The reactions of N2O5 with the anions X(-)(H2O)n, where 0 less than or equal to n less than or equal to 5 and X = O, OH, O-2, HO2, and O-3, in helium at several temperatures within the range 163-298 K and at pressures between 0.22 and 0.46 Torr were studied using a fast-flow apparatus. The ions O-(H2O)(n=0-2), OH-(H2O)(n=0-2), O-2(-)(H2O)(n=0,1), HO2-(H2O)(n=0,1), and O-3(-) react with N2O5 at the collision rate to form mainly bare NO3-; the larger hydrates of the reactant anions lead to production of the hydrated species NO3-(H2O)(m), which can react further with N2O5 to form NO3-.HNO3. The rate constants for the observed reactions were determined, and the implications of the present experimental results to atmospheric chemistry are briefly discussed.