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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.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

Endpoint summary

Administrative data

Description of key information

Additional information

For five endpoints (appearance, melting point, density, vapour pressure and water solubility) data on the physical and chemical properties of selenous acid was taken from the handbooks (e.g. CRC, 2008; Merck, 2006). Waivers are proposed for boiling point, partition coefficient, surface tension, flash point, explosiveness, stability in organic solvents, dissociation constant and viscosity, as well as for pyrophoric properties and flammability in contact with water.

No reliable data is available for particle size distribution, auto flammability, flammability (in air) and oxidising properties.


Summary of results:



Substance type

inorganic compound

Appearance/physical state/colour

white, odourless, hygroscopic crystals, prisms or powder (under atmospheric pressure and room temperature)

Melting/freezing point

Substance decomposes at 70 °C

Boiling point (at 1013 hPa)

No boiling point, since substance decomposes before boiling

Density at 20C

Relative density is 3.0 at room temperature / 15 °C

Particle size distribution

No data

Vapour pressure

2 mm Hg at 15 °C

Partition Coefficient

Not required for inorganic substances

Water solubility at 20C

Very soluble

Surface tension at 25C

Not expected to be surface active

Flash point

Not required for inorganic solid substances

Self ignition temperature

Non-combustible (No reliable source)


Non-flammable (No reliable source); pyrophoric properties and flammability in contact with water not expected


Not expected to possess explosive properties

Oxidising properties

No testing data available

Stability in organic solvents and identity of relevant degradation products

Not considered critical for an inorganic substance

Dissociation constant

No relevant functional groups, thus considered not required


Not required for solids