Transition Metals - Colours

Question 1

[Cu(H2O)6]2+ colour

Answer 1

pale blue solution

Question 2

Cu(OH)2(H2O)4 + excess NH3

Answer 2

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

Question 3

[Cr(H2O)6]3+ colour

Answer 3

violet solution

Question 4

Cr(OH)3(H2O)3 + excess NH3

Answer 4

[Cr(NH3)6]3+ + 6H2O
purple solution

Question 5

[Cu(H2O)6]2+ colour

Answer 5

pale blue solution

Question 6

[Cu(H2O)6]2+ + 4Cl-

Answer 6

[CuCl4]2- + 6H2O
yellow

Question 7

Structure of ethane-1,2-diamine ligand

Answer 7

H2NCH2CH2NH2

Question 8

Structure of ethanedioate ligand

Answer 8

Has a charge of 2-.
3 ethanedioates can replace 6 H2Os.

Question 9

How many coordinate bonds can EDTA form?

Answer 9

6 coordinate bonds.
Charge of 4-

Question 10

How does V2O5 act as a catalyst in the contact process?

Answer 10

Allows sulfur dioxide to adsorb to surface.
Uses its variable oxidation states to provide an alternative reaction route.

Question 11

[Fe(H2O)6]2+ colour

Answer 11

green solution

Question 12

[Fe(H2O)6]3+ colour

Answer 12

yellow solution

Question 13

[Mn(H2O)6]2+ colour

Answer 13

pink solution

Question 14

[Cr(H2O)6]3+ colour

Answer 14

violet solution

Question 15

[Fe(H2O)6]2+ + NaOH ->

Answer 15

Fe(OH)2(H2O)4 + 2H2O
green precipitate

Question 16

[Cu(H2O)6]2+ + NaOH ->

Answer 16

Cu(OH)2(H2O)4 + 2H2O
blue precipitate

Question 17

[Mn(H2O)6]2+ + NaOH ->

Answer 17

Mn(OH)2(H2O)4 + 2H2O
light brown precipitate

Question 18

[Fe(H2O)6]3+ + NaOH ->

Answer 18

Fe(OH)3(H2O)3 + 3H2O
brown precipitate

Question 19

[Cr(H2O)6]3+ + NaOH ->

Answer 19

Cr(OH)3(H2O)3 + 3H2O
grey-green precipitate

Question 20

What forms when a metal-aqua ion, e.g. [Cu(H2O)6]2+, reacts with NaOH, and is the product soluble in water?

Answer 20

A metal hydroxide forms, e.g. Cu(OH)2(H2O)4 (s), which is a precipitate. It is insoluble in water.

Question 21

What happens when iron (II) hydroxide, Fe(OH)2(H2O)4 (s), is exposed to air?

Answer 21

Precipitate turns green -> brown.
It is oxidised to Fe3+.

Question 22

What happens when manganese (II) hydroxide, Mn(OH)2(H2O)4 (s), is exposed to air?

Answer 22

Precipitate turns brown -> darker brown.
It is oxidised to Mn3+.

Question 23

What happens when we add excess NaOH to all of the metal hydroxides (precipitates) formed, except Cr(OH)3(H2O)3 (s)?

Answer 23

No change occurs.

Question 24

What happens when we add excess NaOH to Cr(OH)3(H2O)3 (s)?

Answer 24

Grey-green precipitate dissolves.
Forms dark green solution.

Question 25

What happens when we add excess NH3 to Cu(OH)2(H2O)4 (s)?

Answer 25

Cu(OH)2(H2O)4 (s) dissolves when excess NH3 is added.
Dark blue solution forms.
Ligand substitution reaction.

Cu(OH)2(H2O)4 (s) + 4NH3 -> [Cu(NH3)4(H2O)2]2+ +2H2O + 2OH-

Question 26

What happens when we add excess NH3 to Cr(OH)3(H2O)3 (s)?

Answer 26

Cr(OH)3(H2O)3 (s) dissolves when excess NH3 is added.
Purple solution formed.
Ligand substituion reaction.