
Q

What is a redox reaction?

A

A chemical reaction involving the transfer of electrons between two chemical species

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5
Q

List examples of redox reactions

A

Photosynthesis, Respiration, combustion, corrosion, biofouling, rusting

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6
Q

What is the relationship between Redox reactions and gibbs free energy?

A

Redox reactions produce and consume gibbs free energy

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7
Q

List some examples of environmental redox reactions in anoxic environments

A
  • Anaerobic methane oxidation
  • Methanogenesis
  • nitrate reduction
  • sulphate reduction
  • nitrogen fixation
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8
Q

List some examples of environmental redox reactions in oxic environments

A
  • Aerobic methane oxidation
  • Ammonia oxidation
  • Aerobic sulphur oxidation
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9
Q

what are some major forms of iron in the environment?

A

Hematite ((Fe3+)2O3)
Ferrihydrite
Magnetite

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10
Q

What are the main oxidation states you can find iron in?

A

Pure Iron = Fe –> neutral atom

Ferric iron = Fe3+

Ferrous Iron = Fe2+

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11
Q

characteristics of ferric iron

A

(Fe3+)

  • Electron acceptor for anaerobic respiration
  • poorly soluble at neutral pH
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12
Q

examples of ferric iron

A

Hematite, Ferrihydrite

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13
Q

examples of ferrous iron

A

magnetite

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14
Q

characteristics of ferrous iron

A

Electron donor for lithotrophic bacteria

oxidises spontaneously at neutral pH

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15
Q

Main forms of Manganese in the environment

A

Pure Mn

Mn (IV) oxide (Mn4+ or MnO2)

Mn (III) oxide-hydroxide

Oxyhydroxide

Mn (III) oxide

Mn (II) oxide

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16
Q

give an example of an Oxyhydroxide

(hint: Mn)

A

Magnatite

17
Q

Reasons why life might be limited by iron

A

in oceans, due to oxygen levels, iron is usually in its most oxidised state, Fe(III). This is not bioavailable to organisms due to its low solubility

Oceans main iron input is from aeolian dust from continent meaning that central open oceans which are further away from iron inputs have less iron available
- Moore and Braucher 2008

iron is needed for photosynthetic activity so a scarcity of it significantly impacts primary production and phytoplankton growth
- Schoffman 2016

18
Q

Why might weaker oxygen minimum zones (OMZ) increase the iron supply?

A

OMZ is a region in the ocean where the dissolved concentration of oxygen is at its lowest.

Low oxygen environments favour iron reduction, forming Fe(II) which is more soluble in seawater than ferric iron, increasing the concentration of Fe(II) in the water. This is more bioavailable for phytoplankton to use

  • Scholz 2014
19
Q

what type of bacteria are iron-oxidising bacteria?

A

chemolithoautotrophs

20
Q

What reaction does iron have with oxygen at differing pH levels?

A

spontaneous reaction at neutral pH

stable raction at an acidic pH

21
Q

what is the term used to describe iron oxidising bacteria that favour acidic conditions

A

acidophilic iron oxidisers

22
Q

what is the term used to describe iron oxidisers that favour neutral environments

A

Neutrophilic iron oxidisers

23
Q

Example of stalk-forming iron oxidising bacteria in freshwater and marine environment

A

Freshwater Betaproteobactera
- Gallionella furreginea (neutrophillic)
- Ferriphaselus

Marine Zetaproteobacteria
- Mariprofundus ferroxydans

24
Q

what forms of iron oxidising bacteria can you have?

A
  • sheath-formers
  • stalk-formers
25
Q

why is iron reduction dissimilatory?

A

because the iron 2 produced is not taken up by

26
Q

what conditions does dissimilatory iron reduction occur under?

A

anoxic conditions

27
Q

is the surface of the earth rich or poor in electrons?

A

poor due to the presence of oxygen

28
Q

what happens to water when conditions are very oxidising?

A

water transforms to oxygen gas

29
Q

what happens when conditions are very reducing?

A

water transforms to hydrogen gas

(very reducing = deep in earth)

30
Q

what are the trends of iron Eh/pH diagram?

A

when the pH is acidic, iron 2 is more abundant in the absence of oxygen

when oxygen becomes present, iron 3 is more abundant

31
Q

characteristics of iron in acidic conditions

A

Fe(II) and Fe(III) are soluble

Fe(II) is more stable because the spontaneous oxidation of Fe(II) by oxygen is inhibited

32
Q

characteristics of iron in neutral to alkaline conditions

A

Fe(III) precipitates as FeOOH or Fe(OH)3

This removal of the reaction product drives the oxidation of Fe(II)

At dynamic equilibrium, dissolved Fe(III) concentrations remain low

33
Q

what causes acid mine drainage

A

the exposure of pyrite to the surface (oxygen)

34
Q

what is pyrite?

A

a rock… doi

no lol

reduced iron bound to sulphur which is found in anoxic conditions

35
Q

how does acid mine /rock drainage cause environmental pollution?

A

When pyrite is exposed to oxygen, it produces iron 2, sulphuric acid and H+. In acidic conditions, the oxidation of iron 2 to iron 3 is inhibited and appears in solution.

Iron oxidising bacteria oxidise the iron 2 to iron 3 which then ‘attacks’ the pyrite exposed, further producing more iron 2 and sulphuric acid.

As iron 3 and pyrite have large surface areas, lots of metals can bind to them (such as nickle, arsenic (toxic!!), lead, copper etc). These get released into the solution resulting in environmental pollution

36
Q

Why endergonic reaction not spontaneous?

A

Because they require activation energy for the reaction to start

37
Q

how does ammonia become available through the use of an enzyme?

A

Mo-dependent nitrogenase donates 8 electrons to nitrogen gas so it can form ammonia and become bioavailable and assimilate

38
Q
A

Biogeochem - Ernest (9 decks)

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