hydrodynamic radius

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The effective radius of an ion in a solution measured by assuming that it is a body moving through the solution and resisted by the solution's viscosity. If the solvent is water, the hydrodynamic radius includes all the water molecules attracted to the ion. As a result, it is possible for a small ion to have a larger hydrodynamic radius than a large ion – if it is surrounded by more solvent molecules. Experiments involving nuclear magnetic resonance (NMR) and isotope tracers indicate that there is considerable movement between solvent molecules within the hydrodynamic radius and the rest of the solution.

Subjects: Chemistry.

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