CH23 Transition metals Flashcards
Define a transition metal
An element which forms at least 1 stable ion with a partially full d-shell of electrons
Physical properties of transition metals
Metallic Good conductors of heat and electricity Hard - strong - shiny High MP and BP Low reactivity
Uses of Iron
Vehicle bodies
Reinforce concrete
Uses of titanium
Jet engine parts
Uses of copper
Water pipes
Chemical properties of transition metals
Variable oxidation states
Coloured
Good catalysts
Form complex ions
Define complex ion
Central transition metal surrounded by ligands that are co-ordinate bonded to it
Example of transition metals as catalysts
Iron - Haber process
Vanadium (V) oxide - Contact process
MnO2 - decomposition of H2O2
Which electrons do transition metals lose first when forming ions
4s
Define ligand
An ion or molecules with at least 1 pair of electrons, that donates them to a transition metal ion to form a co-ordinate bond and thus a complex ion
Define monodentate ligand
A ligand that forms one co-ordinate bond to the central metal ion
Define bidentate ligand
A ligand that forms 2 co-ordinate bonds to the central metal ion
Define multidentate ligand
A ligand that forms 3 or more co-ordinate bonds to the central metal ion
Examples of monodentate ligands
Cl-
H2O
NH3
CN-
How many co-ordinate bonds does EDTA4- form
6
Define coordination number
The number of co-ordinate bonds the metal ion has formed to surrounding ligands
What is the Chelate effect
Chelate complexes with multidentate ligands are favoured over ligands with fewer co-ordinate bonds per molecule
Explain Chelate effect in terms of entropy
Number of molecules increases when multidentate ligands, displace ligands that form fewer co-ordinate bonds per molecule
Significant increase in entropy and a more stable complex ion is formed
What ion is formed when a transition metal dissolves ion water
Aqua ion
6 H2O ligands
Octahedral complex ion
If a transition metal has 2 ligands what shape is it
Linear
If a transition metal has 4 ligands what shape is it
Tetrahedral
Exception to 4 ligand rule
Platin - square planar in cisplatin
If a transition metal has 6 ligands what shape is it
Octohedral
How can complex ions display E-Z isomerism
Ligands differ in the way that they are arranged in space. Same side or opposite sides of the metal ion
Applies to square planar and octahedral complex ions
What happens to Co2+, Cu2+ and Fe3+ when Cl- ligands replace NH3 or H2O
Decreases from 4 to 6 as Cl- is much larger
What is haem
A molecules that makes up protein chains
Fe2+ metal ion
Coordination number of 6
How does haemoglobin transport O2
O2 forms weak coordinate bond
Bond breaks when cell is reached
Why is CO toxic
Also bonds coordinately to Fe2+
Stops O2 from bonding
Why are transition metals coloured
Partially filled d-orbitals, electrons move between d-orbitals
d-orbitals can split into energy levels
Electrons absorb energy in form of photons and turn into an excited state moving to a higher energy level
Energy of photon related to freq of light E = hf
How to calculate ΔE from f and / or λ
ΔE = hf = hc / λ
What affects colour of transition metal
ΔE affects frequency of absorbed photons, so determines colour
ΔE is changed by oxidation state of the metal, number and type of ligands, shape and co-ordination number
Oxidation number and colour for VO2 +, VO2+, V3+, V2+
VO2 + ==> 5+ , Yellow
VO2+ ==> 4+, Blue
V3+ ==> 3+, Green
V2+ ==> 2+, Violet
What is used to reduce vanadium
Zinc
What colour is Fe2+ aqua ion
Green
What colour is Fe3+ aqua ion
Pale brown
What colour is Cr2+ aqua ion
Blue
What colour is Cr3+ aqua ion
Red / violet
What colour is Co2+ aqua ion
Brown
What colour is Co3+ aqua ion
Yellow
What does a colorimeter do
Measures absorbance of a particular wavelength of light by a solution
How would you use colorimetry experimentally
Use solutions of known concentration to create a calibration graph; find unknown concentration
What information can a colorimeter provide
Concentration of a certain ion
Why can transition metals have variable oxidation states
They have partially filled d-orbitals, so can lose 4s and 3d electrons
Which oxidation states do all transition metals have (except Sc) - why
+2 - Loss of electrons from 4s orbital
When oxidation state is high, do transition metals exist as simple ions
No, they covalently bond to other species
Use of complex [Ag(NH3)2]+ ion
Tollen’s reagent to test for aldehydes / ketones
What colour is MnO4-
Deep purple
What colour is Mn2+
Pink
Why are redox titrations with transition metals said to be self indicating
Usually involve a colour change due to change in oxidation state
What colour is Cr2O7 2-
Orange
What colour is Cr3+
Green
What happens to aqua metal ions in acidic conditions
They get reduced
What happens to aqua metal ions in alkaline conditions
They get oxidised
What happens to aqua metal ions in neutral conditions
No change
What does; whether reduction / oxidation occurs and the readiness of the raction depend on
E° values
What can change these E° values
pH, ligands involved
Define a catalyst
A substance that increases the rate of reaction without being chemically changed at the end of the reaction
How do catalysts work
Provide an alternative reaction pathway with a lower activation energy
Why are transition metals good catalysts
Exist in variable oxidation states, easily provide alternative pathways
Why are group 1, 2 and 3 metals not good catalysts
Only exist in 1 oxidation state
What are advantages of using a catalyst for a reaction
Allows reactions to proceed at lower temperatures and pressures
What are used in a catalytic converter and which reactions do they catalyse
Platinum, Rubidium, Palladium
Catalyse CO and NO to CO2 and N2
Define heterogenous catalyst
A catalyst that is present in the reaction in a different phase to the reactants
Catalytic activity occurs on the solid surface as the reactants pass over it
Advantage of using a heterogenous catalyst
No need for separation of products from catalyst
How do heterogenous catalysts work
Reactants adsorb to the catalysts surface at active sites
Weaken bonds within the reactants, holds reactants close together on surface to react
Once reaction occurs products desorb
What properties does the catalyst need to have
Can’t adsorb too strongly - no release
Can’t adsorb too weakly - no attachment
How can you increase the efficiency of heterogeneous catalysts
Increase SA to increase number of active sites present
Also spread onto an inert support medium to increase surface area:mass ratio
What is catalyst poisoning
Unwanted impurities adsorb to the catalyst’s active sites and do not desorb
What effect does this have
Decreases effectiveness of catalyst over time
How else can a catalyst be degraded
Finely divided catalysts can be gradually lost from their support medium
What is in the Haber process
Makes ammonia from nitrogen and hydrogen
Fe catalyst
Size and shape of catalyst for Haber process
Pea sized lumps to increase SA
How long until catalyst is poisoned in Haber cycle
5 years - poisoned by sulfur impurities in gas stream
What is the Contact process
Makes H2SO4 from SO2 and O2
Vanadium (V) oxide catalyst
Why is V a good catalyst
Can change oxidation state
Define homogenous catalyst
A catalyst in the same phase as the reactants
How do they work
Form intermediates to give a reaction with lower activation energy
Define autocatalysis
When a product of a reaction is also a catalyst
