Theodore R. Williams and Robert Carter' The College of Wooster
Wooster, Ohio
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I
The Use of Polyekctrolytes to improve Qualitative Analysis Preparations
The presence of hoped-for precipitates in colloidal form has long caused considerable difficulty for qualitative analysis students. Often the cloudy mixture cannot be separated even by prolonged centrifugation. Several techniques have been suggested2 to eliminate this problem. Electrolytes may be added to flocculate the colloidal solution (sols). Unfortunately, most of the electrolytes which are effective are highly charged anions or cations, such as magnesium chloride, and therefore introduce interferences into the qualitative analysis scheme. Raising the temperature has the effect of increasing the thermal motion of the particles and thus allowing the charged sol particles to overcome the mutual repulsion. This technique, however, is not very effective for student separations. The recent development of flocculating agents, "Primafloc Polyelectrolytes," by the Rohm and Haas Co., has made possible a new approach to this problem. These reagents are organic polymers which possess a great number of cationic or anionic sites that will neutralize charged sol particles and bind them together. The Primafloc Polyelectrolytes have been used to clarify turbid waters in sewage and industrial sludges. The effectiveness of these reagents with industrial material has been sufficient to warrant consideration of their use in qualitative and quantitative analysis. I n order to determine the applicability of these reagents to qualitative analysis, 0.2% solutions of each flocculant were prepared. The anionic material sliould be prepared as thr sohhle arnt~~ouium or $odiu~rl sulr h\. neutmliziur! the comr~lcrcinllvnvailable ~.t%zrtlt (20%"in water) with ammonia or sohiurn hydroxide.
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Class of 1966. Collexe of Wooster.
Before allowing the student to use this reagent, it is wise to familiarize him with the properties of colloids. The silver halides and the Group I1 sulfides give considerable separation trouble. A typical introductory experiment was as follows: Four samples of silver iodide and arsenic trisulfide were prepared. To one of these samples, 0.02 M magnesium chloride was added, to another a cationic flocculant and to a third, an anionic flocculant. A fourth sample was used as a blank. The student was asked to compare the effectiveness of these three reagents and explain his results. Experiments were performed on the colloids most often found in the qualitative analysis scheme. Two or three drops of fluocculant (0.2%) in a total volume of 3 ml mere sufficient to flocculate the precipitates. The following precipitates were found to he successfully separated using the Primafloc Reagents: silver halides, arsenic trisulfide, manganese sulfide, iron(II1) hydroxide, aluminum hydroxide, nickel dimethylglyoximate, and sodium magnesium uranyl acetate. In several cases, such as the precipitation of nickel with dimethylglyoxime, flocculation was instantaneous and centrifugation was not necessary. Separations involving all of the precipitates listed were improved by addition of several drops of the Primafloc Reagents to 1-3 rnl of the test solution being precipitated. Too much flocculating agent (more than 5 drops) should not be added for this produces a harmful effect on the separations. The flocculation of the precipitates of Group N sulfates and lead chloride were not improved by using tliwe reagents. The aualitntivr resultr indicate the vossible uw of Primafloc Reagents in improving gravimetric precipitates. -?auld l i e to express gratitude to the Co. for research samples of Primafloc ,c XA-10.
Reminder: NSF Fellowships Applications Deadlines Cooperative Graduate Fellowships. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Nov. . 2, 1964 Summer Fellowships for Graduate Teaching Assistants. . . . . . . . . . . . . . . . . . . . . . . . .Dec. 4, 1964 Science Faculty Fellowships. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..Oct. 12, 1964 Postdoctoral Fellowships: Firat award period.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..Sept. 8, 1964 Second award period. . . . . . . . . . . . . . . . . . . . . . . . ..Early Dee., 1964 Senior Postdoctoral Fellowships. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Oct. . 12,1964 NATO Postdoctoral Fellowships in Science. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Oct. 5, 1964
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Journd of Chemical Education
