transition metals [I2] PAPER 1 Flashcards
Explain why complexes formed from transition metal ions are coloured.
• absorbs wavelengths of visible light, which excites electrons in d-orbitals
• remaining wavelengths of visible light are reflected
Copper(I) iodide is a white solid. Explain why copper(I) iodide is white.
• full d shell
• no d-d transitions possible / cannot absorb visible light
what is a transition metal?
incomplete d shell
general properties of a transition metal?
• form complexes
• form coloured ions
• have variable oxidation states
• good catalysts
what is a ligand?
molecule/ion that forms a co-ordinate bond with a transition metal by donating a pair of electrons
what is a complex?
a central metal atom/ion surrounded by ligands
what is co-ordination number?
number of co-ordinate bonds to the central metal atom/ion
examples of some monodentate ligands?
H2O, NH3, Cl–
why does a change in coordination number arise when the ligands NH3/H2O are exchanged with Cl– ?
Cl– ligand is larger than NH3/H2O ligand
examples of bidendate ligands?
• H2NCH2CH2NH2
• C2O4–
example of a multidentate ligand?
EDTA4–
what is the chelate effect?
• bidentate/multidentate ligands replace monodentate ligands in a ligand substitution reaction
• in ligand substitution reactions, a positive entropy change is favoured and is achieved in this way (hence the reaction is more feasible), since it means a more stable complex is formed
example of a complex with multidentate ligands?
• haem - iron (II) complex with a multidentate ligand
why is carbon monoxide toxic?
• oxygen forms a co-ordinate bond to Fe (II) in haemoglobin, which allows oxygen transport in the blood
• carbon monoxide replaced oxygen that is co-ordinately bonded to Fe (II) in haemoglobin
what shape are the complexes commonly formed by transition metals with small ligands, e.g. H2O and NH3 ?
octahedral
octahedral complexes can display _____ isomerism with monodentate ligands
cis-trans
octahedral complexes can display _____ isomerism with bidentate ligands
optical
what shape are the complexes commonly formed by transition metals with larger ligands, e.g. Cl– ?
tetrahedral
Ag+ always forms ____ complexes
linear
what complex of Ag+ is used in Tollens’ reagent?
[Ag(NH3)2]+
an exchange in ligands in a complex is a ____ reaction
ligand substitution
why is the overall enthalpy change for ligand substitution reactions near zero?
same/very similar number and type of bond being broken and made
platinum and nickel form ____ complexes, e.g. _____
• square planar
• cisplatin
The energy difference between the ground state and the excited state of the d electrons is given by:
ΔE = hv = hc/λ
• ΔE = energy difference
• h = Planck’s constant
• c = speed of light
• v = frequency
• λ = wavelength
what can lead to a change in colour of a complex?
• change in oxidation state
• change in ligand
• change in co-ordination number
how are different species of vanadium with variable oxidation states formed?
oxidation of vanadium by zinc in acidic solution
vanadium oxidation states and colours?
acidity of transition metal complex ions in aqueous solution?
greater charge density of the metal ion means they polarise water molecules more, so more O–H bonds in ligands break to release H+ ions, lowering the pH
what is a multidentate ligand?
molecule/ion that forms many co-ordinate bonds with the central metal ion
what is a bidentate ligand?
molecule/ion that forms two co-ordinate bonds with the central metal ion
what is a monodentate ligand?
molecule/ion that forms one co-ordinate bon with the central metal ion
Describe how a calibration graph is produced and used to find the concentration of the iron(Ill) complex.
• measure absorbance for a range of known concentrations
• plot graph of absorbance (y axis) against concentration (x axis)
• read value of concentration for the measured absorbance from this graph
B as only one with an incomplete d shell
A - no lone pair
Solution A contains the compound [Cu(H2O)6]Cl2.
State why the chloride ions in this compound are not considered to be ligands.
chloride ions isn’t forming a co-ordinate bond to Cu2+
how can vanadium be reduced from oxidation states 4, to 3, then 2?
reduction of vanadate (V) ions by zinc in acidic solution
redox titration equations for Fe2+ and C2O4- with MnO4- ?
what is a heterogeneous catalyst?
a catalyst that is in a different phase from the reactants
How does iron act as a heterogeneous catalyst in the Haber process?
• reactants adsorb onto the surface / active sites of iron
• bonds weaken and the reaction takes place
• products desorb from the surface of the iron
factors that affect the lifetime and efficiency of a catalyst?
• large surface area by using powder/ small pellets/support medium
• catalyst poisoned (e.g. sulfur binds to the catalyst) - blocks the active site
two negative ions repel, so activation energy is high
Give a reason why Zn2+ ions do not catalyse the reaction.
Zn ions have only one oxidation state
what colour is MnO4– ?
deep purple
what colour is Mn2+ ?
pink
why are transition metals with transition metal compound said to be self-indicating?
usually involves a colour change as metal is changing oxidation state
what happens to aqua metal ions in acidic conditions?
they get reduced
what happens to aqua metal ions in alkaline conditions?
they get oxidised
the redox potential for a transition metal changing from a higher to lower oxidation state is influenced by…
• pH
• ligand
why are transition metals good catalysts?
exist in variable oxidation states, so provide alternative pathways easily
advantage of a heterogeneous catalyst?
no need for separation of products from the catalyst
two reactions in the Contact process, which is catalysed by vanadium (V) oxide, V2O5 ?
overall reaction: 2SO2 (g) + O2 (g) → 2SO3 (g)
what is a homogeneous catalyst?
a catalyst that is in the same phase as the reactants
how do homogeneous catalysts work?
form intermediates to give a different reaction pathway with a lower activation energy
what is autocatalysis?
when the product of the reaction is also a catalyst for the reaction
what is the colour change seen at the end point of a redox titration of Fe2+ with MnO4– ?
colourless to pink
• reactants adsorbed onto platinum surface
• bonds weaken on the surface - reaction occurs
• desorption of the product
