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EC number: 236-743-4 | CAS number: 13472-45-2
Dissociation constant
Administrative data
Link to relevant study record(s)
- Endpoint:
- dissociation constant
- 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:
- The equilibrium constant was estimated using VISUAL MINTEQ Version 2.3. Very few details were provided regarding the modeling process; however, data were obtained from peer-reviewed handbook or collection of data.
- Principles of method if other than guideline:
- The equilibrium constant was estimated using VISUAL MINTEQ Version 2.3 based on a 0.005 M total concentration of sodium tungstate in a 0.01 M solutions of NaCl, allowing solid species to precipitate.
- GLP compliance:
- no
- Dissociating properties:
- yes
- No.:
- #1
- pKa:
- 8.7
- Temp.:
- 20 °C
- Remarks on result:
- other: Estimate using VISUAL MINTEQ Version 2.3 based on a 0.005 M total concentration of sodium tungstate in a 0.01 M solutions of NaCl, allowing solid species to precipitate, assumed to be conducted at room temperature.
- No.:
- #2
- pKa:
- 65.16
- Temp.:
- 20 °C
- Remarks on result:
- other: Estimate using VISUAL MINTEQ Version 2.3 based on a 0.005 M total concentration of sodium tungstate in a 0.01 M solutions of NaCl, allowing solid species to precipitate, assumed to be conducted at room temperature.
- No.:
- #3
- pKa:
- 3.62
- Temp.:
- 20 °C
- Remarks on result:
- other: Estimate using VISUAL MINTEQ Version 2.3 based on a 0.005 M total concentration of sodium tungstate in a 0.01 M solutions of NaCl, allowing solid species to precipitate, assumed to be conducted at room temperature.
- No.:
- #4
- pKa:
- 71.24
- Temp.:
- 20 °C
- Remarks on result:
- other: Estimate using VISUAL MINTEQ Version 2.3 based on a 0.005 M total concentration of sodium tungstate in a 0.01 M solutions of NaCl, allowing solid species to precipitate, assumed to be conducted at room temperature.
- No.:
- #5
- pKa:
- 48.4
- Temp.:
- 20 °C
- Remarks on result:
- other: Estimate using VISUAL MINTEQ Version 2.3 based on a 0.005 M total concentration of sodium tungstate in a 0.01 M solutions of NaCl, allowing solid species to precipitate, assumed to be conducted at room temperature.
- No.:
- #6
- pKa:
- 111.5
- Temp.:
- 20 °C
- Remarks on result:
- other: Estimate using VISUAL MINTEQ Version 2.3 based on a 0.005 M total concentration of sodium tungstate in a 0.01 M solutions of NaCl, allowing solid species to precipitate, assumed to be conducted at room temperature.
- Conclusions:
- Dissociation constants of tungsten species ranged from pKa 3.62 to 111.5 when estimated using VISUAL MINTEQ Version 2.3 based on a 0.005 M total concentration of sodium tungstate in a 0.01 M solutions of NaCl, allowing solid species to precipitate.
- Endpoint:
- dissociation constant
- 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
- Principles of method if other than guideline:
- Equilibrium constants were estimated for dilute solutions at 25 degrees C.
- GLP compliance:
- not specified
- Dissociating properties:
- yes
- No.:
- #1
- pKa:
- 3
- Temp.:
- 25 °C
- Remarks on result:
- other: see remarks on results for equations
- No.:
- #2
- pKa:
- 12.25
- Temp.:
- 25 °C
- Remarks on result:
- other: see remarks on results for equations
- No.:
- #3
- pKa:
- 15.8
- Temp.:
- 25 °C
- Remarks on result:
- other: see remarks on results for equations
- No.:
- #4
- pKa:
- 3.5
- Temp.:
- 25 °C
- Remarks on result:
- other: see remarks on results for equations
- No.:
- #5
- pKa:
- 8.1
- Temp.:
- 25 °C
- Remarks on result:
- other: see remarks on results for equations
- No.:
- #6
- pKa:
- 13.4
- Temp.:
- 25 °C
- Remarks on result:
- other: see remarks on results for equations
- Conclusions:
- Dissociation constants of tungsten species ranged from pKa 3.0 to 15.8 in dilute solutions at 25 deg. C.
Referenceopen allclose all
Reactions represented by pKas above:
| No. | Reaction | pK |
| 1 | WO42-+ 2H+= WO3(H2O)aq |
8.7 |
| 2 | WO42-+ 8H+= W7O246- + 4H2O |
65.16 |
| 3 | WO42-+ H+= HWO4- |
3.62 |
| 4 | 7WO42-+ 9H+= HW7O245- + 4H2O |
71.24 |
| 5 | 6WO42-+ 6H+= H2W6O226- +2H2O |
48.4 |
| 6 | 12WO42-+ 14H+= H2W12O4210- + 6H2O |
111.5 |
Reactions represented by pKas above:
| No. | Reaction | log K | pKa |
| 1 | W+ 4H2O= WO42-+ 8H+ + 6e | -3.0 | 3.0 |
| 2 | alpha-WO3 +H2O = WO42-+ 2H+ | -12.25 | 12.25 |
| 3 | H2WO4(s) = WO42-+ 2H+ | -15.8 | 15.8 |
| 4 | HWO4- = WO42-+ 2H+ | -3.5 | 3.5 |
| 5 | H2WO4(aq) = WO42-+ 2H+ | -8.1 | 8.1 |
| 6 | WO2 + 2H2O = WO42- + 4H+ + 2e | -13.4 | 13.4 |
Description of key information
The speciation of tungsten compounds in water is complex and several species exist together, depending on the pH of the system. Sodium tungstate is soluble and dissolution will occur at environmentally relevant pHs according to the Transformation/Dissolution testing (IUCLID endpoint 4.8, CSR section 1.3). The endpoint study records indicate that the pKa for species generated in an aqueous solution of sodium tungstate range from 3-115. The pKa for the dissociation of HWO4- = WO42-+ 2H+ is equal to 3.5, while the pKa of H2WO4(aq) = WO42-+ 2H+ is 8.1.
Key value for chemical safety assessment
- pKa at 20°C:
- 3.5
Additional information
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