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12/22/2011
prananto@ub.ac.id 1
Kimia Reaksi AnorganikYuniar Ponco Prananto
2nd Mid-Semester Topics
• Frontier Orbitals (2 sks)
• HSAB Application (5 sks)
• Heterogeneous Acid Base Reaction (2 sks)
• Reduction and Oxidation (12 sks):
- Extraction of the Elements
- Reduction Potential
- Redox Stability in Water
- Diagrammatic Presentation of Potential Data
Huheey, J.E., Keiter, E.A., and Keiter, R.L., 1993, Inorganic
Chemistry, Principles of Structure and Reactivity, 4th
ed., Harper Collins College Publisher, New York
Miessler, D. L. and Tarr, D. A., 2004, Inorganic Chemistry, 3rd ed., Prentice Hall International, USA
Atkins, P., Overton, T., Rourke, J., Shriver, D. F., Weller, M., and Amstrong, F., 2009, Shriver and Atkins’ Inorganic
Chemistry, 5th ed., Oxford University Press, UK
Gary Wulfsberg, 2000, Inorganic Chemistry, University Science Book, California, USA
• Frontier orbitals, which are HOMO (highest occupied
molecular orbital) and LUMO (lowest unoccupied molecular
orbital), has been focused nearly since the beginning of
HSAB theory.
• Koopman’s theorem, the energy of HOMO → the
ionization energy, while the energy of LUMO → the
electron affinity for a closed-shell spesies, in which both
orbitals are involved in the electronegativity and HSAB
relationships.
• Hard species → have a large HOMO – LUMO gap
• Soft species → have a small HOMO – LUMO gap.
Frontier Orbitals …..summary
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Frontier orbitals is the HOMO (filled or partly filled) and
the LUMO (completely or partly vacant) of a
MOLECULAR ENTITY.
HOMO
is the highest-energy molecular orbital of an atom or
molecule containing an electron. Most likely the first
orbital, from which an atom will lose an electron.
LUMO
is the orbital that can act as the electron acceptor,
since it is the innermost (lowest energy) orbital that
has room to accept an electron.
HSAB Principle …..summary
• A structure-reactivity concept formulated in terms of
acid-base interaction.
• According to this principle soft acids react faster and
form stronger bonds with soft bases, whereas hard acids
react faster and form stronger bonds with hard bases,
everything else being assumed aproximately equal.
• The soft-soft preference is characteristic mostly of the
reactions controlled by the orbital interaction, and the
hard-hard preference relates to reactions in which
electrostatic factors prevail.
Pure Appl. Chem., Vol. 71, No. 10, pp. 1919-1981, 1999
Hardness is associated with:
1. Small atomic/ionic radius 2. High oxidation state
3. low polarizability, 4. high electronegativity
and 5. energy low-lying HOMO
(bases) or energy high-lying LUMO (acids)
Hard vs Soft
Softness is related to:1. large atomic/ionic radius
2. low or zero oxidation state
3. high polarizability, 4. low electronegativity,
and 5. energy high-lying
HOMO (bases) or energy low lying LUMO
(acids)
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1. Equilibrium direction (reactants or products)
ZnI2 + HgCl2 ZnCl2 + HgI2
b/l A – SB SA – b/l B b/l A – b/l B SA – SB
• The I- is a soft base and Hg2+ is a soft acid,
although Zn2+ is a b/line acid and Cl- is a
b/line base (relative to Hg2+ and I-), both
Zn2+ and Cl- are the harder species, hence
the SA-SB is HgI2 and HA-HB is ZnCl2
→ products are favored
CuI2 + Cu2O 2Cul + CuOb/l A – SB SA – HB SA – SB b/l A – HB
• The I- is a soft base and O2- is a hard base,
since Cu+ is softer acid than Cu+2 therefore
the SA-SB is CuI and the HA-HB is CuO
→ products are favored
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CdCI2 + CaSO4 CdSO4 + CaCl2b/l A – b/l B HA – HB b/l A – HB HA – b/l B
• Both Cd+2 and Cl- are b/line acid and b/line
base, while both Ca+2 and O-2 are hard acid
and hard base, therefore those species in
the left are favorable, due to its stronger
interactions, than those species in the right
→ reactants are favored
Exercise 1
Predict the favorable species (reactants or products) inthe following equilibrium!
1. Hg(CN)2 + Ca(ClO4) 2 Ca(CN) 2 + Hg(ClO4) 2
2. 3FeO + Fe2S3 3FeS + Fe2O3
3. PbCO3 + 2NaBr Na2CO3 + PbBr2
4. MgCl2 + AgI MgI2 + AgCl
5. MnS + NiF2 NiS + MnF2
6. Ti(NO3)2 + ZnCl2 Zn(NO3) 2 + TiCl2
7. Nb2S5 + 5HgO Nb2O5 + 5HgS
2. Solubility of Halides and Chalcogenides
[Ag(H2O)n]+ + [Cl(H2O)m]- AgCl(s) + (m+n)H2OSA – HB b/l B – HA SA – b/l B HA – HB
Hence:
We can predict that “the chlorides, bromides, and iodides of the
soft acids are insoluble in water” → most of the predictions are
generally true for the +1 and +2 ions of the soft-acid metals, i.e:
CuCl, AgCl, AuCl, TlCl, Hg2Cl2, OsCl2, IrCl2, PdCl2, PtCl2, and
PbCl2, except CuCl2, AuCl3, HgCl2, PtCl4.
Similar predictions of the solubility of pseudohalide salts, i.e:
soft base → cyanide (CN), thiocyanate (SCN),
b/l base → azide (-N=N+=N-)
→ “the cyanides, thiocyanates, and azides of the soft acidsare insoluble in water”
• Special case: the sulfides, selenides and tellurides of the soft and borderline acids are insoluble in water due
to the combination of softness and some strength in bases (S2-, Se2- and Te2- ions are stronger bases than
Cl-, Br- and I- ions)
• Moreover…– for a given soft acid, the solubility of the iodide <
bromide < chloride,– similarly, for a given soft acid, the solubility of
telluride < selenide < sulfide
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• Due to the absence of soft base involvement in the precipitation equilibrium, the HSAB principle is
irrelevant to the water solubility’s prediction of the salts from hard bases F- (weak base), OH- and O2-(strong
bases) → “the fluorides, oxides, and hydroxides of acidic
cations are insoluble in water”
• Because there is no soft acid is involved in the solubility equilibrium, the solubility of the sulfides,
selenides and tellurides of the hard acids cannot be predicted by the HSAB principle.
Exercise 2
• Identify all insoluble compounds and
explain it according to HSAB principle:
a. PtAs2 e. TiO2
b. AgI f. CdTe
c. CaF2 g. AgF
d. KI h. CoSO4
3. The Qualitative Analysis Scheme for Metal Ions
• Group I → precipitated with 0.3 M HCl
• Group II
→ precipitated with H2S from acidic solution• Group III
→ precipitated with (NH4)2S from basic solution• Group IV
→ precipitated with (NH4)2CO3
• Group V→ remains in solution
.: the member of each group does not belong to
certain / similar period or group in the periodic
table of elements
?
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Group I and II
• The chloride ion is a borderline base that will combine strongly to soft acid, and if a large excess of Cl- is
present, only Ag+, Hg2+, Tl+ and Pb2+ will be precipitated while others like Cu, Pd, Os, Ir, Pt and Au
will form soluble chloro anions [MCln]x-.
• The sulfide ion is a very soft and a stronger base than Cl-. Therefore when it reacts with Cu, Pd, Os, Ir, Pt
and Au, it will produce more insoluble sulfides.
Note: the scheme should be done properly and in order!!
Group III
• The sulfide ion is present in much higher concentration and also competing with another strong base plus
much harder hydroxide ion.
• Only hard-acid metal ions and small group of borderline acids from the +2 ions of the 1st row transition metals
(Zn, Ni, Co, Fe, and Mn) are in the solution and will be precipitated as sulfides.
• The remains, which is strong - hard acid metal (also all
of the f-block elements), will react with the strong –hard base OH- and gives precipitation of metal
hydroxides or metal oxides.
Group IV and V
• Only the non-acidic and weak acidic hard acid of the 1st two groups of the periodic table are present, and
then moderately-basic carbonate ion is added → only the weak acidic cations will be precipitated.
• The rest will only be the non-acidic cations that prefer
to bind with the (non-basic) hard base water in the form of hydrated-ion (to get the precipitation of these
metals, sometimes the test is continued by adding the non-basic anions)
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Exercise 3
A new qualitative analysis scheme that separate
cations into five existing groups using novel precipitation anions is prepared. Choose the best substitute for:
1. HCl in Group I → HBr, HF, HClO, or HClO4
2. H2S in Group II → H2O, H2Te, H2SO3, or H2SO4
3. (NH4) 2CO3 in Group IV → NH4OH, NH4ClO4, (NH4) 2SO4, (NH4) 4C
4. If you want to precipitate Group V, which compound would do this → LiOH, LiClO4, Li2SO4, Li4C.
Geochemical classification of the elements divided into Primary and Secondary. The primary emphasizes
behavior under condition at the surface of the earth, which are:
• Lithophilesmetals and nonmetals that tend to occur as cations in
oxides, silicates, sulfates and carbonates.
the anions posses oxygen as the donor atom hence the metal ions that attached are hard acid metals,
the nonmetals are, or have been oxidized by atmospheric oxygen to oxo-anions, hard bases.
4. The Geochemical Classification and
Differentiation of the Elements
• Chalcophiles
occur in nature as cations in sulfides (less commonly w/ other soft bases such as telluride, arsenic, etc). Mostly
from the borderline and some soft acids and many of
soft bases.
• Atmophiles
chemically unreactive nonmetals that occur in the
atmosphere in elemental form, i.e: N2 and noble gases
• Siderophiles
soft acid metals that tend to occur native in elemental form (subdivision of chalcopiles)
Hard Acid MetalHard Acid Metal
Gypsum
CaSO4
NatroxalateNa2C2O4
Fluorite CaF2
NatroliteNa2[Al2Si3O10]·2H2O
Sylvite KCl
Magnesite
MgCO3
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(Meta)variscite AlPO4.2H2O
Corundum
Al2O3
Beryl Be3Al2Si6O18
Barite
BaSO4
GaylussiteNa2Ca(CO3) 2·5(H2O) Rhodochrosite
MnCO3
MolybdeniteMoS2
Uvarovite
Ca3Cr2 (SiO4)3 Rutile TiO2
Rutherfordine(UO2)(CO3)
Erythrite Co3(AsO4)2·8(H2O)
Siderite FeCO3 Magnetite Fe3O4Hematite Fe2O3
Pyrite FeS2
StrengiteFePO4.2H2O Fayalite Fe2SiO4
Greenockite CdCO3
CassiteriteSnO3
Stibnite Sb2S3
SmithsoniteZnCO3 Morenosite NiSO4·7H2O
Hard Hard –– b/line Acid Metalb/line Acid Metal
Salesite Cu(IO3)(OH)
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Iodargyrite AgI
GalenaPbS
CinnabarHgS Calaverite AuTe2
Soft Acid MetalSoft Acid Metal
Marshite CuI Sartorite PbAs2S4
Elements Mineral Names Hard / Soft – Acid / Base
1. Sodium Halite, NaCl Hard Acid Na + B/line Base Cl
Natron, Na2CO3.10H2O …
Villiaumite, NaF …
Caliche, NaIO3 …
2. Calcium Calcite, CaCO3 Hard Acid Ca + Hard Base O
Gypsum, CaSO4.2H2O …
Apatite, Ca5(PO4)3OH …
Fluorite, CaF2 …
3. Kalium Sylvite, KCl Hard Acid K + B/line Base Cl
4. Magnesium Magnesite, MgCO3 Hard Acid Mg + Hard Base O
5. Alumunium Bauxite, Al2O3 Hard Acid Al + Hard Base O
Cryolite, NaAlF4 …
Gibbsite, Al(OH)3 …
Gahnite, ZnAl2O4 …
Elements Mineral Names Hard / Soft – Acid / Base
6. Chromium Chromite, FeCr2O4 …
7. Titanium Rutile, TiO2 …
Ilmenite, FeTiO3 …
8. Iron Hematite, Fe2O3 …
Magnetite, Fe3O4 …
Siderite, FeCO3 …
Pyrite, FeS2 …
Arsenopyrite, FeAsS …
9. Manganese Pyrolusite, MnO2 …
Psilomelane, BaMn5O11 …
Elements Mineral Names Hard / Soft – Acid / Base
10. Zinc Sphalerite, ZnS …
Smithsonite, ZnCO3 …
11. Nickel Pentlandite, (Ni,Fe)9S8 …
Heazlewoodite, Ni3S2 …
Melonite, NiTe2 …
Morenosite, NiSO4.7H2O …
Pararammelsbergite, NiAs2 …
Vaesite, NiS2 …
12. Tin Cassiterite, SnO2 …
13. Antimony Stibnite, Sb2S3 …
14. Molybdenum Molybdenite, MoS2 …
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Exercise 4
• Choose and explain the most likely
mineral sources of this elements based
on HSAB principle!
a. LaPO4, LaAs, LaI3, or LaCl3
b. ZrSiO4, ZrPbO4, or ZrCl4
c. PtAs2, PtN2, PtSiO4, or PtF2
d. CoAs2, CoCO3, CoSO4, or CoBr2
e. TeF4, Na2Te, PbTe, or TeI4
5. Biochemistry, Biological Functions, Toxicology, and Medicinal
• HSAB principle can organize the chemistry of the metal ions in ecology, biochemistry and medicine
• The donor atom of biochemical ligands to which the
essential metal ions prefer to bind indicates the general pattern of HSAB principle, as well as the
kind of biochemical sites at which toxic metal ions are likely to bind.
• Mimicking the behavior of complicated biochemical
complexes with simpler coordination complexes (bioinorganic chemistry) → catalysts, metal-activated
enzymes, template, etc.
Some of the most important reactions involving the
Lewis acidity of inorganic compounds occur at solid
surfaces.
For example, SURFACE ACIDS, which are solids with
a high surface area and Lewis acid sites, are used as
catalysts in the petrochemical industry for the
isomerization and alkylation of aromatic compounds.
The surfaces of many materials that are important in
the chemistry of soil and natural waters also have
Lewis acid sites.
Heterogeneous Acid-Base Reaction Surface acidity
Alumina (Al2O3)• Termasuk salah satu asam permukaan karena Al dgn biloks Al yang
tinggi (+3).
• Ketika alumunium oksida hidrat yang baru mengendap dipanaskan di
atas 150°C, proses dehidrasi terjadi dan permukaan mengalami
reaksi:
• Reaksi tsb menghasilkan spesi Al3+ di permukaan, yg bertindak sbg
asam Lewis, begitu juga spesi O2-, yg bertindak sbg basa Lewis.
• Kedua asam-basa Lewis ini akan dihasilkan bersamaan, namun situs
asam Lewis lebih utama untuk katalisis permukaan.
Al
OH
Al
OH
Al
OH
Al Al Al
OHO
+ H2O
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Aluminosilikat (Al2O3)• Berbeda dgn alumina, aluminosilikat memperlihatkan sifat keasaman
Brownsted dimana pembentukkannya diperkirakan melalui
kondensasi unit Si(OH)4 dgn unit H2OAl(OH)3:
• Reaksi tsb menghasilkan asam Brownsted yang kuat pada situs
dimana proton dipertahankan untuk menyeimbangkan muatan
positif yang lebih kecil dari Al3+.
• Karakter dan kekuatan asam permukaan dapat dipelajari melalui
metoda sederhana seperti titrasi dgn larutan basa. Selain itu,
spektrofotometri inframerah dari molekul yang teradsorb dapat juga
digunakan untuk mempelajari situs permukaan yang reaktif.
Si
OH
Al
OH2
Si Al
HO
+ H2O
Silika (SiO2)• Permukaan silika tidak seketika membentuk situs asam Lewis
karena gugus OH terikat kuat pada permukaan turunan SiO2, dan
keasamaan Brownsted lebih dominan.
• Keasaman Brownsted permukaan silika relatif sedang dibandingkan
asam asetat, berbeda dgn aluminosilikat yang menunjukkan
keasamaan Brownsted yang kuat.
• Reaksi permukaan oleh situs asam Brownsted gel silika digunakan
untuk membuat lapisan tipis beberapa gugus organik, yang salah
satunya dipakai untuk memodifikasi permukaan fase diam kolom
kromatografiSi + H2OOH + HOSiR3
Si O SiR3
Si + HClOH + ClSiR3 Si O SiR3
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