NMR Studies of Aqueous Electrolyte Solutions. II. Hydration of Al(NO3)3 Determined from Temperature Effects on Proton Shift

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Abstract
Proton shifts of aqueous Al(NO3)3 solutions are measured as a function of temperature and concentration. Using a two‐state model which is applicable to dilute solutions, the total hydration of Al(NO3)3 is found to be 13.4. Two explanations of this value are postulated: (1) Each of the six water molecules in the primary layer of the aluminum ion are bound to two molecules of the secondary layer, with nitrate ions replacing some secondary water molecules; (2) The aluminum ion is hydrated to six water molecules whereas each nitrate ion is hydrated to two or three water molecules.