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Transition Metals and Aqueous Ions (Complexes (Ligands (Bidentate ligands,…
Transition Metals and Aqueous Ions
Properties
High Density
High melting and boiling point
Complex ions
Form coloured ions
Good catalysts
Variable oxidation states
Complexes
Complex ion
A positively charged metal ion surrounded by coordinatly bonded ligands
Coordinate bond
Dative covalent bond, a covalent bond where both of the electrons come from one atom - in complexes they come from the ligands
Ligands
An atom, molecule or ion that forms a coordinate bond with a transition metal by donating a pair of electrons. e.g. EDMA, H2O, Cl- etc
Ligands can have different amounts of lone pairs/bonding zones and thus may each be able to form more than one coordinate bond
Bidentate ligands
Forms two coordinate bonds with the metal ion
e.g. Ethane 1, 2, diamine
Monodentate Ligands
Can only form one coordinate bond
e.g. H2O, NH3 Cl-
Even though water has two lone pairs it can only form a single coordinate bond as the lone pairs are so close together
Polydentate ligands
Forms more than two coordinate bonds
e.g. EDMA4-
forms 6 coordinate bonds so only 1 EDMA per ion
Ligand substitution reactions
Enthalpy change
Entropy change
Coordination number
Number of coordinate bonds of a complex
Complex charge
Metal ion charge + total ligand charge = Complex charge
Shapes
Octahedral
VI Coordinate bonds
Tetrahedral
Usual shape for IV coordinate bonds
Square planar
Shape for IV coordinate bonds if the ligands are particularly big or there is another factor
Linear
II Coordinate bonds
Formed if the ligands are a similar size to the metal e.g. [Ag(NH3)2]
Isomerism
Optical
This is when an ion can exist as two separate non-super imposable mirror images
Can happens in octahedral complexes when 3 bidentate ligands are attached to the central ion
Cis/Trans or E/Z
Happens when 2 paired ligands can be either next to or opposite each other
e.g. Cis-platin and Trans-platin , Cis-platin is an anticancer drug, Trans-platin is toxic
Colourimetry
Colours come from the variable oxidation state
Meaning that the energy gap between the orbitals differ and so different coloured ions are produced by what wavelengths of light are absorbed
e.g. Vanadium colour change experiment
Take 50cm3 of acidified NH4 VO2
add1.5g of powdered zinc
Observe the colour changes
Identify species formed
Calculate energy of the absorbed light
Results
V2O5
+5
Yellow
Purple/dark blue
450nm
1 more item...
Species
Oxidation state
Transmitted light colour
Absorbed light colour
Wavelength of absorbed light (nm)
1 more item...
VO2
+4
Blue
Orange
600nm
1 more item...
VO+
+3
Green
Red
650nm
1 more item...
VO
+2
Purple/ Dark blue
Yellow
550nm
1 more item...
Energy of light absorbed = hc/lambda
Absorption is proportional to concentration
So graph is a straight line
As ligand is added to complex graph increases until no more ligands can fit around the complex, at this point the graph will either flatten or decrease.
Catalysis
Heterogeneous catalysis
The Contact Process
2SO2 + O2 - > 2SO3
V2O5 catalyst
SO2 + V2O5 - > SO3 + V2O4
2V2O4 + O2 - > 2V2O5
The Haber Process
N2 +3H2 - > 2NH3
Iron catalyst
Hydrogenation
Catalyst in different phase to reactants
Homogeneous catalysis
Fe2+ S2O8- and I-
S2O8- + 2I- - > 2SO2- + I2
S2O82- + 2Fe2+ - > 2SO2- +2Fe3+
2Fe3+ + 2I- - > 2Fe2+ + I2
Catalyst in same phase as reactants
Auto-catalysis
manganate (VII) ion and ethanedioate
2MnO4- + 16H+ + 5C2O42- - > 2Mn2+ + 8H2O + 10CO2
Manganate(VII) ions + hydrogen ions + ethanedioate ions - > manganese(II) ions + water + carbon dioxide
4Mn2+ + MnO42- + 8H+ - > 5Mn3+ + 4H2O
2Mn3+ + C2O42- - > 2CO2 + 2Mn2+
When a product of a reaction, catalyses the reaction itself
Catalyst poisoning
This is the partial or total deactivation of a catalyst caused by exposure to a range of chemical compounds.
May render the catalyst ineffective.
Reactions of ions in aqueous solution
Theories of acids and bases
Bronsted-Lowry theory
Acid
Proton Donor
Base
Proton Acceptor
Lewis Theory
Acid
Lone Pair Acceptor
Base
Lone Pair Donor
How transition metals can act as acids
[Fe(H2O)6]2+ is not noticeably acidic
Fe3+ is more acidic than Fe2+ and ethanoic acid
This is because it will readily accept lone pairs of electrons
Ions with different solutions
[Fe(H2O)6]2+
OH- little
Causes Hydrolysis of water forming OH- ions which replace H2O ligands until ligand charge = ion charge
[Fe(H2O)4(OH)2]
Green ppt
OH- Excess
Same as OH- Little
NH3 Little
NH3 accepts a proton, splitting up the water, forming OH- ions
[Fe(H2O)4(OH)2]
Green ppt
NH3 Excess
Water ligands are replaced by ammonia to form ammonia ligands, (rare for this to happen as ppt has to redissolve)
[Fe(NH3)6]2+
Green ppt
CO32-
Only 2+ charge thus more gentle than 3+ charge so CO32- ion stays together and a carbonate ppt is formed
FeCO3
Green ppt
[Fe(H2O)6]3+
OH- Excess
Same as OH- Little
NH3 Little
NH3 accepts a proton, splitting up the water, forming OH- ions
[Fe(H2O)3(OH)3]
Brown ppt
OH- little
Causes Hydrolysis of water forming OH- ions which replace H2O ligands until ligand charge = ion charge
[Fe(H2O)3(OH)3]
Brown ppt
NH3 Excess
Water ligands are replaced by ammonia to form ammonia ligands (rare for this to happen as ppt has to redissolve)
[Fe(NH3)6]3+
Brown ppt
CO32-
More polarising than a 2+ charge so CO32- breaks up so CO2 is released
Effervescence seen
No ppt
[Cu(H2O)6]2+
OH- Excess
Same as OH- Little
NH3 Little
NH3 accepts a proton, splitting up the water forming OH- ions
[Cu(H2O)4(OH)2]
Blue ppt
OH- little
Causes Hydrolysis of water forming OH- ions which replace H2O ligands until ligand charge = ion charge
[Cu(H2O)4(OH)2]
Blue ppt
NH3 Excess
Water ligands are replaced by ammonia to form ammonia ligands, this will happen as copper is special
[Cu(NH3)6]2+
Dark blue ppt
CO32-
Only 2+ charge thus more gentle than 3+ charge so CO32- ion stays together and a carbonate ppt is formed
CuCO3
Blue ppt
Cl-
Cl- ions replace H2O ligands
[CuCl4]2-
yellow ppt
[Al(H2O)6]3+
OH- Excess
Same as OH- Little
NH3 Little
NH3 accepts a proton, splitting up the water, forming OH- ions
[Al(H2O)3(OH)3]
White ppt
OH- little
Causes Hydrolysis of water forming OH- ions which replace H2O ligands until ligand charge = ion charge
[Al(H2O)3(OH)3]
White ppt
NH3 Excess
Water ligands are replaced by ammonia to form ammonia ligands (rare for this to happen as ppt has to redissolve)
[Al(NH3)6]3+
White ppt (amphoteric)
CO32-
More polarising than a 2+ charge so CO32- breaks up so CO2 is released
Effervescence seen
No ppt
