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Dissociation constant

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Reference
Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1999-05-20 - 1999-05-20
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 112 (Dissociation Constants in Water)
Version / remarks:
1981
Deviations:
no
GLP compliance:
yes
Dissociating properties:
no

Results the pKa of the ammonium acetate

The equivalent points for the titration by the HCl and NaOH solutions were the following:

chloridric acid 1.0 mol/L = 8.75 mL

sodium hydroxide 1.0 mol/L = 9.30 mL

Starting from the values of the 50% equivalent point, it was observed the following values by titration:

chloridric acid 1.0 mol/L = 4.37 mL pH = 5.11

sodium hydroxide 1.0 mol/L = 4.65 mL pH = 8.98

Using interpolation calculations, it was obtained the correspondents means of pH in function of the determines volume above and, consequently the refereed pKa. The results obtained for the references substances are shown here:

 Reference substanc  pKa experimental 20 °C  pKa literature
 Acetic acid  5.11  4.75
 Ammonium  8.98

 9.26

Test substance

The Table below presents the used values for the determinations of titration curves Ferbam, by means of titration with NaOH 1.0 mol/L and HCl 1.0 mol/L.

Table Values pH of Ferbam in function of the addition of NaOH 1.0 mol/L and HCl 1.0 mol/L.

Volume pH Potential Variation Volume pH Potential Variation
of NaOH solution (mV) of of HCl solution (mV) of
1.0 mol/L (mL)     potential (mV) 1.0 mol/L (mL)     potential (mV)
- 5,60 240 - - 5,88 260 -
0,25 10,31 016 224 0,25 3,48 250 010
0,50 10,64 012 004 0,50 3,18 242 008
0,75 10,83 007 005 0,75 3,00 231 011
1,00 10,96 001 006 1,00 2,88 218 013
1,25 11,06 -005 -004 1.25 2,78 216 002
1,50 11,14 -011 016 1,50 2,70 216 000
1,75 11,19 -017 028 1,75 2,64 216 000
2,00 11,26 -022 039 2,00 2,58 217 -001
2,25 11,31 -027 049 2,25 2,53 218 -001
2,50 11,35 -032 059 2,50 2,49 219 -001
2,75 11,39 -038 070 2,75 2,44 220 -001
3,00 11,42 -042 080 3,00 2,41 221 -001
3,25 11,46 -046 088 3,25 2,37 223 -002
3,50 11,49 -050 096 3,50 2,34 224 -001
3,75 11,53 -054 104 3,75 2,31 225 -001

pKa results of the substance

It was not possible to determine the dissociation constant of test substance in water, because there were not equivalent points when titration with HCl or NaOH solutions.

Conclusions:
The methodological procedures using the reference substance ammonium acetate, results pKa values consistent with those found in the literature.
It was not possible to determine the dissociation constant of test substance in water, because there were not equivalent points when titration with HCl or NaOH solutions.
Executive summary:

The dissociation constant of the test substance Ferbam was analyzed according to OECD Guideline 112 (Dissociation Constants in Water), through titration methodology by measuring the direct pH in the aqueous solution at 20°C. A solution of ammonium acetate was used as reference substance. According to the results, it was not possible to determine the dissociation constant of test substance in water, because there were not equivalent points when titrating with HCl or NaOH solutions.

Description of key information

The dissociation constant of the test substance Ferbam was analyzed according to OECD Guideline 112 (Dissociation Constants in Water) It was not possible to determine the dissociation constant of test substance in water, because there were not equivalent points when titrating with HCl or NaOH solutions.

Key value for chemical safety assessment

Additional information

Key: Pessin, 1999

The dissociation constant of the test substance Ferbam was analyzed according to OECD Guideline 112 (Dissociation Constants in Water), through titration methodology by measuring the direct pH in the aqueous solution at 20°C. A solution of ammonium acetate was used as reference substance. According to the results, it was not possible to determine the dissociation constant of test substance in water, because there were not equivalent points when titrating with HCl or NaOH solutions.

Other information: Vandegans, 1987

The study was equivalent or similar to OECD guideline n°108, Ed. 1981. For the various reasons mentioned, we consider that the determination of the stability constant of FERBAM is pointless and, especially for electrochemical reasons, impossible if the OECD prescriptions are to be followed.