Chemical reactions

Reaction of aluminium with acids

Aluminium dissolves readily in dilute sulphuric or hydrochloric acid under the formation of Al(III) and hydrogen H2. Concentrated nitric acid passivates aluminium metal.

2 Al(s) + 3 H2SO4(aq) 2 Al3+(aq) + 2 SO42−(aq) + 3 H2(g) [2]
2 Al(s) + 6 HCl(aq) 2 Al3+(aq) + 6 Cl(aq) + 3 H2(g) [2]

Reaction of aluminium with air

Aluminium reacts with oxygen, forming a protective layer of alumnium(III) oxide that prevents further reaction with oxygen. Like magnesium, aluminium burns in oxygen with a brilliant white flame. The product in this reaction is also alumnium(III) oxide.

4 Al(s) + 3 O2(g) 2 Al2O3(s)

Reaction of aluminium with ammonia

Aluminum ions are precipitated by NH3 as Al(OH)3. Al does not form complexes with NH3. NH4+ precipitates the [Al(OH)3] complex upon evaporation of NH3.

[Al(OH)4](aq) + NH4+(aq) Al(OH)3(s) + NH3(g) + H2O(l)

Reaction of aluminium with carbonates

Aluminum ions are precipitated by carbonate as Al(OH)3 due to the equilibrium:

CO32−(aq) + H2O(l) HCO3(aq) + OH(aq)
[Al(H2O)6]3+(aq) + 3 OH(aq) [Al(OH)3(H2O)3](s) [white] + 3 H2O(l)

The hydroxide is partially soluble in excess alkalimetal carbonate.

[Al(OH)3(H2O)3](s) + 3 OH(aq) [Al(OH)6]3−(aq) + 3 H2O(l)

Reaction of aluminium with halogens

Aluminium metal reacts vigorously with all the halogens to form aluminium(III) halides.

2 Al(s) + 3 Cl2(g) 2 AlCl3(s) [2]
2 Al(s) + 3 Br2(g) Al2Br6(s)
2 Al(s) + 3 I2(g) Al2I6(s)

Reaction of aluminium with hydroxide ions

Aluminium dissolves in sodium hydroxide with the formation of hydrogen gas, H2, and the formation of aluminates of the type [Al(OH)4].

2 Al(s) + 2 NaOH(aq) + 6 H2O(l) 2 Na+(aq) + 2[Al(OH)4](aq) + 3 H2(g) [2]

Aluminum ions are precipitated by OH as a white gelatinous precipitate [2]:

Al3+(aq) + 3 OH(aq) Al(OH)3(s) Ksp = 1.9·10-33

At excess OH the Al(OH)3 is dissolved:

Al(OH)3(s) + OH(aq) [Al(OH)4](aq)

Reaction of aluminium with phosphates

Aluminum ions are precipitated by hydrogen phosphate ions as AlPO4 in neutral and acetic solutions (white precipitate):

Al3+(aq) + H2PO4(aq) AlPO4(s) + 2H+(aq)

The precipitate is readily soluble in strong acids and bases:

AlPO4(s) + 3 H+(aq) Al3+(aq) + H3PO4(aq)
AlPO4(s) + 4 OH(aq) [Al(OH)4](aq) + PO43−(aq)

Reaction of aluminium with sulfide

Aluminum is not precipitated by sulfide ions at 0.4M HCl. Sodium sulfide will precipitate Al-ions as Al(OH)3 [2]:

S2−(aq) + H2O(l) HS(aq) + OH(aq)

Al3+(aq) + 3 OH(aq) Al(OH)3(s)

Misc. reactions of aluminium

Thermite reaction [2]:

2 Al(s) + Fe2O3(s) 2 Fe(s) + Al2O3(s) ΔH° = -851.4 kJ

Quantitative analysis

Method 3500-Al C Inductively Coupled Plasma Method [1]. A portion of the sample is digested in a combination of acids. The digest is aspirated into an 8,000 K argon plasma where resulting light emission is quantified for 30 elements simultaneously.

Method limit of detection in water = 0.05 mg/L
Method limit of detection in soil = 100 mg/kg