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INDUSTRIAL AND ENGINEERING CHEMISTRY
under any circumstances, accurate enough to give good comparisons; tests run on seven different columns a t three different locations have indicated changes which have led to safer operating conditions. For more exact work where the absolute value of acetylene is desired, the rubber stoppers and tubing may be replaced with glass and cold filters as described by Shepherd (6) used. ACKNOWLEDGMENTS
The autliors nish to acknowledge the assistance of George R. West and the siaii of the Stuart Oxygen Co. Research Department who did some of the preliminary work on the method; and of llerle Randall who gave many valuable suggestions. They also
Vol. 18, No. 2
wish to acknowledge the work of the operators in the various plants who ran most of the actual tests after the method had been developed. LITERATURE aTED (1) Burbo, P. Z., J. Tech. Phys. ( U S S R ) , 13, 116-22 (1943). (2) Coulson-Smith a n d Seyfang, Analyst, 67, 39-41 (1942). (3) Oks,R . S., Zavodskaya Lab., 6, 1399-402 (1937). (4) Pollitzer, V. F., Z . angew. Chem., 36, 26F (1923). ( 5 ) Riese, Wilhelm, Ibid., 44, 701 (1931). (6) Shepherd, Martin, Bur. Standards Research Pub. 75 (1929). (7) Striehevskii, I. I.,Bull. m a d . sci. U R S S , Sir. technol., 1939, No. 3, 51-62; Khirn. Referat. Zhur., 1939, No. 10, 138-9. (8) Weaver, E. R., J . Am. Chem. Soc , 3 8 , 352 (1916).
Determination of Cuprous Chloride LEWIS F. HATCH
AND
REEDUS RAY ESTES
Department of Chemistry, University of Texas, Austin, Texas
DuR’-
irrG recent hydrolysis studies (5) it became necessary to determine accurately the purity of solid cuprous chloride and the cuprous chloride content of dilute solutions. As direct titration of cuprous chloride did not give satisfactory results, the SOCIETY Committee indirect method of the ditlERIC.4N CHEMICAL on Analytical Reagents (1) was tried. This method lacked both the precision and accuracy required for the analysis of samples of essentially pure solid cuprous chloride. This paper calls attention to the defects of the A.C.S. method and proposes analytical procedures which are more satisfactory for both solid cuprous chloride and its dilute solutions.
OXIDIZINGAGENTS OTHERTHAN POTASSIUM PERA comparison of the effect of the presence of cupric chloride on the titration of ferrous chloride using oxidizing agents other than potassium permanganate was made. The data in Table I11 were obtained by the titration of 25-m1. samples of a 1% sulfuric acid solution of ferrous ammonium sulfate by the indicated oxidizing agents, using standard procedures. The effect of the acid used to dissolve the ferric ammonium sulfate when cuprous chloride is analyzed was also determined. A comparison of the different acids and of the three oxidizing agents used is given in Table I V (analytical methods are given below under Recommendations). To determine the effect of dissolved oxygen on the determination of cuprous chloride the ferric ammonium sulfate solution used was made “oxygen-free” as follows: OF
MANGANATE.
REAGENTS.Merck reagent grade cuprous chloride was carefully purified by the usual methods (6). Determination of chloride ion (by the Volhard method) and of total copper by electrodeposition (after conversion to cupric sulfate) indicated a composition of 99.8% cuprous chloride and, 0.2% cupric chloride. The dry cuprous chloride was placed in small glassstoppered vials and stored in a desiccator over magnesium perchlorate. Cuprous chloride thus prepared and stored showed no chan e in composition over a period of several months. All otker chemicals used were of reagent grade. A.C.S. METHOD. Following is the method which is approved by the A.C.S. Committee on Analytical Reagents (I) for the determination of cuprous chloride in a solid sample: Dissolve 0.5 gram in the cold in 25 ml. of ferric ammonium sulfate solution, made by dissolving 10 grams of ferric ammonium sulfate in 100 ml. of dilute hydrochloric acid (1 I), add 5 ml. of phosphoric acid, dilute with 200 ml. of water, and titrate with permanganate, correcting for blank on reagents.
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Careful application of this method consistently gave low values and poor precision when the sample was essentially 100% cuprous chloride. The degree of error is related to the sample size (Table I). On the basis of the oxidation-reduction potentials involved, it is expected that complete oxidation of cuprous copper will occur, if a slight excess of ferric iron is present (4). Actually, the determination of cuprous chloride by this method is the same as a determination of the equivalent amount of ferrous iron in the presence of the excess ferric iron added and an amount of cupric chloride equivalent to the cuprous chloride of the sample. Factors which would influence the titration are cupric ion, chloride ion, and ferric ion concentration and the nature of the acid medium and of the oxidizing agents. Present address, Armour Laboratories. Chicago, 111.
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USE
EXPERIMENTAL
1
A study of some of these factors was made by the titration with 0.1 N potassium permanganate of 25-m1. samples of a standard solution of ferrous chloride in 1 1 hydrochloric acid, in the presence of added cupric chloride and ferric ammonium sulfate as indicated in Table 11. Two hundred milliliters of water and 5 ml. of phosphoric acid were used as in the A.C.S. procedure. The added amounts of cupric chloride are the oxidation equivalents of the recorded amounts of cuprous chloride. The indicated amounts of cupric chloride and of ferric alum were added by measuring appropriate volumes of their standard solutions. The amount of ferrous chloride found by titration, in the absence of added cupric chloride or ferric alum, is taken as 100% to simplify comparison.
More than the required amount of distilled water was boiled for 30 minutes and cooled quickly while being svept by carbon dioxide. Part of this water wm poured into a volumetric flask which had been swept with carbon dioxide, and the correct amounts of h drochloric acid and of ferric ammonium sulfate were added. 6arbon dioxide was bubbled through until solution was complete and water had been added to give the correct total volume. The use of 25 ml. of this “oxygen-free” N hydrochloric acid solution of ferric ammonium sulfate followed by
1.
Effect of Sample Size in Analysis of Cuprous €hloride (Actual CuCl = 99.8) ’(Veight of Sample Cuprous Chloride Found Precision Gram % * %
Table
0.50 0.45 0.40 0.35 0.30
0.23 0.20
97.5 98.6 98.8 98.9 98.9 98.9
98.9
1.0 0.2 0.2
0.1
0.1
0.1 0.1
ANALYTICAL EDITION
February, 1946
11.
Table
Effect of Cupric Chloride and Ferric A l u m on Titration of Ferrous Chloride b y Permanganate CuCl Equivalent Ferric Alum Ferrous Chloride Run t o Added CuCIz Added Found Gram Gram %
Table
111. Effect of Cupric Chloride upon Titration of a 1% Sulfuric
A c i d Solution of Ferrous Ammonium Sulfate CuCl Equivalent Ferrous Chloride Found to .4dded CuCh KLlnO4 KzCrzO7 Ce(SOG Gram 70 % % 0 00 0 25 0 50
100 0 96.9 95.3
100.0 99.7 99.5
100.0 99.8 99.8
titration with potassium dichromate gave 99.5% cuprous chloride as compared with 99.2% of a similar solution, made in contact with air was used. DISCUSSION
The poor results obtained in the analysis of 0.5-gram samples of cuprous chloride by the A.C.S. method may be caused by an insufficient amount of ferric ammonium sulfate solution for the oxidation of the cuprous copper. From the specification “25 ml. of ferric ammonium sulfate solution, made by dissolving 10 grams of ferric ammonium sulfate in 100 ml. of dilute hydrochloric acid” it is assumed that the intention is to use 2.5 grams of ferric ammonium sulfate. This would allow a slight excess of oxidizing agent, since 0.5 gram of cuprous chloride is equivalent to 2.44 grams of ferric alum. However, the addition of 100 grams of ferric ammonium sulfate to 1000 ml. of 1 1 hydrochloric acid, in a constant-temperature bath a t 30” resulted in 1060 ml. of solution, containing only 2.36 grams of ferric ammonium sulfate per 25 ml. Thus, part of the cuprous chloride is oxidized by ferric iron, part by permanganate, and an indefinite amount by atmospheric and dissolved oxygen (S),the latter amount being proportional to time and to the amount of agitation (2). For 0.5-gram samples of essentially pure cuprous chloride, the permanganate concentration should be slightly more than 0.1 N , since 0.5 gram of cuprous chloride is equivalent to more than 50 ml. of 0.1 N solution. Table I1 indicates that the adverse effects of cupric ion are partially, but not entirely, offset by the presence of the ferric alum. Comparison of runs A, B, and D of Table I1 with the data in Table I11 indicates that the effect of cupric chloride upon the permanganate titration of ferrous iron is lessened by decreased chloride ion concentration and that the effect of cupric chloride is less when potassium dichromate or ceric ammonium sulfate is used.
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RECOMMENDATIONS
The following three methods for the determination of the cuprous chloride content of solid cuprous chloride have all proved superior to that recommended by the A.C.S. Committee on Analytical Reagents:
POTASSIUM PERMANQANATE. Weigh 0.3 gram of cuprous chloride into a dry 500-ml. Erlenmeyer flask, add 25 ml. of ferric ammonium sulfate solution, made by dissolving 10 grams of ferric ammonium sulfate in sufficient 3 M sulfuric acid to make 100 ml., and swirl gently until dissolved. Add 200 ml. of water and 5 ml. of phosphoric acid, and titrate with 0.1 N permany a t e t o the first pink color which persists for 15 seconds. A lank must be run on the reagents. POTASSIUM DICHROMATE.Wei h 0.3 gram of cuprous chloride into a dry 500-ml. Erlenmeyer task, add 25 ml. of ferric ammonium sulfate solution, made by dissolving 10 grams of ferric ammonium sulfate in sufficient N hydrochloric acid to make
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100 ml., and swirl gently until dissolved. Add 300 ml. of a solution containing 80 ml. of sulfuric acid and 25 ml. of phosphoric acid per liter, add 5 drops of 0.2% barium diphenylaminesulfonate indicator solution, and titrate with 0.1 N dichromate to the first permanent purplish tinge. A blank must be run on the reagents. CERIC AMMONIUMSULFATE. Weigh 0.3 gram of cuprous chloride into a dry 500-ml. Erlenmeyer flask, add 25 ml. of ferric ammonium sulfate solution, made by dissolving 10 grams of ferric ammonium sulfate in sufficient 3 $1 sulfuric acid to make 100 ml., and swirl gently until dissolved. Add one drop of ferrousphenanthroline indicator solution and titrate with 0.1 N ceric ammonium sulfate solution (made up in 0.5 AT sulfuric acid solution). A blank must be run on the reagents.
For determination of the cuprous copper content of dilute solut ions the following procedure is recommended: Pipet 25 ml. of the cuprous copper solution into 25 ml. of ferric ammonium sulfate solution, made by dissolving 33 grams of ferric ammonium sulfate in sufficient 3 $1 sulfuric acid to make 1000 ml. Add 250 ml. of water and 1 drop of ferrousphenanthroline complex indicator solution, and titrate with 0.1 N ceric ammonium sulfate solution (made up in 0.5 AI‘ sulfuric acid). A blank must be run on the reagents. This quantity of ferric iron is sufficient for solutions Containing up to 0.6% cuprous chloride. For applications which do not require the highest accuracy, the dichromate procedure for solid cuprous chloride is suggested. (For analysis of dilute solutions, a modification similar to that given for ceric ammonium sulfate may be used.) The N hydrochloric acid solution of ferric alum has the advantage of dissolving the cuprous chloride in only a few seconds.
Table
IV. Effect of A c i d Used in Ferric Ammonium Sulfate Solution
Acid Used as Ferric Alum Solvent“
KMnOd
%
Cuprous Chloride Found KzCrzOi Ce(SO4)z 70 %
N HC1 99.4 6 ,V HCI 98.9 0.5 ”vf HzSOI 99.3 3 hf HzS04 99.i Solutions prepared in contact with air. b Oxygen-free value = 99:5. Purity by electrodeposition 99.8.
99.28 98.7 99.2 99.4
99.6 99.2 99.6 99.8c
-
The stability and transparency of its solutions, its ease of standardization, and the high precision resulting from its use with the suggested indicator recommended potassium dichromate, instead of potassium permanganate, for general use as an oxidizing agent in cuprous chloride analysis. For the highest accuracy and dependability, the procedures using ceric ammonium sulfate should be employed, with oxygen-free solutions of ferric ammonium sulfate. Whatever the procedure, the chloride ion concentration should be kept low and an excess of ferric iron must be assured. It is recommended that the amount of ferric iron used be a t least 1.5 times the theoretical. The precision then becomes that which is attained in the determination of ferrous iron using the same oxidizing agent. The accuracy to be expected of a particular procedure may be estimated from Table IV. ACKNOWLEDGMENT
The authors would like to thank Gordon Sutherland for his help in part of the experimental work. LITERATURE CITED
(1) Abx. CHEY.SOC.Committee on Analytical Reagents, IND.EXQ. CHEM.,ANAL.ED., 2,351 (1930). (2) Birnbaum and Edmonds, Ibid., 12, 155 (1940). (3) Filson and Walton, J . Phye. Chem., 36,740 (1932). (4) Glasstone, “Introduction to Electrochemistry”, pp. 278-84, New York, D. Van Nostrand Co.,1942. (5) Hatch and Estes, J . Am. Chem. Soc., 67, 1730 (1945). (6) Henderson and Fernelius, “Inorganic Preparations”, p. 24, New York, McGraw-Hill Book Co.. 1935.
