«The Ionization of Various Acids.»—The table given on page 104 shows the ionization constants for a number of acids of interest in analysis. Before proceeding to give the table, we must consider further two important points. In the first place, for the strongest acids, such as hydrochloric, nitric, hydrobromic and similar acids, chemists have been unable to determine ionization constants on the basis of the law of chemical equilibrium. Strong acids, strong bases and most salts (see pp. 106–8, below), the three classes comprising ‹all› the ‹very readily ionizable electrolytes, do not give constants› when the values of the equilibrium ratio,[182] [Cation] × [Anion] / [Molecules], are calculated for different concentrations, and ‹they therefore do not ionize simply in accordance with the law of chemical equilibrium›. The reasons for this abnormal behavior will be discussed presently (p. 108), when other necessary facts are before us. In order to have, at least, a rough basis for comparison of these strong acids with the weak ones, which do obey the law of chemical equilibrium, the table will give for the strong acids ‹the value of the above ratio as calculated from their ionization in 0.1 molar solutions›. «The Ionization of Polybasic Acids.»—In the second place, the meaning of the ‹constants for polybasic acids›, such as sulphuric, phosphoric, carbonic and similar acids, requires explanation. The relations for carbonic acid will be first developed, as representing a typical case. Carbonic acid, in ionizing, forms the carbonate-ion CO_{3}^{2−}, and the hydrogen-ion, as expressed in the [p101] equation[183] H_{2}CO_{3} ⇄ 2 H^{+} + CO_{3}^{2−}. According to the law of chemical equilibrium for the case where a product (here the hydrogen-ion) appears twice on one side of the reaction equation, we have, for the condition of equilibrium (p. 94) [H^{+}]^2 × [CO_{3}^{2−}] / [H_{2}CO_{3}] = K. (1) We may ask, however, whether both the hydrogen atoms of carbonic acid show the ‹same tendency to ionize›, or, since there is a vast difference in the ease of ionization of different acids, whether there is not also a difference in the ease of ionization of the different hydrogen atoms in a polybasic acid. As a matter of experiment, we find that a molecule of carbonic acid does ionize, first, and more readily, into one hydrogen ion and an ‹acid carbonate› ion HCO_{3}^{−}, according to H_{2}CO_{3} ⇄ H^{+} + HCO_{3}^{−}. For this reversible reaction we have[184] [H^{+}] × [HCO_{3}^{−}] / [H_{2}CO_{3}] = K_{1}. (2) The value of this constant,[185] called the ‹primary ionization constant› of carbonic acid, is 0.3E−6. The acid carbonate-ion HCO_{3}^{−}, in turn, is ionized to a certain extent, producing another hydrogen ion and the carbonate-ion, CO_{3}^{2−}. We have HCO_{3}^{−} ⇄ H^{+} + CO_{3}^{2−}, and [H^{+}] × [CO_{3}^{2−}] / [HCO_{3}^{−}] = K_{2}. (3)