The ultrasonic velocities, densities, viscosities, and electrical conductivities 
of aqueous solutions of magnesium nitrate and magnesium acetate have been measured
from dilute to saturation concentrations at 0 . t/.C . 50. The temperature derivative 
of the isentropic compressibility, .s, became zero at 2.28 mol kg.-1 and 2.90 mol kg.-1 
for Mg(OAc)2 and Mg(NO3)2 solutions, respectively, at 25 oC. The total hydration numbers
 of the dissolved ions were estimated to be, respectively, 24.3 and 19.2 at these 
concentrations. Differences in .s for various M2+ salts, using the present and 
literature data, correlated with reported M2+.OH2 bond lengths and to a lesser extent 
with cationic charge density (ionic radius). The influence of anions on .s appears to 
follow the Hofmeister series and also correlates approximately with the anionic charge 
density. Substantial differences between Mg(OAc)2(aq) and Mg(NO3)2(aq) occur with 
respect to their structural relaxation times (derived from compressibility and 
viscosity data) and their electrical conductivities. These differences were attributed 
to much greater ion association in Mg(OAc)2 solutions. Raman spectra recorded at 28 oC 
confirmed the presence of various types of contact ion pairs including mono- and 
bidentate complexes in Mg(OAc)2(aq). In Mg(NO3)2(aq) only non-contact ion pairs appear 
to be formed even at high concentrations. The experimental results are supported by 
molecular dynamics simulations, which also reveal the much stronger tendency of OAc. 
compared to NO3. to associate with Mg2+ in aqueous solutions. The simulations also 
allow an evaluation of the ion-ion and ion-water radial distribution functions and 
cumulative sums, and provide a molecular picture of ion hydration in Mg(OAc)2(aq) 
and Mg(NO3)2(aq) at varying concentrations.