15.2.1 - Types of reaction

Question 1

What are the four main types of transition metal reactions?

Answer 1

Redox - the oxidation number of the transition metal ion changes.
Acid-base - One or more ligands loses a H+ ion.
Ligand exchange - One or more ligands is replaced with another ligand.
Coordination number change - Number of ligands changes.

Question 2

Example of a redox transition metal reaction.

Answer 2

Fe 2+ ions are pale green.
When exposed to air they gradually turn yellow or brown.
Oxidation number increases from 2+ to 3+

Question 3

Example of an acid-base equation.

Answer 3

hexaaquacopper(II) reacts with 2 OH-
The 2 OH- deprotonates 2 water molecules.
2 water molecules are formed from the OH- ions gaining H+ ions.
The new ligands are 4 water and 2 OH
pale blue solution forms a blue precipitate.

Question 4

hexaaquacopper(II) reacts with 2 ammonia molecules and also in another reaction with 4 ammonia molecules (excess).
How do these reactions differ?

Answer 4

With 2 ammonia molecules, the reaction is an acid-base reaction. A pale blue solution forms a blue precipitate.
When excess ammonia is used, the reaction is ligand exchange.

Question 5

Give an example of a coordination number change reaction.

Answer 5

(cu(H2O)6)2+ + 4Cl- = (CuCl4)- + 6H2O

Coordination number changes from 6 to 4.
CuCl4- is yellow.
Colour change is blue to green and finally to yellow.

Question 6

Give the appearance of the following:
1) (Cu(H20)6)2+
2) (Cu(H2O)4(OH)2)
3) (Cu(NH3)4(H2O)2)2+

Answer 6

1) pale blue solution
2) Blue precipitate
3) deep blue solution