Ligand Substitution

Question 1

What is ligand substitution?

Answer 1

Where one ligand in a complex ion is substituted by another

Question 2

What is formed when copper (ll) sulphate is dissolved in water?

Answer 2

Pale blue complex ion
[Cu(H2O)6]2+

Question 3

What is formed when an excess of aqueous ammonia is added to [Cu(H2O)6]2+?

Answer 3

Pale blue solution becomes a dark blue solution [Cu(NH3)4(H2O)2]2+

Question 4

What is formed when aqueous ammonia is added to [Cu(H2O)6]2+ drop wise?

Answer 4

A pale blue precipitate

Question 5

What happens when an excess of HCl is added to [Cu(H2O)6]2+?

Answer 5

1. Forms [CuCl4]2-
2. Pale blue solution turns yellow
3. Octahedral shape becomes tetrahedral as Cl- is larger so not as many fit around
4. Coordination number reduces from 6 to 4

Question 6

What happens when chromium (lll) potassium sulphate is dissolved in water?

Answer 6

[Cr(H2O)6]3+ is formed which is a pale purple solution.

Question 7

What happens when chromium (lll) sulphate is dissolved in water?

Answer 7

A green solution is formed

Question 8

What happens when an excess of ammonia is reacted with [Cr(H2O)6]3+?

Answer 8

All 6 water ligands are replaced by 6 NH3 and the pale purple solution turns purple

Question 9

What happens when ammonia is added drop wise to [Cr(H2O)6]3+?

Answer 9

A grey green precipitate forms Cr(OH)3