Various Preparation Methods of Aluminum Hydroxide
Laboratory method: Chemical equation: 2Al 3H2SO4 (dilute)=Al2(SO4) 3 3H2?¨1 2Al 2NaOH 6H2O=2Na[Al(OH)4] 3H2?¨1 Al2(SO4)3 6Na[Al(OH)4] 12H2O=8Al(OH)3?y 3Na2(SO4)?? or Al2(SO4)3 6NH3.H2O=2Al(OH)3?y 3(NH4)2SO4 Ion equation: 2Al 6H =2Al3 3H2?¨1 2Al3 2OH- 6H2O=2[Al(OH)4]- 3H2?¨1
Chemical reaction Al3 3[Al(OH)4]- 6H2O=4Al(OH)3?y
Or Al3 3NH3??èH2O=Al(OH)3? y 3NH4
?é¨′Al(OH)3 is amphoteric hydroxide, it might communicate with strong acidity and effective base at normal temperature:
Al(OH)3 3HCl=AlCl3 3H2O Al(OH)3 3H =Al3 3H2O
Al(OH)3 NaOH=Na[Al(OH)4]Al(OH)3 OH?ê-=[Al(OH)4]?ê-
?é¨2Al(OH)3 is certainly decomposed into Al2O3 when heated: 2Al(OH)3==Al2O3 3H2O (rule: insoluble alkali will decompose when heated)
?é?Preparation of Al(OH)3:
a. The soluble aluminum salt reacts to ammonia to arrange Al(OH)3
AlCl3 3NH3??èH2O=Al(OH)3?y 3NH4Cl
Al2(SO4)3 6NH3??èH2O=2 Al(OH)3? y 3(NH4)2SO4 (Al3 3NH3??èH2O=Al(OH)3? y 3NH4 )
Because strong bases (for instance NaOH) easily communicate with Al(OH)3, the laboratory does not use strong bases to arrange Al(OH)3 but uses ammonia
