Aluminum

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