Abstract :
The chemical species of silica, whose concentration was measured by colorimetry, were examined in alkaline hydroxide solutions. The total amount of SiO2 measured by colorimetry is in good agreement with that measured by weight loss on drying. The monomer (Si(OH)3O−), monomer-Na+ complex (Si (OH)2O2Na−), dimer (Si2(OH)5O2−), dimer-Na+ complex (Si2(OH)4O3Na−), linear tetramer (Si4(OH)9O4−), cyclic tetramer (Si4(OH)7O5−) and cyclic tetramer-Na+ complex (Si4(OH)6O6Na−) were observed in NaOH and KOH solutions by fast atom bombardment-mass spectrometer. When the NaOH solutions containing silica were neutralized, they were found to contain the monomer-Na+ complex, dimer, dimer-Na+ complexes (Si2(OH)3O4Na2−, Si2(OH)2O5Na3−) in addition to dimer-Na+ complex (Si2(OH)4O3Na−), linear tetramer, cyclic tetramer and cyclic tetramer-Na+ complex. The solutions of silica in natural water and of silica at pH 7–12 contain monomer, monomer-Na+ complex, dimer, dimer-Na+ complexes, linear tetramer, cyclic tetramer and cyclic tetramer-Na+ complex of silica, as determined by colorimetry with ammonium molybdate.
