G e o r g e S. Kriz, Jr. and Kay Dian Kriz Western Washington State College Bellingham, 98225
Analysis of Phosphates in Detergents
Today's college student is increasingly concerned t.hat his cburses rerate to current social problems. The need for course materials which deal with these problems extends to the physical as well as to the social sciences. One area which can readily be dealt with in basic chemical lahoratory courses is environmental pollution. The experiment described here is a response to the need mentioned above and is specifically concerned with water pollution caused by phosphates in detergents. It is designed to he a part of a laboratory course in general chemistry for students whose primary interest is not in the sciences, but %rhostudy chemistry as part of a broad general education curriculum. The Exrreriment Before the student is permitted to perform the experiment, i t is advisable to provide him with some discussion ahout the presence of phosphates in detergents, the utility of phosphates in these applications, and the dangers to the environment resulting from the presence of phosphates. Such a discussion could he presented either in written form accompanying the procedure for the experiment, or in n. disclwion session. Four stock solotions are prepared, one containing a 0.5% aqueous solution of a liquid dish detergent, one containing a. 0.5y0 aqueous solution of a liquid laundry detergent, one containing a 1% aqueous solution of a powdered cold-water laundry detergent, and one containing a 1% aqueous solution of a powdered hot-water laundry detergent. These concentrations approximate the actual concentrations used in the average washing machine. The student marks four test tubes for identification. Into each test tube he places 10 drops of one of the soap solutions, 10 drops of 6 N nitric acid, and 10 drops of 0.5 M ammonium molyhdate solution. All four test tubes are placed simultaneously into a beaker in which water has been brought to a boil. The test tuhes are held in the boiling water for 5 min. After 5 min, the test tuhes are removed from the boiling water and inspected for the presence of a yellow precipitate, which indicates the presence of phosphate. On the basis of the intensity of the yellow color, the student should decide whether each sample had no phosphate, a small amount of phosphate, or a large amount present. The results are remrded on a reportsheet. In a second part of the experiment, the student is asked to make up s n aqUeoU8 solution of a laundry soap, detergent, household cleaner, or some other laundry or dishwashing product which he has brought to class. The solids should he made up as 1% solutions, and the liquids should he made up as 0.5% solutions, in order to obtain similar concentrations to those used in the home. The student is asked to test this solution for the presence of phosphate in a manner similar to that described above and to compare this result with those obtained with the four previous solutions.
' KING, EDWARDJ., "Qualitative Analysis and Electrolytic Solutions," Hareourt, Brace and Co., New York, 1959, p. 552. KOLTHOFF, I. M., SANDEL& E. B., MEEHAN, E. J., AND BRUCKENSTEIN, STANLEY, "Quantitative Chemical Analysis" (4th ed.), The Macmillan Co., Collier-Maemillan Ltd., London, 1969, p. 647
"Weshington Environmental Council Report," March 31, 1970. a
Results a n d Discussion
This experiment is based on a well-known analytical procedure for the determination of phosphate as ammonium phosphomolybdate,~ (NH4)3POP. 12M003.
The polyphosphates used in the detergents are determined as phosphate in this experiment. By using equal amounts of each of the reagents and by perTable 1. Comparison of Typical Student Results with Published Phosphate Analyses of Some Detergents
Detergent
Studentdetermined phosphate content
Published percentage phosphate"
High High Low
43.5 36.5 10.5
None
Less than 1 . 0
Heavy Duty Laundry Detergents A B C Liquid Dish Detergents D
"Washington Environmental Council Report," March 31, 1970. Table 2.
Phosphate Analyses of Cleaning Agents* Percentage phosphate
Product Hemv Dutv Laundry Detergents Amway Trisyme Oxydol Drive Amwav SA8 Fah Dus Surf Amaze Miscellaneous Use Snowy Bleach Mr. Clean
Product Cheer Tide All Arctic Power' Ajax 2 Bold Breeze Wisk Spio and Span Arm & Hammer Soda ~
Laundry Soaps Instant Fels Lux Automatic Dishwasher Compounds All Calgonite Amway Liouid Dish Detergents All liquids Conditioners Calgon Light Duty Whistle T.t%tttl
Percentage phosphate
9.0
