Topic 30 - Test tube reactions of ions in solution

Question 1

Colour of [Cu(H2O)6]2+

Answer 1

Blue

Question 2

Colour of [Fe(H2O)6]2+

Answer 2

Pale Green

Question 3

[Fe(H2O)6]3+

Answer 3

Orange/brown

Question 4

Colour of [Al(H2O)6]3+

Answer 4

Colourless

Question 5

What occurs in the hydrolysis reaction
Metal complexes

Answer 5

In solution, metal aqua ions lose H+ from one or more H2O ligands in a hydrolysis reaction.

Question 6

Hydrolysis of M2+ aqua ions equation

Answer 6

[M(H2O)6]2+ –> [M(H2O)4(OH)2] + 2H+

Question 7

Hydrolysis of M3+ aqua ions

Answer 7

[M(H2O)6]3+ –> [M(H2O)3(OH)3] + 3H+

Question 8

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

Answer 8

• 2+ - only partially dissociates so fewer H+ ions are released compared to 3+
• Metal 3+ ions are pretty small but have a big charge so have higher charge density.
• This means they are more polarising so attract more strongly electrons from the oxygen atoms of the co-ordinated water molecules - weakening the O-H bond.
• More likely the hydrogen ion will be released.
• The more hydrogen ions means a more acidic solution.

Question 9

What is amphoteric?

Answer 9

Can act as an acid or a base

Question 10

Which metal hydroxide is amphoteric and why?

Answer 10

Aluminium hydroxide

In the presence of a base eg. NaOH, it acts as an acid and donates H+ ions to the OH- ions, forming a soluble compound.
In the presence of an acid it can act as a base and accepts H+ ions from the H3O + ions in solution.

Question 11

Equation with Al(OH)3(H2O)3 (s)
with acid and base

Answer 11

With acid
Al(OH)3(H2O)3 + 3H3O+ –> [Al(H2O)6]3+ +3H2O

With base

Al(OH)3(H2O)3 + 3OH- –> [Al(OH)6]3- +3H2O

Question 12

Equation of ammonia dissolving in water

Answer 12

NH3 + H2O <–> NH4+ + OH-

Question 13

aqua ion: [Fe(H2O)6] 2+
reaction: some NH3

Answer 13

Equation: [Fe(H2O)6] 2+ + 2NH3 –> [Fe(H2O)4(OH)2] + 2NH4+
Observation: Pale green solution to green precipitate

Question 14

aqua ion: [Fe(H2O)6] 2+
reaction: excess NH3

Answer 14

NO CHANGE

Question 15

aqua ion: [Cu(H2O)6] 2+
reaction: some NH3

Answer 15

Equation: [Cu(H2O)6] 2+ + 2NH3 –> [Cu(H2O)4(OH)2] + 2NH4+
Observation: Blue solution to Blue gelatinous precipitate

Question 16

aqua ion: [Cu(H2O)6] 2+
reaction: excess NH3

Answer 16

Equation: [Cu(H2O)4(OH)2] + 4NH3 –> [Cu(H2O)2(NH3)4]2+ + 4H2O
Observation: Deep blue solution forms

Question 17

aqua ion: [Fe(H2O)6] 3+
reaction: some NH3

Answer 17

Equation: [Fe(H2O)6] 3+ + 3NH3 –> [Fe(H2O)3(OH)3] + 3NH4+
Observation: Orange/ yellow solution to brown gelatinous precipitate

Question 18

aqua ion: [Fe(H2O)6] 3+
reaction: excess NH3

Answer 18

NO CHANGE

Question 19

aqua ion: [Al(H2O)6] 3+
reaction: some NH3

Answer 19

Equation: [Al(H2O)6] 3+ + 3NH3 –> [Al(H2O)3(OH)3] + 3NH4+
Observation: Colourless solution to white precipitate after a few drops

Question 20

aqua ion: [Al(H2O)6] 3+
reaction: excess NH3

Answer 20

NO CHANGE

Question 21

aqua ion: [Fe(H2O)6] 2+
reaction: some (CO3)2-

Answer 21

Equation: [Fe(H2O)6] 2+ + (CO3) 2- –> FeCO3 + 6H2O
Observation: Pale green solution to green precipitate

Question 22

aqua ion: [Cu(H2O)6] 2+
reaction: some (CO3) 2-

Answer 22

Equation: [Cu(H2O)6] 2+ + (CO3) 2- –> CuCO3 + 6H2O
Observation: Blue solution to greeny blue precipitate

Question 23

aqua ion: [Fe(H2O)6] 3+
reaction: some (CO3) 2-

Answer 23

Equation: 2[Fe(H2O)6] 3+ + (CO3) 2- –> 2[Fe(H2O)3(OH)3] + 3H2O + 3CO2
Observation:Orange/yellow solution to brown gelatinous precipitate and effervescence

Question 24

aqua ion: [Al(H2O)6] 3+
reaction: some (CO3) 2-

Answer 24

Equation: 2[Al(H2O)6] 3+ + (CO3) 2- –> 2[Al(H2O)3(OH)3] + 3H2O + 3CO2
Observation: colourless solution to a white precipitate and effervescence

Answer 25

Equation:
Observation:

Question 26

Which metal complex goes colourless in excess OH ions

Answer 26

Al 3+

Question 27

How to remember vanadium oxidation states

Answer 27

Yellow
Blue
Green
Violet