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EC number: 222-492-8 | CAS number: 3495-36-1
Dissociation constant
Administrative data
Link to relevant study record(s)
- Endpoint:
- dissociation constant
- Type of information:
- not specified
- Adequacy of study:
- key study
- Study period:
- 2007
- Reliability:
- 2 (reliable with restrictions)
- Rationale for reliability incl. deficiencies:
- other: Secondary literature source, rating as per REACH Guidance document 7.a. Endpoint-specific guidance.
- Principles of method if other than guideline:
- Method followed unknown, data from handbook.
- GLP compliance:
- not specified
- Dissociating properties:
- yes
- No.:
- #1
- pKa:
- ca. 3.75
- Remarks on result:
- other: data on temperature not reported in Handbook
- Conclusions:
- The data were obtaied from the CRC Handbook of Chemistry and Physics. According to this literature source the dissociation constant (pKa) of the test substance brine is 3.75 (2007).
- Executive summary:
The data were obtaied from the CRC Handbook of Chemistry and Physics. According to this literature source the dissociation constant (pKa) of the test substance brine is 3.75 (2007).
- Endpoint:
- dissociation constant
- Type of information:
- experimental study
- Adequacy of study:
- key study
- Study period:
- 1998
- Reliability:
- 1 (reliable without restriction)
- Rationale for reliability incl. deficiencies:
- guideline study
- Qualifier:
- according to guideline
- Guideline:
- OECD Guideline 112 (Dissociation Constants in Water)
- Deviations:
- not specified
- GLP compliance:
- not specified
- Dissociating properties:
- yes
- pKa:
- ca. 3.74
- Remarks on result:
- other: obtained by titration method
- pKa:
- ca. 3.76
- Remarks on result:
- other: obtained by calculation method
- Conclusions:
- Under the study conditions, the dissociation constant (pKa) of the test substance solution was determined to be 3.74.
- Executive summary:
A study was conducted to determine the dissociation constant of the test substance solution, according to OECD Guideline 112 (titrimetric method).0.01 M Cesium Formate solution containing 0.0082 M Cesium was titrated against 0.2 N HCl. A midpoint value of titration was obtained from the plot of pH difference versus volume added. The dissociation constant was considered equivalent to this value. Subsequently, a calculation of the dissociation constant was also made using the first 10 pH values. The dissociation constant value from titration method was 3.74 and that from the calculation method was 3.76. Under the study conditions, the dissociation constant (pKa) of the test substance solution was determined to be 3.74 (Gibb, 1998).
Referenceopen allclose all
The pH changes and the volume of 0.2 N HCl added are presented in the table given below:
0.2 N HCl Volume Added (mL) |
0.01 M Formate Solution pH |
0.2 N HCl Volume Added (mL) |
0.01 M Formate Solution pH |
0.0 |
6.665 |
8.0 |
1.735 |
0.2 |
4.785 |
8.2 |
1.720 |
0.4 |
4.422 |
8.4 |
1.709 |
0.6 |
4.197 |
8.6 |
1.695 |
0.8 |
4.022 |
8.8 |
1.683 |
1.0 |
3.874 |
9.0 |
1.672 |
1.2 |
3.737 |
9.2 |
1.660 |
1.4 |
3.604 |
9.4 |
1.649 |
1.6 |
3.474 |
9.6 |
1.637 |
1.8 |
3.344 |
9.8 |
1.627 |
2.0 |
3.208 |
10.0 |
1.617 |
2.2 |
3.070 |
10.2 |
1.607 |
2.4 |
2.931 |
10.4 |
1.599 |
2.6 |
2.801 |
10.6 |
1.590 |
2.8 |
2.682 |
10.8 |
1.582 |
3.0 |
2.577 |
11.0 |
1.571 |
3.2 |
2.489 |
11.2 |
1.564 |
3.4 |
2.411 |
11.4 |
1.556 |
3.6 |
2.344 |
11.6 |
1.547 |
3.8 |
2.286 |
11.8 |
1.540 |
4.0 |
2.233 |
12.0 |
1.532 |
4.2 |
2.187 |
12.2 |
1.524 |
4.4 |
2.145 |
12.4 |
1.517 |
4.6 |
2.106 |
12.6 |
1.510 |
4.8 |
2.072 |
12.8 |
1.503 |
5.0 |
2.038 |
13.0 |
1.497 |
5.2 |
2.010 |
13.2 |
1.490 |
5.4 |
1.981 |
13.4 |
1.483 |
5.6 |
1.956 |
13.6 |
1.476 |
5.8 |
1.931 |
13.8 |
1.470 |
6.0 |
1.909 |
14.0 |
1.464 |
6.2 |
1.887 |
14.2 |
1.458 |
6.4 |
1.867 |
14.4 |
1.453 |
6.6 |
1.848 |
14.6 |
1.446 |
6.8 |
1.829 |
14.8 |
1.441 |
7.0 |
1.812 |
15.0 |
1.436 |
7.2 |
1.793 |
15.2 |
1.430 |
7.4 |
1.779 |
15.4 |
1.425 |
7.6 |
1.764 |
15.6 |
1.420 |
7.8 |
1.748 |
15.8 |
1.415 |
Calculation of pKa using the first 10 pH values:
0.2 N HCl Volume Added (mL) |
0.0096 M Formate Solution pH |
X- (M) |
HX (M) |
pKa |
0.2 |
4.785 |
0.0088 |
0.0008 |
3.74 |
0.4 |
4.422 |
0.0080 |
0.0016 |
3.72 |
0.6 |
4.197 |
0.0072 |
0.0024 |
3.72 |
0.8 |
4.022 |
0.0064 |
0.0032 |
3.72 |
1.0 |
3.874 |
0.0056 |
0.0040 |
3.73 |
1.2 |
3.737 |
0.0048 |
0.0048 |
3.74 |
1.4 |
3.604 |
0.0040 |
0.0056 |
3.75 |
1.6 |
3.474 |
0.0032 |
0.0064 |
3.78 |
1.8 |
3.344 |
0.0024 |
0.0072 |
3.82 |
2.0 |
3.208 |
0.0016 |
0.0080 |
3.91 |
2.4 |
2.931 |
0.0000 |
0.0096 |
- |
Mean |
3.760 |
|||
Standard Deviation |
0.0596 |
|||
Description of key information
Brine: the dissociation constant was determined according to OECD Guideline 112.
Key value for chemical safety assessment
- pKa at 20°C:
- 3.74
Additional information
Brine:
-3.75 (CRC Handbook of Chemistry and Physics)
-pKa of 3.74
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