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Physical & Chemical properties

Melting point / freezing point

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Endpoint:
melting point/freezing point
Type of information:
experimental study
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.
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.
Decomposition:
yes
Decomp. temp.:
ca. 100 °C
Endpoint:
melting point/freezing 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.
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
Melting / freezing pt.:
1 472 °C
Sublimation:
yes
Remarks:
: significant sublimation at >750 °C
Executive summary:

No melting point data are available for tungstic acid (target substance). However, melting 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:
melting point/freezing 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. Dihydrogen wolframate (WO3.H2O) is a hydrate form of tungsten trioxide (WO3). Per Annex V, hydrates and water-free forms (anhydrous) of compounds shall be regarded as the same substance for registration purposes. Therefore, dihydrogen wolframate will be considered equivalent to WO3. For more details, refer to the attached description of the read-across approach.
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.
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
Melting / freezing pt.:
1 472 °C
Atm. press.:
1 013 hPa

Assumed to be performed under standard conditions. Pressure not given.

Executive summary:

No melting point data are available for tungstic acid (target substance). However,melting 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:
melting point/freezing 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.
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
Melting / freezing pt.:
1 473 °C
Atm. press.:
1 013 hPa
Remarks on result:
other: assumed to be conducted under standard conditions
Executive summary:

No melting point data are available for tungstic acid (target substance). However, melting 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 melting point for tungstic acid is not technically possible. The melting/freezing 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

Melting / freezing point at 101 325 Pa:
1 472 °C

Additional information

Tungstic acid decomposes at approximately 100°C. 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, crystallised 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).