aqueous ions

Question 1

what is a coordinate bond

Answer 1

Definition: A Coordinate Bond is a shared pair of electrons which have both come from the same atom.

Question 2

what is a ligand

Answer 2

Definition: A Ligand is an ion or molecule with a lone pair of electrons which can form a coordinate bond with a transition metal ion.

Question 3

what is a complex ion

Answer 3

A complex ion is a positive metal ion surrounded by ligands

Question 4

what is the coordination number

Answer 4

Definition: The Coordination Number is the number of coordinate bonds a transition metal ion forms.

Question 5

what are the 4 aqueous ions and colours do they form

Answer 5

[Fe(H2O)6]2+ -pale green solution
[Cu(H2O)6]2+ -blue solution
[Fe(H2O)6]3+ More acidic - purple solution ( may seem yellow/brown)
[Al(H2O)6]3+ More acidic - colourless solution

Question 6

why are the 3+ ions more acidic

Answer 6

• Fe3+ is smaller and more highly charged than Fe2+
• So Fe3+ is more polarising
• This means Fe3+ strongly attracts the lone pair on the Oxygen of the water ligands.
• In turn this weakens the O-H bond strength.
• This means the Fe(III) complex more easily releases H+ ions making the solution acidic.
• The Fe(II) complex doesn’t release H+ ions.

Question 7

equation which represents fe3+ acting as an acid

Answer 7

[Fe(H2O)6]3+ —> [Fe(H2O)5(OH)]2+ + H+

Question 8

equation which represents al3+ acting as an acid

Answer 8

Al(H2O)6]3+ —-> [Al(H2O)5(OH)]2+ + H+

Question 9

Reactions of [Fe(H2O)6]2+
With Na2CO3

Answer 9

[Fe(H2O)6]2+ + CO32- —-> FeCO3(s) + 6H2O
Observation: Green solution —-> green precipitate

Question 10

Reactions of [Fe(H2O)6]2+
With NaOH

Answer 10

[Fe(H2O)6]2+ + 2OH- ——>Fe(H2O)4(OH)2 + 2H2O
Observation: Green solution —–> green precipitate

Question 11

Reactions of [Fe(H2O)6]2+
With NH3

Answer 11

[Fe(H2O)6]2+ + 2NH3 —-> Fe(H2O)4(OH)2 + 2NH4+
Observation: Green solution —–> green precipitate
As before the green precipitate will turn brown on standing as the oxygen in the air oxidises it from Fe2+ to Fe3+.
This reaction is [Fe(H2O)4(OH)2] forms [Fe(H2O)3(OH)3]

Question 12

Reactions of [Cu(H2O)6]2+
With Na2CO3

Answer 12

Cu(H2O)6]2+ + CO32- —-> CuCO3(s) + 6H2O
Observation: blue solution ——> blue green precipitate

Question 13

Reactions of [Cu(H2O)6]2+
With NaOH

Answer 13

[Cu(H2O)6]2+ + 2OH- —–> Cu(H2O)4(OH)2 + 2H2O
Observation: Blue solution ——> blue precipitate

Question 14

Reactions of [Cu(H2O)6]2+
With NH3

Answer 14

[Cu(H2O)6]2+ + 2NH3 —-> Cu(H2O)4(OH)2 + 2NH4+
Observation: Blue solution —–> blue precipitate

Question 15

Reactions of [Cu(H2O)6]2+
With excess NH3

Answer 15

[Cu(H2O)6]2+ + 4NH3 —–>[Cu(H2O)2(NH3)4]2+ + 4H2O
Observation : Blue solution —-> deep blue solution
Cu(H2O)4(OH)2 + 4NH3 —–> [Cu(H2O)2(NH3)4]2+ + 2H2O + 2OH-
Observation: blue precipitate —–> deep blue solution

Question 16

Reactions of [Cu(H2O)6]2+
With HCl

Answer 16

Chloride ions are significantly larger and so fewer can fit around the ion.
[Cu(H2O)6]2+(aq) + 4Cl-(aq) —-> [CuCl4]2-(aq) + 6H2O(l)
Observation: Blue solution —-> Yellow solution
The complex also goes from octahedral to tetrahedral.

Question 17

Reactions with [Fe(H2O)6]3+
With Na2CO3

Answer 17

2[Fe(H2O)6]3+ + 3CO32- —–> 2Fe(H2O)3(OH)3 + 3CO2 + 3H2O
Observation: Yellow brown solution —–> brown precipitate and effervescence

Question 18

Reactions with [Fe(H2O)6]3+
With NaOH

Answer 18

[Fe(H2O)6]3+ + 3OH- —–> Fe(H2O)3(OH)3 + 3H2O
Observation: Yellow brown solution —–> brown precipitate

Question 19

Reactions with [Fe(H2O)6]3+
With NH3

Answer 19

[Fe(H2O)6]3+ + 3NH3—-> Fe(H2O)3(OH)3 + 3NH4+
Observation: Yellow brown solution —-> brown precipitate

Question 20

Reactions of [Al(H2O)6]3+
With Na2CO3

Answer 20

2[Al(H2O)6]3+ + 3CO32- —–> 2Al(H2O)3(OH)3 + 3CO2 + 3H2O
Observations: Colourless solution —–> White precipitate and effervescence

Question 21

Reactions of [Al(H2O)6]3+
With NaOH

Answer 21

[Al(H2O)6]3+ + 3OH- —–> Al(H2O)3(OH)3 + 3H2O
Observation: Colourless solution —-> White precipitate

Question 22

Reactions of [Al(H2O)6]3+
With excess NaOH

Answer 22

Al(H2O)3(OH)3 + OH- —-> [Al(H2O)2(OH)4]- + H2O
Observation: White precipitate dissolves to form a colourless solution

Question 23

Reactions of [Al(H2O)6]3+
With NH3

Answer 23

[Al(H2O)6]3+ + 3NH3 —-> Al(H2O)3(OH)3 + 3NH4+
Observation: Colourless solution —-> white precipitate

Question 24

Aluminium hydroxide is amphoteric

Answer 24

Acting as a base (HCl added)
Al(H2O)3(OH)3 + 3H+ —> [Al(H2O)6]3+

Acting as an acid (NaOH added)
Al(H2O)3(OH)3 + OH- —–>[Al(H2O)2(OH)4]- + H2O

Question 25

How to test for metal ions

Answer 25

Get three test tubes and add unknown metal ions
1-add OH- and excess OH- and record observations
2-add nh3 and excess nh3 and record observations
3- add co32- and record observations