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The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

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
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).