Potassium pentaborate

Dissociation constant

Link to relevant study record(s)

Reference

Endpoint:

dissociation constant

Type of information:

experimental study

Adequacy of study:

key study

Study period:

04/06/2010 to 01/07/2010

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

OECD Guideline 112 (Dissociation Constants in Water)

Deviations:

not specified

GLP compliance:

yes

Dissociating properties:

yes

pKa:

8.07

Temp.:

20 °C

Test item determination 1:

Weight of test item taken (g) = 0.7322

Molecular weight of test item = 293.0

Final volume of solution made up in carbon dioxide free distilled water (mL) = 250

Concentration of test item solution (M) = 0.7322/293 x 1000/250 = 0.009996

N.B. In the absence of a certificate of analysis for the test item for the calculations of test item solution concentration the purity of the test item has been assumed to be 100%

Volume of test item solution taken for titration = 50 mL

Volume of 0.1M hydrochloric acid added (mL)	pH of solution	pKa
0.00	8.65	N/A
0.20	8.62	7.24*
0.40	8.58	7.52*
0.60	8.56	7.70*
0.80	8.53	7.81*
1.00	8.50	7.90*
1.20	8.47	7.97*
1.40	8.44	8.03*
1.60	8.40	8.08*
1.80	8.37	8.12*
2.00	8.34	8.17*
2.20	8.31	8.21*
2.40	8.26	8.23*
2.60	8.21	8.25*
2.80	8.18	8.29*
3.00	8.13	8.31*
3.20	8.07	8.33*
3.70	7.92	8.38*
4.20	7.67	8.41*
4.70	7.28	8.52
5.20	3.62	N/A
5.70	2.95	N/A
Mean (using values marked * only) =		8.05
SD (using values marked * only) =		0.32
%RSD =		3.93

Test item determination 2:

Weight of test item taken (g) = 0.7323

Molecular weight of test item = 293.0

Final volume of solution made up in carbon dioxide free distilled water (mL) = 250

Concentration of test item solution (M) = 0.7323/293 x 1000/250 = 0.009997

Volume of test item solution taken for titration = 50 mL

Volume of 0.1M hydrochloric acid added (mL)	pH of solution	pKa
0.00	8.62	N/A
0.30	8.57	7.38*
0.60	8.51	7.65*
0.90	8.49	7.83*
1.20	8.45	7.95*
1.50	8.41	8.05*
1.80	8.35	8.10*
2.10	8.31	8.17*
2.40	8.24	8.21*
2.70	8.18	8.26*
3.00	8.13	8.31*
3.30	8.07	8.37*
3.60	7.91	8.33*
3.90	7.79	8.35*
4.20	7.61	8.35*
4.50	7.39	8.37
4.80	7.01	8.46
5.10	3.69	N/A
5.40	3.18	N/A
5.70	2.90	N/A
Mean (using values marked * only) =		8.09
SD (using values marked * only) =		0.30
%RSD =		3.68

Test item determination 3:

Weight of test item taken (g) = 0.7234

Molecular weight of test item = 293.0

Final volume of solution made up in carbon dioxide free distilled water (mL) = 250

Concentration of test item solution (M) = 0.7323/293 x 1000/250 = 0.009876 

Volume of test item solution taken for titration = 50 mL

Volume of 0.1M hydrochloric acid added (mL)	pH of solution	pKa
0.00	8.63	N/A
0.30	8.58	7.39*
0.60	8.53	7.67*
0.90	8.48	7.83*
1.20	8.42	7.93*
1.50	8.39	8.03*
1.80	8.35	8.11*
2.10	8.24	8.11*
2.40	8.21	8.19*
2.70	8.15	8.24*
3.00	8.08	8.28*
3.30	7.99	8.30*
3.60	7.89	8.33*
3.90	7.77	8.36*
4.20	7.68	8.45*
4.50	7.33	8.37
4.80	6.55	8.19
5.10	3.55	N/A
5.40	3.07	N/A
5.70	2.87	N/A
Mean (using values marked * only) =		8.09
SD (using values marked * only) =		0.29
%RSD =		3.64

Overall Mean pKa = 8.07

Overall standard deviation = 0.30

Overall % RSD = 3.69

Conclusions:

The results show that the mean dissociation constant (pKa) is 8.07.

Executive summary:

The dissociation constant test was performed following OECD Test Guideline 112 under GLP comliance. The results show that the mean dissociation constant (pKa) is 8.07.

Description of key information

The dissociation constant test was performed following OECD Test Guideline 112 under GLP comliance. The results show that the mean dissociation constant (pKa) is 8.07.

Key value for chemical safety assessment

pKa at 20°C:

8.07