A System of Physical Chemistry (Volume 2)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1920 Excerpt: ... 4-ajcfr = (-yc2)-(-S/C, )- Thus from the change in the solubility product we can find the way in which the ratio a/C varies for each ion. The following table contains a summary of some of the results thus obtained, and includes a number of data obtained from an earlier paper of Noyes (Zeitsch. Jhysik. Chem., 9, 603 (1892)). In each case CC' is taken as the extrapolated value for infinite dilution of the solubility product. This extrapolation is performed by plotting the solubility product against the total ion concentration as this seems to be the predominant factor which causes the variation. This extrapolation in the case of thallous chloride is entirely reliable. In the case of the much more soluble salt, patassium perchlorate, it is very rough, and is only made to render the results for this salt comparable with those for thallous chloride. The last four columns show the percentage diminution in the ratio a/C for the ions, between zero (added) salt concentration and the concentration given at the head of each column. The results are very striking arfd show the generality of the lowering of the ratio of a/C with increasing salt or ion concentration. In the case of HC1 the degree of dissociation is assumed to be the same as that of KC1 at each concentration. Passing now from the activity of ions we turn to a consideration of the activity of undissociated molecules as deduced from vapour pressure measurements. Determination of tlie Activity of Molecules by means of Vapour Pressure Measurements. It has already been pointed out that we may take the vapour pressure of a substance as a measure of its active mass, and therefore of its activity. In the case of homogeneous reactions in gases it may be recalled that the law of mass...