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Physical & Chemical properties

Dissociation constant

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Reference
Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
key 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
Reason / purpose:
reference to same study
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
Dissociating properties:
yes
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

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)

Conclusions:

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)

Description of key information

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 molNaClO4/L, 25 °C) [Schindler P, Kamber HR: Helv. Chim. Acta 51 (1968), 1781]

(Note:NaClO4is 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)

Key value for chemical safety assessment

Additional information