11. THE ADSORPTION OF CALCIUM AND COPPER FROM AMMONIACAL MEDIUM BY SILICA GEL1 I. M. KOLTHOFF
AND
V. A. STENGER
School of Chemistry, University of ivinnesota, Minneapolis, Minnesota Received J u l y
$4,
1933
A detailed study has been made of the adsorption of calcium hydroxide alone and of copper hydroxide and of calcium hydroxide in the presence of ammonia and ammonium salts by silica gel with the purpose of finding out in what forms the cations are held at the surface of the gel. The gel used and the general procedure followed are described in previous communications ( 5 , 6). ANALYTICAL
The amount adsorbed was determined by analysis of the supernatant liquid and of the solution obtained after extraction of the mashed gel with a known volume of standard acid. Calcium was determined by the oxalate procedure, ammonia in the absence of copper volumetrically by oxidation with calcium hypochlorite, and copper iodometrically. It was found that ammoniacal copper solutions on standing give rise to the formation of nitrite, which interferes badly with the volumetrid determination. The interference was eliminated by removing the nitrite by evaporation with sulfuric acid. If the presence of nitrite is ignored, deviating results may be obtained from the direct iodometric analysis. A solution originally 0.0522 molar in copper, 0.02 molar in ammonium chloride, and 1.1 molar in ammonia gave an iodometric titer of 0.0522 after three days, 0.0538 after seven days, 0.0568 after twelve days, 0.0588 after nineteen days. After seven months the results of the titration were inconsistent, but a t least 20 per cent high. ADSORPTION OF CALCIUM HYDROXIDE
Although the solubility of the silica gel in calcium hydroxide solutions was very small, no adsorption equilibrium could be attained even after long periods of shaking. This is clearly shown by the curves in figures 1 and 2. In the former case 0.5 g. of gel and in the latter 0.2 g. of gel was shaken 1 From a thesis submitted by Vernon A. Stenger, J. T. Baker Fellow in Analytical Chemistry, 1932-1933, to the Graduate School of the University of Minnesota in partial fulfillment of the requirements for the degree of Doctor of Philosophy, 1933. 475
T H E J O U R N A L OF PHYSICAL CHEMISTRY, VOL. XXXYIII, N O .
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I. M. KOLTHOFF AND V. A. STENGER
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