marvellous metals
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Marvellous Metals. Nyholm Lecture 2002 Professor Tony Baker & Dr Linda Xiao Faculty of Science, UTS. Sir Ronald Nyholm 1917-1971. Coordination Chemist Inspiring Chemical Educator Leader of the Profession. Sponsorship. - PowerPoint PPT PresentationTRANSCRIPT
Marvellous Metals
Nyholm Lecture 2002
Professor Tony Baker & Dr Linda Xiao
Faculty of Science, UTS
Sir Ronald Nyholm 1917-1971
Coordination Chemist
Inspiring Chemical Educator
Leader of the Profession
Sponsorship
The Royal Australian Chemical Institute (RACI) www.chem.unsw.edu.au/raci
Crown Scientific
APS
Marvellous Metals: the Lecture
Redox Chemistry
Spectra and Spectroscopy
Coordination Chemistry
Redox Chemistry
• Many reactions can be classified as redox reactions.
• These are reactions in which the oxidation numbers of the elements involved change
Example: Redox Chemistry
• An acidified solution of permanganate ions reacts with hydrogen peroxide to give dioxygen gas:
2 MnO4- + 6 H+ + 5 H2O2
2 Mn2+ + 8 H2O + 5 O2
Mn +7 +2; O (in peroxide) –1 0
Vanadium
• Vanadium is a transition element that displays a maximum oxidation state of +5 (eg in the oxide V2O5).
• Named after Vanadis, the Norse goddess of beauty because of the beautiful colours in solution
• Used in high strength steels
Vanadium reduction: demo
Initial: solid NH4VO3
Acidification:VO3
- + 2 H+ VO2+ + H2O
Reduction (Zn as reductant):VO2
+ + 2 H+ + e- VO2+ + H2O
VO2+ + 2 H+ + e- V3+ + H2O
V3+ + e- V2+
Vanadium Application
• Sulfuric Acid Manufacture:
SO2 (g) + ½ O2 (g) SO3 (g)
• Vanadium(V) oxide catalysts are used in this process.
• Sulfuric acid: 150 million tonnes produced each year.
Other redox processes
The rusting of ironBatteriesElectrolysis to purify metalsUsing reductants to liberate
metals from ores
Photoreduction: Blueprint
• Blueprints (an early form of copying) were first made around 1840
2 [Fe(C2O4)3]3- 2 Fe2+ + 2 CO2 + 5 C2O4
2-
(K+ +) Fe2+ + [Fe(CN)6]3- Prussian Blue
• The pigment Prussian Blue has been known since 1704
More on Prussian Blue
Fe3+ + [Fe(CN)6]4- Prussian Blue
Fe2+ + [Fe(CN)6]3- Turnbull’s Blue
Found to have same spectra / XRD.Colour arises from charge transfer:Fe3+ + e Fe2+ (max 700nm).
Probable formula: Fe(III)4[Fe(II)(CN)6]3.15H2O
Spectra and Spectroscopy
• Spectrum: solar spectrum, rainbow
• Plot of radiation intensity vs. wavelength / frequency
• May be absorption or emission
Uses of Spectroscopy
• Identification• Quantification• Study bonding / energy
levelsX-ray: inner shell electronsUV-Vis: outer shell electronsIR: molecular vibrationsMicrowave: rotations
Vanadium check-up
VO2+ yellow
VO2+ blue
V3+ green
V2+ violet
Emission Spectra
EmissionhνE2E1
Flame tests
LithiumSodium PotassiumCalciumStrontiumBariumCopper
Flame tests
• The thermal energy is enough to shift electrons to higher energy levels (excited state).
• The electron returns to a lower energy level with emission of visible radiation.
Absorption spectra
AbsorptionhνE2E1
Absorption: demonstration
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
500 550 600 650 700 750 800 850
Wavelength (nm)
Absorbance
Absorption and colour
• The copper solution appears blue and absorbs red light.
• Under white light illumination some wavelengths are absorbed and some are reflected / transmitted.
• The object / solution has the complementary colour to the radiation absorbed.
Atomic absorption
• Atoms in the ground state will absorb radiation that promotes electrons to an excited state.
• The amount of radiation absorbed is proportional to the the number of atoms present.
• This concept is the basis of Atomic Absorption Spectroscopy (AAS).
AAS: schematic diagram
LightsourceFlameDetector
hνE2E1 hνE2E1
AAS: Australia’s contribution
• Alan Walsh had worked on emission spectra and molecular spectroscopy.
• Demonstrated possibility of AAS in early 1952.
• Developed commercially by CSIRO and Australian instrument manufacturers
AAS: application
• AAS was long considered the best technique for trace metal analysis.
• Detection Limits (ppb):Cd 1Cr 3Cu 2Pb 10V 20
Vanadium: one more time
VO2+ yellow
VO2+ blue
V3+ green
V2+ violet
Coordination Chemistry
….it is correct to say that modern inorganic chemistry is, especially in solution, the study of complex compounds.
Nyholm, The Renaissance of Inorganic Chemistry, 1956
Dissolution of a salt
• Water binds to ions at edges of lattice
• When bonds to water are stronger than bonds to ions, the ion enters solution
OHHNaOHH+
Examples
• Nickel(II) ions in solution: Ni2+(aq).
• Species in solution is [Ni(H2O)6]2+.
• Other examples would include [Cu(H2O)6]2+, [Fe(H2O)6]3+, etc.
OH2NiOH2OH2OH2H2OH2O2+
Shapes of Complexes
6-coordinate: Octahedral
4-coordinate: Tetrahedral
Demonstration:[Co(H2O)6]2+ + 4 Cl-
[CoCl4]2- + 6 H2O
Changing shapes: demo
[Co(H2O)6]2+ + 4 Cl- [CoCl4]2- + 6 H2O
pink blueOH2CoOH2OH2OH2OH2OH2ClCoClClCl2-2+OCTAHEDRALTETRAHEDRAL
Coordinate Bond
• Many molecules and ions have lone pairs of electrons (eg NH3) and can act as electron pair donors (Lewis bases).
• Transition metal ions can have vacant orbitals and can accept electron pairs (Lewis acids).
Ligands
• The molecules or ions that bind to a metal ion are known as ligands.
• Many ligands are known ranging from monoatomic ions such as chloride to huge protein molecules.
• Examples include NH3, H2O, NH2CH2CH2NH2 (diaminoethane, a chelating ligand), SCN- (thiocyanate)
Nickel(II) Complexes: Demo
[Ni(H2O)6]2+ green
[Ni(NH3)6]2+ blue
[Ni(NH2CH2CH2NH2)3]2+ blue-purple
[Ni(dmg)2] red
Colours of Metals Complexes
• In an octahedral complex, the d orbitals are split into two energy levels separated by a gap o.
• The size of o depends on the nature of the ligand.
egt2go
Differing interactions
• Different metals react in different ways with the same ligand.
• One example is the difference in interaction of Ni2+ and Co2+ with SCN-.
• In the case of cobalt a stable complex ion is formed [Co(SCN)4]2- which is soluble in some organic solvents.
Demonstration
• A mixture of Ni2+ and Co2+ is treated with excess SCN-.
• 2-Butanone (CH3COCH2CH3) is used to extract the reaction mixture.
• Nickel ions remain in the aqueous phase and cobalt ions (as [Co(SCN)4]2-) are extracted into the organic phase.
Application
• Many extractive metallurgical processes depend on different metals interacting in different ways with ligands.
• Copper can be purified through a solvent extraction technique.
• Treatment of 107 tonnes per year of low grade tailings (1%) recovers a further 105 tonnes of copper.
Thermite: Return to Redox
• The thermite reaction can be used for such applications as welding in remote locations and depends on the activity of aluminium.
• Aluminium powder and iron oxide are mixed together and the reaction is started with burning Mg ribbon.
• Highly exothermic reaction!
Thermite Thermodynamics
Reaction H (kJ mol-1)
2 Al(s) + 3/2 O2(g) Al2O3(s) -1676
Fe2O3(s) 2 Fe(s) + 3/2 O2(g) 824
2Al(s) + Fe2O3(s) Al2O3(s)+ 2Fe(s)
-852