Chromium (III) hydroxide

Water solubility

Administrative data

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Well-documented publication which meets basic scientific principles.

Data source

Reference

Reference Type:

publication

Title:

Chromium(III)Hydrolysis Constants and Solubility of Chromium(III) Hydroxide

Author:

Rai, D.; Sass, B.M. and Moore, D.A.

Year:

1987

Bibliographic source:

Inorganic Chemistry, 2987. 26, 345 - 349

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

experimental determination of solubility, no guideline followed

Type of method:

other: experimental determination of solubility, no guideline followed

Test material

Test material information

Constituent 1

Reference substance name:

Chromium (III) hydroxide

EC Number:

215-158-8

EC Name:

Chromium (III) hydroxide

Cas Number:

1308-14-1

Molecular formula:

CrH3O3

IUPAC Name:

chromium (III) hydroxide

Results and discussion

Water solubility

Water solubility 1

Water solubility:

ca. 520 mg/L

pH:

ca. 4

Remarks on result:

other: room temperature assumed, solubility was derived from a diagram

Water solubility 2

Water solubility:

ca. 0.005 mg/L

pH:

ca. 6.8 - ca. 11.5

Remarks on result:

other: room temperature assumed, solubility was derived from a diagram

Water solubility 3

Water solubility:

ca. 0.005 - ca. 5.2 mg/L

pH:

> 11.5 - <= 14

Remarks on result:

other: room temperature assumed, solubility was derived from a diagram

Details on results:

Chromium(III)hydroxide is an amphoteric hydroxide. Thus the solubilities display a parabolic shape between pH 4 and 14. Between aprox. pH 6.8 to 11.5 the substance is insoluble, sometimes below the detection limit of 2μg/L.
Solubilities were derived from a diagram.

Any other information on results incl. tables

The solubility of solid Chromium(III)hydroxide indicates that the species CrOH²⁺is the dominant species between pH 3.8 and 6.4. Heating suspensions of solid Chromium(III)hydroxide to 90°C shows that the Chromium concentrations in the suspensions are approx. 2.5 orders of magnitude lower than in unheated suspensions. This indicates the formation of a more solid phase with lower solubility. However both, the heated and the unheated suspensions showed the x-ray patterns of an amorphous solid. Cr³⁺has no region of dominance above pH 2.6.

Thermodynamic Equilibrium Constants (log K) for Cr(III) Hydrolysis Reactions:

Reaction	log K
	0,01 M*	0,00 M*
Cr(OH)3(s)+ 3 H^+<----> Cr^3++ 3 H2O	<9.76	<9.35
Cr(OH)3(s)+ 2 H^+<----> CrOH^2++ 2 H2O	5.96 ± 0.08	5.78 ± 0.08
Cr(OH)3(s)+ H^+<----> Cr(OH)2^++ H2O	<-0.44	<-0.49
Cr(OH)3(s)<----> Cr(OH)3^0	<-6.84	<-6.84
Cr(OH)3(s)+ H2O <----> Cr(OH)4^-+ H^+	-18.25 ± 0.12	-18.30 ± 0.12
2 Cr(OH)3(s)+ 4 H^+<----> Cr2(OH2)^4++ 4 H2O	<14.4	<13.7
3 Cr(OH)3(s)+ 5 H^+<----> Cr3(OH)4^5++ 5 H2O	<18.5	<17.3
4 Cr(OH)3(s)+ 6 H^+<----> Cr4(OH)6^6++ 6 H2O	<22.4	<20.8

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information): other: amphoteric hydroxide: The solubility curve is parabolic, depending on pH. >pH 4: moderately soluble, pH 6.8 – 11: insoluble. > pH 11.5 slightly soluble
Chromium(III)hydroxide is an amphoteric hydroxide. The solubility curve is parabolic, depending on pH. The solubility is as follows:
>pH 4: moderately soluble, pH 6.8 – 11.5: insoluble. > pH 11.5 slightly soluble

Executive summary:

In an experiment performed under inert gas atmosphere, the solubility of freshly precipitated Chromium(III)hydroxide was determined from untersaturation and from oversaturation at different pH. As an amphoteric hydroxide, the solubility curve of Chromium(III)hydroxide is parabolic, depending on pH. The solubility is as follows:

>pH 4: moderately soluble

pH 6.8 – 11.5: insoluble

> pH 11.5 – 14 slightly soluble