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Dissociation constant

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Reference
Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Well documented study conducted to good scientific principles
Qualifier:
no guideline available
Principles of method if other than guideline:
The study analyses available data for the solubility of calcium sulphate in water with no added electrolyte. Ion-pairing was taken into account to calculate the standard therodynamic properties of the solution process. pK1 data is presented.
GLP compliance:
not specified
Dissociating properties:
yes
No.:
#1
pKa:
ca. 4.35
Temp.:
298.15 K

Table 1: Predicted and experimental values of pK1for anhydrite between 298 and 623 K

T (K)

pK1

Experimental

Correspondence principle

a

b

c

298.15

4.35

4.35

4.35

4.35

323.15

4.65

4.65

4.63

4.61

373.15

5.34

5.39

5.33

5.29

423.15

6.13

6.25

6.16

6.10

473.15

7.02

7.19

7.07

6.99

523.15

8.00

8.18

8.03

7.94

573.15

9.08

9.21

9.03

8.93

623.15

10.24 (extrapolated)

10.27

10.06

9.95

 a = correspondence principle

b = constant charge principle

c = not stated

Conclusions:
The pK1 value for calcium sulfate anhydrite is 4.35 at 298.15 K

Description of key information

The pK1 value for calcium sulfate anhydrite is 4.35 at 298.15 K  (25 °C).

Key value for chemical safety assessment

pKa at 20°C:
4.35

Additional information

Section 7.16 Corti (1983): Comparing experimentally derived and calculated values, the authors concluded the pK1 value for calcium sulfate anhydrite to be 4.35 at 298.15 K (25 °C).