Calcium sulfate

Dissociation constant

Link to relevant study record(s)

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).