Transition metals Flashcards
Characteristic features of Transition metals
- Coloured ions
- Can form complexes
- Variable oxidation states
- Catalytic activity
What allows them this is their incomplete d orbital
Why are complex ions with partially filled d sub-levels coloured?
- Electrons excited, so there’s a transition from ground state to excited state
- Energy absorbed from visible light
Co-ordinate bond
- A covalent bond
- in which pair of electrons come from one atom
Why can co-ordinate bonds form between transition metal ions and water molecules?
- TM ions can accept electron pairs
- O in H2O can donate pair
Why can CuCl colourless, but CuCl2 coloured?
- Cu+ is present in CuCl
- Cu2+ is in CuCl2
- Cu+ has a fully filled d sub–shell (1)
- Cu2+ has a partially filled d sub–shell (1)
- In Cu+ there is no absorbtion of light as electron transition not possible
Bidentate ligand
- a molecule than can donate 2 lone pairs to a metal ion in order to form 2 co-ordinate bonds
- from 2 different atoms in a molecule
Naturally-occuring complex that contains iron
- Haemoglobin
- transports oxygen around body
Coordination number
- no. of co–ordinate bonds
Multidentate ligand
- a molecule than can donate many lone pairs to a metal ion in order to form co-ordinate bonds
Why can a molecule act as a ligand?
- Have a lone pair
Name the ammonia complex used to distinguish aldehydes and ketones
- Tollen’s reagent (diammine silver)
- [Ag(NH3)2]+
Ligand
- species which can donate a pair of electrons to a metal ion
- acts as a lewis base
E=hf
- E is the energy absorbed by the excited electron to move from the ground to excited state
- h is Planck’s constant
- f is the frequency of light absorbed
Most common shapes found in TM complexes
- octahedral 90°
- tetrahedral 109°
Autocatalysis
- A product of the reaction acts as a catalyst.
How is Mn2+ involved in the reaction between C2O42- and KMnO4
- Mn2+ is oxidised to Mn3+ by MnO4-
- Mn3+ is reduced to Mn2+ by C2O42-
- MnO4- + 4Mn2+ + 8H+ → 5Mn3+ + 4H2O
- C2O42- + 2Mn3+ → 2Mn2+ + 2CO2
Why does poisoning reduce the effectiveness of catalysts and how can it be minimised?
- Poison attaches to surface, blocking active site
- Purify reactants (remove impurities)
Heterogenous catalyst
catalyst in a different phase from that of the reactants.
Homogenous catalyst
catalyst in a same phase from that of the reactants.
,Substance which poisons iron in the Haber process and how does it do it?
- Poison is Sulphur
- Poison is adsorbed onto active sites.
- Poison is not desorbed.
Catalysts used in exhaust systems and how they’re made to maximise efficiency
- Pt, Pd or Rh
- Deposited on a ceramic honeycomb ,
- which increases the surface area of the catalyst.
Why are W and Ag very poor catalysts?
- In W the adsorption is too strong so products not desorbed
- This means the Active sites are blocked
- In Ag the adsorption is too weak
- Reactants not held long enough for a reaction to occur
Oxidising and Reducing agents
- Oxidising agents gains electrons
- Reducing agents lose electrons
Steps in the mechanism of heterogenous catalysts
- Reactants adsorb on the active site of the catalysts (surface)
- Reactants must be correctly oritented
- Bonds of the reactants weaken
- Reactants combine, forming products which desorb from sufarce
2 Risks associated with using cisplatin for anticancer drugs and state how the adverse effects could be minimised
- May lead to patient death as it kills normal cells
- It may attach to DNA in normal cells,leading to hair loss
- Use in very small amounts
- Focus the application to the tumour
Explain the curve: MnO4- and C2O42-
- Curve starts with shallow gradient (slow rate)
- Because negative ions collide so Ea high
- Curve gets steeper because autocatalyst (Mn2+) formed
- Ea lowered because oppositely charged ions attract
- The rate therefore increases
- Curve levels out approaching time axis as MnO4-** ions **used up
Complex ion definition
- TM bonded to 1 or more ligands
- Which are co-ordinately bonded
Why is solution X red
- (Frequencies of) Complementary colour to red is absorbed from the white light
- electrons in d orbital excite as they gain the photon’s energy
- Red light that remains is transmitted and the colour is observed
Why is CO toxic?
- Because it bonds to the haemoglobin, forming carboxyhaemoglobon
- CO has greater affinity
- carboxy is more stable than oxy
- Prevents oxygen being transported
2 ways to maximise the efficiency of catalysts?
- Use powder to increase surface area of catalyst
- Remove catalyst poisons from reactants
Why are inert mediums used for heterogenous catalysts
- to maximize surface area
- and minimise cost
Define active site
- where reactants are adsorbed onto a catalyst surface
Note:
- if the surface area increases, the number of active sites also increases
Explain how and why iron ions catalyse the reaction between iodide ions and S2O82– ions
- Reaction 1 and 2 involving I- and S2O82-
- 2 negative ions would repel leading high Ea
- Positive Fe ions attract negative ions
- (Fe) has a variable oxidation state
- With iron ions, theres an alternative route to the reaction
- One with a lower activation energy
- Fe2+ is involved but regenerated
Why is Fe3+ more acidic than Fe2+
- [Fe(H2O)6]3+⇒ [Fe(H2O)5OH]2+ + H+
- Fe3+ ion has higher charge density than Fe2+
- There’s increased polarisation in the co-ordinatedly bonded water ligands
- O—H bond weakens and H+ ion released
Why is it possible to use a spectrometer to measure the reaction between MnO4- and C2O42-
- Manganate(VII) ions are coloured (purple)
- All other reactants and products are too faint to be detected
Factors that affect the colour of a complex
- Type metal
- Oxidation state of the metal
- Type of ligands
- Co-ordination number
- Shape
Explain why a combustion reaction shouldn’t use a very good catalyst
- Reaction may be too fast** and may become **uncontrollable
- Explosion may occur
