Transition Metals 2 (isomerism and catalysts) Flashcards
What shape complexes show cis-trans isomerism?
Octahedral and square planar
What is required to show cis-trans isomerism?
4 of one monodentate ligand and 2 of another monodentate ligand (look at the least coordinated for octahedral). For square planar, need 2 of each ligand.
What are the conditions for cis isomers?
2 identical monodentate ligands are 90 degrees to each other (next to eachother)
What are the conditions for trans isomers?
2 identical monodentate ligands are 180 degrees to each other (opposite each other)
What shape complexes show optical isomerism?
Octahedral complexes
What are the conditions for the optical isomerism?
Either 3 bidentate ligands or 1 multidentate ligand
What is the formula of cisplatin?
PtCl2(NH3)2
How does cisplatin work?
It is a square planar drug used as an anticancer drug. It prevents DNA replication in cancer cells by a ligand substitution reaction, where the central metal ion in the complex is platinum, which has oxidation state 2+.
What are the risks associated with cisplatin?
Prevents blood cells and hair cells from replicating, so causes:
Suppresses immune system, increasing risk of infection
Hair loss
Kidney damage
Why do the risks associated with cisplatin happen?
It can attach to DNA in healthy cells
How can risks of cisplatin be minimised?
Use in small amounts and target application to the tumor
Why is transplatin ineffective?
It cannot interfere with DNA in the same way as cisplatin
What property of transition metals enables them to be good catalysts?
Incomplete d-orbital (enables variable oxidation states)
What are the 3 main types of catalysts?
Heterogeneous
Homogenous
Autocatalyst (type of homogenous)
What is a heterogenous catalyst?
One in which the reactants are in different physical states/phases
What is a homogenous catalyst?
Catalyst and reactants are in same physical state/phase
What is an autocatalyst?
A type of homogenous catalyst in which the catalyst is a reaction product. It is in the same physical state/phase as reactants.
What are the three reactions involving a heterogenous catalyst?
Contact process:
SO2(g) + 1/2O2(g) -> SO3(g) (Catalyst: V2O5)
Haber process:
N2(g) +3H2(g) <-> 2NH3(g) (Catalyst: Fe)
Methanol production:
CO(g) + 2H2(g) -> CH3OH(g) (Catalyst: Cr2O3)
What is the mechanism of action for the contact process?
SO2 + V2O5 -> SO3 + V2O4
V2O4 + 1/2 O2 -> V2O5
Why is V2O5 used in small pellets?
Increases surface area
Why is a ceramic honeycomb structure used to house transition metals in catalytic converters?
Ceramic honeycomb structure acts as a support medium which is used to increase surface area and minimise cost
Why is a thin layer of transition metal used in catalytic converters?
Thin layer of Pt, Pd, Rh used to increase surface area and minimise cost. So more molecules can react at the same time, improving its effectiveness
Describe how adsorption works
- Reactants are adsorbed (weak chemical bonds are formed) on the active sites and the surface of the catalyst
- Bonds in the reactants weaken and break and new bonds are formed by a reaction on the surface
- Products are desorbed
What are the benefits of adsorption?
- Weakens bond within reactant molecules, making it easier to break, so lower Ea
- Increases surface concentration of the reactant molecules, therefore increases collision frequency and rate of reaction
- Provides reactants with correct orientation for the reaction to occur
Why are transition metals that adsorb strongly not good catalysts?
The products are not desorbed
Why are transition metals which adsorb weakly not good catalysts?
Reactants are not brought together
What is catalytic poisoning?
Impurities are strongly adsorbed on the active sites on the surface of the catalyst
What are the effects of catalytic poisoning?
Reduces the surface area of the catalyst and slows down the rate of reaction (reduced efficiency).
This reduces the amount of product that is formed in a certain time or with a certain amount of energy (reduced efficiency).
Catalyst needs to be replaced, so increased cost
In what type of catalyst does catalytic poisoning take place?
Heterogeneous
What are some examples of catalytic poisoning?
Sulphur poisons the iron catalyst in the Haber process - sulfur comes from impurities in crude oil.
How does a homogenous catalyst work?
Catalyst combines with one of the reactants, forming an intermediate species. Intermediate species reacts with another reactant, forming products and regenerating the original catalyst.
Why does Fe2+/Fe3+ speed up the rate of reaction for S2O8- and I-?
Reactant ions are both negatively charged so repel each other and are therefore unable to collide and react, so activation energy is very high.
Fe2+ catalyst ions are oppositely charged so attract the negative ions and activation energy is lowered.
Give an example of a reaction that is auto catalysed
2MnO4- + 16H+ +5C2O4- -> Mn2+ +8H2O + 10 CO2
Catalyst: Mn2+(aq) (with acidic conditions)
