Van Name and Huff — Acid Solutions. L03 



Art. VIII. — The Rate of Hydrolysis and Electrical Con- 

 ductivity of Hypophosphoric Acid Solutions; by R. G. 

 Van Name and Wilbert J. Huff. 



(Contributions from the Kent Chemical Laboratory of Yale Univ.— ccxeviii.) 



I. 



Rate of Hydrolysis. 



The stability of hypophosphoric acid in water solution 

 is determined entirely by the rate at which the acid 

 undergoes hydrolysis into phosphorous and phosphoric 

 acids and for this reason a knowledge of the approximate 

 rate of this reaction under various conditions is essen- 

 tial for a proper understanding of the chemical behavior 

 of the acid. Though the nature of the reaction has long 

 been known, no definite information about its rate has 

 hitherto been available, investigation of this question 

 having apparently been discouraged by the lack of 

 methods of analysis suitable for the purpose. 1 The 

 needs of the case, however, are fully met by the method 

 for estimating phosphorous acid which we have described 

 in the foregoing article, and it will be shown below that 

 with its aid the velocity of this hydrolysis can be easily 

 and accurately measured. 



From a study of the literature of hypophosphoric acid 

 the following inferences can be drawn concerning its 

 hydrolysis: (a) The reaction yields an equimolecular 

 mixture of phosphorous and phosphoric acid, (b) It is 

 non-reversible. (c) It is accelerated by acids. (d) 

 Solutions of acid sodium hypophosphate are stable at 

 room temperature for long periods. This shows that in 

 solutions whose hydrogen ion concentration is below the 

 turning point of methyl orange, (H+) = lO -4 , the hydrol- 

 ysis at moderate temperatures is negligible. Distinctly 

 alkaline solutions appear to be still more stable. 



Our experience supports the correctness of these 

 inferences: The measurement of the rate of hydrolysis 



1 Salzer, Ann. Chem., 211, 1, 1882, cites a single experiment in which 

 20 cm 3 of a solution of pure hypophosphoric acid, containing 1-154 grams 

 of P 2 4 , were allowed to stand in a desiccator for four weeks, after which 

 the volume of the solution was 1-3 cm 3 and only 0-150 gram of P:;0 4 remained 

 unhydrolyzed. The method of analysis here used was of very doubtful 

 accuracy. Salzer also states that in a 5% solution of hypophosphoric acid 

 which had been allowed to stand for three years, no trace of that acid 

 could be detected. 



