Aqeous Ions

Question 1

define a coordinate bond

Answer 1

Shared pair of electrons that have both come from the same atom

Question 2

Define a ligand

Answer 2

Ion or molecule with a lone pair of electrons which can form a covalent bond with a transition metal ion

Question 3

Define complex ions

Answer 3

Central ion is a central atom or ion surrounded by ligands

Question 4

Define coordination number

Answer 4

Number of coordinate bonds transition metal ion forms

Question 5

What are the colours of the hexa aqua complex ions
- [Cu(H2O)6]2+
- [Fe(H2O)6]2+
- [Fe(H2O)6]3+
- [Al(H2O)6]3+

Answer 5

• blue solution
• pale green solution
• yellow/brown solution
• colourless solution

Question 6

Why are 3+ ions more acidic?

Answer 6

Fe3+ is smaller and more highly charged
So Fe3+ is more polarising
Meaning it strongly attracts the lone pair on the oxygen of the water ligands
This weakens the O-H bond strength
Fe 3 complex more easily releases H+ ions making the solution acidic
Fe 2 doesn’t release H+ ions

Question 7

Write an equation to show Fe3+ acting as an acid

Answer 7

[Fe(H2O)6]3+ —> [Fe(H2O)5OH]2+ + H+

Question 8

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

Answer 8

[Fe(H2O06]2+ + CO32- —> FeCO3 + 6H2O
precipitates are neutral
Observation: green solution to green precipitate

Question 9

[Fe(H2O6]2+ with NaOH

Answer 9

[Fe(H2O6]2+ + 2OH- —> [Fe(H2O)4(OH)2 + 2H2O
Green solution —> green precipitate

Question 10

[Fe(H2O6]2+ with NH3

Answer 10

[Fe(H2O6]2+ + 2NH3 —> [Fe(H2O)4(OH)2] + 2NH4+
Green solution —> Green precipitate
Green precipitate will turn brown standing as oxygen in air oxidise it to 3+
This forms [Fe(H2O)3(OH)3]

Question 11

[Cu(H2O)6]2+ with Na2CO3

Answer 11

[Cu(H2O)6]2+ + CO32- —> CuCO3 + 6H2O
Blue solution —> blue green precipitate

Question 12

[Cu(H2O)6]2+ with NaOH

Answer 12

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

Question 13

[Cu(H2O)6]2+ with NH3

Answer 13

[Cu(H2O)6]2+ + 2NH3 —> [Cu(H2O)4(NH3)2] + 2NH4+
Blue solution—> Blue ppt

Question 14

[Cu(H2O)6]2+ with HCL

Answer 14

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

Question 15

[Fe(H2O)6]3+ with Na2CO3

Answer 15

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

Question 16

[Fe(H2O)6]3+ with NaOH

Answer 16

[Fe(H2O)6]3+ + 3OH- —> [Fe(H2O)3(OH)3] + 3H2O
Yellow brown solution—> brown ppt

Question 17

[Fe(H2O)6]3+ with NH3

Answer 17

[Fe(H2O)6]3+ + 3NH3 —> [Fe(H2O)3(OH)3] + 3NH4+
yellow brown solution —> brown ppt

Question 18

[Al(H2O)6]3+ with Na2CO3

Answer 18

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

Question 19

[Al(H2O)6]3+ with NaOH

Answer 19

[Al(H2O)6]3+ + 3OH- —> [Al(H2O)3(OH)3] + 3H2O
Colourless solution —> white ppt
Excess:

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

Question 20

[Al(H2O)6]3+ with NH3

Answer 20

[Al(H2O)6]3+ + 3NH3 —> [Al(H2O)3(OH)3 + 3NH4+
Colourless solution —> White precipitate

Question 21

Show aluminium hydroxide being amphoteric

Answer 21

Meaning: Can act as a base or acid
Base(HCL needed)
Al(H2O)3(OH)3 + 3H+ —> [Al(H2O)6]3+
Acid (NaOH needed)
al(H2O)3(OH)3 + OH- —> [Al(H2O)2(OH)4] + H2O

Question 22

Copper ion with excess NH3

Answer 22

[Cu(H2O)6]2+ + 4NH3–> [Cu(H2O)2(NH3)4]2+ + 4H2O (blue solution—> deep blue solution)
Excess happens when ppt is formed so equation is:
[Cu(H2O)4(OH)2] + 4NH3 —> [Cu(NH3)4(H2O)2]2+ + 2H2O + 2OH-
Blueppt —> Deep blue solution