886
LEWISL. ASDERSONA N D MILTOPI; KAHX
I n conclusion it has been shown that the equations developed in the previous sections predict linear plots of m/w us. l/sin a. This has been shown to be experimentally true. As a further verification of theory the observed and calculated values of the contact angles were shown to be in generally good agreement. The calculated and
T’ol. 66
estimated values of (ysv - y s ~ )were shown to be in good agreement for the polyethylene-water system. Thus, the predicted results are consistent with those observed. Acknowledgment.-The authors wish to thank Professor George Gubareff for his aid in translating references 1 and 2.
ARSENIC (111)-ARSESIC(V) EXCHANGE REACTION I N HCl SOLUTIOSS’ BY LEWISL. AKDERSOX~ AKD MILTONKAHS Department of Chemistry, The University of New Mexico, Albuquerque, N . M . Received November 10, 1961
A measurable exchange has been observed between As(II1) and As(V) in 10.8 to 12.6f HCl a t 29.7”, and in 10.9.f HCl a t 48.6 and 67.3’. Complex exchange curves were observed a t each temperature. The complexity is attributed to the slow interconversion, via hydrolytic reactions, among two or more forms of $s(V) which exchange a t different rates with As(1II). Spectrophotometric studies revealed that As(V) species in 10.9f HC1 were not in chemical equilibrium even after 19.3 days of aging a t room temperature. There is spectrophotometric evidence for the existence of polymeric forms of As(V) in 10.9f HC1.
Introduction This paper deals with the As(II1)-As(T7) exchange in HC1 solutions. I n the course of a study of the “hot atom” chemistry of arsenic, Maly and Simanova3 observed exchange on heating a mixture of As(II1) and As(V) in concentrated HC1. We hare observed an easily measurable exchange at 29.7, 48.6, and 67.3” in 10.9 f HC1. This exchange, however, is generally complex; that is, the exchange curves are not straight lines. This system is complicated further by the slow attainment of chemical equilibria at room temperature among species of As(V) over several weeks as evidenced by the dependence of exchange curves on the age of the As(V) solutions. Spectrophotometric studies corroborated this aging phenomenon and revealed an extreme dependence of the equilibria among As(V) species on the HC1 concentration. Although the data presented here do not permit the postulation of a mechanism for exchange, we are able to report a number of interesting observations which point up the complexity of this system. Experimental Tracer.-The 17.5-day As74 tracer was obtained from Abbott Laboratories, Oak Ridge, in the form of high specific activity sodium arsenate solution. This solution was made 11 to 1 2 f i n HC1 and distilled in a stream of Clz to one-fourth its original volume (-20 ml.). Excess Clz was removed from the cooled residue by either a stream of nitrogen or the addition of excess owdered FeC12-4HzO. The residue then mas saturated wit% HCl a t 0” and rapidly distilled for 2 min.; the distillate was received in 5 ml. of.12 f HCl a t 0 ” and served as the stock solution of high specific activity 4s(111). The As(II1) tracer solutions used in runs 1-8 were prepared by inoculation of inactive As( 111) solutions and used directly; for subsequent runs, the inoculated ks(II1) was oxidized, reduced, and distilled as described above. The As(V) tracer solutions were prepared by exchange in (1) This communication is based on work done under the auspices of the Los Alamos Scientific Laboratory a n d the Atomic Energy Commission (Contract No. A T (11-1)-733) a n d submitted in partial fulfillment of the requirements for the degree of Doctor of Philosopy in the Graduate School of the University of New Mexico, June, 1961, by Lewis L. Anderson. (2) Eastman Kodak Fellow, 1959-1960. (3) J. Maly and R. Simanova, Chem. Listy, 49, 814 (1955).
10.9f HC1 betmeen inactive As( V) and high-specific-activity As(II1) a t 95’ for 4 hr. in a sealed Pyrex tube. To test for radiochemical purity, a sample of purified highspecific-activity ils(II1) was sealed in a test-tube and counted from time to time, over a t least 5 half-lives of AsT4,on a scintillation counter. The decay curves contained 17.5and 71-day components which correspond to 17.5-day As74 and 76-day As73. Also, the specific activity of an aliquot of an inoculated As(II1) solution was within 2y0of that of an aliquot subjected to oxidation, reduction, and distillation. Reagents and Analyses.-The HC1 solutions were prepared by dilution ot Analvtical grade 37% HC1 a i t h doublydistilled water. The Bs(II1) stock solutions were prepared by dissolving C.P. AsoO? in HC1. The solutions were analvzed for As(11II by titrating aliquots with standard KBrOj solution to the methyl orange end-point in 2.4fHCl.4 Stock solutions of As(V) were prepared by dissolving C.P. As206 in HC1. The As(V) concentration was determined by thiosulfate titration of the iodine liberated from K I by aliquots of the solution.6 All stock solutions except those used in runs 1-4 were stored at room temperature under the normal fluorescent light of the laboratory; the solutions used in rune 1-4 were stored in the dark. Chloride analyses were performed by a modified Volhard method .6 The acid concentration of a stock solution was calculated from the concentrations of As(II1) or As(V) and total chloride assuming that As( 111) and As( V) exist in these solutions as AsCll and AsCla-, respectively. It is noteworthy, however, that whereas >98yo of As(1II) should exist in 10.9 f HC1 as AsC&,~there is no evidence for the existence of AsC16-.* Because the extent of hydrolysis of As(\?) in HC1 solutions is unknown, the actual HC1 concentration of an As(V) stock solution probably was somewhat greater (
