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Physical & Chemical properties

Boiling point

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Endpoint:
boiling point
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Remarks:
Data from peer-reviewed handbook or collection of data.
Justification for type of information:
Tungstic acid (WO3•H2O) is the hydrated form of tungsten trioxide (WO3). Based on Annex V, hydrates and water free forms (anhydrous) of compounds can be regarded as the same substance for registration purposes. Therefore, tungstic acid will be considered equivalent to WO3. For more details on the rationale, refer to the attached description of the read-across approach.
Reason / purpose for cross-reference:
reference to other study
Principles of method if other than guideline:
Data in this peer-reviewed publication were taken from many sources, including both compilations and primary literature. Where conflicts were found, the value deemed most reliable was chosen for inclusion in the handbook. Reference sources were not provided for this parameter, nor was the experimental method.
GLP compliance:
not specified
Boiling pt.:
1 837 °C
Atm. press.:
1 Bar
Executive summary:

No boiling point data are available for tungstic acid (target substance). However, boiling point data are available for tungsten trioxide (source substance), which were used for read-across. Tungstic acid (WO3•H2O) is the hydrated form of tungsten trioxide (WO3). Based on Annex V, hydrates and water free forms (anhydrous) of compounds can be regarded as the same substance for registration purposes. Therefore, tungstic acid will be considered equivalent to WO3. For more details on the rationale, refer to the attached description of the read-across approach.

Endpoint:
boiling point
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Remarks:
Data from peer-reviewed handbook or collection of data.
Justification for type of information:
Tungstic acid (WO3•H2O) is the hydrated form of tungsten trioxide (WO3). Based on Annex V, hydrates and water free forms (anhydrous) of compounds can be regarded as the same substance for registration purposes. Therefore, tungstic acid will be considered equivalent to WO3. For more details on the rationale, refer to the attached description of the read-across approach.
Reason / purpose for cross-reference:
reference to other study
Principles of method if other than guideline:
Data in this peer-reviewed publication were taken from many sources, including both compilations and primary literature. Where conflicts were found, the value deemed most reliable was chosen for inclusion in the handbook. Reference sources were not provided for this parameter, nor was the experimental method.
GLP compliance:
not specified
Key result
Boiling pt.:
1 837 °C
Atm. press.:
760 mm Hg
Executive summary:

No boiling point data are available for tungstic acid (target substance). However, boiling point data are available for tungsten trioxide (source substance), which were used for read-across. Tungstic acid (WO3•H2O) is the hydrated form of tungsten trioxide (WO3). Based on Annex V, hydrates and water free forms (anhydrous) of compounds can be regarded as the same substance for registration purposes. Therefore, tungstic acid will be considered equivalent to WO3. For more details on the rationale, refer to the attached description of the read-across approach.

Description of key information

One secondary source indicates that tungstic acid decomposes at a relatively low temperature as it undergoes dehydration (loss of water molecules); therefore, obtaining a boiling point for tungstic acid is not technically possible. The boiling point key value reported herein is for tungsten trioxide (WO3) from a reliable source.  It is noted that tungstic acid (WO3.H2O) is the hydrated form of tungsten trioxide (WO3).  Per Annex V, hydrates and water free forms (anhydrous) of compounds shall be regarded as the same substance.  

Key value for chemical safety assessment

Boiling point at 101 325 Pa:
1 837 °C

Additional information

As discussed in the Endpoint Summary for Melting/freezing point for tungstic acid, the substance decomposes at approximately 100°C making it technically unfeasible to obtain a boiling point for the substance. As the boiling point of water (100°C) is reached during the heating of tungstic acid, the water molecules of hydration are dissociating from tungstic acid (a hydrated form of tungsten trioxide), leading to decomposition of the substance at a relatively low temperature. Heating of tungstic acid to approximately 500°C leads to the final stage of dehydration: water-free, crystallized tungsten trioxide.

As noted herein, tungstic acid (WO3.H2O) is the hydrated form of tungsten trioxide (WO3). Based on Annex V, hydrates and water free forms (anhydrous) of compounds shall be regarded as the same substance for registration purposes. Therefore, tungstic acid will be considered equivalent to WO3. For more details, refer to the read-across category approach document (Annex 3).