Transition Metals 2 (isomerism and catalysts)

Question 1

What shape complexes show cis-trans isomerism?

Answer 1

Octahedral and square planar

Question 2

What is required to show cis-trans isomerism?

Answer 2

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.

Question 3

What are the conditions for cis isomers?

Answer 3

2 identical monodentate ligands are 90 degrees to each other (next to eachother)

Question 4

What are the conditions for trans isomers?

Answer 4

2 identical monodentate ligands are 180 degrees to each other (opposite each other)

Question 5

What shape complexes show optical isomerism?

Answer 5

Octahedral complexes

Question 6

What are the conditions for the optical isomerism?

Answer 6

Either 3 bidentate ligands or 1 multidentate ligand

Question 7

What is the formula of cisplatin?

Answer 7

PtCl2(NH3)2

Question 8

How does cisplatin work?

Answer 8

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+.

Question 9

What are the risks associated with cisplatin?

Answer 9

Prevents blood cells and hair cells from replicating, so causes:
Suppresses immune system, increasing risk of infection
Hair loss
Kidney damage

Question 10

Why do the risks associated with cisplatin happen?

Answer 10

It can attach to DNA in healthy cells

Question 11

How can risks of cisplatin be minimised?

Answer 11

Use in small amounts and target application to the tumor

Question 12

Why is transplatin ineffective?

Answer 12

It cannot interfere with DNA in the same way as cisplatin

Question 13

What property of transition metals enables them to be good catalysts?

Answer 13

Incomplete d-orbital (enables variable oxidation states)

Question 14

What are the 3 main types of catalysts?

Answer 14

Heterogeneous
Homogenous
Autocatalyst (type of homogenous)

Question 15

What is a heterogenous catalyst?

Answer 15

One in which the reactants are in different physical states/phases

Question 16

What is a homogenous catalyst?

Answer 16

Catalyst and reactants are in same physical state/phase

Question 17

What is an autocatalyst?

Answer 17

A type of homogenous catalyst in which the catalyst is a reaction product. It is in the same physical state/phase as reactants.

Question 18

What are the three reactions involving a heterogenous catalyst?

Answer 18

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)

Question 19

What is the mechanism of action for the contact process?

Answer 19

SO2 + V2O5 -> SO3 + V2O4
V2O4 + 1/2 O2 -> V2O5

Question 20

Why is V2O5 used in small pellets?

Answer 20

Increases surface area

Question 21

Why is a ceramic honeycomb structure used to house transition metals in catalytic converters?

Answer 21

Ceramic honeycomb structure acts as a support medium which is used to increase surface area and minimise cost

Question 22

Why is a thin layer of transition metal used in catalytic converters?

Answer 22

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

Question 23

Describe how adsorption works

Answer 23

1. Reactants are adsorbed (weak chemical bonds are formed) on the active sites and the surface of the catalyst
2. Bonds in the reactants weaken and break and new bonds are formed by a reaction on the surface
3. Products are desorbed

Question 24

What are the benefits of adsorption?

Answer 24

1. Weakens bond within reactant molecules, making it easier to break, so lower Ea
2. Increases surface concentration of the reactant molecules, therefore increases collision frequency and rate of reaction
3. Provides reactants with correct orientation for the reaction to occur

Question 25

Why are transition metals that adsorb strongly not good catalysts?

Answer 25

The products are not desorbed

Question 26

Why are transition metals which adsorb weakly not good catalysts?

Answer 26

Reactants are not brought together

Question 27

What is catalytic poisoning?

Answer 27

Impurities are strongly adsorbed on the active sites on the surface of the catalyst

Question 28

What are the effects of catalytic poisoning?

Answer 28

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

Question 29

In what type of catalyst does catalytic poisoning take place?

Answer 29

Heterogeneous

Question 30

What are some examples of catalytic poisoning?

Answer 30

Sulphur poisons the iron catalyst in the Haber process - sulfur comes from impurities in crude oil.

Question 31

How does a homogenous catalyst work?

Answer 31

Catalyst combines with one of the reactants, forming an intermediate species. Intermediate species reacts with another reactant, forming products and regenerating the original catalyst.

Question 32

Why does Fe2+/Fe3+ speed up the rate of reaction for S2O8- and I-?

Answer 32

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.

Question 33

Give an example of a reaction that is auto catalysed

Answer 33

2MnO4- + 16H+ +5C2O4- -> Mn2+ +8H2O + 10 CO2
Catalyst: Mn2+(aq) (with acidic conditions)