Precipitation of Cuprous Hydroxide by Ferrous Ethylenediamine Tetraacetate KUANG LU CHENG D e p a r t m e n t o f Chemistry, University o f Connecticut, Storrs, Conn.
Application of the ferrous ethylenediamine tetraacetate complex as a reducing agent has been extended to the precipitation of copper as cuprous hydroxide. The procedures for the qualitative test and for the turbidity measurement are described. Only silver, gold, iridium, and palladium interfere.
B
OTH ferric and ferrous iron form complex ions with ethylene diamine tetraacetate (EDTA), but the ferric complex is much more stable than that of ferrous. The former has a stability constant of log K 25.1 and the latter log K 14.2 I n the presence of oxidizing agents such as silver(I), copper(II), etc., the equilibrium Fey-Feye
+
~
wholly displaced in favor of the ferric complex. The reducing power of the ferrous complex is stronger than the uncomplexed ferrous ion. Pfibil and others (3)and Cheng ( 1 ) have reported that silver ion is reduced to metallic silver by ferrous ethylenediamine tetraacetate complex Ordinarily, copper(I1) is not reduced by iron( 11). However, copper(I1) was found t o be reduced rapidly by the ferrous sulfate in the presence of ethylenediamine tetraacetate, tartrate, and sodium hydroxide. Silver(I), gold( III), iridium(III), and palladium( 11) were also reduced by the ferrous compley to the metals. X o other interference was found in the reduction of copper with ferrous ethylenediamine tetraacetate. This new reaction may find application in analysis. IS
REACTION
The formal potential of the ferric-ferrous system is reported to be the order of -0.77. However, the formal potentials of the ferric-ferrous ethylenediamine tetraacetate system were found to be the order of -0.10 volt (slightly acid medium) and the order of $1.6 volts (in the presence of tartrate and sodium hydroxide). The ferrous ethylenediamine tetraacetate complex is gradually oxidized by air t o ferric ethylenediamine tetraacetate complex, but it changes to ferric complex rapidly in the presence of copper(I1)-ethylenediamine tetraacetate complex which is reduced by the ferrous complex. The copper( 1)-ethylenediamine tetraacetate complex is not stable. Therefore, copper( I ) hydroxide is precipitated in the presence of sodium hydroxide. KO copper( I ) hydroxide was formed when ammonium hydroxide was used instead of sodium hydroxide. I n the reduction of copper(I1) with ferrous ethylenediamine tetraacetate complex, the reactions may be written as follows: Cui+ Fe++ Fey-CuY---
CU+
+ H*Y-+ H*Y-+ CuY-
=
=
cu+
+OIL-
=
CuOH
CUY-FeY-= Fey-
+ 2H" + 2H+ + CuY--+y----
EXPERIMENTAL
Reagents and Instrument. The complexing mixture was prepared by dissolving 10 grams of disodium salt of ethylenediamine tetraacetic acid, 10 grams of tartaric acid, and 10 grams of sodium hydroxide in 100 ml. of water. The ferrous sulfate solution was prepared by dissolving 5 grams of ferrous sulfate
septihydrate in 100 nil. of 0 . 1 S sulfuric acid. The Fisher S e fluoro-Photometer was used for measuring the turbidity. QUALITATIVE T E S T
One or two drops of the solution t o be tested were mixed with one or two drops of the complexiiig mixture on a white porcelain dish, then one drop of the ferrous sulfate solution was added. A yellowish coloration or precipitate was formed if more than 1 y of copper were present. KOvisible precipitate was observed from 1 or 2 drops of solution which contained 1,000 p.p.m. of any of the following ions: aluminum, ammonium, antimony(III), arsenic(III), barium, beryllium, bismuth(III), calcium, cadmium, cerium( I11), cesium, chromium(III), cobalt, columbium, gadolinium, gallium, ,germanium, hafnium, indium, iron( 111), lanthanum, lead, lithium, magnesium, manganese(II), mercuryiII), neodymium, nickel, osmium( VIII), potassium, praseodymium, rhodium, rubidium, ruthenium, samarium, scandium, selenium(IV), sodium, strontium, tantalum, tellurium( IV), thallium(I), thorium, tin( 111), titanium(III), uranyl, yttrium, zinc, zirconium(III), bromide, chloride, acetate, borate, fluoride. iodide, nitrate, sulfate, molybdate, tungstate, phosphate, and vanadate. PlatinumjIV) gave a grayish coloration. Silver(I), gold(III), palladium( 11),and iridium(111) gave a dark precipitate. Gadolinium and samarium showed an intense yellowish coloration in the acid medium but not in the alkaline medium. TURBIDITY ME4SCRE\IEYT
Procedure. Exactly 0-, 1-, 2-, 3-, 4, and 5-ml. portions of 100 p.p.m. of copper solution were transferred to test tubes. The volumes were adjusted to 5 ml. by the addition of water. Then 1 ml. of the complexing mixture was added to each test tube, and the solution was thoroughly mixed. Five drops of the ferrous sulfate solution were added without mixing. After 2 minutes, the solutions were mixed. After 5 minutes, the solutions were diluted t o the 12.5-ml. mark and mixed again. The reference solution was made from 5 ml. of 0.01M copper sulfate solution by treating in the same manner. The relative turbidities were measured in the Fisher Sefluoro-Photometer. The tube a t the far right was filled with the reference solution. The 430 filters were in the center and a t the right. the blank filter a t the left. X straight line was obtained when the turbidity readings of these solutions were plotted against copper concentration present in the solution. The turbidity readings (per cent trawmittance) of 100, 84.0, 67.5, 48.5, 32.5, and 17.0 were obtained for 0.5! 0.4, 0.3, 0.2, 0.1, and 0.0 mg. of copper in 12 5 ml., respectively. A reading of 25% was obtained for 0.05 mg. of copper. The precision for the triplicate measurements was approximately 5% or better. The addition of gelatin solution qhowed an inhibiting effect on the formation of the precipitate. The copper(1) hydroxide precipitate was so fine t h a t the use of protecting rolloids was not necessary. The effect of electrolytes on the properties of the precipitates has not been studied. However, the addition of sodium chloride and of magnesium nitrate affected the size and the physical properties of precipitates. PROPERTIES OF PRECIPITATE
I n the literature ( 4 , 5 ) , the existence of cuprous hydroxide is described as questionable-and these authors prefer the name cuprous oxide (CuO zH20). The copper(1) hydroxide precipitate obtained in the above procedure was stable a t room tempernture, but turned to dark red copper oxide by heating or by adding concentrated sulfuric acid. The precipitate was soluble in mineral acids, ammonium hydroxide, cyanide, and thiosulfate. When the precipitate a-as diwolved in dilute ammonium hydroxide, a purplish color of the cuprous test was obtained h j shaking TT-ith biquinoline in isoamj 1 alcohol ( 2 ) .
1165
ANALYTICAL
1166
The pure precipitate could not be recovered quantitatively because i t tended to be peptized by washing with water or dilute sodium hydroxide. Such peptization can be prevented considerably by washing with 1%magnesium sulfate solution which adjusted to pH 10 with sodium hydroxide. ACKNOWLEDGMENT
The author thanks Philip DiMeola for his aid with the turbidity measurements.
CH‘EM~STRY
LITERATURE CITED
Cheng, K.L., ANAL.HEM., 2 6 , 1 0 3 8 - 4 0 (1954). (2) Cheng, K. L., and Bray, R. H.,Ibzd.. 2 5 , 6 5 5 - 9 (1953). (3) Piibil, R., DoleZal, J., and Sirnon, V., CoUection Czechoslov. (1)
Chem. Communs., 18,780-2 (1953). (4) Sidgwick, N. V., “Chemical Elements and Their Compounds ” Vol. I. D. 118. Oxford Universitv Press. N e w York 1950. (5) Thorne, p. C. L., and Roberts, ‘E. R., “Ephraim’s Inorganic Chemistry,” 5th ed., p. 457, Interscience, Sew York, 1949.
RECEIVED for review December 15, 19.54. Accepted February 17, 1955
Ceriometric Determination of Sugars A. A. FORIST and 1. C. SPECK, JR. Kedzie Chemical Laboratory, M i c h i g a n State College, East Lansing, M i c h .
T w o procedures have been developed for determination of small changes in sugar concentration by ceric per.chlorate oxidation. Both methods are applicable to estimation of semimicro quantities of sugars. Results obtained for several reducing sugars are given.
being the number of carbon atoms in the sugar molecule. Among the sugars tested only DL-glyceraldehyde was incompletely ovidized in 1 hour. I n Table 11, a &hour oxidation period waa required to achieve the theoretical consumption of oxidant for this substance.
T
HE oxidinietrio determination of glycerol, glucose, sucrose, and related compounds by means of the ceric perchlorate re.agent was described by Smith and Duke ( 1 , 2 ) . Two modificartions of the procedure have been useful in investigating the kinetics of certain reactions involving small changes in the con$centrations of various sugars. Results obtained M ith t n o pentoses and one triose are given, which evtend the list of tcarbohydrate substances determined by oxidation n ith this reagent.
Table I.
Ceriometric Determination of Sugars
Sugar
Added, RIg.
D-Glucose
30.03
D-Xylose
30.03
D-Ribose
36.03
~~-Giyceraldehyde
36.03
REAGETVTS
Ceric perchlorate, approximately 0.28.V in 4 M perchloric acid. One liter of G. F. Smith Chemieal Co. reagent-grade ceric perEhlorate acid (in 6 M perchloric acid) is mixed with 172 ml. of 12% perchloric acid. The resuiting mixture is diluted to 2 liters with distilled water. This reagent is standardized against sodium oxalate or sodium arsenite and is stored in the absence of ‘light. Ceric perchlorate, 0.01 t o 0.03~V,in 25f perchloric acid. This solution is prepared by appropriate dilution of the above reagent. It is standardized daily against sodium oxalate or sodium arsenite and is also stored in the absence of light. Sodium o d a t e , 0.1800Ar, in 0.1M perchloric acid. Sodium arsenite, 0.1300N. Aecurately weighed arsenious oxide (approximately 13 0 grams) is dissolved in a mixture of 10 grams of anhydrous sodium carbonate and 1 liter of u-atci. T h i s solution is then diluted to 2 liters with water. Osmic acid, 0.01M, in 0.1M sulfuric acid. Yitro-ferroin indicator, 0.02511.
Found, RZg.
~ I E T H OID 36.08 36.21 36.94 36.13 36.16 35,85 35.91 36.02 35.82 36.13 36.10 35.97 36.06 35.91a 35.85=
METHODI1 18.02
D-Glucose a
18.09 18.12
1s
Results for 4-hour oxidation.
06
The present procedures offer the advantages of sensitivity to small changes in sugar Concentrations and titration to the disappearance of the indicator color rather than through a serim of color changes as occurs in the reverse titration. These methods may be readilv altered to accommodate different ranges of sugar concentration by appropriate changes in reagent concentrations.
PROCEDURES
Method I. T o 18 to 36 mg. of the sugar, in aqueous solution ,not esceeding5ml:in volume, add 20 nil. of the 0.28:\- ceric perchlorate reagent. A4110wthe oxidation to proceed a t 26” C. for 1 ‘hour,then add 2 5 ml. of the sodium oxalate solution to the mixture. ‘Titrate the excess oxalate ion with the 0 . 0 3 5 ceric perchlorate reagent to a nitro-ferroin end point. Method 11. To 15 to 21 mg. of the sugar, in aqueous solution not exceeding 5 ml. in volume, add 10 ml. of the 0.28N ceric perchlorate reagent. After allowing the oxidation to proceed a t , 2 j 0 C. for 1 hour, add 2 drops of the osmic acid solution followed by 15.00 nil. of the arsenite solution to the oxidation mixture. Then titrat,e the excess arsenite u-ith the 0.01S ceric perchlorate reagent to a nitro-ferroin end point.
Table 11. Effect of Time on Ceric Perchlorate Oxidation of DL-Glyceraldehyde Time,
Hr.
1 2
DISCUSSIOli
Theory 6.0
3.75
LITERATURE CITED
(1)
Typical results are given in Table I. All calculations are based #onconsumption of 2n equivalents of cerate per mole of aldose, n
Equivalents of Cerate Consumed per Mole of Sugar
Smith, G. F., and Duke, F. R.. IND. ENG.CHEM.,;IK.LL. ED., 13, 558 (1941).
(2) Ibid.. 15, 120 (1943). RECEIVED for review October Z:, 1954.
Accepted .January 7, 1935.
