Transition Metals Flashcards
Transition Metals
What’s a complex ion
A central metal ion surrounded by ligands
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What’s a ligand
Molecules/ ions which donate a pair of electrons forming coordinate bonds
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What’s a coordinate bond
One of the bonded atoms provide both electrons in the covalent bond
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What’s the vanadium colours and the oxidation states
+2, (V²⁺): purple
+3 (V³⁺): green
+4 (VO²⁺): blue
+5 (VO₄²⁻): yellow
You’d Better Getting Practicing
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What is haemoglobin
Haem is a multidentate ligand that is found in the molecule haemoglobin
It’s a protein and used to transport oxygen around the body in blood
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What happens when electrons absorb light
- They move from the group state to the excited state
- the side of the energy change depends on the central ion and oxidation state and the coordinate number
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Why are 3+ metal aqua ions more acidic than 2+ metal aqua ions
Because the metal aqua ion have a higher charge it’s more polarising to the surrounding bonds this makes it easier to loose the O - H bond in water
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What are the Chromium oxidation state colours
+2 : blue
+3 : green
+4 : colourless
+5 : colourless
+6 : orange
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What is tollens reagent
It contains the silver transition metal which forms a complex ion which is used to distinguish between aldehyde and ketones
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What are amphoteric metal hydroxides
Metal hydroxides that can act as an acid or base which means they are amphoteric
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What does adding a small amount of ammonia to metal aqua ions do
Adding a small amount of ammonia to a metal aqua ions forms a metal hydroxide precipitate
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What does adding excess ammonia to metal aqua ions do
Leads to ligand exchange
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How does haemoglobin transport oxygen
Haemoglobin has a water molecule bonded to it which the oxygen molecule easily replaces and when it gets to where it needs to it breaks off
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Why is breathing carbon monoxide (CO) dangerous
The CO molecule replaces the water ligand on the haemoglobin and it bonds strongly to the haemoglobin so oxygen can’t easily replace it and so O2 can’t be transported
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test for cooper (II) ions
- ammonia
add excess ammonia and a dark blue precipitate will form
[Cu(NH3)4]+2(aq) - sodium hydroxide
by adding sodium hydroxide a light blue precitate will form
Cu2+ + 2OH − →Cu(OH)2(s)
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when is a yellow precipitate formed with hexaaqua copper(II) ions
when hexaaqua copper(II) reacts with concentrated chloride to form tetrachloride copper(II) is formed
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what is ligand substitution
its where one ligand is replaced by another ligand
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how does different sized ligands affect a complex ion
if the ligand that is replacing another ligand is bigger there would be less coordinate bonds round the central metal
(e.g. chloro ligands can only bond 4 times to copper)
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what affects the amount of coordinate bonds
- the size of the ligand
- the amount of coordinate bonds a ligand can form (e.g. bidentate ligands)
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what makes affects feasibility in a ligand substitution reaction
- when ligands are replaced by those that form more co-ordinate bonds there is a significant increase in entropy
- when ligands are replaced by those that form less co-ordinate bonds there is a decrease in entropy
- if there is an entropy decrease the bonds wont be feasible as ΔH is most times negligible
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why do metal complex ion become harmless when reacted with EDTA
EDTA is a chelating agent these are good at bonding to metal ions and difficult to remove this makes the metal ions harmless as it cant bond to anything else
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what is a chelating agent
these are ligands that form more than one coordinate bond and are very good at bonding to metal ions
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what is the ΔH in many ligand substitution reactions and why
the ΔH is negligible in many of these reactions as the same number of bonds are being broken and formed
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what is the chelate affect
in general ligand substitution reactions where ligands are replaced by those that form more co-ordinate bonds the reaction is feasible and this is driven by an entropy increase
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why are complexes coloured
- in transition metals the 5d orbital do not all have the same energy
- the gap in energy between d orbitals correspond to the energy of UV/ visible light
- the electrons absorb UV/visible light tot provide the energy to promote electrons the a higher energy
- the gap between the higher and lower d orbitals are ΔE
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what factors affect the colour of transition metals and why
- the central metal ion
- oxidation state of the metal
- the ligands
- the coordinate number
this is beacsue the affect the size of the energy gap
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how does concerntration affect absorbancy
the more concerntrated the more light it absorbs
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what do you do when the colour of a complex is weak
you add a ligand such as “bipy” to increase the absorbancy so the colour is stronger
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write an eqaution for the hydolysis of a 3+ ion to release a proton
[Fe(H2O)6]3+ (aq) → [Fe(H2O)5(OH)]2+(aq) + H+(aq)
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define a lewis acid
electron pair acceptor
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define a lewis base
electron pair donor
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what is acting as the lewis acid and what is acting as the lewis base during the formation of complex ions
the metal ion is acting as the lewis acid and the ligands as the lewis bases
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colour and equation of Fe2+ in aqueous solution
Fe(H2O)4(OH)2
green
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colour and equation for Fe2+ and NaOH (dropwise and excess)
- Fe(H2O)4(OH)2
- green ppt goes brown on standing in air
As it turns to Fe3+
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colour and equation for Fe2+ and NH3 (dropwise and excess)
- Fe(H2O)4(OH)2
- green ppt goes brwon on standing in air
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colour and equation for Fe2+ and Na2CO3
FeCO3 and green ppt
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colour change for the reaction of Cu2+ and
* NaOH (dropwise and excess)
* NH3 (dropwise)
* NH3 (excess)
* Na2CO3
* conc HCl
- Cu(H2O)4(OH)2](s) (blue ppt)
- Cu(H2O)4(OH)2 (blue ppt)
- [Cu(H2O)2(NH3)4]2+(aq) (dark blue solution)
- CuCO3 (blue-green ppt)
- [CuCl4]2-(aq) (pale green/ yellow solution)
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colour change and equation for Fe3+
* aqueous solution
* NaOH (dropwise and excess)
* NH3 (dropwise and excess)
* Na2CO3
- [Fe(H2O)6]3+ (purple solution)
- Fe(H2O)3(OH)3) ( brown ppt may look orange brown)
- Fe(H2O)3(OH)3 (brown ppt may look orange brown)
- Fe(H2O)3(OH)3 (brown ppt may look orange brown, effervecnence)
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colour and equaiton for Al3+
* aqueous solution
* NaOH (dropwise)
* NaOH (excess)
* NH3 (dropwise and excess)
* Na2CO3
- [Al(H2O)6]3+ (colourless)
- Al(H2O)3(OH)3 (white ppt)
- [Al(OH)4]-(aq) (colourless)
- Al(H2O)3(OH)3 (white ppt)
- Al(H2O)3(OH)3 (white ppt, effervecence)
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colour and equation for Co2+
* aqueous solution
* NaOH (dropwise and excess)
* NH3 (dropwise and excess)
* Na2CO3
* HCl
- [Co(H2O)6]2+ (pink)
- Co(H2O)4(OH)2 ( blue ppt)
- [Co(NH3)]2+(aq) (pale brown solution)
- CoCO3(s) (purple ppt)
- [CoCl4]2-(aq) (blue solution)
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why might [Fe(H2O)6]3+ look yellow-brown when you react Fe3+ and aqueous solution
it may look yellow-brown because of [Fe(H2O)3
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what does a calorimeter do
measure the aborbance of a particular wavelength of light by a solution
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whta affects the colour of a transition metal compound
- ΔE effects the frequency of absorbed photons, so determines the colour
- ΔE is changed by oxidation state of the metal, number and type of ligands, shape, co-ordinate number
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why can transition metals have variable oxidation states
they have partially filled d orbitals so can loose 4s and 3d electrons
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When’s it easy to oxidise transition metals
When it’s in alkaline conditions
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When is it easier to reduce transition metals
When they are in acidic conditions
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Definition of a transition metal
Transition metals are d-block elements that form at least one stable ion with an incomplete d-subshell.
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Role of Transition Metal Catalyst in Haber Process
The transition metal iron (Fe) acts as a catalyst in the Haber process by providing an alternative reaction pathway with lower activation energy, allowing the synthesis of ammonia from nitrogen and hydrogen.
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amphoteric meaning
a molecule or ion that reacting as an acid or base
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what is the role of iron as a heterogenous catalyst in the harber process
- Hydrogen and nitrogen/reactants adsorb onto the surface/
active sites of the iron - Bonds weaken/reaction takes place
- Products desorb/leave from the surface (of the iron)
- Large surface area (of iron) by using powder or small pellets
or support medium/mesh - Catalyst poisoned / sulfur poisons or binds to the catalyst
Active sites blocked
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How can you improve a heterogenous catalyst?
- use an inert support medium
- maximises surface area
- faster rate of reaction
- increases surface area/mass ratio
- minimises cost
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How do ligands affect redox potential of Co and Fe?
Co2+ oxidises to Co3+ more easily with ammonia ligands than with aqua ligands
Ammonia ligands make redox potential more negative
Fe2+ oxidises to Fe3+ more easily with hydroxide ligands than with aqua ligands
Hydroxide ligands make redox potential more negative
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How do you reduce Vanadium ions?
- zinc
- conc sulfuric acid
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How do you use colourimetry to measure complex concentration?
- prepare solution with molar ratio of ligands and metal ions corresponding to complex
- maximum concentration of complexes
- measure absorbance
- repeat for smaller moles of ligands
- plot calibration curve
- add excess ligand/metal ion to sample
- measure absorbance of sample and compare to calibration curve
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How does heterogenous catalysis work?
- reactants adsorb to active site on catalyst surface
- weakens bonds within reactants and holds them in close proximity
- reaction occurs on catalyst surface
- products desorb from surface
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How does the shape of benzene differ from cyclohexane?
benzene is planar
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What are zwitterions?
- species with permanent positive charge and permanent negative charge
- but neutral overall
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What is a heterogenous catalyst?
- different phase to reactants
- usually a solid
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What is a homogenous catalyst?
- same phase as reactants
- catalysed reaction will involve intermediate species
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Suggest one reason why electron pair repulsion can’t be used to predict the shape of [CoCl4]2-
It has to many electrons in the d subshell
