3.2.5.2 Substitution Reactions Flashcards
What is a hexaaqua ion?
Complex transition metal ions bonded with water
They are formed when simple ions of transition metals dissolve in water
They are called hexaaqua cations because they have six water ligands bonded to the metal ion
e.g. [ Cu (H2O)6 ]2+
What is formed when nickel sulfate is dissolved in water?
[ Ni (H2O)6 ]2+ is formed
Sulfate is present in the solution
Which non-transition metal ions can form hexaaqua ions?
Mg2+, Zn2+ and Al3+ as they have empty orbitals
How do you represent complexes?
Square brackets
The charge is written as a power
How do you work out the charge of a hexaaqua ion?
The water is not charged so the charge of the hexaaqua ion equals the charge of the transition metal ion
What is the co-ordination number?
The number of co-ordinate bonds between a metal ion and ligands
Some have more than one lone pair
What are the types of ligands?
Unidentate or monodentate
Bidentate
Multidentate
What are monodentate ligands?
Ligands which form one co-ordinate bond
e.g. water, ammonia, chloride, cyanide
What are bidentate ligands?
Ligands which form two co-ordinate bonds
The lone pairs must be on different atoms to allow the ligand to form more than one co-ordinate bond
Water has two lone pairs but these are both on the oxygen atom so it is monodentate
What are multidentate ligands?
Ligands which form more than two co-ordinate bonds per ligand
EDTA derivatives form 6 co-ordinate bonds
All multidentate ligands form complexes which are called chelates
What is EDTA?
Multidentate ligand
Charge of 4+
It can act as a hexadentate ligand using lone pairs on four oxygen and both nitrogen atoms
What are chelates?
Complex ions with polydentate ligands
What can chelates do?
They can be used to effectively remove d-block metal ions from solution
What is a haem group?
An iron(II) complex with a multidentate ligand
Oxygen forms a co-ordinate bond to Fe(II) in haemoglobin, enabling oxygen to be transported in the blood.
Carbon monoxide is toxic because it replaces oxygen
co-ordinately bonded to Fe(II) in haemoglobin
What is the chelate effect?
If you add a hexadentate ligand to a solution of a transition metal salt, the ligand will replace all six water ligands in the hexaaqua ion
This creates more species due to the number of water molecules removed
This increase causes a significant increase in entropy which forces the reaction to the right so that more hexadentate ligands react
For this reason, chelate complexes with polydentate ligands are favoured over complexes with monodentate ligands
This is called the chelate effect
