transition metal colours

Question 1

[Cu(H2O)6]2+

Answer 1

pale blue solution

Question 2

Cu(OH)2

Answer 2

pale blue solution

Question 3

[Cu(NH3)4(H2O)2]+2

Answer 3

dark blue solution

Question 4

[CuCl4]2-

Answer 4

yellow solution

Question 5

[Cr(H2O)6]+3

Answer 5

pale purple solution (violet)

-usually appears green as often contains other mixed complexes of chromium(III) ions

Question 6

[Cr(H2O)5SO4]+

Answer 6

green solution

Question 7

Cr(OH)3

Answer 7

grey green precipitate

Question 8

[Cr(NH3)6}+3

Answer 8

purple

Question 9

Cu2+ with sodium hydroxide

Answer 9

-blue precipitate, insoluble

Cu2+ +2OH- –> Cu(OH)2

Question 10

Fe2+ with sodium hydroxide

Answer 10

pale green solution reacts to form a green precipitate (ironIIhydroxide)
-insoluble in excess
Fe2+ + 2OH- –> Fe(OH)2

Question 11

Fe2+ with air

Answer 11

• turns brown at its surface as is oxidised to form iron(III)
• Fe(OH)2 –> Fe(OH)3

Question 12

Fe3+ with sodium hydroxide

Answer 12

• pale yellow solution reacts to form an orange brown precipitate
• Fe3+ +3OH- –> Fe(OH)3
• insoluble in excess

Question 13

Mn2+ with sodium hydroxide

Answer 13

• pale pink solution reacts to form a light brown precipitate of manganese (II) hydroxide which darkens on standing in air
• Mn2+ (aq) + 2OH- (aq) –> Mn(OH)2 (s)
• insoluble in excess

Question 14

Cr3+ with sodium hydroxide

Answer 14

violet solution reacts to form a grey green precipitate of chromium hydroxide
-Cr3+ +3OH- –> Cr(OH)3
the precipitate is soluble in excess sodium hydroxide forming a dark green solution
-Cr(OH)3 +3OH- –> [Cr(OH)6]3-

Question 15

Cu(OH)2 with ammonia

Answer 15

-blue precipitate which dissolved in excess ammonia to form a deep blue solution [Cu(NH3)4(H2O)2]2+

Question 16

Fe2+, Fe3+, Mn2+ react with ammonia

Answer 16

same way as with sodium hydroxide forming precipitate of X(OH)X
-no further reaction so the precipitates don’t dissolve

Question 17

[Co(H2O)6]2+

Answer 17

pink

Question 18

[Co(Cl4)]2-

Answer 18

blue

Question 19

ammonium ions

Answer 19

• when heated with hydroxide ions procured ammonia gas
• NH4+ + OH- –> NH3 + H2O
• should turn damp red PH paper blue

Question 20

Cu2+

Answer 20

• pale blue solution
• forms blue ppt that is insoluble in excess NaOH
• blue ppt then deep blue solution soluble in excess NH3

Question 21

Fe2+

Answer 21

• pale green solution
• green ppt, insoluble in excess NaOH
• turns brown in air
• green ppt insoluble in excess NH3

Question 22

Fe3+

Answer 22

pale yellow solution

• orange/brown ppt, insoluble in excess NaOH
• orange/brown ppt, insoluble in excess NH3

Question 23

Mn2+

Answer 23

-pale pink solution
light brown ppt that is insoluble in excess NaOH
-light brown ppt insoluble in excess NH3

Question 24

Cr3+

Answer 24

violet solution but can appear green due to impurities

• grey ppt that IS soluble n excess NaOH and forms a dark green solution
• grey ppt with ammonia that is soluble in excess, dissolving to form a purple solution