D-block ions colours

Question 1

Excess NH3 (aq) added to [Cu(H2O)6]2+

Answer 1

pale blue [Cu(H2O)6]2+ to dark blue [Cu(NH3)4(H2O)2]2

[Cu(H2O)6]2+ + 4NH3 –> [Cu(NH3)4(H2O)2]2+ + 4H20

Question 2

Excess ammonia added drop wise to [Cu(H2O)6]2+

Answer 2

• pale bue Cu(OH)2 will from first
• The Cu(OH)2 precipitate then dissolves in excess ammonia to form the dark blue [Cu(H2O)2(NH3)4]2+

Question 3

Excess concentrated hydrochloric acid added to [Cu(H2O)6]2+

Answer 3

pale blue [Cu(H2O)6]2+ to yellow [CuCl4)2-

[Cu(H2O)6]2+ + 4Cl- –> [CuCl4]2- + 6H20

*Pale blue - green (mix of both colours) - yellow

Question 4

Chromium (III) potassium sulfate dissolved in water

Answer 4

[Cr(H20)6]3+ A pale purple solution

Question 5

Chromium (III) Sulfate dissolve in water

Answer 5

[Cr(H2O)5SO4]+ A green solution

Question 6

[Cr(H2O)6]3+ will excess ammonia (aq)

Answer 6

[Cr(NH3)6]3+ a purple precipitate/solution

[Cr(H2O)6]3+(voilet) + 6NH3 –> [Cr(NH3)6]3+(purple) + 6H20

Question 7

[Cr(H2O)6]3+ aqueous ammonia added dropwise

Answer 7

1. initially a grey-green precipitate Cr(OH)3 formed
2. Cr(OH)3 precipitate dissolves in the excess ammonia to from [Cr(NH3)6]3+ (purple)

violet - grey green precipitate - purple

Question 8

Cu2+ with NaOH

Answer 8

Cu2+ + 2OH- –> Cu(OH)2 (s) (insoluble in excess sodium hydroxide)

blue solution to blue precipitate

Question 9

Fe2+ with NaOH

Answer 9

Fe2+ + 2OH- –> Fe(OH)2 (insoluble in excess sodium hydroxide)
Pale green solution to form a green precipitate (turns brown at its surface through oxidation)

Question 10

Fe3+ with NaOH

Answer 10

Fe3+ + 30H- –> Fe(OH)3 (insoluble in excess sodium hydroxide)

pale yellow to form an orange brown precipitate

Question 11

Mn2+ with NaOH

Answer 11

Mn2+ + 2OH- –> Mn(OH)2 (insoluble)

pale pink to light brown precipitate (darkens in air)

Question 12

Cr3+ with NaOH

Answer 12

Cr3+ + 3OH- –> Cr(OH)3
Violet to grey-green precipitate
Soluble in excess sodium hydroxide
Cr3+ –> Cr(OH)3 –> [Cr(OH)6]3- (dark-green solution)

Question 13

Reaction with ammonia with [Cr(H2O)6]3+ and [Cu(H2O)6]2+

Answer 13

Cu2+ + 2OH- –> Cu(OH)2 (blue precipitate) dissolves in excess ammonia to form [Cu(NH3)4(H2O)2]2+ deep blue.

Cr3+ + 3OH- –> Cr(OH)3 (green precipitate/grey green) dissolves in excess ammonia to form [Cr(NH3)6]3+ purple solution

Question 14

Reaction with ammonia with Fe2+, Fe3+ and Mn2+

Answer 14

reacts with same way they react wot aqueous sodium hydroxide forming
- Fe(OH)2 (s)
- Fe(OH)3 (s)
- Mn(OH)2 (s)
no further reactions as precipitates do not dissolve