2.6- reactions of aqueous ions

Question 1

Give the definition of lewis acid and bases

Answer 1

Lewis acids are electron pair acceptors
Lewis bases are electron pair donors

Question 2

Where are metal aqua ions formed

Answer 2

They are formed in aqueous solutions

Question 3

Why does Fe 3 appear yellow/brown in solution

Answer 3

The violet colour is only seen in solid hydrated salts, otherwise the colour is yellow/brown

Question 4

What is the equilibrium that occurs in aqueous solutions of metal ions

Answer 4

[M(H2O)6]2+ + H2O > [M(H2O)5(OH)]+ + H3O+

[M(H2O)6]3+ + H2O > [M(H2O)5(OH)]2+ + H3O+

.Cu 2+ - Blue
.Fe 2+ - Green
.Fe 3+ - Yellow
.Al 3+ - Colourless

Question 5

Why are the aqeuous solutions of the metal complexes acidic

Answer 5

Becuase H+ ions are produced in solution with the equilibrium, 3+ ions have a stronger acidity than the 2+ ions

Question 6

Why is the acidity of the 3+ ions stonger than the acidity for the 2 + ions

Answer 6

The 3 + ions have a higher charge density and have a greater polarising power, the greater the polarising power the more strongly it attracts the water molecule, this weakens the OH bond so it breaks more easily and releases H+ ions

Question 7

What occurs when you add OH- and NH3 to aqeuous ions

Answer 7

[M(H2O)6]3+(aq) + 3OH-(aq) > M(H2O)3(OH)3 (s) + 3H2O (l)

[M(H2O)6]2+(aq) + 2OH-(aq) > M(H2O)4(OH)2 (s) + 2H2O (l)

.Deprontonation acid base reaction, this process can also happen stepwise where on proton is removed ech time

.Cu 2+ - Blue ppt
.Fe 2+ - Green ppt
.Fe 3+ - Brown ppt
.Al 3+ - White ppt

Question 8

What happens in the reaction of Aluminium hyrdorxide in excess OH-

Answer 8

Al(H2O)3(OH)3 (s) + OH-(aq ) > [Al(OH)4]-(aq) + 3H2O (l)

.White ppt - colourless solution

Question 9

What is the reactions of Cu with excess NH3

Answer 9

Cu(OH)2(H2O)4(s) + 4NH3 (aq) > [Cu(NH3)4(H2O)2]2+(aq) + 2H2O (l) + 2OH-
(aq)

.Blue to deep blue solution

Question 10

What is the reactions of the aqueous ions with carbonate solutions

Answer 10

[M(H2O)6]2+ + CO32- > MCO3 + 6H2O

2[M(H2O)6]3+(aq) + 3CO32-(aq) > 2M(OH)3(H2O)3(s) +3CO2 + 3H2O(l)

. 2+ precipitation reaction
.3+ acidity reaction

.Cu 2+ - Blue ppt
.Fe 2+ - Green ppt
.Fe 3+ - Brown ppt and bubbles of CO2
.Al 3+ - White ppt and bubbles of CO2

Question 11

Why is a carbonate not formed with the 3+ ions when reacting with CO3 2-

Answer 11

Because there is a greater polarising power of the 3+ ion due to its higher charge density

Question 12

What happens when you add concentrated Cl- to 2+ ions

Answer 12

[Cu(H2O)6]2+(aq) + 4Cl-(aq) > [CuCl4]2- (s) + 6H2O (l)

Cu 2+- Green solution
Fe2+- Yellow solution