Equilibrium and structural studies of silicon(iv) and aluminium(iii) in aqueous solution. V. Acidity constants of silicic acid and the ionic product of water in the medium range 0.05–2.0 M Na(CI) at 25°C
| Autor: | Staffan Sjöberg, Yvonne Hägglund, Agneta Nordin, Nils Ingri |
|---|---|
| Rok vydání: | 1983 |
| Předmět: |
Activity coefficient
Aqueous solution Standard hydrogen electrode Chemistry Inorganic chemistry Potentiometric titration Analytical chemistry Ionic bonding Sodium silicate General Chemistry Oceanography Acid dissociation constant chemistry.chemical_compound Environmental Chemistry Silicic acid Water Science and Technology |
| Zdroj: | Marine Chemistry. 13:35-44 |
| ISSN: | 0304-4203 |
| DOI: | 10.1016/0304-4203(83)90047-6 |
| Popis: | The apparent ionization constants for silicic acid, k 1 and k 2 , and the ionic product of water, k w , have been determined in 0.05, 0.1, 0.2, 0.4 and 2.0 M Na(CI) media at 25°C. The medium dependence of these constants was found to fit equations of the form log k i = log K i +a i I 1 2 (1+I 1 2 )+b i I where K 1 is the ionization constant in pure water, α i and b i are parameters of which b i has been adjusted to present data. The following results were obtained (α i , b i ): p K 1 = 9.84, (1.022, −0.11); p K 2 = 13.43, (2.044, −0.20); and p K w = 14.01 (1.022, −0.22). k i values are collected in Tables I and II. Attempts have been made to explain the medium dependence of k 1 and k 2 with weak sodium silicate complexing according to the equilibria Na + + SiO(OH) − 3 ⇌ NaSiO(OH) 3 ;k 11 Na + + SiO 2 (OH) 2 2 ⇌ NaSiO 2 (HO) − 2 ; k 21 giving k 11 = 0.37M −1 and k 21 = 3.0M −1 . However, these weak interactions cannot be interpreted unambiguously from potentiometric data at different 1 -levels. Probably the medium dependence could equally well be expressed by variations in the activity coefficients. The measurements were performed as potentiometric titrations using a hydrogen electrode. The average number of OH - reacted per Si(OH) 4 , Z, has been varied within the limits 0 ⩽ Z ⩽ 1.1 and B 1 , the total concentration of Si(OH) 4 , between 0.001 M and 0.008 M. k 1 was evaluated from experimental data with B ⩽ 0.003 M, and k 2 with B ⩽ 0.008 M and Z ≳ 0.95. |
| Databáze: | OpenAIRE |
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