Lecture #26 Coordination Chemistry: Hydrolysis · 2020-03-04 · Lecture #26. Coordination...

Lecture #26Coordination Chemistry: Hydrolysis

(Stumm & Morgan, Chapt.6: pg.260-271)

Benjamin; Chapter 8.1-8.6

David Reckhow CEE 680 #26 1

Updated: 4 March 2020 Print version

http://www.ecs.umass.edu/cee/reckhow/courses/680/slides/680l26p.pdf


Α

Β

Titrant Volume (mL)

0 5 10 15 20 25 30 35 40 45

pH

2

345

678

9101112

1st Equivalence Point

2nd Equivalence Point

Vph Vmo

H ++HCO3

-=H

2 CO3

H ++CO3-2

=HCO3-

H++OH

-=H2O

A

B

Acid Titration Curve for a Water Containing Hydroxide and Carbonate Alkalinity

From

Lec

ture

#20

A

B

T

i

t

r

a

n

t

V

o

l

u

m

e

(

m

L

)

0

5

1

0

1

5

2

0

2

5

3

0

3

5

4

0

4

5

p

H

2

3

4

5

6

7

8

9

1

0

1

1

1

2

1

s

t

E

q

u

i

v

a

l

e

n

c

e

P

o

i

n

t

2

n

d

E

q

u

i

v

a

l

e

n

c

e

P

o

i

n

t

V

p

h

V

m

o

H

+

+

H

C

O

3

-

=

H

2

C

O

3

H

+

+

C

O

3

-

2

=

H

C

O

3

-

H

+

+

O

H

-

=

H

2

O

A

B

Acid Titration Curve for a Water Containing Carbonate and Bicarbonate Alkalinity


Α

Β

Titrant Volume (mL)

0 5 10 15 20 25 30 35 40 45

pH

2

345

678

9101112

1st Equivalence Point

2nd Equivalence Point

Vph Vmo

Y[CO3-2

] + Z[HCO3-]

C

(Y + Z)[HCO3-]

(Y + Z)[H2CO3]

(Y + Z)Vs/Nt(Y)Vs/Nt

From

Lec

ture

#20

A

B

T

i

t

r

a

n

t

V

o

l

u

m

e

(

m

L

)

0

5

1

0

1

5

2

0

2

5

3

0

3

5

4

0

4

5

p

H

2

3

4

5

6

7

8

9

1

0

1

1

1

2

1

s

t

E

q

u

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v

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l

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P

o

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n

t

2

n

d

E

q

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a

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P

o

i

n

t

V

p

h

V

m

o

Y

[

C

O

3

-

2

]

+

Z

[

H

C

O

3

-

]

C

(

Y

+

Z

)

[

H

C

O

3

-

]

(

Y

+

Z

)

[

H

2

C

O

3

]

(

Y

+

Z

)

V

s

/

N

t

(

Y

)

V

s

/

N

t

Buffer Intensity Amount of strong

acid or base required to cause a specific small shift in pH

David Reckhow CEE 680 #17 4f-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2

pH

2

3

4

5

6

7

8

9

10

11

12

g-0.20.00.20.40.60.81.01.2

pH 3.35

pH 4.7

pH 8.35

Starting Point

Mid-point

End Point

dpHdC

dpHdC AB −==β

10-2M HAc

BC∆

pH∆BC

∆

pH∆

Slope = 1/β

From

Lec

ture

#17

Base titration of an acid For a monoprotic

Lecture #16 CB ≡ [Na+] = [A-] + [OH-] - [H+]

For a diprotic Using the same ENE

approach


T

T

T

B

s

B

ss

BB

CHOH

CHOHA

CC

molesequ

MVNVf

][][

][][][

1

+−

+−−

−+=

−+=

===

α

𝑓𝑓 =2 𝐴𝐴−2 + 𝐻𝐻𝐴𝐴− + 𝑂𝑂𝐻𝐻− + 𝐻𝐻+

𝐶𝐶𝑇𝑇

𝑓𝑓 = 2𝛼𝛼2 + 𝛼𝛼1 +𝑂𝑂𝐻𝐻− + 𝐻𝐻+

𝐶𝐶𝑇𝑇

11

221

2 ][][ ++++

KH

KKH

][][ 2

111

+

+

++HK

KH1

𝐻𝐻+𝐾𝐾𝑎𝑎

+ 1

Example Titration Base titration

Vs = 1000 mL Ms = 0.001 M NB = 0.1 M

Starting acids Pure water 1 mM HAc 1 mM H2CO3


s

B

ss

BB

molesequ

MVNVf ==

pHi = 3.85 pKa = ??

pKas = ??

Titration of Humics Model for

aquatic humic substances Acetic acid +

phenol


From

Lec

ture

#18

Protons & Metals Ions


Fig 6.2 pg.259

Why??

FeOH(H2O)5+2


Fe

O

H

Fe(OH)2(H2O)4+


H

O

Fe

O

H

Lake Taihu


C106H263O110N16P

CO2 H2ONO3-

HPO4-2

Limits to Growth

Another Problem Statement

Photosynthesis with nitrate assimilation 106 CO2 + 16 NO3- + HPO4-2 + 122 H2O + 18 H+

= C106H263O110N16P + 138 O2 Basis for stoichiometry and limits to growth Algal cells are: C106H263O110N16P But what if they are: C106H263O110N16P1Fe0.001


Elemental abundance in crust O Si Al Fe Ca Na Mg K Ti H P Mn F


Elemental abundance in fresh water


From: Stumm & Morgan, 1996; Benjamin, 2002; fig 1.1

Complexation of hydroxide?


NoYes, a bit

Yes, quite a bit

Precipitation and Dissolution Environmental Significance

Engineered systems coagulation, softening, removal of heavy metals

Natural systems composition of natural waters formation and composition of aquatic sediments global cycling of elements

Composition of natural waters S&M, 3rd ed., figure 15.1 (pg. 873)


Intro: Chemical Reactions Driving force

Reactants strive to improve the stability of their electron configurations (i.e., lower ∆G)

Types Redox reactions: change in oxidation state Coordinative reactions: change in

coordinative relationships


Intro: Coordinative Reactions Definition: where the coordination number or

coordination partner changes Types

Acid/base reactions

Precipitation reactions

Complexation reactions


HClO + H2O = H3O+ + ClO-

Mg+2 + 2OH- = Mg(OH)2(s)

Cu+2 + 4NH3 = Cu(NH3)4+2

HClO = H+ + ClO-

Mg(H2O)2+2 + 2OH- = Mg(OH)2(s) + 2H2O

Cu(H2O)4+2 + 4NH3 = Cu(NH3)4+2 + 4H2O

Coordination Chemistry: References Benjamin, 2002: Chapt. 8

Appendix A4 Stumm & Morgan, 1996: Chapt. 6 Butler, 1998: Chapt. 7 & 8 Pankow, 1991: Chapt. 18 Langmuir, 1997: Chapt. 3 Snoeyink & Jenkins, 1980: Chapt. 5 Morel & Hering, 1993: Chapt. 6

Morel, 1983: Chapt. 6 Buffle, 1988: Chapt. 5 & 6


Coordination Definition

Any combining of cations with molecules or anions containing free pairs of electrons


Cu+2 + 4NH3 = Cu(NH3)4+2

Central atom

Ligand

Ligand atom

NH

HH

Complex or Coordination Compound

Ligand types Constituent Ligand atoms

Nitrogen Oxygen Others: halides

Numbers of active ligand atoms per ligand One: monodentate (e.g., ammonia) Two: bidentate (e.g., oxalate) Three: tridentate (e.g., citrate) Six: hexadentate (e.g., EDTA)


MultidentateResulting complexes are called chelates

http://en.wikipedia.org/wiki/File:Zitronens%C3%A4ure_-_Citric_acid.svghttp://en.wikipedia.org/wiki/File:Zitronens%C3%A4ure_-_Citric_acid.svghttp://en.wikipedia.org/wiki/File:Ethylenediaminetetraacetic.pnghttp://en.wikipedia.org/wiki/File:Ethylenediaminetetraacetic.png

Coordination Basics Importance

Affects solubility of metals e.g., Al(OH)3 solubility

Used in Analytical chemistry Determination of hardness

Metals act as buffers in natural waters

Coordination Number 1 for Hydrogen 2, 4, or 6 for most metals


Ion Pairs & Complexes Two types of complex species

Ion Pairs Ions of opposite charge that form an association of lesser charge Ion pairs are separated by at least one water molecule

These are called “outer-sphere” complexes

Complexes Metal ion and neutral or anionic ligand Direct bond formed with no water molecule between

These are called “inner-sphere” complexes


Ion pair stability Determined based on simple coulombic interactions


Ion Charge

Log K (I=0)

Log K (seawater)

1 0 to 1 -0.5 to 0.5

2 1.5 to 2.4 0.1 to 1.2

3 2.8 to 4.0

Natural Particle as Ligands Natural Particles

High surface area Usually coated with oxygen-containing surface

groups which can donate electrons to metals (i.e., act as ligands)


OH

S

O-

S

O-M

S

M+

Chemical Speciation

David Reckhow CEE 680 #26 26Fig 6.1, pg. 258

Protons & Metals Ions


Fig 6.2 pg.259

All “free” metals and protons are actually hydrated in water Both can bind with hydroxide


Fig 6.3Pg.259

Cu(NH3)X

Brønsted & Lewis Acidity Definition of Acids

Brønsted: proton donors Species with excess H+

Lewis: electron acceptors H+, metal ions, others

Strength Tendency to accept electrons (or donate protons)

Measured by equilibrium constant


PresenterPresentation NotesOthers include: SOCl2, AlCl3, SO2, and BF3

Complexes: Coordination #

Me(Ligand)x Fe(H2O)6+3

Fe(H2O)4(OH)2+1

PtCl6-2

Cu(NH3)4+2

Si(OH)4 HgS2-2

HOH


6

4

2

CoordinationNumber

Coordination # Depends on:1. Size of central Atom2. Charge of central Atom3. Size of Ligand

To next lecture


http://www.ecs.umass.edu/cee/reckhow/courses/680/slides/680l27.pdf

CEE 680: Water ChemistryAcid Titration Curve for a Water Containing Hydroxide and Carbonate AlkalinityAcid Titration Curve for a Water Containing Carbonate and Bicarbonate AlkalinityBuffer IntensityBase titration of an acidExample TitrationTitration of HumicsProtons & Metals IonsFeOH(H2O)5+2Fe(OH)2(H2O)4+Limits to GrowthAnother Problem StatementElemental abundance in crustElemental abundance in fresh waterComplexation of hydroxide?Precipitation and DissolutionIntro: Chemical ReactionsIntro: Coordinative ReactionsCoordination Chemistry: ReferencesCoordinationLigand typesCoordination BasicsIon Pairs & ComplexesIon pair stabilityNatural Particle as LigandsChemical SpeciationProtons & Metals IonsSlide Number 28Brønsted & Lewis AcidityComplexes: Coordination #Slide Number 31

Lecture #26 Coordination Chemistry: Hydrolysis · 2020-03-04 · Lecture #26. Coordination...

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Transcript of Lecture #26 Coordination Chemistry: Hydrolysis · 2020-03-04 · Lecture #26. Coordination...