Transition Elements Colour Changes

Question 1

[Cr(H2O)6]3+

Answer 1

Violet

Question 2

Cr3+ with OH-

Answer 2

Cr(OH)3 green precipitate

Question 3

Cr3+ with excess OH-

Answer 3

[Cr(OH6)]3- dark green solution

Question 4

Cr3+ with NH3

Answer 4

Cr(OH)3 - grey green precipitate

Question 5

Cr3+ with excess NH3

Answer 5

[Cr(NH3)6]3+ purple solution

Question 6

[Fe(H2O)6]2+

Answer 6

Pale green solution

Question 7

Fe2+ with OH-

Answer 7

Fe(OH)2 green pp

Question 8

Fe(OH)2+ —> Fe(OH)3+ (in the presence of air)

Answer 8

Guacamole - green to brown

Question 9

Fe3+ and OH-

Answer 9

Fe(OH)3 brown pp

Question 10

Fe2+

Answer 10

Pale green

Question 11

[Fe(H2O)6]3+

Answer 11

Yellow solution

Question 12

Fe3+ with OH-

Answer 12

Fe(OH)3 brown pp

Question 13

[Mn(H2O)6]2+

Answer 13

Pale pink

Question 14

Mn2+ and OH-

Answer 14

Mn(OH)2 - pale brown pp

Question 15

[Cu(H2O)6]2+

Answer 15

Blue solution

Question 16

Cu2+ and OH-

Answer 16

Cu(OH)2 - blue pp

Question 17

Cu2+ with excess NH3

Answer 17

[Cu(NH3)4(H2O)2]2+ - dark blue solution

Question 18

[Cu(H2O)6]2+ and Cl-

Answer 18

[CuCl4] - yellow solution + 6H2O but can often look green because equilibrium

Question 19

[Cr(H2O)6]3+ and Sulphate

Answer 19

[Cr(H2O)5SO4]+ Green

Question 20

Fe3+ reaction with I-

Answer 20

Fe3+ reduced to Fe2+ goes from brown to pale green but colour is obscured by brown since I- forms I2(aq)

Question 21

Fe2+ with MnO4-

Answer 21

• Fe2+ is oxidised to Fe3+
• MnO4- is reduced to Mn 2+
  Purple to colourless

Question 22

Cu2+ and iodine

Answer 22

Cu2+ is reduced to Cu+, forms white pp of CuI(s) and I2

Question 23

V2+ ——> Zn2+

Answer 23

Vbpigpigbc

• Violet, blue, pink, green, pink, green, blue and colourless
• 2 pigs means 2+ ions
• Colourless because zinc doesn’t have an unpaired d sub shell

Question 24

Sc3+ —-> Co3+

Answer 24

• K-pop group name is cpu gv2 yb (colourless, purple, green, violet, violet, yellow, blue)
• They have been a group for 3 years (3+)
• The oldest member name is Scandium and the youngest is Colbalt

Question 25

V4+, V3+, V2+, Ti3+

Answer 25

The remaining blue,green, violet and colourless