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Physical & Chemical properties

Dissociation constant

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Administrative data

Endpoint:
dissociation constant
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Study based on accepted scientific principles, conducted as part of a comprehensive testing programme, basic data given, in accordance with published data
Cross-reference
Reason / purpose for cross-reference:
reference to same study

Data source

Reference
Reference Type:
publication
Title:
Current considerations for the dissolution kinetics of solid oxides with silica
Author:
Löbbus M, Vogelsberger W, Sonnefeld J, Seidel A
Year:
1998
Bibliographic source:
Langmuir 14(16), 4386-4396 (American Chem. Society)

Materials and methods

Test guideline
Qualifier:
no guideline available
Principles of method if other than guideline:
Experiments carried out with a well-defined amorphous silica, Monospher 250 (Merck Darmstadt), included dependence on pH and NaCl concentration at 40 °C. pK determination was based on calculations combined with experimental studies.
GLP compliance:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
Synthetic amorphous silicas:
CAS-No. 112945-52-5, CAS-Name: Silica, amorphous, fumed, crystalline-free;
CAS-No. 112926-00-8, CAS-Name: Silica gel, precipitated, crystalline-free.

Results and discussion

Dissociating properties:
yes
Dissociation constantopen allclose all
No.:
#1
pKa:
6
Temp.:
40 °C
Remarks on result:
other: for silanol groups: mean value of 4 (+-0.08) at 0.1 mol NaCl/L
No.:
#2
pKa:
6.42
Temp.:
40 °C
Remarks on result:
other: for silanol groups: mean value of 4 (+-0.10) at 0.01 mol NaCl/L
No.:
#3
pKa:
6.65
Temp.:
40 °C
Remarks on result:
other: for silanol groups: mean value of 4 (+-0.11) at 0.001 mol NaCl/L

Any other information on results incl. tables

According to the authors (publication, p. 4391 - 4393, Tab. 2), the data are largely consistent with others given in the literature:

pKa = 6.8 (titrated in 0.1 mol NaClO4/L, 25 °C) [Schindler P, Kamber HR: Helv. Chim. Acta 51 (1968), 1781]

(Note: NaClO4 is correct.)

pKa = 6.13 - 6.24 (0.1 mol NaCl/L, 25 °C) [Sonnefeld J: J. Colloid Interface Sci. 183 (1996), 597]

Note: The pKa for the dissolved ortho (mono-) silicic acid is higher: pKa = 9.8

(based on data given by Iler RK;: The Chemistry of Silica. John Wiley & Sons, N.Y., 1979)

Applicant's summary and conclusion