Transition Metals Flashcards
What is a transition metal?
A metal that can form one or more stable ions with an incomplete d sub-level
What is the electron configuration of:
Ti
V
Cr
Mn
Fe
Co
Ni
Cu?
Ti: [Ar]3d2,4s2
V: [Ar]3d3,4s2
Cr: [AAr]3d5,4s1
Mn: [Ar] 3d5,4s2
Fe: [Ar] 3d6,4s2
Co: [Ar] 3d7,4s2
Ni: [Ar] 3d8, 4s2
Cu: [Ar] 3d10, 4s2
Why are Scantium and zinc not transition metals?
As their stable ions don’t have incomplete d sub-levels
-Sc3+ has an empty d sub level
-Zn2+ has a full d sub level
What are the physical properties of the transition metals?
High density
High melting and boiling points
What are the chemical properties of transition metals?
Form complex ions
Form coloured ions
Good catalysts
Exist in variable oxidation states
What is a complex ion?
A metal ion surrounded by co-ordinately bonded ligands
Define co-ordinate bond and ligand:
Co-ordinate bond: covalent bond in which both electrons in shared pair come from same atom
Ligand: an atom, ion or molecule that donates a pair of electrons to a central metal ion
Define monodentate, multidentate and bidentate:
Mono- only form one co-ordinate bond
Bi- form two co-ordinate bonds
Multi- more than one co-ordinate bonds
Define Lewis base and Lewis acid:
Base- lone pair donor
Acid- lone pair acceptor
What shape is a complex with a co-ordination number of 2?
Linear, common with Ag+ complex
What is the shape of a complex with co-ordination number of 4?
Square planar with Pt2+ and Ni2+ complexes
Tetrahedral with larger ligands (e.g Cl-) as too big for 6 to fit
What is the shape of a complex with a co-ordination number of 6?
Octahedral, common with small ligands (e.g H2O and NH3)
What is the structure of haemoglobin?
4 Fe2+ centres, each with a porphyrin ligand, taking up 4 of the 6 co-ordination sites
One of the other four sites is bonded to the rest of haemoglobin leaving one site free for oxygen to bond
Why do CO and CN- bond to haemoglobin instead of O2?
O2 is not a particularly good ligand and so easily comes off the iron
CN- and CO are better ligands and so bond in preference to O2. This is why they’re toxic as prevent the transport of O2 around the body
What is a ligand substitution reaction?
Where one ligand is replaced by another ligand
What is partial substitution?
When only some of the ligands are replaced
What happens when ligands are substituted by smaller/bigger ligands?
Co-ordination number may change.
If bigger ligands, then fewer fit round molecule
What is the Chelate effect?
Substitution of unidentate ligands with bi- or multidentate ligands leads to a more stable complex because reaction results in an increase in entropy
What are ligands that form more than one co-ordinate bond sometime called?
Chelating agents as very good at bonding to metal ion and very difficult to remove so renders the metal ion harmless, e.g. EDTA4-
Why are reactions where ligands are replaced by those that form more co-ordinate bonds feasible?
because ∆H is negligible and ∆S very positive so ∆G is very negative and reaction is feasible
Why do electrons in transition metals absorb UV/visible light?
To provide energy to promote electrons to higher energy levels
What is the equation to measure gap in energy?
∆E = hf = hc ÷ λ
Where h=plancks constant
F= frequency of light
C=velocity of light
λ= wavelength of light
Why are transition metals compounds coloured?
The light seen is a mixture of the colours that are not absorbed when visible light is absorbed to excite electrons to higher energy level (the light reflected (solids) or transmitted (solution) )
What are the factors which affect colour?
Identity of metal
Oxidation state of metal
Identity of ligands
Co-ordination number
How does UV/visible spectroscopy work?
Frequencies at which a complex absorbs uv/vis light can be measured with a UV/visible light spectrometer
UV/visible light passed through complex and frequencies of UV/vis passing through detected
The more conc. the solution, the more light that’s absorbed
Why are ligands added to some ions for colorimetry?
The colour would be too weak so ligand intensifies the colour as otherwise machine wouldn’t detect well
What conditions are better for oxidising/reducing transition metals?
Oxidise- alkaline conditions
Reduce- acidic conditions
Why do ligands affect how easy it is to reduce transition metals compounds?
Different ligands have different attractions to the central ion, and could also be affected by shape
What are the colours of the different oxidation states if vanadium?
V(+5) e.g VO2 + - yellow
V(+4) e.g VO 2+ - blue
V(+3) e.g. V 3+ - green
V(+2) e.g. V 2+ - violet
What conditions are used to reduce vanadium?
Acidic conditions using Zinc as reducing agent
What transition metal complex is used in redox titrations and what conditions?
Potassium manganate (VII) as contains MnO4- ion
dilute sulfuric acid as needs acidic conditions
Why are other acids not used?
HCl- as MnO4- would also oxidise Cl- to Cl2 so would affect volume of KMnO4 needed
Conc. sulfuric and conc. nitric cannot be used as they are oxidising agents so would affect volume of KMnO4 needed
Ethanoic acid cannot be used as it is weak and would not provide enough H+
What’s the ratio for titrating Fe2+ with KMnO4, and what do you do if iron not in +2 oxidation states?
5:1
If Fe(0) react with sulfuric acid
If Fe(3+) react with zinc
What is the ratio of C2O4 2- to MnO4- in a titration, and why does the reaction require warming?
5:2
Both ions are negative and so repel each other and need warming for reaction to proceed, however once Mn2+ produced, it acts as catalyst so speeds up (auto catalysis)
What is a catalyst and how do they work?
Substance that increases the rate of reaction but is not used up
Provide an alternative route with lower activation energy
What is a heterogenous catalyst and how does it work?
Catalyst is in different phase to reactants, so usually solid and reaction takes place on surface
At least one reactant is adsorbed onto surface at active sites which:
A. Concentrates reactants so increases likelihood of collision
B. May weaken some bonds in molecule
C. Position molecule in favourable orientation
What happens if adsorption is:
A. Too strong?
B. Too weak?
Too strong: molecules unable to move around active sites so less likely to meet another reactant
too weak: not many molecules adsorbed so the catalyst will have very little effect
How is surface area maximised to save costs?
Using very thin coating on some sort of support medium (e.g honeycomb structure)
What is catalyst poisoning and what effect does this have?
Other substances adsorb strongly onto surface
Lowers efficiency of catalyst or makes it completely useless
Very difficult to remove so very costly.
What is the catalyst for the contact process?
V2O5 (vanadium (V) oxide)
What is a homogenous catalyst and how does it work?
In same state as reactants (usually in solution) and proceed via intermediate species (reactant and catalyst) which then reacts further and regenerates catalyst
What property of transition metals allows them to act as catalysts?
Able to vary oxidation states
What are metal aqua ions?
Metal ions surrounded by 6 water ligands
What are the colours of the metal aqua ions?
[Cu(H2O)6]2+ blue
[Fe(H2O)6]2+ green
[Fe(H2O)6]3+ pale violet
[Al(H2O)6]3+ colourless
What is a hydrolysis reaction?
Where molecules are split apart by water so metal aqua ions lose one or more H2O ligands
Why are [M(H2O)4(OH)2] and [M(H2O)3(OH)3] complexes insoluble in water?
Neutral complexes so form as precipitates
Why are solutions of aqueous metal ions often acidic?
Metal aqua ions lose H+ from one or more water ligands so H+ makes solution acidic
The higher the charge on metal in metal aqua ion the more acidic the solution as electrons in the covalent bond are pulled more strongly a way from H and towards O breaking O-H bond
How do the metal aqua ions react with NaOH?
[Fe(H2O)6]2+ + 2OH- —> [Fe(H2O)4(OH)2] + 2H2O (green ppt)
[Cu(H2O)6]2+ + 2OH- —> [Cu(H2O)4(OH)2] + 2H2O (blue ppt)
[Fe(H2O)6]3+ + 3OH- —> [Fe(H2O)3(OH)3] + 3H2O (brown ppt)
[Al(H2O)6]3+ + 3OH- —> [Al(H2O)3(OH)3] + 3H2O (white ppt)
WITH XS OH-: [Al(H2O)3(OH)3] + OH- —> [Al(H2O)2(OH)4] + H2O (white ppt dissolves)
How do metal aqua ions react with NH3?
[Fe(H2O)6]2+ + 2NH3 —> [Fe(H2O)4(OH)2] + 2NH4+ (green ppt)
[Cu(H2O)6]2+ + 2NH3 —> [Cu(H2O)4(OH)2] + 2NH4+ (blue ppt)
WITH XS: [Cu(H2O)4(OH)2] + 4NH3 —> [Cu(H2O)2(NH3)4]2+ + 2H2O + 2OH- (deep blue solution)
[Fe(H2O)6]3+ + 3NH3 —> [Fe(H2O)3(OH)3] + 3NH4+ (brown ppt)
[Al(H2O)6]3+ + 3NH3 —> [Al(H2O)3(OH)3] + 3NH4+ (white ppt)
How do metal aqua ions react with Na2CO3?
[Fe(H2O)6]2+ + CO3 2- —> FeCO3 + 6H2O (green ppt)
[Cu(H2O)6]2+ + CO3 2- —> CuCO3 + 6H2O (blue-green ppt)
2[Fe(H2O)6]3+ + 3CO3 2- —> 2[Fe(H2O)3(OH)3] + 3H2O + 3CO2 (brown ppt with gentle bubbles CO2)
2[Al(H2O)6]3+ + 3CO3 2- —> 2[Al(H2O)3(OH)3] + 3H2O + 3CO2 (white ppt with gentle bubbles of CO2)
