6I- Ions In aq Solutions

Question 1

What are metal aqua ion complexes

Answer 1

Transition metal salt dissolved in water

H2O molecules act as ligands forming complexes with the transition metal ion

Question 2

What’s a Lewis acid and a Lewis base

Answer 2

Lewis acid, e- pair acceptor
Lewis base, e- pair donor

Question 3

What metals form a [M(H2O)6] 2+ complex

Answer 3

Fe firms a green solution
Cu firms a blue solution

Question 4

What metals form a [M(H2O)6] 3+ complex

Answer 4

Al forms a colourless solution
Fe forms a yellow/brown solution

Question 5

Why is [M(H2O)6] 3+ more acidic than [M(H2O)6] 2+

Answer 5

3+ metal ions have a higher charge density and therefore a greater polarising power
It then has a stronger attraction to a water molecule, weakening the O-H bond so it breaks, H+ ions are released

Question 6

What’s amphoteric

Answer 6

A species which dissolves in acids and bases

Question 7

Which metal hydroxide shows amphoteric character give eq

Answer 7

Limit OH-
[Al(H2O)6] 3+ +3OH- —> Al(H2O)3(OH)3 + 3H2O
Excess OH-
Al(H2O)3(OH)3 + OH- —> [Al(OH)4]- + 3H2O

Al(H2O)3(OH)3 + 3H+ —> [Al(H2O)6] 3+

With limit OH- colourless solution forms a white precipitate
With exs OH- a white precipitate redissolves

Question 8

Reaction of [Fe(H2O)6] 2+ with OH-

Answer 8

Limit OH- (2OH- due to the 2+ charge on Fe)

[Fe(H2O)6] 2+ + 2OH- —> [Fe(H2O)4(OH)2] + 2H2O

Green solution turns to a green precipitate

Excess OH-
NVC, green precipitate remains

Question 9

Reaction of [Cu(H2O)6] 2+ with OH-

Answer 9

Limit OH-
[Cu(H2O)6] 2+ + 2OH- —> [Cu(H2O)4(OH)2] + 2H2O

Blue solution forms a blue precipitate

Exs OH-
NVC, blue precipitate remains

Question 10

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

Answer 10

Limit OH-

[Fe(H2O)6] 3+ + 3OH- —> [Fe(H2O)3(OH)3] + 3H2O
A yellow solution forms a brown precipitate

Exs OH-
NVC, brown precipitate remains

Question 11

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

Answer 11

Limit NH3
[Fe(H2O)6] 2+ + 2NH3 —> [Fe(H2O)4(OH)2] + 2NH4 +
Green solution forms a green precipitate

Exs NH3
NVC green precipitate remains

Question 12

Reaction if [Cu(H2O)6] 2+. And NH3

Answer 12

Limit NH3

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

Blue solution forms a blue precipitate

Exs NH3

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

Blue precipitate forms a darker blue precipitate

Question 13

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

Answer 13

Limit NH3

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

A yellow solution Forms a brown precipitate

Exs NH3
NVC brown precipitate remains

Question 14

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

Answer 14

Limit NH3

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

A colourless solution forms a white precipitate

Exs NH3
NVC, a white precipitate remains

Question 15

Reaction of [Fe(H2O)6] 2+ and CO3 2-

Answer 15

[Fe(H2O)6] 2+ + CO3 2- —> FeCO3 + 6H2O

Green solution forms a green precipitate

Question 16

Reaction of [Cu(H2O)6] 2+ and CO3 2-

Answer 16

[Cu(H2O)6] 2+ + CO3 2- —> CuCO3 + 6H2O
A blue solution forms a blue precipitate

Question 17

Reaction of [Fe(H2O)6] 3+ and CO3 2-

Answer 17

2 [Fe(H2O)6] 3+ + 3CO3 2- —> 2[Fe(H2O)3(OH)3] + 3H2O + 3CO2

Yellow solution forms an brown precipitate

Question 18

Reaction of [Al(H2O)6] 3+ and CO3 2-

Answer 18

2[Al(H2O)6] 3+ + 3CO3 2- —> 2[Al(H2O)3(OH)3] + 3H2O + 3CO3

Colourless solution forms a white precipitate