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.

    27/388 (page 13)
    Since, at equilibrium, vi=v2, it is also true that k^A]■[/?] — A’o[C ] [Z)], and this equation may be written as follows: [cm=h=K [A][B] k‘2 kl k2’ “equilibrium constant” of the reaction, and it is always the same, for any given reaction, as long as the temperature does not change. Ionization of Water.—Ordinary ionization reactions are practically instantaneous, and come to equilibrium immediately., Accordingly, in applying the Law of Mass Action to such a case as the ionization of water, all that need be considered is the situation when equilibrium has been reached. In water, which dissociates into hydrogen and hydroxyl ions (H2O^H+ + OH“), the condition at equilibrium is shown by the following equation: The ratio of the two velocity constants or K) is called the [H+][OH-] [HaO] or [H+][0H-]=/l[H20] Inasmuch as the extent to . which water ionizes is very small (corresponding with the fact that it is a poor conductor of elec¬ tricity), the concentration of undissociated water, or [H20], is not appreciably diminished because of the ionization, and the en¬ tire expression on the right of the equation (K[H20]) has a con¬ stant value, determined experimentally to be o.oooooooooooooi, or icr14, at room temperature (250). That is, [H+] [OH-] = icr14 which is the value of the product of the two ion concentrations at that temperature, not only in pure water, but in any aqueous solution. In pure water, there must be equal quantities of positive (hydrogen) and negative (hydroxyl) ions, or [H+] = [OH-]. Consequently, [H+] [OH-] = [H+]2= io-14 and [H+] = [OH-] = icr7 n The [H+] and the [OH-] of pure water are then both io-7 n, which means that the acidity of water is roughly one ten-mil¬ lionth as great as that of a normal solution of hydrochloric acid