Electrochemistry. Fundamental concepts Electron flow, nomenclature Energy in the electron flow Kinetics of the electron transfer event as influenced by

ElectrochemistryElectrochemistry is a very diverse area. It can be broadly divided into a) analytical electrochemistry which is concerned with methods of measurement involving

potentiometry (pH meters etc), voltammetry, and modern sensors (generally voltammetricin nature)

b) physical electrochemistry is the basis of analytical electrochemistry, but is generallyconcerned with the effect of electric fields, charge balance, and diffusion.

c) Chemical electrochemistry usually is less interested in quantitative analysis but is devotedto understanding the mechanisms of electron transfer based on chemical structure.

d) Biologic electrochemistry can be understood as a form of physical electrochemistry(charge and fields around biomolecules) and of chemical electrochemistry (electron transferevents in biological systems)

e) Geologic and environmental electrochemistry is concerned with all of the above as theytake place in the natural environment . Of particular interest are the oxidation reductionreactions of iron, manganese, chromium, arsenic, sulfur, as these set the parameters inwhich life can grow and, as the oxidation state of iron has substantial implications for thestability of various minerals and their dissolution/formation.

f) Technical - in this field fall the major areas of batteries, solar energy, fuel cells, andcorrosion sciences.

ElectrochemistryFundamental concepts

Electron flow, nomenclatureEnergy in the electron flowKinetics of the electron transfer event as

influenced by a) energy b) homogeneous vs heterogeneous system

Electrochemistry

Energy :1. Heat out/Heat in = enthalpy, H2. Equilibrium Constants, K3. Universal Entropy ~ Free energy, G

Use total free energy – not just enthalpy

This reaction is exothermic.How much?

8 5 5 442 2 3

2H M nO F e M n F e H Oaq aq aq aq aq

,

species Hfo (kJ/mol)

8H+(aq) 0

4H2O(liquid) -286MnO4

-(aq) -543

Mn2+(aq) -218.8

5Fe2+(aq) -47.69

5Fe3+(aq) -87.86

H n H n Hrxo

i p roducts f i p roductso

i reac ts f i reac tso , , , , tan , , tan

H rxo

1 2 1 8 8 5 8 7 8 6 4 2 8 6

8 0 1 5 4 3 5 4 7 6 9

. .

.

H rxo 2 1 2 6 7 8 1 4 5.

H kJrxo 1 3 4 4

This reaction could do a lot of work for us if we could get the energy

MnO4-Fe2+

H kJrxo 1 3 4 4

8 5 5 424

2 32H F e M nO M n F e H Oaq aq aq aq aq

,

Heat water to convert energy?

Water Bath

Water circulation

inefficientclumsyheat loss

steam drive pistons

Make electricity

MnO4-Fe2+

Alternative Strategy: Capture electrons directly

MnO4-Fe2+

eMn2+

Fe3+

Split into 2 partial reactions

To do thisNeed to balanceRedox reactions

Writing the Net Ionic Reaction of an Oxidation-Reduction Reaction

Write oxidation half reaction Write reduction half reaction

Split into Reactions to be balanced

A. Balance atoms of element oxidizedb. Balance Rx sides by adding ec. Balance charge by adding H+

or OH-

d. Balance hydrogen by adding H2Oe. Balance oxygen

A. Balance atoms of element reducedb. Balance Rx sides by adding ec. Balance charge by adding H+

or OH-

d. Balance hydrogen by adding H2O

e. Balance oxygen

Combine and balance electrons

Writing the Net Ionic Reaction of an Oxidation-Reduction Reaction

Write oxidation half reaction Write reduction half reaction

Reaction to be balanced

A. Balance atoms of element oxidizedb. Balance Ox number with ec. Balance charge by adding H+

or OH-

d. Balance hydrogen by adding H2Oe. Balance oxygen

A. Balance atoms of element reducedb. Balance Ox number with ec. Balance charge by adding H+

or OH-

d. Balance hydrogen by adding H2O

e. Balance oxygen

Combine and balance electrons

Protons are addedin an acidic solutionand hydroxyls are added in a basic solution.

When in doubt add protons

Example: Balance the following redox equation in an acidic solution

F e M nO F e M naq aq aq aq( ) ( ) ( ) ( )2

43 2

F e F eaq aq( ) ( )2 3

F e F e eaq aq( ) ( )2 3

Mass balance

2+ 3+

Mass balance

-1 = 4(-2) +?8-1 = ? 7 = ?

+2

+7 +2

ox# balance

Ox #balance

M nO M naq aq42

( ) ( )

M nO e M naq aq425( ) ( )



43 2

F e F eaq aq( ) ( )2 3

F e F e eaq aq( ) ( )2 3

Mass balanced

2+ 3+

Mass balanced

Ox numbers

+7 +2

M nO e M naq aq425( ) ( )

M nO e H M naq aq aq425 8( ) ( )

Charge balance

+2-1 + -5 = -6

M nO M naq aq42

( ) ( )



43 2

F e F e eaq aq( ) ( )2 3 M nO e H M naq aq aq4

25 8( ) ( ) ( )

Balance hydrogen by adding water

M nO e H M n H Oaq aq aq42

25 8 4( ) ( ) ( )

Check oxygen balance

4O =4O

Check total charge balance: (-1)+5(-1)+8(+1)=+2

=+2



43 2

F e F e eaq aq( ) ( )2 3


25 8 4( ) ( ) ( )

Recombine while balancing electrons

5 5 52 3F e F e eaq aq( ) ( )



43 2

F e F e eaq aq( ) ( )2 3


25 8 4( ) ( ) ( )

5 5 52 3F e F e eaq aq( ) ( )

M nO F e H F e M n H Oaq aq aq aq aq42 3 2

25 8 5 4( ) ( ) ( ) ( ) ( )

Final equation does not show any electronsbecause electrons “do not exist” in solution

OJO: Important Point

The reactions

1. do not really occur by themselves2. they are linked through the electrons3. DEFINITION: = 1/2 reactions


25 8 4( ) ( ) ( )

5 5 52 3F e F e eaq aq( ) ( )

If all reactions are consideredHalf reactions where does the Electron go?

e nH O e aq 2

e nH O H H O k x M saq 3 2

1 0 1 12 3 1 0, .

e H O H H O k x M saq 2

1 1 11 9 1 0, .

Hydrated electrons not only react with waterBut with other species including biological,Hence it is a good way to sterilize water

e R SH H S R k x M saq , .1 1 1 0 1 0 1 1

e O O H O O H O k M saq

H O

pK H A

2 2

4 9

1 0 1 12

1 0.

, ~

Hydrated electrons in aerobic biology will produceFinite fluxes of the soft radical HOO

Not only have to consider rateBut energy

e nH O e E V vsN H Eaqo 2 3 0, .

e nH O H H O k x M s

E V vs N H E

aq

o

3 21 0 1 12 3 1 0

2 1 0

, .

, .

e H O H H O k x M s

E V vs N H E

aq

o

21 1 11 9 1 0

2 9 3 0

, .

, .H-O bondWater 464 kJHydronium 301 kJ

Some other practical considerations

1MnO4-

5Fe2+

eFe3+

e

Mn2+

M nO e H

M n H O

aq aq

aq

4

22

5 8

4

( ) ( )

( )

5 5 52 3F e F e eaq aq( ) ( )

--

--

-

--

--

-

Net charge=0

Net charge=0

Net charge=10(-1)+5(+3)=+5

Net charge = (+2)+2(+1)+(-1)=+3

+-

Do you think the Mn/Fe reaction will continue for long?

- anion+ cation

+

Will want to let spectator ions flow(but not the reactants!)

e

“jelly” (salt bridge) retards motion of Fe3+/2+ MnO4-

(current)

+15+

“jelly” allows motion of spectators which producesCharge balance

Fe3+

-

1. Always make electrons flow to right2. Electrons flow down to the cathode

(cat = Greek for down).3. Electrons flow up into the anode

(an = Greek for up)

Weird Grammar Rules: Those Italians!Volta discovered this process

Count Alessandro Volta, Italy~1800, first battery

e

Cl-

(current)

cathodeanode

oxidation reduction

Oxidationelectrons takenOut (up = anode)

Reductionelectrons acceptedIn (down = cathode)

AnAn oxAn ox jumped overAn ox jumped over a redAn ox jumped over a red cat

Rsb

Rsoln

There isResistanceIn the system,We will comeBack to this

Vocabulary for Work when usingelectrons instead of heat.

Ohm’s Law: Voltage = current x resistance

Voltage = energy required to move charge

= Joules/Coulomb

Georg Simon Ohm, 1789-1854German physicist having a good hair day

V IR

n m oles e F

C oulom b

m ole e

FV

Jou le

C ou lom bV

a coulomb is a unit of charge

F=Faraday = 96,485 coulombs of charge/mole of e

neg sign accounts for negative electron

n m oles e

nF V J nF V G

V directly relates to free energy because we are notSeparately the work terms into heat and changing surrounding randomness with the heat

OhmJouleCoulombNernst

n m oles e F n m oles e F

C oulom b

m ole e

F

n m oles e F

C oulom b

m ole e

FV

n m oles e F

C oulom b

m ole e

FV

Jou le

C oulom bV

J

Marie the Jewess, 300 Jabir ibn Hawan, 721-815

Galen, 170 Jean Picard1620-1682

Galileo Galili1564-1642

Daniel Fahrenheit1686-1737

Evangelista Torricelli1608-1647

Isaac Newton1643-1727

Robert Boyle, 1627-1691

Blaise Pascal1623-1662

Anders Celsius1701-1744

Charles Augustin Coulomb 1735-1806

John Dalton1766-1844

B. P. Emile Clapeyron1799-1864

Jacques Charles 1778-1850

Germain Henri Hess1802-1850

Fitch Rule G3: Science is Referential

William ThompsonLord Kelvin, 1824-1907

James Maxwell1831-1879

Johannes D.Van der Waals1837-1923

Justus von Liebig (1803-1873

Johann Balmer1825-1898

James Joule (1818-1889)

Johannes Rydberg1854-1919

Rudolph Clausius1822-1888

Thomas Graham1805-1869

Heinrich R. Hertz, 1857-1894

Max Planck1858-1947

J. J. Thomson1856-1940

Linus Pauling1901-1994

Werner Karl Heisenberg1901-1976

Wolfgang Pauli1900-1958

Count Alessandro GA A Volta, 1747-1827

Georg Simon Ohm 1789-1854

Henri Louis LeChatlier1850-1936

Svante Arrehenius1859-1927

Francois-Marie Raoult1830-1901

William Henry1775-1836

Gilbert N Lewis1875-1946

Fritz Haber1868-1934

Michael Faraday1791-1867

Luigi Galvani1737-1798

Walther Nernst1864-1941

Lawrence Henderson1878-1942

Amedeo Avogadro1756-1856

J. Willard Gibbs1839-1903

Niels Bohr1885-1962

Erwin Schodinger1887-1961

Louis de Broglie (1892-1987)

Friedrich H. Hund1896-1997

Fritz London1900-1954

An alchemist

Ludwig Boltzman1844-1906

Richard AC E Erlenmeyer1825-1909

Johannes Bronsted1879-1947

Thomas M Lowry1874-1936

James Watt1736-1819

Dmitri Mendeleev1834-1907

Marie Curie1867-1934

Henri Bequerel1852-1908

Rolf Sievert, 1896-1966

Louis Harold Gray1905-1965

Jacobus van’t Hoff1852-1911

For standard conditions (1 mole, 1 atm, 25C):

Greek GKomodo (Indonesia) KVamale (Polynesia) Vo

Different languages, same information. RepresentTotal energy (heat + entropy) associated with a reaction

nF V Go o nF V G R T Ko o ln

VR T

nFKo ln

Relationship G, K, V Example Problem 1 :What are K and the standard voltage associated with theFire oxidation of lead given tabulated free energies?

K eG

R T 0

K x 5 2 3 1 0 6 2.

2 22P b O P bOs g s ( )

G n G n Grxo

f products f reac tso , , tan

0

G kJrxo 3 5 7 8.

G m olP bOkJ

m olP bOm olP b

kJ

m olP bm olO

kJ

m olOrxo

s ss

21 8 7 9

20

10

22

.

K e

kJ

m ol

xkJ

m ol KK

3 5 7 8

8 3 1 4 1 0 2 9 83

.

.G R T Ko ln


K x 5 2 3 1 0 6 2.

2 22P b O P bOs g s ( )

-nFV0 = Go

G kJrxo 3 5 7 8.

?

Ox # = 0

Compound neutralO usually -2So Pb = +22(+2)=4

+4

=-4electrons


K x 5 2 3 1 0 6 2.

2 22P b O P bOs g s ( )

-nFV0 = Go

nF V G

VG

nF

kJ

m ol rx as w ritten

J

kJ

m ol elec trons

m ol reaction

cou lom bs

m ol elec tron

VJ

cou lom b

V

o o

oo

3 5 7 8

3 5 7 8 1 0 0 0

4 9 6 4 8 7

10 9 2

.

.

.

G kJrxo 3 5 7 8.

? n=4

K x 5 2 3 1 0 6 2.

2 22P b O P bOs g s ( )

V Vo 0 9 2.

G kJrxo 3 5 7 8. All tell us that reaction

Will spontaneously Proceed to the rightFavoring products

How will we conveniently store info?

Vo values for 1/2 reactionsCompared to protons

Reaction Vo

Cs+ + e Cs ?K+ + e K -2.95Na+ + e Na -2.71Fe2+ + 2e Fe -0.44Pb2+ + 2e Pb -0.132H+ + 2e H2(gas) 0Cu2+ + 2e Cu 0.34O2 + 2H2O + 4e 4OH- 0.40O2 + 2H+ + 2e H2O2 0.68Br2 + 2e 2Br- 1.09Cl2

+ 2e 2Cl- 1.36F2 + 2e 2F- 2.87

Observations, Please!!!!

1. What seems to be the “grammar” for the reactions?

2. What is the zero point?3. What do you expect the value for Cs to be?4. How do the values for the halogens compare

to the group I elements?5. Is there a trend in the halogens?6. How does this relate to the periodic chart?7. How does this relate to “charge density”?8. Who wants the electrons?9. Where are the guys that want the electrons

located on the chart?

We said that electrons are rapidlyAquated and, rapidly reactWhat about their energy?

e nH O e E V vsN H Eaqo 2 3 0, .

e nH O H H O k x M s

E V vs N H E

aq

o

3 21 0 1 12 3 1 0

2 1 0

, .

, .

e H O H H O k x M s

E V vs N H E

aq

o

21 1 11 9 1 0

2 9 3 0

, .

, .

H-O bondHydronium 301 kJWater 464 kJ

Reaction Vo

e + H2O eaq -3.0Cs+ + e Cs ?K+ + e K -2.95Na+ + e Na -2.71Fe2+ + 2e Fe -0.44Pb2+ + 2e Pb -0.132H+ + 2e H2(gas) 0Cu2+ + 2e Cu 0.34O2 + 2H2O + 4e 4OH- 0.40O2 + 2H+ + 2e H2O2 0.68Br2 + 2e 2Br- 1.09Cl2

+ 2e 2Cl- 1.36F2 + 2e 2F- 2.87want most

want least

have edon’t have e

Reaction Vo


+ 2e 2Cl- 1.36F2 + 2e 2F- 2.87Don’t havewant most

Have ewant least

electronsflow down hillaway fromnegative voltage

Start arrow on right hand side and end on left hand

Think ofA watertower

Reaction Vo


+ 2e 2Cl- 1.36F2 + 2e 2F- 2.87

Uphill reactions: not probableStart arrow on right hand side and end on left hand

Reaction Vo


+ 2e 2Cl- 1.36F2 + 2e 2F- 2.87

Can I react F2 with K+?


No, there is nobody to give away electrons,no electron source!

Reaction Vo


+ 2e 2Cl- 1.36F2 + 2e 2F- 2.87

Can I exchange e between Cs with Pb?


There is nobody to accept electrons!

Which reactions will go?

a) Cs metal plus KBr?b) F2 gas plus PbCl2

c) Na metal plus chlorine gasd) Na+ + Cl-

Strategy:1. Pick one who has electrons2. Pick one who doesn’t 3. Draw an arrow, starting where the electron

is. 4. Is it up or downhill?

Example problem Standard V (good exam prototypes)

Reaction Vo

e + H2O eaq -3.0K+ + e K -2.95Na+ + e Na -2.71NCl3_4H+ + 6e 3Cl- + NH4

+ -1.37Fe2+ + 2e Fe -0.44Pb2+ + 2e Pb -0.132H+ + 2e H2(gas) 0N2(g) + 8H+ + 6e 2NH4

+ 0.275Cu2+ + 2e Cu 0.34O2 + 2H2O + 4e 4OH- 0.40O2 + 2H+ + 2e H2O2 0.68Ag+ + e Ag 0.799NO3

- + 4H+ + 3e NO(g) +2H2O 0.957Br2 + 2e 2Br- 1.092NO3

- + 12H+ + 10e N2(g) +6H2O 1.246Cl2

+ 2e 2Cl- 1.36Au+ + e Au 1.83F2 + 2e 2F- 2.87

Who rusts most?PbFeCuAgAu

Why?What do we use for plumbing?Why was gold considered the sacred material?

Reaction Vo

Fe2+ + 2e Fe -0.44Pb2+ + 2e Pb -0.132H+ + 2e H2(gas) 0Sn4++2e Sn2+ 0.154N2(g) + 8H+ + 6e 2NH4

+ 0.275Cu2+ + 2e Cu 0.34O2 + 2H2O + 4e 4OH- 0.40O2 + 2H+ + 2e H2O2 0.68Fe3

+ +e Fe2+ 0.769Hg2

2+ +2e 2Hg(l) 0.796Ag+ + e Ag 0.799NO3

- + 4H+ + 3e NO(g) +2H2O 0.957Br2 + 2e 2Br- 1.092NO3

- + 12H+ + 10e N2(g) +6H2O 1.246Cl2

+ 2e 2Cl- 1.36Au+ + e Au 1.83F2 + 2e 2F- 2.87

Sunday

Monday

Saturday

Tuesday

Wednesday

Friday

Thursday

M L M xL

M ne M

M L ne M xL

x aqueousn

aqueousn

aqueous

aqueousn

so lid

x aqueousn

so lid aqueous

,

,

Change in metalsequenceoccurs at timethat acids weredeveloped (1100-1400AD)(Islamic Chemists)

xM O M Oso lid

y

y so lid 2 2 2 ,

Chemical oxidation

V1/Kf

G

Air oxidation

~1300A.D

~100 B.C (Context Slide 1)

(Context Slide 2)

Some Rules1. Voltages sum2. Reversed reactions =change of sign3. Don’t worry about #electrons (n)

since V = Joule/coulomb of charge

Example Calculation: Summing V equationsWhat is the voltage for the reaction:

A e A V ao

A e B V a bo

/

2 A A B V ?

Given that

A A e V ao

A e B V a bo

/

2 A A B V V Va bo

ao

/

Example Summing V equations: If your lab partner attempts to add fluorine gas to a beaker containing potassium metal what should you do? Justify by calculating the reaction voltage and the free energy

Say your prayers and duck.

K e K V o 2 9 5.

F e F Vgo

2 2 2 2 8 7, .

2 2 2 2 9 5K e K V o .

2 2 2 2 9 5K K e V o

.

F e F Vgo

2 2 2 2 8 7, .

2 2 2 5 8 22K F K F V o

.

G nF Vo o

G o

2 2 9 5F . 2 2 8 7F .

2 5 8 2F .

2 9 6 4 8 1 0 5 8 24. .x 11 2 3kJ

How does concentration fit In?

G G R T Qo ln

nF V G G nF V o0

nF V nF V R T Qo ln

VnF V

nF

R T

nFQ

o

ln

V VR T

nFQo ln

V VR T

nF

C D

A Bo

c d

a b ln

Nernst Equation:

At 25 oC

V VR T

nF

C D

A Bo

c d

a b ln

V Vn

C D

A Bo

c d

a b 0 0 5 9 2.

lo g

When the reaction favors products, it isSpontaneous, or Galvanic

LuigiGalvani:

“Frog leg Guy”1780

M a Ca

M Ma a

More accurately:

lo g .

0 5 0 91

2zu

u

activity concentration

Activity coefficient

Ionic strength

u C Zi i 12

2

Marie the Jewess, 300 Jabir ibn Hawan, 721-815

Galen, 170 Jean Picard1620-1682

Galileo Galili1564-1642

Daniel Fahrenheit1686-1737

Evangelista Torricelli1608-1647

Isaac Newton1643-1727

Robert Boyle, 1627-1691

Blaise Pascal1623-1662

Anders Celsius1701-1744

Charles Augustin Coulomb 1735-1806

John Dalton1766-1844

B. P. Emile Clapeyron1799-1864

Jacques Charles 1778-1850

Germain Henri Hess1802-1850

Fitch Rule G3: Science is Referential

William ThompsonLord Kelvin, 1824-1907

James Maxwell1831-1879

Johannes D.Van der Waals1837-1923

Justus von Liebig (1803-1873

Johann Balmer1825-1898

James Joule (1818-1889)

Johannes Rydberg1854-1919

Rudolph Clausius1822-1888

Thomas Graham1805-1869

Heinrich R. Hertz, 1857-1894

Max Planck1858-1947

J. J. Thomson1856-1940

Linus Pauling1901-1994

Werner Karl Heisenberg1901-1976

Wolfgang Pauli1900-1958

Count Alessandro GA A Volta, 1747-1827

Georg Simon Ohm 1789-1854

Henri Louis LeChatlier1850-1936

Svante Arrehenius1859-1927

Francois-Marie Raoult1830-1901

William Henry1775-1836

Gilbert N Lewis1875-1946

Fritz Haber1868-1934

Michael Faraday1791-1867

Luigi Galvani1737-1798

Walther Nernst1864-1941

Lawrence Henderson1878-1942

Amedeo Avogadro1756-1856

J. Willard Gibbs1839-1903

Niels Bohr1885-1962

Erwin Schodinger1887-1961

Louis de Broglie (1892-1987)

Friedrich H. Hund1896-1997

Fritz London1900-1954

An alchemist

Ludwig Boltzman1844-1906

Richard AC E Erlenmeyer1825-1909

Johannes Bronsted1879-1947

Thomas M Lowry1874-1936

James Watt1736-1819

Dmitri Mendeleev1834-1907

Marie Curie1867-1934

Henri Bequerel1852-1908

Rolf Sievert, 1896-1966

Louis Harold Gray1905-1965

Jacobus van’t Hoff1852-1911

ElectrochemistryElectrochemistry is a very diverse area. It can be broadly divided into a) analytical electrochemistry which is concerned with methods of measurement involving

potentiometry (pH meters etc), voltammetry, and modern sensors (generally voltammetricin nature)

b) physical electrochemistry is the basis of analytical electrochemistry, but is generallyconcerned with the effect of electric fields, charge balance, and diffusion.

c) Chemical electrochemistry usually is less interested in quantitative analysis but is devotedto understanding the mechanisms of electron transfer based on chemical structure.

d) Biologic electrochemistry can be understood as a form of physical electrochemistry(charge and fields around biomolecules) and of chemical electrochemistry (electron transferevents in biological systems)

e) Geologic and environmental electrochemistry is concerned with all of the above as theytake place in the natural environment . Of particular interest are the oxidation reductionreactions of iron, manganese, chromium, arsenic, sulfur, as these set the parameters inwhich life can grow and, as the oxidation state of iron has substantial implications for thestability of various minerals and their dissolution/formation.

f) Technical - in this field fall the major areas of batteries, solar energy, fuel cells, andcorrosion sciences.

A preview……

Note the negativeTo positive Arrangement ofVoltages.

Electrons flow awayFrom the Negative sign.

Biological “Galvanic”(Spontaneous) Cell:Respiration

Note also verySmall voltage steps, 0.01 V is a large driver!

http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb1/part2/redox.htm

See also:Awesome site

CoQ = Coenzyme Q

Ubiquinone, Q

Ubiquinol, QH2

2e, 2H+

http://www.reciprocalnet.org/recipnet/showsample.jsp?sampleId=27344188&sampleHistoryId=13823

Open browser to see and rotate molecule

Q H e H Q V 2 2 0 6 9 9 92

0~ .

What is the role of the long tail?

BiologicalElectrochemistry

Cytochrome c oxidaseCytochrome C

FeContainingHeme group

8 2H Oin g , 4 H ou t

Membrane

Fe issquare planarwith 2 morecoordinationsites top and bottom.

One is used for oxygen transport

Hemeglobin:Oxygen carrier

http://www.elmhurst.edu/~chm/vchembook/568globularprotein.htmlReview: Module 18: Complex IonsReview: Module 17B: Acid Bases

Biological “Electrolytic” orNon-spontaneous cell:Photosynthesis

Electrons are “pumped” up towardsMore negative voltage

The pump chemistry is Similar (but not identical) to metal ligand crystalField splitting

light

700nm

680nm

Photosystems I and II

Electrochemistry in Mining

“In just a few years a large area of forest has been destroyed [near the Taxco silver mines], and it appears that the wood supply will be depleted sooner than the ore. Ordinances have been made regarding the conservation of the forest, and likewise regarding the paths that the Indian workers use for making charcoal, cutting wood, and on the maximum loads that may carry.”

The Conquest of Mexico

In 1550 the Viceroy wrote to the King

Requires a less fuelIntensive method

Mercury consumed in New World Spanish silver mines(1560-1820):170,000 tons; USA gold rush (1850-1900): 70,000 tons

(Context Slide 1)

Amalgamation was introduced in the 1550s in Mexico by a Spanish immigrant, Bartolome deMedina, who wrote Dec. 29, 1555 (1):

I, Bartolome de Medina do declare that I learned in Spain through discussion with aGerman, that silver can be extracted from ore without the necessity for smelting it, orrefining it, or incurring any other considerable expense. With this information Iresolved to come to New Spain. Leaving my home, my wife and my children in Spain, Icame to test it, knowing that if I were successful, I would render a great service to OurLord, and to his Majesty and to all this realm. And having spent much time and moneyand suffered mental anguish, and seeing that I was not going to be able to make itwork, I commended myself to Our Lady and I begged Her to enlighten me and guideme, so that I might be successful and it pleased Our Lady to enlighten me and put meon the right path so that I could make it work.

1. Probert, A. Bartolome de Medina: The Patio Process and the Sixteenth Century Silver Crisis. In M inesof Silver and Gold in the Americas.

Grind the ore fine. Steep it in strong brine. Add mercury and mix thoroughly. Repeatmixing daily for several weeks. Every day take a pinch of ore mud and examine themercury. See? It is bright and glistening. As times passes, it should darken as silverminerals are decomposed by salt and the silver forms an alloy with mercury. Amalgam is pasty. Wash out the spent ore in water. Retort residual amalgam;mercury is driven off and silver remains.

A description of the process 1555.

(Context Slide 2)

8 1 6 3 2 8 8 0 1 5 842

2 3 2 10SO e H H SO H O V .

8 1 6 8 4 1 2 0 4 0 02 3 2 32

2 2H SO e H S O H O V o . S S e Vs

o232 0 4 4 7 .

2 4 2 2 9 1 0 8 4 1 1 0 1 02 32

2 3 2

3 21 3 2 2 6 2 6 9A g S O A g S O K x xf

. . .

A g S A g S K sp22 5 12 1 0

A g S SO e H A g S O H O S s2 42

2 3 2

3

28 3 0 4 0 2 2 0

8 3 0 4 0 4 2 0 1 0 0 542

2 32

2SO e H S O H O S Vs neto .

lo g.

Kn

Vnet ne to

0 0 5 9 2

lo g.

. .K net 3 0

0 0 5 9 21 0 0 2 5 0 7 7

K vo ltage net,.1 0 5 0 7 7

K K K Kto ta l net f sp 2

5 0 7 7 2 6 9 5 0 1 4 8 4 51 0 1 0 1 0 1 0. . . .

Solubility

Complexation

ReductionOf S(how toGet the ligand)

(Context Slide 2)

insoluble

Could drive solubility

Couple Reactions Example• Most native silver has long since been used: 2. but we still mine silver dust.3. How is this economically feasible?4. How could we get rich with a new process involving CN

extraction?

A g C N O A g C Ns aq g aq

2 2, ,

What is the voltage, free energy, and K Associated with this reaction?

A g C N O A g C Ns aq g aq

2 2, ,

A g C N A g C Ns aq aq

2 ,

1. Balance the equationa. Split into ½ reactionsb. Balance each ½ reactionc. Recombine

A g C N A g C Ns aq aq

2 2 ,

A g C N A g C N es aq aq

2 12 ,

O g2 , ?

O H Og2 22,

O H H Og aq2 24 2,

O H e H Og aq2 24 4 2, 4 8 4 42A g C N A g C N es aq aq

,

4 8 4 42A g C N A g C N es aq aq

,

O H e H Og aq2 24 4 2,

4 8 4 4 22 2 2A g C N O H A g C N H Os aq g aq aq

, ,

V o 0 3 1.

V o 1 2 3.

V rxo 1 5 4.

The free energy for the reaction is a mere:

G = -nFVorx = -4(96485)(1.53) = -5.9x105 J

G = -RTln K

K = e(-G/RT) = e(-(-590000/(298x8.314)) = e238 = 10238/2.3

= 10103

all you need is:CN (cheap)O2 (air is cheap (an aerator))

Hypothetical Modern Silver/Gold Mine

Bulldozer

CN-

aerator

O2

Same process used to recover silver at photography studios, in silver plating.

Major cyanide spills: Czech, Elbe River, Jan. 2006; Romania, Tisza River, Nov. 2005; Laos, June, 2005; Ghana River Kubreko, Jan, 2005; China, Papua New Guinea, Ghana, Romania (10 tons Danube River, Mar. 2004), Ghana, Honduras, Nicaragua, China, 2002: Nevada, USA

Tibor Kocsis

(Context Slide)

Using Bugs to Mine Cu from CuS

8 82 3F e F ebugs

C u S F e H O F e C u SO Hs

22

2 32

2 2428 4 8 2 1 6

-14e

Catalytic reagent, supplied courtesy of bugs, Thiobacillus ferridoxin

collectKsp=10-36

Biomining forGold and Copper in Botswana

(Context Slide)

(Context Slide)

Coupled Chemical Equation Example Calculate the formal potential for the reaction to form the initial corrosion product, Fe(OH)3,s reaction at pH 7

2 2 4 0 4 42F e F e e V

.

O H O e O H V Oo

2 2 22 4 4 0 4 0

.

2 33 2 2 3F e O H H O F e Oslow( )

2 2 2 0 7 7 12 3F e F e e V

.12 2 2 22 2 0 4 0O H O e O H V O

o

.

F e O H F e O H K xsp3

33 83 6 3 1 0

( ) .

Introduction: Key Concepts

1. Grammer Rules: write all reactions as reductions

2. Half reactions3. Aquated electrons (carry electrons from

electrode to solution species) (disinfectants)4. Voltage is an energy term5. Applications

1. Disinfectants2. Biology3. Geology4. Industry

Documents

Electrochemistry. Fundamental concepts Electron flow, nomenclature Energy in the electron flow Kinetics of the electron transfer event as influenced by