12/22/2011 Kimia Reaksi Anorganik 2nd Mid-Semester Topics Yuniar Ponco Prananto • 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 Frontier Orbitals …..summary Huheey, J.E., Keiter, E.A., and Keiter, R.L., 1993, Inorganic • Frontier orbitals, which are HOMO (highest occupied Chemistry, Principles of Structure and Reactivity , 4 th molecular orbital ) and LUMO (lowest unoccupied molecular ed., Harper Collins College Publisher, New York orbital ), has been focused nearly since the beginning of Miessler, D. L. and Tarr, D. A., 2004, Inorganic Chemistry , HSAB theory. 3rd ed., Prentice Hall International, USA • Koopman’s theorem , the energy of HOMO → the Atkins, P., Overton, T., Rourke, J., Shriver, D. F., Weller, M., ionization energy, while the energy of LUMO → the and Amstrong, F., 2009, Shriver and Atkins’ Inorganic electron affinity for a closed-shell spesies, in which both th Chemistry , 5 ed., Oxford University Press, UK orbitals are involved in the electronegativity and HSAB Gary Wulfsberg, 2000, Inorganic Chemistry , University relationships. Science Book, California, USA • Hard species → have a large HOMO – LUMO gap • Soft species → have a small HOMO – LUMO gap. [email protected] 1 12/22/2011 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 Hard vs Soft Pure Appl. Chem. , Vol. 71, No. 10, pp. 1919-1981, 1999 • A structure-reactivity concept formulated in terms of Hardness is associated Softness is related to: acid-base interaction. with: 1. large atomic/ionic radius 1. Small atomic/ionic radius 2. low or zero oxidation • According to this principle soft acids react faster and 2. High oxidation state state form stronger bonds with soft bases , whereas hard acids 3. low polarizability, 3. high polarizability, react faster and form stronger bonds with hard bases , 4. high electronegativity 4. low electronegativity, everything else being assumed aproximately equal. and and 5. energy low-lying HOMO 5. energy high-lying • The soft-soft preference is characteristic mostly of the (bases) or energy high- HOMO (bases) or reactions controlled by the orbital interaction , and the lying LUMO (acids) energy low lying LUMO hard-hard preference relates to reactions in which (acids) electrostatic factors prevail. [email protected] 2 12/22/2011 1. Equilibrium direction (reactants or products) ZnI 2 + HgCl 2 ZnCl 2 + HgI 2 CuI 2 + Cu 2O 2Cul + CuO b/lA–SB SA–HB SA–SB b/lA–HB b/lA–SB SA–b/lB b/lA–b/lB SA–SB • The I - is a soft base and Hg 2+ is a soft acid, • The I - is a soft base and O 2- is a hard base, although Zn 2+ is a b/line acid and Cl - is a since Cu + is softer acid than Cu +2 therefore b/line base (relative to Hg 2+ and I -), both the SA-SB is CuI and the HA-HB is CuO Zn 2+ and Cl - are the harder species, hence → products are favored the SA-SB is HgI 2 and HA-HB is ZnCl 2 → products are favored [email protected] 3 12/22/2011 Exercise 1 Predict the favorable species (reactants or products) in CdCI 2 + CaSO 4 CdSO 4 + CaCl 2 b/lA–b/lB HA–HB b/lA–HB HA–b/lB the following equilibrium! 1. Hg(CN) 2 + Ca(ClO 4) 2 Ca(CN) 2 + Hg(ClO 4) 2 • Both Cd +2 and Cl - are b/line acid and b/line 2. 3FeO + Fe 2S3 3FeS + Fe 2O3 +2 -2 base, while both Ca and O are hard acid 3. PbCO 3 + 2NaBr Na 2CO 3 + PbBr 2 and hard base, therefore those species in 4. MgCl 2 + AgI MgI 2 + AgCl the left are favorable, due to its stronger 5. MnS + NiF 2 NiS + MnF 2 interactions, than those species in the right 6. Ti(NO 3)2 + ZnCl 2 Zn(NO 3) 2 + TiCl 2 → reactants are favored 7. Nb 2S5 + 5HgO Nb 2O5 + 5HgS 2. Solubility of Halides and Chalcogenides + - [Ag(H 2O) n] + [Cl(H 2O) m] AgCl (s) + (m+n)H2O • Special case: the sulfides, selenides and tellurides of SA–HB b/lB–HA SA–b/lB HA–HB the soft and borderline acids are insoluble in water due to the combination of softness and some strength in Hence: bases (S 2-, Se 2- and Te 2- ions are stronger bases than We can predict that “the chlorides, bromides, and iodides of the - - - soft acids are insoluble in water ” → most of the predictions are Cl , Br and I ions) generally true for the +1 and +2 ions of the soft-acid metals, i.e: CuCl, AgCl, AuCl, TlCl, Hg 2Cl 2, OsCl 2, IrCl 2, PdCl 2, PtCl 2, and • Moreover… PbCl 2, except CuCl 2, AuCl 3, HgCl 2, PtCl 4. – for a given soft acid, the solubility of the iodide < bromide < chloride, Similar predictions of the solubility of pseudohalide salts, i.e: – similarly, for a given soft acid, the solubility of soft base → cyanide (CN), thiocyanate (SCN), b/l base → azide (-N=N +=N -) telluride < selenide < sulfide → “the cyanides, thiocyanates, and azides of the soft acids are insoluble in water ” [email protected] 4 12/22/2011 Exercise 2 • Due to the absence of soft base involvement in the • Identify all insoluble compounds and precipitation equilibrium, the HSAB principle is explain it according to HSAB principle: irrelevant to the water solubility’s prediction of the salts - - 2- from hard bases F (weak base ), OH and O (strong a. PtAs 2 e. TiO 2 bases ) → “ the fluorides, oxides, and hydroxides of acidic b. AgI f. CdTe cations are insoluble in water ” c. CaF 2 g. AgF • Because there is no soft acid is involved in the d. KI h. CoSO 4 solubility equilibrium, the solubility of the sulfides, selenides and tellurides of the hard acids cannot be predicted by the HSAB principle. 3. The Qualitative Analysis Scheme for Metal Ions • Group I → precipitated with 0.3 M HCl • Group II → precipitated with H 2S from acidic solution • Group III → precipitated with (NH 4)2S from basic solution • Group IV → precipitated with (NH 4)2CO 3 • 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 [email protected] 5 12/22/2011 Group I and II Group III • The chloride ion is a borderline base that will combine • The sulfide ion is present in much higher concentration strongly to soft acid, and if a large excess of Cl - is and also competing with another strong base plus present, only Ag +, Hg 2+ , Tl + and Pb 2+ will be much harder hydroxide ion. precipitated while others like Cu, Pd, Os, Ir, Pt and Au x- will form soluble chloro anions [MCl n] . • Only hard-acid metal ions and small group of borderline acids from the +2 ions of the 1 st row transition metals • The sulfide ion is a very soft and a stronger base than (Zn, Ni, Co, Fe, and Mn) are in the solution and will be Cl -. Therefore when it reacts with Cu, Pd, Os, Ir, Pt precipitated as sulfides . and Au , it will produce more insoluble sulfides. • The remains, which is strong - hard acid metal (also all of the f-block elements), will react with the strong – Note: the scheme should be done properly and in order!! 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 ) [email protected] 6 12/22/2011 Exercise 3 4. The Geochemical Classification and Differentiation of the Elements A new qualitative analysis scheme that separate Geochemical classification of the elements divided into cations into five existing groups using novel Primary and Secondary . The primary emphasizes precipitation anions is prepared. Choose the best behavior under condition at the surface of the earth, substitute for: which are: 1. HCl in Group I → HBr, HF, HClO, or HClO 4 • Lithophiles 2. H2S in Group II → H 2O, H 2Te, H 2SO 3, or H 2SO 4 metals and nonmetals that tend to occur as cations in 3. (NH 4) 2CO 3 in Group IV → NH 4OH, NH 4ClO 4, oxides, silicates, sulfates and carbonates. (NH 4) 2SO 4, (NH 4) 4C 4. If you want to precipitate Group V, which the anions posses oxygen as the donor atom hence the metal ions that attached are hard acid metals , compound would do this → LiOH, LiClO 4, the nonmetals are, or have been oxidized by Li 2SO 4, Li 4C. atmospheric oxygen to oxo-anions, hard bases . Natroxalate Hard Acid Metal Na 2C2O4 Natrolite Na [Al Si O ]·2H O • Chalcophiles 2 2 3 10 2 Magnesite Gypsum CaSO occur in nature as cations in sulfides (less commonly w/ MgCO 3 4 other soft bases such as telluride, arsenic, etc).