reaction of aqueous ions in solution

lewis acid and lewis base definition

• lewis acid: electron pair acceptor

• lewis base: electron pair donor

in the formation in complex ions what is the Lewis base and the Lewis acid

• the ligand is the lewis base because its donating a pair of electrons in the coordinate bond

• the metal ion is the lewis acid

Acidity or hydrolysis reactions

reaction of hexaaquacopper with hydroxide ions w/ colour change

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

colour change from blue solution to blue ppt.

reaction of hexaaquacopper with limited NH3 w/ colour change

[Cu(H2O)₆]²⁺ (aq) + 2NH₃ (aq) ———> Cu(H2O)₄(OH)₂ (s) + 2NH_4⁺ (aq)

colour change from blue solution to blue ppt.

reaction with of copper with excess NH3 w/ colour change

blue ppt. dissolves to form deep blue solution

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

reaction of hexaaquairon (II) with hydroxide ions w/ colour change

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

colour change from green solution to green ppt.

reaction of hexaaquairon (II) with limited NH3 w/ colour change

[Fe(H2O)₆]²⁺ (aq) + 2NH₃ (aq) ———> Fe(H2O)₄(OH)₂ (s) + 2NH_4⁺ (aq)

colour change from green solution to green ppt.

reaction of hexaaquairon(III) with hydroxide ions w/ colour change

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

colour change from purple solution to brown ppt.

reaction of hexaaquairon(III) with NH3 w/ colour change

[Fe(H2O)₆]^₃⁺ (aq) + 3NH₃ (aq) ———> Fe(H2O)₃(OH)₃(s) + 3NH_4⁺ (aq)

colour change from purple solution to brown ppt.

reaction of hexaaquaaluminium (III) with hydroxide ions w/ colour change

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

colour change from colourless to white ppt

reaction of hexaaquaaluminium (III) with NH3 w/ colour change

[Al(H2O)₆]^₃⁺ (aq) + 3NH₃ (aq) ———> Al(H2O)₃(OH)₃(s) + 3NH_4⁺ (aq)

colour change from colourless solution to white ppt.

what type of molecule is Al(H2O)₃(OH)₃ and what does that mean

Al(H2O)₃(OH)₃ is an amphoteric molecule

• reacts with both acids and bases

reaction of hexaaquaaluminium (III) with excess hydroxide ions w/ colour change

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

colour change from white ppt. to colourless solution

reaction of Al(H2O)₃(OH)₃ with acid

Al(H2O)₃(OH)₃ + 3H+ (aq) ———> [Al(H2O)6]³⁺ (aq)

reaction of hexaaquacopper with CO₃²⁻ , including colour change

[Cu(H₂O)₆]²⁺ (aq) + 2CO₃²⁻ —→ CuCO₃ (s) + 6H₂O (l)

colour change from blue to blue/green ppt.

reaction of hexaaquairon (II) with CO₃²⁻ , including colour change

[Fe(H₂O)₆]²⁺ (aq) + 2CO₃²⁻ —→ FeCO₃ (s) + 6H₂O (l)

colour change from green sol. to green ppt.

reaction of hexaaquairon (III) with CO₃²⁻ , including colour change

2[Fe(H₂O)₆]³⁺ (aq) + 3CO₃²⁻ —→ 2Fe(H₂O)₃(OH)₃(s) + 3CO₂ (g) + 3H₂O (l)

colour change from purple sol. to brown ppt.

effervescence

reaction of hexaaquaaluminium (III) with CO₃²⁻ , including colour change

2[Al(H₂O)₆]³⁺ (aq) + 3CO₃²⁻ —→ 2Al(H₂O)₃(OH)₃(s) + 3CO₂ (g) + 3H₂O (l)

colour change from colourless sol. to white ppt.

effervescence

Explain why an aqueous solution containing [Fe(H₂O)₆]³⁺ ions has a lower pH than an aqueous solution containing [Fe(H₂O)₆]²⁺ ions

• Fe3+ is smaller than Fe2+ / has a higher charge density

• so Fe3+ is more polarising - it polarises water molecules more

• so there more O-H bonds are weakened/break and more H+ ions are released

An aqueous solution of iron(II) sulphate is a pale-green colour.

When aqueous sodium hydroxide is added to this solution a green precipitate is formed.

On standing in air, the green precipitate slowly turns brown.

Suggest an explanation for the change in the colour of the precipitate.

Fe²⁺ is oxidised to Fe³⁺ by the oxygen in the air

Fe(II) ions are pale green and Fe(III) ions are are brown.

Explain, with reference to electrons, why the two ions are different colours.

• Fe(II) and Fe(III) ions have different number of electrons in d sub-shell

• Therefore different wavelengths of light are absorbed by the different ions

• So the electrons get excited and are raised to higher energy levels, causing different wavelengths of light to be transmitted