Transcript 2 I - Bryn Mawr College

Previously in
Chem104:
Today in Chem104:
•Redox reactions are
donor-acceptor chemistry
like acid/base reactions
• Standard Reduction Table
(trends)
•Important Equations:
•Erxn = Ered + Eox
•DG = -n F Erxn
(Faraday Law)
•Balancing Redox Equations
(#1-easy)
(#2-harder)
• Why the Correct Oxidation
State Matters
• The Great Cycle of Energy
•Not at Standard?
First, a recap of terms!
Redox Terminology
1. Electron Donation:
• Done by the Reductant = Reducing Agent
• Causes the reductant to become oxidized
• Occurs in the Oxidation Half Reaction
2. Electron Acceptance:
• Done by the Oxidant = Oxidizing Agent
• Causes the oxidant to become reduced
• Occurs in the Reduction Half Reaction
3. The Processes
• Oxidation = Loss of Electrons
• Reduction = Gain of Electrons
a question from Monday remains to be answered:
Where is the additional oxygen atom in the oxidized
glucose from?
- 2 e-
C6H12O6
C6H12O7
But first, let’s practice.
Exercise 1. (easy)
Write spontaneous redox equations
Example: Pick any two redox couples.
How Do I Choose
Ered + Eox ?
You need to know
the
the TRENDS
Let’s get a closer
look….
TABLE OF STANDARD REDUCTION POTENTIALS
E o (V)
stronger Ag + + e-  Ag
+0.80
oxidizing
Fe3+ + e-  Fe2+
+0.77
ability
I2 + 2e-  2 ICu 2+ + 2e-  Cu
2 H + + 2e-  H2
Pb 2+ + 2e-  Pb
+0.53
+0.34
0.00
-0.13
Fe 2+ + 2e-  Fe
Zn 2+ + 2e-  Zn
Al 3+ + 3e-  Al
-0.44
Na +
K+
+2.71
+ e-  Na
+ e-  K
-0.76
-1.66
stronger
reducing
+2.93 ability
But first, let’s practice.
Exercise 1. (easy)
Write spontaneous redox equations
Example: Pick any two redox couples.
Back to this question:
Where is the additional oxygen atom in the oxidized
glucose from?
- 2 e+ H2O
- 2 H+
- 2 eC6H12O6
C6H12O7
Water often is needed to balance redox equations
when there is a difference of O atoms on each side
(this is the harder type of redox balancing problem)
Next, more practice!
Exercise 2. (harder)
Write spontaneous redox equations
An Example to get going:
What is the spontaneous redox rxn
Between nitrate and Fe(2+)?
Why the correct oxidation state matters
MRI of brain of deceased baby
with Sulfite Oxidase Deficiency
MRI of a healthy
infant brain
The baby died because this reaction didn’t happen:
SO32- +
Sulfite
H 2O
--->
SO42- + 2H+ +
Sulfate
S4+
2e-
S6+
The baby has a genetic defect in the enzyme
that catalyzes this reaction.
Babies with this genetic disease die within hours.
The enzyme is Sulfite Oxidase.
You have it in your liver.
Review the terms:
Oxidation SO32- + H2O ---> SO42- + 2H+ + 2ehalf reaction
S4+ in Sulfite
S6+ in Sulfate
Reduction
Mo6+ +
half reaction
2e-
--->
Mo4+
Net redox reaction
SO32- +
H 2O
+
Mo6+ --->
SO42- +
2H+ +
Mo4+
Is this reaction spontaneous?
If you look deeper into the protein….
You find this:
The
Molybdenum
Cofactor
Can Human Molybdoenzyme Deficiencies Be Cured with more Mo?
defective molybdoenzymes
Not repaired by adding Mo alone
+ Mo
Non-functional enzyme
Cysteine,
Amino acid
Ligand on Mo
Big
Ligand
on Mo
S
O
S
Mo
S
O
SO42-
A catalytic cycle for how Mo oxidizes SO32-
The Great Cycle of Energy
Derived like this:
The Great Cycle of Energy
DG
DG = -n F Erxn
DG = -RTlnK
Keq
lnK = (nF/RT)Erxn
E
Electron Transfer Reactions: NOT just for Metals!
NOT just about batteries!
It’s EVERYWHERE in biology!!
5 Large Protein Complexes in Respiration
Detailed View of One Complex
The Mechanism of O2 Reduction to Water
oxy
peroxy
- H2O
Ferryl