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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

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

Administrative data

Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1962
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: This study is similar to, but precedes the development of OECD Guideline 112.

Data source

Reference
Reference Type:
publication
Title:
Thermodynamics of Metal-Cyanide Coordination I. pK, ∆Ho and ∆So values as a function of temperature for hydrocyanic acid dissociation in aqueous solution
Author:
Izatt RM, JJ Christensen, RT Pack, R Bench
Year:
1962
Bibliographic source:
Inorganic Chemistry 1: 828-831

Materials and methods

Test guideline
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 112 (Dissociation Constants in Water)
Deviations:
yes
Remarks:
precedes guideline
GLP compliance:
no

Test material

Constituent 1
Chemical structure
Reference substance name:
Hydrogen cyanide
EC Number:
200-821-6
EC Name:
Hydrogen cyanide
Cas Number:
74-90-8
Molecular formula:
CHN
IUPAC Name:
hydrogen cyanide
Details on test material:
Stock HCN solution was prepared by passing a 0.05 F NaCN solution through an Amberlite GC-120, Type 1 ion exchange column until the Na concentration as determined by a flame test was less than 0.05% of that originally present.

Results and discussion

Dissociating properties:
yes
Dissociation constant
No.:
#1
pKa:
ca. 9.36
Temp.:
20 °C
Remarks on result:
other: 95 % Confidence Limit ± 0.012

Applicant's summary and conclusion

Conclusions:
The pKa of hydrocyanic acid is 9.36 at 20°C and 9.11 at 30°C.
Executive summary:

The pKa of hydrocyanic acid is 9.36 at 20 °C.The predominant speciation of all inorganic cyanide in the body is HCN due to this weak acid dissociation constant.