The acid-base and oxidation-reduction properties of aqueous HCl + NaCl mixtures (HCl + NaCl less than or equal to 5 M) are characterized by means of the Ro(H) acidity function and the Ro(Cl-) function, which respectively represent their ability to give up the proton and the chloride ion. The electrochemical windows of these mixtures at various working electrodes including mercury drop, carbon, platinum, and gold are determined. The solvation properties of these media are characterized by means of the solvation transfer activity coefficients of the solutes, which are calculated from the normal potential values of the corresponding redox system.