Reaction of aqueous ions

Question 1

What is the colour of the solution when Cu2+ ions are hydrated to [Cu(H2O)6]2+

Answer 1

Blue solution

Question 2

What is the colour of the solution when Fe2+ ions are hydrated to [Fe(H2O)6]2+

Answer 2

Pale green solution

Question 3

What is the colour of the solution when Fe3+ ions are hydrated to [Fe(H2O)6]3+

Answer 3

Yellow brown solution (purple)

Question 4

What is the colour of the solution when Al3+ ions are hydrated to [Al(H2O)6]3+

Answer 4

Colourless solution

Question 5

Why are Fe3+ and Al3+ ions more acidic than Cu2+ and Fe2+?

Answer 5

Fe3+ is smaller and more highly charged than Fe2+
Fe3+ is more polarising
Fe3+ strongly attracts the lone pair on the oxygen of the water ligands
Weakens the O-H bond strength
Fe3+ complexes more easily release H+ ions making the solution acidic
Fe2+ ions do not release H+ ions

Question 6

Write an equation to show Fe3+ complex act as an acid

Answer 6

[Fe(H2O)6]3+ → [Fe(H2O)5(OH)]2+ + H+

Question 7

Reaction of [Fe(H2O)6]2+ with Na2CO3 equation

Answer 7

[Fe(H2O)6]2+ + CO32- —> FeCO3(s) + 6H2O

Question 8

Observation of [Fe(H2O)6]2+ reacting with Na2CO3

Answer 8

Green precipitate

Question 9

Reaction of [Fe(H2O)6]2+ with NaOH equation

Answer 9

[Fe(H2O)6]2+ + 2OH- → Fe(H2O)4(OH2) + 2H2O

Question 10

Observation of [Fe(H2O)6]2+ with NaOH

Answer 10

Green precipitate
(goes brown on standing in air as the oxygen oxidises Fe2+ to Fe3+)

Question 11

Reaction of [Fe(H2O)6]2+ with NH3 equation

Answer 11

[Fe(H2O)6]2+ + 2NH3 → [Fe(H2O)4(OH)2] + 2NH4+

Question 12

Observation of [Fe(H2O)6]2+ with NH3

Answer 12

Green precipitate
Brown on standing in air

Question 13

Reaction of [Cu(H2O)6]2+ with Na2CO3 equation

Answer 13

[Cu(H2O)6]2+ + CO32- → CuCO3(s) + 6H2O

Question 14

Observation of [Cu(H2O)6]2+ with Na2CO3

Answer 14

Blue-green precipitate

Question 15

Reaction of [Cu(H2O)6]2+ with NaOH equation

Answer 15

[Cu(H2O)6]2+ + 2OH- → Cu(H2O)4(OH)2 + 2H2O

Question 16

Observation of [Cu(H2O)6]2+ with NaOH

Answer 16

Blue precipitate

Question 17

Reaction of [Cu(H2O)6]2+ with NH3 equation

Answer 17

[Cu(H2O)6]2+ + 2NH3 → Cu(H2O)4(OH)2 + 2NH4+

Question 18

Observation of [Cu(H2O)6]2+ with NH3

Answer 18

Blue precipitate

Question 19

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

Answer 19

[Cu(H2O)6]2+ +4NH3 —> [Cu(H2O)2(NH3)4]2+ +4H2O

Question 20

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

Answer 20

Deep blue solution

Question 21

Reaction of Cu(H2O)4(OH)2] with excess NH3 equation

Answer 21

Cu(H2O)4(OH)2] + 4NH3 → [Cu(H2O)2(NH3)4]2+(aq) + 2H2O + 2OH-

Question 22

Reaction of [Cu(H2O)6]2+ with chloride ions

Answer 22

[Cu(H2O)6]2+ + 4Cl- —> [CuCl4]2- + 6H2O

Question 23

Observation of [Cu(H2O)6]2+ with chloride ions

Answer 23

Yellow solution

Question 24

Reaction of [Fe(H2O)6]3+ with Na2CO3

Answer 24

2[Fe(H2O)6]3+ + 3CO32- → 2Fe(H2O)3(OH)3 + 3CO2 + 3H2O

Question 25

Observation of [Fe(H2O)6]3+ with Na2CO3

Answer 25

Brown ppt and CO2 gas evolved which gives effervescence

Question 26

Reaction of [Fe(H2O)6]3+ with NaOH

Answer 26

[Fe(H2O)6]3+ + 3OH- → Fe(H2O)3(OH)3 + 3H2O

Question 27

Observation of [Fe(H2O)6]3+ with NaOH

Answer 27

Brown precipitate

Question 28

Reaction of [Fe(H2O)6]3+ with NH3

Answer 28

[Fe(H2O)6]3+ + 3NH3 → Fe(H2O)3(OH)3 + 3NH4+

Question 29

Observation of [Fe(H2O)6]3+ with NH3

Answer 29

Brown precipitate

Question 30

Reaction of [Al(H2O)6]3+ with Na2CO3

Answer 30

2[Al(H2O)6]3+ + 3CO32- → 2Al(H2O)3(OH)3 + 3CO2 + 3H2O

Question 31

Observation of [Al(H2O)6]3+ with Na2CO3

Answer 31

White precipitate and effervescence as CO2
gas evolved

Question 32

Reaction of [Al(H2O)6]3+ with NaOH

Answer 32

[Al(H2O)6]3+ + 3OH- → [Al(H2O)3(OH)3] + 3H2O

Question 33

Reaction of [Al(H2O)3(OH)3] with excess NaOH

Answer 33

[Al(H2O)3(OH)3] + OH- → [Al(H2O)2(OH)4]- + H2O

Question 34

Observation of [Al(H2O)6]3+ with NaOH

Answer 34

White precipitate

Question 35

Observation of [Al(H2O)3(OH)3] with excess NaOH

Answer 35

White precipitate dissolves to form a colourless solution

Question 36

Reaction of [Al(H2O)6]3+ with NH3

Answer 36

[Al(H2O)6]3+ + 3NH3 → [Al(H2O)3(OH)3] + 3NH4+

Question 37

Observation of [Al(H2O)6]3+ with NH3

Answer 37

White precipitate

Question 38

How do Al3+ show amphoteric character?

Answer 38

Acting as a base (HCl added):
[Al(H2O)3(OH)3] + 3H+ → [Al(H2O)6]3+
Acting as an acid:
[Al(H2O)3(OH)3] + OH- → [Al(H2O)2(OH)4]- + H2O