Aluminium potassium bis(sulphate)

Hydrolysis

Description of key information

In aqueous solution the inorganic substance is dissolved and dissociated in their cations and anion Al3 +, K+ and SO42-.
A cluster formation, depending on concentration and time, is possible, especially near saturation point (see chapter 5.4.1 Adsorption/desorption.002). 
The trivalent aluminum ion is surrounded by six water molecules in solution. The hydrated aluminum ion, [Al(H2O)6]3+, undergoes hydrolysis, in which a stepwise deprotonation of the coordinated water ligands forms bound hydroxide ligands (e.g., [Al(H2O)5(OH)]2+, [Al(H2O)4(OH)2]+). The speciation of aluminum in water is pH dependent. The hydrated trivalent aluminum ion is the predominant form at pH levels below 4. Between pH 5 and 6, the predominant hydrolysis products are (Al(OH)2)+ and (Al(OH))2+, while the solid Al(OH)3 is most prevalent between pH 5.2 and 8.8. The soluble species Al(OH)4- is the predominant species above pH 9, and is the only species present above pH 10. Polymeric aluminum hydroxides appear between pH 4.7 and 10.5, and increase in size until they are transformed into colloidal particles of amorphous Al(OH)3, which crystallize to gibbsite in acidic waters. 
In aqueous solution, potassium aluminium bis sulphate shows as other alums all the chemical properties that their components show separately. Physical properties, such as color, electrical conductivity, and freezing-point lowering, are the sum of the properties of the components, provided the solutions are very dilute. At higher concentrations, complexes, such as [Al(SO4)2 (H2O)2], are formed. Alums are crystalline double salts of the general formula (cation 1) 1+, (cation 2)3+ (anion2-)2 * 12 H2O. The most useful alums are those with trivalent aluminum cations and sulfate anions, (M+)(Al3+)(SO4) 2-)4*12 H2O.
Basic potassium aluminum sulfate, K[Al(OH)2]3(SO4)2 3/2 H2O, occurs in nature as loewigite.  

Additional information

In aqueous solution the inorganic substance is completely dissolved and dissociated in the cations and anion Al3 +, K+ and SO42-.

A cluster formation, depending on concentration and time, is possible, especially near saturation point (see chapter 5.4.1 Adsorption/desorption.002).

The trivalent aluminum ion is surrounded by six water molecules in solution. The hydrated aluminum ion, [Al(H2O)6]3+, undergoes hydrolysis, in which a stepwise deprotonation of the coordinated water ligands forms bound hydroxide ligands (e.g., [Al(H2O)5(OH)]2+, [Al(H2O)4(OH)2]+). The speciation of aluminum in water is pH dependent. The hydrated trivalent aluminum ion is the predominant form at pH levels below 4. Between pH 5 and 6, the predominant hydrolysis products are (Al(OH)2)+ and (Al(OH))2+, while the solid Al(OH)3 is most prevalent between pH 5.2 and 8.8. The soluble species Al(OH)4- is the predominant species above pH 9, and is the only species present above pH 10. Polymeric aluminum hydroxides appear between pH 4.7 and 10.5, and increase in size until they are transformed into colloidal particles of amorphous Al(OH)3, which crystallize to gibbsite in acid waters.

In aqueous solution, potassium aluminium bis sulphate shows as other alums show all the chemical properties that their components show separately. Physical properties, such as color, electrical conductivity, and freezing-point lowering, are the sum of the properties of the components, provided the solutions are very dilute. At higher concentrations, complexes, such as [Al(SO4)2 (H2O)2], are formed. Alums are crystalline double salts of the general formula (cation 1) 1+, (cation 2)3+ and (anion2-)2 * 12 H2O. The most useful alums are those with trivalent aluminum cations and sulfate anions, (M+)(Al3+)(SO4) 2-)4*12 H2O.

Basic potassium aluminum sulfate, K[Al(OH)2]3(SO4)2 3/2 H2O, occurs in nature as loewigite. The compound is made synthetically as a rather insoluble, amorphous powder by heating aluminum sulfate, water, and an excess of potassium sulfate or by heating potassium alum with water in the ratio 1 : 4 to 200 °C. Another basic potassium aluminum sulfate, K[Al3(OH)6(SO4)2] [1302-91-6], containing less water, is the alum stone (alunite) occurring in nature.