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Diss Factsheets

Physical & Chemical properties

Dissociation constant

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Administrative data

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Reference
Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
key study
Study period:
3 Feb 2012
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 112 (Dissociation Constants in Water)
GLP compliance:
no
Dissociating properties:
yes
No.:
#1
pKa:
1.35
Temp.:
20 °C
Remarks on result:
other: Mean of two determinations A and B

Sample measurements, solutions A and B:

Dilution factor

Solution A, concentration,

g/L

Solution A, conductivity,

µS/cm

Solution B,

concentration,

g/L

Solution B, conductivity,

µS/cm

0

5.061

834

4.000

677

2

2.5305

427

2.000

349

4

1.26525

216.9

1.000

180.1

8

0.632625

115.3

0.5000

92.3

16

0.3163125

60.5

0.2500

48.3

32

0.1581563

32.1

0.1250

25.4

64

0.0790781

17.4

0.0625

13.39

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

5.061

0.0134601

0.834

61.9609

0.01613922

2.5305

0.0067301

0.427

63.4467

0.01576125

1.26525

0.0033650

0.2159

64.1600

0.01558604

0.632625

0.0016825

0.1153

68.5284

0.01459248

0.3163125

0.0008413

0.0605

71.9162

0.01390507

0.1581563

0.0004206

0.0321

76.3144

0.01310369

0.0790781

0.0002103

0.0174

82.7334

0.01208702

1/L = a*k + b, slope a = 0.0039842, intercept b = 0.0134847

Ostwald dilution law: Ka = 1/(a*(1/b)2) = 0.04563936; pKa = - log Ka = 1.34

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

4.000

0.0106383

0.677

63.6380

0.01571388

2.000

0.0053191

0.349

65.6120

0.01524111

1.000

0.0026596

0.1801

67.7176

0.01476721

0.5000

0.0013298

0.0923

69.4096

0.01440723

0.2500

0.0006649

0.0483

72.6462

0.01376591

0.1250

0.0003324

0.0254

76.4032

0.01308846

0.0625

0.0001662

0.01339

80.5542

0.012414

1/L = a*k + b, slope a = 0.0041051, intercept b = 0.0133872

Ostwald dilution law: Ka= 1/(a*(1/b)2) = 0.04365714; pKa= - log Ka= 1.36

Average pKa= 1.35.

Description of key information

pKa = 1.35 at 20 °C

Key value for chemical safety assessment

pKa at 20°C:
1.35

Additional information

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