Equilibrium and structural studies of silicon(IV) and aluminium(III) in aqueous solution. II. Formation constants for the monosilicate ions SiO(OH)3 and SiO2(OH)2. A precision study at 25°C in a simplified seawater medium |
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| Authors: | Staffan Sjberg Agneta Nordin Nils Ingri |
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| Institution: | Staffan Sjöberg, Agneta Nordin,Nils Ingri |
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| Abstract: | The hydrolysis of silicic acid, Si(OH)4, was studied in a simplified seawater medium (0.6 M Na(Cl)) at 25°C. The measurements were performed as potentiometric titrations (hydrogen electrode) in which OH− was generated coulometrically. The total concentration of Si(OH)4, B, and logH+] were varied within the limits 0.00075 B 0.008 M and 2.5 -logH+] 11.7, respectively. Within these ranges the formation of SiO(OH)3− and SiO2(OH)22− with formation constants log β−11(Si(OH)4 SiO(OH)3− + H+) = −9.472 ±0.002 and log β−21(Si(OH)4 SiO2(OH)22− + 2H+) = −22.07 ± 0.01 was established. With B > 0.003 M polysilicate complexes are formed, however, with -logH+] 10.7 their formation does not significantly affect the evaluated formation constants. Data were analyzed with the least squares computer program LETAGROPVRID. |
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