Reactions and Colours

Question 1

Cr 6+

Answer 1

Orange

Question 2

Cr 3+

Answer 2

Green

Question 3

Cr 2+

Answer 3

Blue

Question 4

Cr2O7 2-

Answer 4

Orange

Question 5

CrO4 2-

Answer 5

Yellow

Question 6

MnO4 -

Answer 6

Purple

Question 7

Mn 2+

Answer 7

Pink

Question 8

Fe 2+

Answer 8

Green

Question 9

Fe 3+

Answer 9

Pale violet

Question 10

[Fe(H2O)6] 2+

Answer 10

Pale green

Question 11

[Fe(H2O)6] 2+ with NaOH

Answer 11

Green gelatinous ppt of Fe(H2O)4(OH)2

-Soon oxidised by air to brown [Fe(H2O)3(OH)3]-

Question 12

[Fe(H2O)6] 2+ with excess NaOH

Answer 12

No change
Green gelatinous ppt of Fe(H2O)4(OH)2
-Soon oxidised by air to brown [Fe(H2O)3(OH)3]-

Question 13

[Fe(H2O)6] 2+ with NH3

Answer 13

Green gelatinous ppt of Fe(H2O)4(OH)2

-Soon oxidised by air to brown [Fe(H2O)3(OH)3]-

Question 14

[Fe(H2O)6] 2+ with excess NH3

Answer 14

No change
Green gelatinous ppt of Fe(H2O)4(OH)2
-Soon oxidised by air to brown [Fe(H2O)3(OH)3]-

Question 15

[Fe(H2O)6] 2+ with Na2CO3

Answer 15

Green precipitate of FeCO3

Question 16

[Co(H2O)6] 2+

Answer 16

Pink

Question 17

[Co(H2O)6] 2+ with NaOH

Answer 17

Blue ppt of CO(H2O)4(OH)2

Question 18

[Co(H2O)6] 2+with excess NaOH

Answer 18

No change

Blue ppt of CO(H2O)4(OH)2

Question 19

[Co(H2O)6] 2+ with NH3

Answer 19

Blue ppt of CO(H2O)4(OH)2

Question 20

[Co(H2O)6] 2+ with excess NH3

Answer 20

Pale yellow-brown sol of [Co(NH3)6]2+

• Oxidised by air to dark brown mixture containing Co(II) compounds.
• A blue ppt is formed as an intermediate

Question 21

[Co(H2O)6] 2+ with Na2CO3

Answer 21

Pink ppt of CoCO3

Question 22

[Co(H2O)6] 2+ with HCl

Answer 22

Dark blue sol of [CoCl4]2-

Question 23

[Cu(H2O)6] 2+

Answer 23

Pale blue

Question 24

[Cu(H2O)6] 2+with NaOH

Answer 24

Pale blue ppt of Cu(H2O)4(OH)2

Question 25

[Cu(H2O)6] 2+ with excess NaOH

Answer 25

No change | Pale blue ppt of [Cu(H2O)4(OH)2](s)

Question 26

[Cu(H2O)6] 2+ with NH3

Answer 26

Pale blue ppt of [Cu(H2O)4(OH)2](s)

Question 27

[Cu(H2O)6] 2+ with excess NH3

Answer 27

Deep blue ppt of [Cu(NH3)4(H2O)2]2+

Question 28

[Cu(H2O)6] 2+ with Na2CO3

Answer 28

Blue-green ppt of CuCO3

Question 29

[Cu(H2O)6] 2+ with HCl

Answer 29

Yellow sol of [CuCl4]2- | -Likely to appear green as some blue [Cu(H2O)6)]2- will remain.

Question 30

[Fe(H2O)6] 3+

Answer 30

Purple/yellow/brown

Question 31

[Fe(H2O)6] 3+ with NaOH

Answer 31

Brown gelatinous ppt of [Fe(H2O)3(OH)3](s)

Question 32

[Fe(H2O)6] 3+ with excess NaOH

Answer 32

No change | Brown gelatinous ppt of [Fe(H2O)3(OH)3](s)

Question 33

[Fe(H2O)6] 3+ with NH3

Answer 33

Brown gelatinous ppt of [Fe(H2O)3(OH)3](s)

Question 34

[Fe(H2O)6] 3+ with excess NH3

Answer 34

No change | Brown gelatinous ppt of [Fe(H2O)3(OH)3](s)

Question 35

[Fe(H2O)6] 3+ with Na2CO3

Answer 35

Brown gelatinous ppt of [Fe(H2O)3(OH)3] with bubbles of CO2

Question 36

[Al(H2O)6] 3+

Answer 36

Colourless

Question 37

[Al(H2O)6] 3+ with NaOH

Answer 37

White ppt of [Al(H2O)3(OH)3](s)

Question 38

[Al(H2O)6] 3+ with excess NaOH

Answer 38

Colourless sol of [Al(OH)4]-

Question 39

[Al(H2O)6] 3+ with NH3

Answer 39

White ppt of [Al(H2O)3(OH)3](s)

Question 40

[Al(H2O)6] 3+ with excess NH3

Answer 40

No change | White ppt of [Al(H2O)3(OH)3](s)

Question 41

[Al(H2O)6] 3+ with Na2CO3

Answer 41

White ppt of [Al(H2O)3(OH)3] with bubbles of CO2

Question 42

[Cr(H2O)6] 3+

Answer 42

Violet/ruby

Question 43

[Cr(H2O)6] 3+ with NaOH

Answer 43

Green ppt of [Cr(H2O)3(OH)3](s)

Question 44

[Cr(H2O)6] 3+ with excess NaOH

Answer 44

Green sol of [Cr(OH)6]3-

Question 45

[Cr(H2O)6] 3+ with NH3

Answer 45

Green ppt of [Cr(H2O)3(OH)3](s)

Question 46

[Cr(H2O)6] 3+ with excess NH3

Answer 46

Purple sol of [Cr(NH3)6]3+ | -A green ppt is formed as an intermediate

Question 47

[Cr(H2O)6] 3+ with Na2CO3

Answer 47

Green ppt of Cr(OH)3 + with bubbles of CO2