Transition metal colours

Question 1

Cu2+ metal-aqua ion?

Answer 1

blue solution

Question 2

Cr3+ metal-aqua ion?

Answer 2

violet solution

Question 3

Mn2+ metal-aqua ion?

Answer 3

pale pink solution

Question 4

Fe2+ metal-aqua ion?

Answer 4

green solution

Question 5

Fe3+ metal-aqua ion?

Answer 5

yellow solution

Question 6

Cu2+ with OH-?

Answer 6

blue ppt (OH)2

Question 7

Cr3+ with OH-?

Answer 7

green ppt, (OH)3

Question 8

Mn2+ with OH-?

Answer 8

Pale brown ppt, (OH)2

Question 9

Fe2+ with OH-?

Answer 9

Green ppt, (OH)2

Question 10

Fe3+ with OH-?

Answer 10

orange/brown ppt, (OH)3

Question 11

Which is the only one out of Cu2+, Cr3+, Mn2+, Fe2+ and Fe3+ that changes with XS OH-?

Answer 11

• Cr3+; goes from a green precipitate to a dark green solution, (OH)6

Question 12

How does the reaction of the metal-aqua ions with OH- compare with NH3 (neither in XS)?

Answer 12

• Produce the same complex ions. As many OH ligands to make charge neutral.

Question 13

Which two metal aqua ions form a new product when NH3 is in XS?

Answer 13

Cu2+ and Cr3+

Question 14

What happens to Cu2+ in XS NH3?

Answer 14

A dark blue solution is formed, (NH3)4

Question 15

What happens to Cr3+ in XS NH3?

Answer 15

A purple solution is formed, (NH3)6

Question 16

What happens to Cu2+ in XS HCl?

Answer 16

Yellow solution formed (CuCl4 2-)

Question 17

What happens to Co2+ in XS HCl?

Answer 17

CoCl4 2- formed, blue

Question 18

What colour is the metal-aqua ion of cobalt?

Answer 18

Pink

Question 19

What happens when Cu2+ is reduced with I-?

Answer 19

CuI (white ppt) and I2 (brown liquid) formed

Question 20

What are the products of the disproportionation of Cu+ (in hot sulfuric acid maybe)?

Answer 20

• Cu (brown solid) and CuSO4 (blue solution

Question 21

What happens when KCr(SO4)2.12 H2O (s) is heated?

Answer 21

pale purple –> green [Cr(H2O)6]3+
due to its impurities Cr3+ often appears green in solution

Question 22

What happens when Cr3+- is oxidised with hot alkaline H2O2?

Answer 22

Yellow CrO4 2- formed

Question 23

What happens when 0.1 mol dm-3 H2SO4 is added to K2Cr2O7?

Answer 23

Orange solution

Question 24

What is the redox reaction which reduces MnO4- to Mn2+?

Answer 24

MnO4-/Fe2+ –> Mn2+/Fe3+?
Purple (MnO4-) to pale pink (Mn2+).
in titrations the Mn2+ is dilute it is practically colourless

Question 25

What is the redox reaction which occurs to oxidise I- to I2?

Answer 25

I-/Fe3+ --> I2/Fe2+ Orange brown (Fe3+) to brown (I2)