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Dissociation constant

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Reference
Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
key study
Study period:
21 Aug 2018
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 112 (Dissociation Constants in Water)
GLP compliance:
no
Dissociating properties:
yes
No.:
#1
pKa:
1.39
Temp.:
20 °C
Remarks on result:
other: Mean of three determinations, A, B and C
Remarks:
1.39 ± 0.10

Sample measurements, solutions A, B, C:

Dilution factor

Solution A, concentration g/L

Solution A, conductivity, µS/cm

Solution B, concentration g/L

Solution B, conductivity, µS/cm

Solution C, concentration g/L

Solution C, conductivity, µS/cm

0

4.0206

261.3

4.5529

294.2

5.0789

327.0

2

2.0103

133.5

2.27645

150.6

2.53945

167.9

4

1.00515

67.9

1.138225

76.9

1.269725

85.5

8

0.502575

34.7

0.569113

39.3

0.634863

43.6

16

0.251288

17.97

0.284556

20.1

0.317431

22.44

32

0.125644

9.54

0.142278

10.6

0.158716

11.6

Solution A:

Concentration solution A, g/L

Concentration solution A,

mol/L

Specific conductivity k,

mS/cm

Equivalent conductivity L,

S cm2/mol

Reciprocal equivalent conductivity 1/L, mol/S cm2

4.0206

0.003555853

261.3

73.4845

0.01361

2.0103

0.001777927

133.5

75.0875

0.01332

1.00515

0.000888963

67.9

76.3811

0.01309

0.502575

0.000444482

34.7

78.0685

0.01281

0.251288

0.000222241

17.97

80.8582

0.01237

0.125644

0.00011112

9.54

85.8528

0.01165

The lowest concentration was neglected.

1/L = a*k + b, slope a = 0.0043348, intercept b = 0.0125922

Ostwald dilution law: Ka = 1/(a*(1/b)2) = 0.036579; pKa = - log Ka = 1.4368

Solution B:

Concentration solution B, g/L

Concentration solution B,

mol/L

Specific conductivity k, mS/cm

Equivalent conductivity L,

S cm2/mol

Reciprocal equivalent conductivity 1/L, mol/S cm2

4.5529

0.004026624

294.2

73.0637

0.01369

2.27645

0.002013312

150.6

74.8021

0.01337

1.138225

0.001006656

76.9

76.3915

0.01309

0.569113

0.000503328

39.3

78.0803

0.01281

0.284556

0.000251664

20.1

79.8684

0.01252

0.142278

0.000125832

10.6

84.239

0.01187

The lowest concentration was neglected.

1/L = a*k + b, slope a = 0.0038788, intercept b = 0.0126439

Ostwald dilution law: Ka= 1/(a*(1/b)2) = 0.041217; pKa= - log Ka= 1.3849

Solution C:

Concentration solution C, g/L

Concentration solution C,

mol/L

Specific conductivity k, mS/cm

Equivalent conductivity L,

S cm2/mol

Reciprocal equivalent conductivity 1/L, mol/S cm2

5.0789

0.004491823

327

72.7990

0.01374

2.53945

0.002245911

167.9

74.7581

0.01338

1.269725

0.001122956

85.5

76.1384

0.01313

0.634863

0.000561478

43.6

77.6522

0.01288

0.317431

0.000280739

22.44

79.9319

0.01251

0.158716

0.000140369

11.6

82.6391

0.01210

The lowest concentration was neglected.

1/L = a*k + b, slope a = 0.0035428, intercept b = 0.0124775

Ostwald dilution law: Ka= 1/(a*(1/b)2) = 0.043945; pKa= - log Ka= 1.3571

Average pKa= 1.393.

Description of key information

pKa = 1.39 at 20 °C

Key value for chemical safety assessment

pKa at 20°C:
1.39

Additional information

The dissociation constant of the substance was determined according to OECD Guideline 112 (conductometric method).