Transition Metals

Question 1

(V)2+

Answer 1

Oxidation number: +2
Colour: lavender

Question 2

(V)3+

Answer 2

Oxidation number: +3
Colour: green

Question 3

(VO)2+

Answer 3

Oxidation number: +4
Colour: blue

Question 4

(VO2)+

Answer 4

Oxidation number: +5
Colour: yellow
State: solution

Question 5

(VO3)-

Answer 5

Oxidation number: +5
Colour: colourless
State: solid

Question 6

Reduction of Vanadium

Answer 6

1. Via zinc
2. Via iron (II)

Question 7

Reduction of Vanadium via zinc

Answer 7

Reagents: powdered zinc, ammonium vanadate, 50% HCl
Conditions: warm
Colour change: yellow –> lavender
Change in oxidation number: +5 –> +2

Question 8

Reduction of Vanadium via iron (II)

Answer 8

Reagents: equal volumes of dilue HCl and iron (II) sample, few drops of ammonium vanadate
Conditions: mix at room temperature
Colour change: yellow –> blue
Change in oxidation number: +5 –> +4

Question 9

(Cr)2+

Answer 9

Oxidation number: +2
Colour: blue

Question 10

(Cr)3+

Answer 10

Oxidation number: +3
Colour: green

Question 11

(CrO4)2-

Answer 11

Oxidation number: +6
Colour: yellow

Question 12

(CrO7)2-

Answer 12

Oxidation number: +6
Colour: orange

Question 13

Reduction of dichromate

Answer 13

Reagents: x
Conditions: x
Colour change: orange ==> blue
Change in oxidation number: +6 –> +2
(Cr2O7)2- –> Cr2+

Question 14

Oxidation of chromium

Answer 14

Reagents: hydrogen peroxide
Conditions: alkaline solution
Colour change: green ==> yellow
Change in oxidation number: +6 –> +2
Cr(OH)3 + 5OH- –> CrO42- + 3e- + 4H2O

Question 15

Cr3+ with NaOH

Answer 15

Hydrated colour: green
Precipitate colour: green
Effect of adding excess: green solution
Type of reaction: deprotonation/further deprotonation
Cr3+ + NaOH –> [Cr(H2O)6]3+ –> Cr(H2O)3(OH)3 –> [Cr(OH)6]3-

Question 16

Fe2+ with NaOH

Answer 16

Hydrated colour: green
Precipitate colour: green
Effect of adding excess: none
Type of reaction: deprotonation
Fe2+ + NaOH –> [Fe(H2O)6]2+ –> Fe(H2O)4(OH)2

Question 17

Fe3+ with NaOH

Answer 17

Hydrated colour: yellow
Precipitate colour: red-brown
Effect of adding excess: none
Type of reaction: deprotonation
Fe3+ + NaOH –> [Fe(H2O)6]3+ –> Fe(H2O)3(OH)3

Question 18

Co2+ with NaOH

Answer 18

Hydrated colour: pink
Precipitate colour: blue
Effect of adding excess: none
Type of reaction: deprotonation
Co2+ + NaOH –> [Co(H2O)6]2+ –> Co(H2O)4(OH)2

Question 19

Cu2+ with NaOH

Answer 19

Hydrated colour: blue
Precipitate colour: blue
Effect of adding excess: none
Type of reaction: deprotonation
Cu2+ + NaOH –> [Cu(H2O)6]2+ –> Cu(H2O)4(OH)2

Question 20

Cr3+ with ammonia

Answer 20

Hydrated colour: green
Precipitate colour: green
Effect of adding excess: green solution
Type of reaction: deprotonation
[Cr(H2O)6]3+ + NH3 –> Cr(H2O)3(OH)3 –> [Cr(NH3)6]3+

Question 21

Fe2+ with ammonia

Answer 21

Hydrated colour: green
Precipitate colour: green
Effect of adding excess: none
Type of reaction: deprotonation/ligand exchange
[Fe(H2O)6]2+ + NH3 –> Fe(H2O)4(OH)2

Question 22

Fe3+ with ammonia

Answer 22

Hydrated colour: yellow
Precipitate colour: red-brown
Effect of adding excess: none
Type of reaction: deprotonation
[Fe(H2O)6]3+ + NH3 –> Fe(H2O)3(OH)3

Question 23

Co2+ with ammonia

Answer 23

Hydrated colour: pink
Precipitate colour: blue
Effect of adding excess: brown solution
Type of reaction: deprotonation/ligand exchange
[Co(H2O)6]2+ + NH3 –> Co(H2O)4(OH)2 –> [Co(NH3)6]2+

Question 24

Cu2+ with ammonia

Answer 24

Hydrated colour: blue
Precipitate colour: blue
Effect of adding excess: deep blue solution
Type of reaction: deprotonation/ligand exchange
[Cu(H2O)6]2+ + NH3 –> Cr(H2O)4(OH)2 –> [Cu(NH3)4(H2O)2]2+