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Physical & Chemical properties

Dissociation constant

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No experimental determination of the dissociation constants in water was performed for the test materials as it was anticipated that on performance of the test procedures, as detailed in Method 112 of the OECD Guidelines for Testing of Chemicals, 12 May 1981, that the resulting dissociation constants determined would be that of the parent anions only, for which literature values are available. For example, it is anticipated that different types of orthophosphate will demonstrate significantly different pH values in water due to increasing numbers of protons being substituted with the particular cation on titration with acid or base as appropriate, the actual dissociation constants determined for each compound would be common, i.e. that of the triprotic acid anion. Titrations would also be expected to be similar irrespective of the counter ion. Read-across is justified on the basis that pyrophosphoric acid is the parent acid for all inorganic pyrophosphates. 

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Results:

 No. pKa  Temperature (°C)
 #1  0.9  25
 #2  2.31  25
 #3 6.69  25
 #4  9.42  25