text: Depending on the solute and range of concentration, an aqueous electrolyte solution can have either a larger or smaller viscosity compared with pure water at the same temperature and pressure. For instance, a 20% saline (sodium chloride) solution has viscosity over 1.5 times that of pure water, whereas a 20% potassium iodide solution has viscosity about 0.91 times that of pure water.
  An idealized model of dilute electrolytic solutions leads to the following prediction for the viscosity  of a solution:
  where  is the viscosity of the solvent,  is the concentration, and  is a positive constant which depends on both solvent and solute properties. However, this expression is only valid for very dilute solutions, having  less than 0.1 mol/L. For higher concentrations, additional terms are necessary which account for higher-order molecular correlations:
  where  and  are fit from data. In particular, a negative value of  is able to account for the decrease in viscosity observed in some solutions. Estimated values of these constants are shown below for sodium chloride and potassium iodide at temperature 25 °C (mol = mole, L = liter).