Laboratory manual of biological chemistry : with supplement / by Otto Folin.

  • Folin, Otto, 1867-1934.
Date:
[1934], ©1934
Catalogue details

Licence: Public Domain Mark

Credit: Laboratory manual of biological chemistry : with supplement / by Otto Folin. Source: Wellcome Collection.

    23/388 (page 9)
    for example, only 90 per cent of the ions are “active,” and in a tenth normal solution only 79 per cent (at 250 C.). Some inor¬ ganic acids (H2S, II2CO3) are weak electrolytes, as are most organic acids. Bases, in a similar way, are strong or weak, according as they are to a large or small extent dissociated into hydroxyl ions. The alkali metal hydroxides (NaOH, KOH, etc.) are strong bases; ammonium hydroxide is a typical weak base. Hydrogen Ion Concentration.—The complete neutraliza¬ tion of one liter of a normal solution of acid requires one liter of normal alkali, and from that standpoint all acids are alike. But the actual acidity of a normal solution depends entirely upon the nature of the acid, and is determined, not by the amount of replaceable hydrogen per liter, but by the concentration of active ionized hydrogen. Thus, in a tenth-normal solution of hydro¬ chloric acid, the hydrogen ion concentration, or activity ([H+])1 is 79 per cent of tenth normal, or 0.079N. On the other hand, in a tenth-normal solution of acetic acid, only 1.36 per cent of the acid is ionized, and the [H+] is only 1.36 per cent of tenth nor¬ mal, dr 0.00136N. Although these two solutions are equivalent as far as titration is concerned, the acidity of one is nearly sixty times that of the other. This illustrates the difference between strong and weak acids, and leads to a distinction between two kinds of acidity, (1) titratable acidity, which is measured by the amount of standard alkali required to neutralize a given solution; and (2) actual acidity, or [H+]—the number of gram-molecules or gram-ions of ionized hydrogen per liter (or, approximately, the number of grams of ionized hydrogen per liter, since the atomic weight of hydrogen is practically 1). The dividing line between acid and alkaline solutions is water itself, which is ionized to a slight degree, as follows: ii2o^h+toh- Water, in other words, is largely undissociated water (HaO), in equilibrium with a small proportion of H+ and OH in equiva¬ lent quantities, so that the hydrogen ion concentration and the hydroxyl ion concentration, or [OH], are equal. That is true 1 The symbol for a substance, enclosed in brackets, is the customary method of denoting its concentration.