23 - The transition metals Flashcards
Define a transition metal.
An element which gives an ion or atom with an incomplete d sub-level
Give the four characteristics of transition metals.
- Complex formation
- Variable oxidation states
- Formation of coloured ions
- Catalytic activity
Define a ligand.
A molecule or ion which forms a co-ordinate bond with a transition metal by donating a pair of electrons.
Define a complex.
A central metal atom or ion surrounded by ligands.
Define co-ordination number.
Number of co-ordinate bonds to the central metal atom or ion.
Give three monodentate ligands.
H2O, NH3, Cl-
Compare the size and charges of Cl-, NH3 and H2O.
- Cl- is larger than NH3 and H2O
- NH3 and H2O are non-charged, whereas Cl- is negative
Give two bidentate ligands.
- H2NCH2CH2NH2 (ethandiamine)
- C2O4 2-
Give a multidentate ligand.
EDTA 4-
What is haem?
Iron (II) complex with a multidentate ligand.
How is haemoglobin formed?
Oxygen forms a co-ordinate bond to Fe (II) in haemoglobin, which allows oxygen to be carried in the blood.
Why is CO toxic?
Replaces oxygen co-ordinately bonded to Fe (II) in haemoglobin.
Describe and explain the chelate effect.
- Multidentates replace bidentates which replace monodentates.
- This is because the entropy is increased
- Complex + multidentate –> Complex + 6 monodentates
What shape do complexes with small ligands commonly form?
Octahedral –> it’s like 6 bonding pairs but they’re ligands instead
What forms of isomerism are displayed by octahedral complexes?
- Monodentates –> cis-trans isomerism
- Bidentates –> optical isomerism
What shape do complexes with larger ligands, such as Cl-, commonly form?
Tetrahedral
Give the formula of the complex found in Tollen’s reagent.
[Ag(NH3)2]+
What shape does cisplatin form?
Square-planar
How does colour arise?
Some light is absorbed, some is reflected/transmitted.
When light is absorbed, d electrons move from ground state to excited state.
Give the equation for the difference in energy between ground state and excited state.
E change = hv = h(c/lamda)
h = Planck’s constant
v = frequency (units s-1)
c = speed of lights (m s-1
lamda = wavelength of absorbed light (m)
What causes a colour change?
Change in oxidation state
Change in co-ordination number
Type of ligand
Describe the process of spectroscopy.
Add an appropriate ligand to intensify colour
*Make up solutions of known concentration
*Measure absorption or transmission
*Plot graph of absorption vs concentration
*Measure absorption of unknown and compare
How is Vanadium (V) reduced by the addition of acidified zinc?
VO2^+ (5) –> VO^2+ (4) –> V^3+ (3) –> V^2+ (2)
What colours are vanadium ions?
5+ is yellow
4+ is blue
3+ is green
2+ is violet
What is the redox potential for a transition metal ion changing from a higher to lower oxidation state influenced by?
The redox potential for a transition
metal ion changing from a higher to a
lower oxidation state is influenced by
pH and by the ligand.
Give half equations equations for the use of Tollen’s reagent to distinguish between ketones and aldehydes.
Red: [Ag(NH3)2]+ + e- –> Ag + 2NH3
Oxi: CH3CHO + H2O –> CH3CO2H + 2H+ + 2e-
Give the ionic equation between MnO4- and Fe2+ in a titration.
MnO4- + 8H+ + 5Fe2+ –> MN2+ + 4H2O + 5Fe3+
Give the overall equation for the reaction between MnO4- and ethanedioate.
2MnO4- + 16H+ + 5C2O4- –> 10CO2 + 2Mn2+ + 8H2O
Give two types of catalyst.
- Homogenous
- Hetrogenous
What is a hetrogenous catalyst?
Different phase from the reactant
Where do reactions involving a hetrogenous catalyst occur?
On the surface of the solid catlyst
What is a support medium, and how does it work?
A support medium increases the surface area of a solid catalyst. For example, the usage of a Rb catlyst supported on a hexagon frame to increase SA.
Give equations to describe the use of vanadium as a catalyst in the Contact Process.
- SO2 + V2O5 –> SO3 + V2O4
- 2V2O4 + O2 –> 2V2O5
Overall: 2SO2 + O2 –> 2SO3
Which process does Fe (II) catalyse?
Name, equation, type of catalyst
Haber
N2 + 3H2 –> 2NH3
Hetrogenous
What is catalytic poisoning?
Hetrogenous catalysts active sites are blocked by impurities
Activity reduced
Cost implication
Define a homogenous catalyst.
Same state as reactants
How do hetrogenous catalysts work?
Reaction proceeds through an intermediate species. That being the catlysts will be changed oxidation state, and then reform its original oxidation state.
Give equations to explain how Fe2+ catalyses the reaction between I- and S2O8^2-.
S2O8^2- + 2Fe2+ –> 2SO4^2- + 2Fe3+
2I- + 2Fe3+ –> 2Fe2+ + I2
Define autocatalysis.
One of the products of the reaction can act as a catalyst and increases the rate of reaction.
Give the equations for the reaction of MnO4- and C2O4-, including autocatalysis using Mn2+.
- 4Mn2+ + MnO4- + 8H+ –> 5Mn3+ + 4H2O
- 2Mn3+ + C2O4- –> 2Mn2+ + 2CO2
Why are some reactions very slow? (2)
Specifically two negative ions
- Negative ions repel
- Increases activation energy
Explain why an aqueous solution containing [Fe(H2O)6]3+ ions has a lower pH than an aqueous solution containing [Fe(H2O)6]2+ ions. (4)
Fe3+ has a greater charge density
Fe3+ ions polarise water molecules more
O-H bond in water ligands is weakened
More H+ ions are released
How does a hetrogenous catalyst work?
Reactants adsorb onto surface
Weakens bonds
Products desorb from surface
