Transition Metals Flashcards
Transition metal definition
Forms at least one stable ion with a partially filled d sublevel
Transition metal features
Form complex ions
Coloured ions
Catalytic properties
Variable oxidation states
Mono dentate ligands
Each ligand forms 1 coordinate bond
Bidentate ligands
Each ligand forms 2 coordinate bonds
Multidentate ligands
Each ligand forms 2 or more coordinate bonds
Need to know monodentate ligands
Water h2o:
Chloride cl-:
Ammonia :nh3
Cyanide :c-n
Need to know bidentate ligands
NH2ch2ch2nh2
Coordinate bonds from the lone pairs on the 2 n
C2o42-
Bonds form between 2 o- atoms
EDTA4-
Can form six coordinate bonds
Two from n atoms
Fourth from o- atoms
Chelate effect
Large increase in entropy
When does chelate effect occur
When a monodentate ligand is substituted by a bidentate or multidentate ligand
Number of moles increase so entropy change is positive
Why reaction is thermodynamically favourable
Use gibs equation
>h is zero as six n bonds broken and six n bonds made
<s is positive as entropy change is positive
G<0 so reaction is feasible
Heamoglobin
Can make six coordinate bonds
Four between fe2+ and n
One between fe 2+ and globin protein
Space for one more with oxygen
When oxygen has been transported bond is broken and co2 forms a bond to brung back to the lungs
Co makes a stronger bond so could permanently bind which is co poisoning
If ligands are next to each other
Cis isomers
Can show optimal isomerism if at least 2 bidentate ligands present
If ligands are not next to each other
Trans isomers
Visible light
Some colours from white light are absorbed and some transmitted through
Transmitted colours combine to make the visible colour
Process of absorbing and transmitting light
The d orbitals split in energy levels
D electrons are promoted to a higher d orbital by absorbing energy in the form of light
The colour transmitted through and observed is the light not absorbed by the compound
Equation for change in energy
Change in energy = h(Planck constant 6.26x10-34) x f(frequency of light)
Change in energy = h x c/l
C=speed of light
L= wavelength of light
Large change in energy between d subshells
High energy light absorbed to excite electrons (blue and purple)
Red/orange transmitted through
Small change in energy between d subshells
Low energy light will be absorbed to excite electrons (red and orange)
Blue and purple will be transmitted
Change in colour
Transition metal compounds can change colour
Can be caused by
Change in ligands
Change in oxidation state
Change in coordination number
Change in shape of a complex
Calorimetry
Measure the amount of light absorbed when it passes through a sample
Heterogenous catalysts
Catalysts is in a different phase to the reactants
Reactants adsorb onto surface of the catalyst
Reaction occurs on the surface of catalyst
Products desorb from surface of the catalyst
Catalysts are expensive so
Make it more efficient by increasing surface area or spread catalyst over an inert support medium
Catalyst poisoning can happen though as impurities can block the active sites
Need to know heterogenous catalyst examples
Ammonia in haber process
N2 + 3h2 <-> 2nh3
Catalysed by solid iron
Making sulfur trioxide in the contact process
Catalysed by vanadium oxide v2o5
2so2 + o2 <-> 2so3
Steps
1-so2 + v2o5 <-> so3 + v2o4
2-2v2o4 + o2 <-> 2v2o5
Homogenous catalysts
Catalysts and reactants are in the same phase
S2o82- + 2I- -> 2so42- + I2
Catalysed by fe2+ ions
1-2fe2+ + s2o82- -> 2so42- + 2fe3+
2- 2fe3+ +2I- -> I2 + 2Fe2+
These could happen in either order
Autocatalyst
Where a product of the reaction catalysts the reaction further
16H+ + 2mno4- + 5c2o42- -> 2mn2+ + 8h2o + 10co2
Mn2+ catalyse the reaction further
4mn2+ mno4- + 8h+ -> 5mn3+ + 4h2o
2mn3+ + c2o42- -> 2co2 + 2mn2+
Potassium manganate reactions
8h+ + mno4- + 5fe2+ -> mn2+ +4h2o + 5fe3+
When using in titration ratio is always 1:5
Reducing vanadium(v) to vanadium(IV)
Zn + 4h+ + 2vo2+ -> zn2+ 2vo^2+ + 2h2o
Yellow to blue
Can look green if there’s some left
Reducing vanadium(V) to vanadium(III)
Zn + 4h+ + vo2+ ->zn2+ + v3+ + 2h2o
Yellow to green
Reducing vanadium (V) to vanadium(II)
3Zn + 8h+ + 2vo2+ -> 3Zn2+ + 2v2+ + 4h2o
Yellow to purple
