Transition Metals Flashcards
Colour change arises from a change in (what affects delta E)
- Oxidation state
- Co-ordination number
- Ligand
Delta E equation
Energy gap between d orbitals
=hv or =hv/λ
Uses of EDTA
Medicinal
Treat patients with lead poisoning -chelation therapy. Makes toxins harmless
Complexometric titration
Calculate concentration of metal ions in solutions. Always a 1:1 ratio so moles of EDTA used = moles of metal ion present
Indicator is used (inorganic dye)
Shows 1 colour when ligand, 1 colour when not
-M-
Co-ordination number of 2
180 degrees
Occurs in Ag+ complexes
Characteristics of transition metals
- Complex ion formation surrounded by ligands
- Variable oxidation states
- Catalytic activity
The chelate effect
Bidentate or multidentate ligands substitute monodentate ligands to create a more stable complex in a ligand substitution reaction
Positive delta S so more stable
Chelating agents remove harmful metal ions in solutions
optical isomerism in bidentate ligands
octahedral complexes with bidentate ligands show optical isomerism
> M<
4 co ordinate bonds
90 degree bond angle
occurs in Pt 2+ and Ni 2+ complexes
|
M
/|\
4 co ordinate bonds
109.5 degrees
when ligands are too big to fit 6
Cl-
method of determining concentration of transition metal ion
add ligand to intensify colour
set the wavelength to max
standard solutions of known concentrations
measure absorbance
graph- absorbance v. concentration
measure absorbance of unknown
catalyst poisoning
Impurities can adsorb strongly to the surface of the catalyst, blocking the active sites.
this lowers its effect or makes it completely unusable
poisons are difficult to remove
Haber process
N2(g)+3H2(G)<->2NH3(G)
Fe(s) heterogenous catalyst
contact process
vanadium oxide catalyst: V2O5(S)
1. V2O5+SO2->V2O4+SO3(G)
reform catalyst
V2O4+1/2O2->V2O5(S)
Overall: SO2(G)+1/2O2(G)_>SO3(G)
Reaction between iodide and persulfate ions
example of homogeneous catalyst
High activation energy as both reactants are negative. Harder to collide
Fe2+ catalyst lowers the activation energy as oppositely charged
S2O8,2-+2Fe2+->2SO4,2-+2Fe3+
2I-+2Fe2+->I2+2Fe2+
overall
S2O82-+2I-,->2SO4,2-+I2
Autocatalysis
ethanedioate and manganate ions
-one of the products is a catalyst
-reactions start slowly until catalyst produced
MnO4-+8H+,+5e-,->Mn2+,+4H2O
Mn2+->Mn3+,+e-
5Mn2+,+MnO4-+8H+->Mn2+,+5Mn3+,+H2O
but you need to simplify it
C2O4-,->2CO2+e-
Mn3+,+e-,->Mn2+
C2O4-+2Mn2+->2CO2+Mn2+
Maximising efficiency of catalyst
Maximise surface area to reduce cost
surface area maximised by using a very thin coating on some type of support medium like a ceramic honeycomb
How do catalysts work?
Reactants are adsorbed onto active sites on the catalyst surface
the reaction occurs with a lower activation energy as bonds are weakened or new bonds are made between reactants held close together
products are desorbed
Why do transition metals change colour
Partially filled d sublevel
d orbitals split in energy levels
d electrons can be promoted to a higher energy by absorbing light energy
colour transmitted is light not absorbed
gap between is delta e
