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CONDUCTANCE OF SOLUTIONS OF Ce IN LIQUIDNHI
The Conductance of Solutions of Cesium in Liquid Ammonia1 by Robert R. Dewald L)epartment of Chemistry, T u f t s University, Medford, Massachusetts 06166 (Received November 67,1968)
The conductivity of cesium-ammonia solutions at -33.9, -45.0, and -65.0’ has been measured over the concentration range of 0.425 to 1.23 X M. The method of Shedlovsky was used to evaluate the data in the dilute range. Values of 1142, 954, and 672 for the apparent limiting equivalent conductance, and for the ion-pairing dissociation constants at -33.9, -45.0, and and 2.19 X 4.87 x lo+, 3.30 x -- 65.0’, respectively, were determined. The results are compared with data reported for other metal-ammonia solutions. Introduction The properties of metal-ammonia solutions have been studied extensively for the past ~ e n t u r y . ~ -There ~ appears to be general agreement that in the very dilute M ) , the solutions consist concentration region (< predominantly of solvated electrons and cations.5~~Recent conductance studies7 indicate that the metal solutions in the dilute region conform to laws which govern the behavior of normal electrolytes. The conductance mechanism is typically ionic except the mobility of the solvated electron is about eight times that of the sodium ion, which suggests that an electron-jump6 or an inversion mechanism7&is operative rather than migration of the cavity. As the metal concentration increases from infinite dilution, the equivalent electrical conductance decreases ~ ~ ~ conductivity ~ then inuntil a minimum O C C U ~ S . The creases with increasing metal concentration until it becomes metallic in nature for very concentrated solut i o n ~ . ~For , ~ the intermediate concentration region between approximately 0.04 and l M , Arnold and Pattersonlo have proposed a conduction mechanism which proceeds by the jumping of electrons from M centers to metal ions. To obtain moire information about the electrical properties of metal-ammonia solutions, the conductance of cesium-ammonia solutions was measured in the dilute and intermediate concentration range at - 33.9, -45.0, and -65”. Experimental Section
Materials. Ammonia (Matheson 99.99%) was purified in a manner which has been previously described.7b The specific conductance of the purified ammonia was determined prior to distillation of the metal in a number of runs. The pure solvent was found to have a specific conductance on the order of lo-’ ohm-l cm-l or less a t -33.9’ and hence the conductance of the solvent was considered negligible in this study. Cesium was obtained in 10-g ampoules as a gift from the Dow Chemical Co. (analysis: Na,
