3.2.6 Reactions Of Ions In Aqueous Solution

Question 1

Name 4 metal-aqua ions + their colour

Answer 1

[Fe(H2O)6]^2+ - green solution
[Cu(H2O)6]^2+ - blue solution
[Fe(H2O)6]^3+ - purple solution
[Al(H2O)6]^3+ - colourless solution

Question 2

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

Answer 2

Deprotonation
Drops- green ppt formed- goes brown on standing in air Fe(H2O)4(OH)2(s)
Excess- no further change

Question 3

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

Answer 3

Deprotonation
Drops- blue ppt formed Cu(H2O)4(OH)2(s)
Excess- no further change

Question 4

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

Answer 4

Deprotonation
Drops- brown ppt formed Fe(H2O)3(OH)3(s)
Excess- no further change

Question 5

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

Answer 5

Deprotonation
Drops- white ppt formed Al(H2O)3(OH)3(s)
Excess- no further change

Question 6

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

Answer 6

Deprotonation
Drops- green ppt formed- goes brown on standing in air Fe(H2O)4(OH)2(s)
Excess- no further change

Question 7

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

Answer 7

Deprotonation
Drops- blue ppt formed Cu(H2O)4(OH)2(s)
Excess- deep blue solution formed [Cu(H2O)2(NH3)4]2(aq)

Question 8

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

Answer 8

Deprotonation
Drops- brown ppt formed Fe(H2O)3(OH)3(s)
Excess- no further change

Question 9

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

Answer 9

Deprotonation
Drops- white ppt formed Al(H2O)3(OH)3(s)
Excess- no further change

Question 10

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

Answer 10

Green ppt FeCO3(s)

Question 11

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

Answer 11

Blue-green ppt CuCO3(s)

Question 12

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

Answer 12

Brown ppt Fe(H2O)3(OH)3(s) + CO2(g)

Question 13

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

Answer 13

White ppt Al(H2O)3(OH)3(s) + CO2 (g)

Question 14

Explain, with the use of an equation, why a solution containing [Al(H2O)6]3+ has
a pH ˂7

Answer 14

[Al(H2O)6]^3+ <=> [Al((H2O)5OH]^2+ + H^+

Question 15

Describe metal aqua complexes

Answer 15

Water molecules form coordinate bonds with central metal ions

Question 16

What determines the acidity of metal aqua ions in aqueous solution

Answer 16

The charge of central ion
Higher charge density = more acidic
Pull of electrons in O-H bonds away from H towards ion stronger, releasing the H^+ ion

Question 17

Why are complexes formed with multidentate ligands more stable than those with monodentate ligands

Answer 17

Ligands attached at multiple points to metal ion more strongly attracted
Chelate effect