transition metals

Question 1

why are TM complexes usually coloured

Answer 1

• in the presence of ligands, the partially filled 3d orbitals are split into 2 energy levels with a small energy gap
• when a 3d electron absorbs energy from the visible light region corresponding to the energy gap, the electron is promoted from a lower energy d orbital to a higher energy d orbital (d-d transition)
• the colour of the compound observed is the complementary of the colour absorbed

Question 2

how does it function as a homogeneous catalyst

Answer 2

• TM provides an alternative pathway of a lowered Ea
• TM reacts with reactant 1 to form an intermediate
• Intermediate reacts with reactant 2 to revert back to TM

Question 3

why can it function as a homogeneous catalyst

Answer 3

• ability to exist in variable O.S
• convert to different O.S easily (Ecell)

Question 4

how does it function as a heterogeneous catalyst

Answer 4

Reactants are adsorbed in the catalyst surface. Catalyst uses the partially filled 3d orbitals to form weak temporary bonds with reactants.

• This weakens existing bonds in reactants which lead to a lowering in Ea
• Reactants are brought closer together at the active sites, this results in higher concentration of reactants and increases the number of molecules with energy more that it equal to Ea

Hence rate increases.

Question 5

Why can it function as a heterogeneous catalyst?

Answer 5

Presence of partially filled 3d orbitals in TM
- donate 3d electrons to reactants to form temporary bonds
- provide low lying 3d orbitals to accept electrons from reactants to form temporary bonds