Activity Coefficients of Uranyl Fluoride from Freezing Point Depressions

J \ M B S S. JOFTNSON

4-m

[ C O \ T R I B U T I O N ITROM T H E 0 4 K

IND

K ~ R-4T K R i i ~ q

RIDGET A T I O U A L

T 2 4 R O R A TORY,

Yol, 74

CHEMISTRY DIVISIOY1

Activity Coefficients of Uranyl Fluoride from Freezing Point Depressions : Undissociated Species and Dimerization1 BY JAMES 5.J o m s m

AND

KECEIVED 11.4RcH

KURTA. KRAUS

27, 1$)52

Freezing point depressions of aqueous uranyl fluoride solutions were obtained in the region 0.1-5 molal UO.F? by a warming curve method. A thermistor was used as the temperature sensitive element in an autoniatically recording system. Activity coefficients of UOsF? were calculated from these d a t a . From these it can he concludetl t h a t u r ~ t ~fluoride yl in the concentration range studied is essentially undissociated axid has a considerable tendency to associate. -4dimerization constant K = 1.5 was evaluated for the reaction 2U02F2 (L‘OsFp):!on the assumption that the logarithm of the activitycoeflicients of the monomer and dimer vary linearly with molality of I,.OaF?.

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In the course of the determination of the phase diagram of the system U02F2-H20, Xarshall, Gill and Secoy2 found that the freezing point depressions 0 were very small if interpreted on the assumption that uranyl fluoride dissociates into three ions ( U 0 2 + c and F - ) . Thus it appeared

that uranyl fluoride cannot be completely dissnciated. .i more detailed study of the freezing point depressions of uranyl fluoride solutions has now been carried out in an attempt to obtain accurate values of the activity coefficients. These have been interpreted in terms of the postulated species (undissociated) I:OzF2and its dimer (V‘O2F2j?. Experimental

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