Reactions of TM ions with NaOH, Na2CO3 and NH3

How are complex ions formed (water example)?

• TM salt dissolved in water

• Water molecules cluster around TM ion

• 6 water ligands donate LP each

Why do different complex ions (with diff. central TM ion) have different degrees of acidity?

TM ions with a higher charge (e.g., Fe3+ vs. Fe2+) are more acidic. This is because:

• they are smaller and have greater charge density

• they attract electrons from (oxygen) water more easily

• this weakens O-H bonds in ligands causing H+ to be released

What complex ion is formed when iron (II) is dissolved in water and what colour is it?

[Fe(H2O)6]2+ is formed which is green

What is an equation for the reaction of [Fe(H2O)6]2+ with sodium hydroxide solution, what is the colour of the solution and does it red-dissolve with excess NaOH?

[Fe(H2O)6]2+ + 2OH- → Fe(OH)2(H2O)4 + 2H2O

Green solution formed

The Iron (II) precipitate does not re-dissolve in excess NaOH.

What is an equation for the reaction of [Fe(H2O)6]2+ with ammonia solution, what is the colour of the solution and does it red-dissolve with excess ammonia?

[Fe(H2O)6]2+ + 2NH3 → Fe(OH)2(H2O)4 + 2NH4 +

Green solution formed

The Iron (II) precipitate does not re-dissolve in excess ammonia.

What is an equation for the reaction of [Fe(H2O)6]2+ with sodium carbonate solution and what is the colour of the solution?

[Fe(H2O)6]2+ + CO3 2- → FeCO3 + 6H2O

Green solution formed

What complex ion is formed when copper (II) compounds dissolve in water and what colour is it?

[Cu(H2O)6]2+ is formed which is blue

What is an equation for the reaction of [Cu(H2O)6]2+ with sodium hydroxide solution, what is the colour of the solution and does it red-dissolve with excess NaOH?

[Cu(H2O)6]2+ + 2OH- → Cu(OH)2(H2O)4 + 2H2O

Blue solution

The copper (II) hydroxide precipitate does not re-dissolve with excess sodium hydroxide.

What is an equation for the reaction of [Cu(H2O)6]2+ with ammonia solution, what is the colour of the solution and does it red-dissolve with excess NH3?

[Cu(H2O)6]2+ + 2NH3 → Cu(OH)2(H2O)4 + 2NH4+

Blue solution

The copper (II) hydroxide precipitate does re-dissolve with excess ammonia.

What is formed when copper (II) hydroxide precipitate dissolves in excess ammonia and what is an equation for the reaction?

Cu(OH)2(H2O)4 + 4NH3 → [Cu(NH3)4(H2O)2]2+ + 2H2O + 2OH-

Deep blue solution formed

What is an equation for the reaction of [Cu(H2O)6]2+ with sodium carbonate solution and what is the colour of the solution?

[Cu(H2O)6]2+ + CO3 2- → CuCO3 + 6H2O

Green solution (the same as [Fe(H2O)6]2+ with CO3 2- !)

What complex ion is formed when Iron (III) is dissolved in water and what colour is it?

[Fe(H2O)6]3+ is formed which is often yellow but can also be brown/purple/lilac/violet

What is an equation for the reaction of [Fe(H2O)6]3+ with sodium hydroxide solution, what is the colour of the solution and does it red-dissolve with excess NaOH?

[Fe(H2O)6]3+ + 3OH- → Fe(OH)3(H2O)3 + 3H2O

Brown solution

The Iron (III) hydroxide precipitate does not re-dissolve with excess NaOH solution.

What is an equation for the reaction of [Fe(H2O)6]3+ with ammonia solution, what is the colour of the solution and does it red-dissolve with excess NH3?

[Fe(H2O)6]3+ + 3NH3 → Fe(OH)3(H2O)3 + 3NH4+

Brown solution

The Iron (III) hydroxide precipitate does not re-dissolve in excess NH3.

What is an equation for the reaction of [Fe(H2O)6]3+ with sodium carbonate solution, and what colour solution is formed?

2[Fe(H2O)6]3+ + 3CO3 2- → 2Fe(OH)3(H2O)3 + 3CO2 + 3H2O

Note that a carbonate is not made (unlike with Fe (II) and Cu (II)

Brown solution

What is Fe (III)’s dream?

To be a brown precipitate of Fe(OH)3(H2O)3

What complex ion is formed when Al (III) compounds are dissolved in water and what colour is it?

[Al(H2O)6]3+ is formed which is colourless.

What is the equation for the reaction of [Al(H2O)6]3+ with sodium hydroxide, what is the colour of the solution formed and does the precipitate dissolve in excess NaOH?

[Al(H2O)6]3+ + 3OH- → Al(OH)3(H2O)3 + 3H2O

White precipitate is formed

The Al (III) hydroxide precipitate does re-dissolve in excess NaOH

What are two equations showing the re-dissolving of Al(OH)3(H2O)3 with excess NaOH?

Al(OH)3(H2O)3 + OH- → [Al(OH)4(H2O)2]- + H2O

through to

Al(OH)3(H2O)3 + 3OH- → [Al(H2O)6]3- + 3H2O

What is the equation for the reaction of [Al(H2O)6]3+ with ammonia solution, what is the colour of the solution formed and does the precipitate dissolve in excess NH3?

[Al(H2O)6]3+ + 3NH3 → Al(OH)3(H2O)3 + 3NH4 +

White precipitate formed

The Al (III) hydroxide precipitate formed does not re-dissolve in excess NH3.

What is the equation for the reaction of [Al(H2O)6]3+ with sodium carbonate and what colour is the resulting precipitate?

2[Al(H2O)6]3+ + 3CO3 2- → 2Al(OH)3(H2O)3 + 3CO2 + 3H2O

White precipitate formed