Colours

Question 1

What is a hexaaqua ion?

Answer 1

Transition metal ions in aqueous solution form ionic complexes with 6 coordinately bonded water molecules surrounding a central metal ion. The complex overall has a charge

Question 2

What is the colour of [Fe(H20)6]2+?

Answer 2

Green solution

Question 3

What happens if [Fe(H20)6]2+ is left in air?

Answer 3

Oxidised (to Fe3+) - yellow solution

Question 4

What happens to [Fe(H20)6]2+ when OH- is added?

Answer 4

Acid-base reaction

[Fe(H20)4(OH)2] PRECIPITATE FORMS

This is a green precipitate

Question 5

What happens if Fe(H20)2(OH)2 is left in air?

Answer 5

Oxidised to form a red-brown precipitate

Question 6

What happens to [Fe(H20)6]2+ in a reaction with ammonia?

Answer 6

[Fe(H20)4(OH)2] PRECIPITATE FORMS

This is a green precipitate

Question 7

What happens to [Fe(H20)6]2+ in a reaction with carbonate?

Answer 7

FeCO3

This is a green precipitate

Question 8

What is the colour of [Cu(H20)6]2+?

Answer 8

Blue solution

Question 9

What happens to [Cu(H20)6]2+ when OH- is added?

Answer 9

[Cu(H20)4(OH)2] ppt forms

This is a blue precipitate

Question 10

What happens to [Cu(H20)6]2+ when NH3 is added (including in excess)?

Answer 10

[Cu(H20)4(OH)2] ppt forms initially: blue precipitate (acid-based)

Excess ammonia leads to ligand substitution: [Cu(NH3)4(H2O)2] ppt forms

Question 11

What happens to [Cu(H20)6]2+ in a reaction with carbonate?

Answer 11

CuCO3 ppt - blue-green precipitate

Question 12

What is the colour of [CoH20)6]2+?

Answer 12

Pink solution

Question 13

Under what conditions can cobalt be oxidised?

Answer 13

Under alkaline conditions

Question 14

What happens to [Co(H20)6]2+ when OH- is added? And what happens if this is left standing in air?

Answer 14

[Co(H20)4(OH)2] ppt forms initially: blue-green precipitate (acid-base)

On standing it is a bit weird so a pink solution can form which then turns to a brown precipitate (in which you have a cobalt (III) hydroxide: Co(H20)3(OH)3)

Question 15

What is the difference between a complex ion and a precipitate?

Answer 15

Precipitates are uncharged! If the transition metal complex is uncharged it is a precipitate

Question 16

What happens to [Co(H20)6]2+ when ammonia is added? What happens when ammonia is in excess? And what happens if this is left standing in air?

Answer 16

[Co(H20)4(OH)2] ppt forms initially: blue-green precipitate (acid-base)

[Co(NH3)6]2+ (this really is awesome … COMPLETE SUBSTITUTION IN EXCESS!)

Again in air a bit weird … but can be oxidised to a dark brown solution (again reflects the fact that cobalt (III) is in the solution

Question 17

What happens to cobalt when carbonate is added?

Answer 17

CoCO3 forms which is a purple precipitate

Question 18

What is the colour of [Cr(H20)6]3+?

Answer 18

Pale green solution

Question 19

What is the colour of [Fe(H20)6]3+?

Answer 19

Yellow solution

Question 20

What is the colour of [Al(H20)6]3+?

Answer 20

Colourless

Question 21

What happens to [Cr(H20)6]3+ when OH- is added? What happens when OH- is in excess?

Answer 21

Grey green precipitate: Cr(OH)3(H2O)3 (acid-base)

Dark green solution: [Cr(OH)6]3- (ligand substitution when in excess - one of the only ones that do this with hydroxide)

Question 22

What happens to [Fe(H20)6]3+ when OH- is added? What happens when OH- is in excess?

Answer 22

Red-brown precipitate: Fe(OH)3(H2O)3 (acid-base)

IN EXCESS: Erm … nothing new!

Question 23

What happens to [Al(H20)6]3+ when OH- is added? What happens when OH- is in excess?

Answer 23

White precipitate: Al(OH)3(H2O)3 (acid-base)

Colourless solution: [Al(OH)4(H2O)2]- (ligand substitution when in excess - one of the only ones that do this with hydroxide)

Question 24

What happens to [Cr(H20)6]3+ when NH3 is added? What happens when NH3 is in excess?

Answer 24

Grey green precipitate: Cr(OH)3(H2O)3 (acid-base)

Violet solution: [Cr(NH3)6]3+ (ligand substitution)

Question 25

What happens to [Fe(H20)6]3+ when NH3 is added? What happens when NH3 is in excess?

Answer 25

Red-brown precipitate: Fe(OH)3(H2O)3 (acid-base)

IN EXCESS: nothing new!

Question 26

What happens to [Al(H20)6]3+ when NH3 is added? What happens when NH3 is in excess?

Answer 26

White precipitate: Al(OH)3(H2O)3 (acid-base)

IN EXCESS: nothing new!

Question 27

What happens to [Cr(H20)6]3+ when CO3 is added?

Answer 27

Grey green precipitate: Cr(OH)3(H2O)3 (acid-base)

AND bubbles of CO2

Question 28

What happens to [Fe(H20)6]3+ when CO3 is added?

Answer 28

Red-brown precipitate: Fe(OH)3(H2O)3 (acid-base)

AND bubbles of CO2

Question 29

What happens to [Al(H20)6]3+ when CO3 is added?

Answer 29

White precipitate: Al(OH)3(H2O)3 (acid-base)

AND bubbles of CO2