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    Behaviour of phosphorus pentachloride (PCl5)

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    PCl5 is a white solid, which volatilises at 160oC and melts at 148oC under pressure. Molten PCl5 conducts an electric current readily. At 180oC PCl5 vapour has a density of 9.3 g/L corrected to the standard conditions. At 250oC a sample of PCl5 exerts a pressure, which is twice the expected value. Discuss these observations and comment on the species present in the melt and at 180o and 250o in the vapour.

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    Solution Preview

    Since PCl5 volatilises at 160oC (relatively low temperature) we can assume that PCl5 is mostly covalent solid.

    The fact that molten PCl5 conducts electricity can be explained by the fact that PCl5 is ionic liquid due to auto dissociation. (Please reffer to the attached document for detailed explanations and equations!)

    In order to explain the observed density, we have to employ the ideal law gas equation: pV = nRT. If we remember that n=m/M, we get pV = (m/M)RT. From here we can ...

    Solution Summary

    The problem explains behaviour of phosphorus pentachloride (PCl5) at various temperatures from the point of bonding and structure.