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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

Diss Factsheets

Physical & Chemical properties

Dissociation constant

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Description of key information

Dissociation constant (dichlorosilane): Not relevant
Dissociation constant (silicic acid): pKa1 = 9.9

Key value for chemical safety assessment

Additional information

The requirement to conduct a dissociation constant study for dichlorosilane is waived because in contact with water the substance very rapidly hydrolyses to form silanediol as an intermediate hydrolysis product. The ultimate hydrolysis product is silicic acid.

Monosilicic acid was reported to have dissociation constant values of pKa1 = 9.9, pKa2 = 11.8, pKa3 and pKa4 = 12 at 30°C in a secondary data source which has been subject to peer review and in which the original sources are traceable. Monosilicic acid is therefore, an extremely weak acid. In neutral solution, the undissociated form will dominate.