This concept depends on the mode of self-ionization of the solvent. Each solvent is considered to consist of an acidic part and a basic part and on auto-ionization (self-ionization) is split into these two parts, i.e., acidic part (or defined as solute which increases the concentration of cations characteristic of the solvent and a solvo base (or a base) is a solute which increases the concentration of the characteristic anions of the solvent. The behavior of any solute is thus determined in terms of the release of characteristic cation or anion of that behavior of any solute is thus determined in terms of the release of a characteristic cation or anion of that solvent. In other words, self-ionization is very essential in determining the behavior of a solute in a solvent. For example, ammonium chloride (NH₄CI) is defined as an acid and sodium amide (NaNH₂) as a base in liquid ammonia.

    2NH₃ <==> NH₄⁺  +  NH₂^-      (self-ionization)
 NH₄CI  <==>  NH₄⁺  +  CI^-          (acid)
NaNH₂  <==>  Na⁺  +  NH₂^-        (base)

Similarly, the behavior of acidic and basic solutes in phosphorus oxychloride (POCI₃) solvent may be defined as :

                            2POCI₃  <==>  POCI₂⁺  +  POCI₄^-       (self-ionization)
             FeCI₃  +  POCI₃  <==>  POCI₂⁺  + FeCI₄^-          (acid)
(CH₃)₄N⁺CI^-  +  POCI₃  <==>  (CH₃)₄N⁺  + POCI₄^-     (bace)

The reaction between tetramethylammonium chloride and ferric chloride, may be investigated as a titration (and observed conductometically) in POCI₃.

                                       POCI₃
(CH₃)₄N⁺CI^-  +  FeCI₃    →    (CH₃)₄N⁺FeCI₄^-

Behavior of acidic and basic solutes is determined by the self-ionization species of the solvents. Therefore, self-ionization of the solvent to give ionic species is very essential in solvent system concept. This concept lays lot of emphasis on ionic reactions in solution.

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