Calcium Acid Malate Hexahydrate - Analytical Chemistry (ACS

1451

V O L U M E 2 4 , NO. 9, S E P T E M B E R 1 9 5 2

comtituents with several other elements as minor constituents. % ’ Total Zirconium Aluminum, iron, hydrogen, Gravi- ColoriVariamanganese, nickel, and silicon tion metric metric decrease the proportion of acid0.62 -0.02 0.64 0.63 0.64 -0.01 soluble zirconium present in 0.63 0.65 +0.02 the magnesium (6). An investi0 . 6 4 0 . 6 3 -0.01 gation of the effect of various 0.64 0.64 0.00 0.64 0.63 -0.01 acids upon the separation of 0.39 0.39 0.00 the soluble from the insoluble 0.41 0.38 -0.03 0.41 0.39 -0.02 zirconium waa necessary. In 0.41 0.41 0.00 Table 11, dilute hydrochloric 0.36 0.39 -0.03 acid was used in the photo0.37 0.36 +0.01 0.84 0.86 -0.02 metric determinations and 0.84 0.86 t O 02 dilute sulfuric acid in the gravi0.85 0.8.5 0.00 metric tests. 0.84 0.8i t0.03 In another ssries of esperi-.. ments, dilute nitric wyas compared to dilute sulfuric acid (9). The conclusion was reached that dilute nitric, hydrochloric, and sulfuric acids are equally effective in separating soluble from insoluble zirconium. Data of Taylor (8) on the corrosion of zirconium by these dilute acids confirm that none of them attacks the unalloyed metal appreciably.

Table 11. Comparison of Colorimetric with Gravimetric Results % Insoluble Zirconium Gravi- ColoriVariametric metric tion

Sample 67333

Rar;

-3

0.04 0.03 0.03

0.05 0.05 0.05

67333

Rod1

0.04 0.04 0.04 0.06 0.07 0.06 0.07 0.03 0.04 0.06 0 04 0 04 0 03

67365

2 3

Bar 1 2 3

67365

Rod1 2 3

Bar 67366 Rod 1 2 67366

3

% Soluble Zirconium Gravi- ColoriVariametric metric tion

iO.02 f0.02

‘0.01

0.60 0.60 0.60

0.57 0.59 0.60

-0.03 -0.01 0.00

0.04 0.04 0.05 0.06 0.07 0.06

0.00 0.00 +0.01

0.60 0.60

0.00 0.00 0.00

0.33 0.34 0.35

0.59 0.60 0 58 0.33 0.31 0.33

0.00 -0.02 0.00 -0.03 -0.02

0.06 0.06 0.06

-0.01 t0.03 +0.02

0.07 0 05

iO.01 +O 01 TO 02 -0 02

0.34 0.33 0.33 0.78 0 80 0 81 0 81

0.33 0.33 0.32 0.79 0 81 0 79 0 81

0 06 0 05

0.60

-0.01

+0.01 0.00

-0.01 f O 01 -0 01 -0 02 LO 01

~

paper into a 500-ml. volumetric flask and add 10 ml. of concentrated hydrochloric acid. Make to volume and save. Place the paper containing the insoluble zirconium in a porcelain crucible and char slowly. Heat at 950’ C. for 30 minutes. .4dd about a gram of potassium bisulfate and fuse. Cool and dissolve the melt in 100 ml. of water containing 1 ml. of concentrated hydrochloric acid and 1 ml. of ferric chloride solution. Add ammonium hydroxide until all of the iron and zirconium are precipitated. Filter through No. 40 Whatman paper and wash with warm water. Dissolve the hydroxides from the filter paper with 10 ml. of hot 1 to 1 hydrochloric acid. Transfer to a 250ml. volumetric flask and make to volume. Procedure. Pipet an aliquot from each flask to contain from 0.1 to 0.3 mg. of zirconium and place in 100-mI. volumetric flasks. Add 5 ml. of 0.05y0 alizarin red S solution; measure in enough hydrochloric acid t o give approximately an 0.1 A‘ solution and make t o volume. Prepare a blank containing all of the reagents used. Shake and dlow t o stand for 15 minutes. Determine the optical density at a wave length of 510 mp, using a 40-mm. cell. From the standard curve determine the amount of zirconium present. Results. Table I1 shows a comparison of results obtained by the gravimetric phosphate method and the photometric alizarin red S method. The samples used are magnesium alloy standards which contain varying amounts of zinc and rare earths as major

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LITERATURE CITED

( 1 ) Boer, J . H. de, Chem. Weekblad, 21,404 (1924,. (2) Feigl, F., ”Qualitative Analysis by Spot Test,” pp. 124-9, Xew

York, Nordemann Publishing Co., 1939. (3) Hillebrand, W. F., and Lundell, G. E. F., ”hpplied Inorganic Analysis,” pp. 442-61, New York, John Wiley & Sons, 1929. (4) Hopkins, B. S., ”Chapters in the Chemistry of Less Familiar Elements,” Vol. 11, Chap. 12. p. 16. Champaign. Ill., Stipes

Publishing Co., 1939. ( 5 ) Selson. X. E., and Strieter, F. P., Trrrna. .4174. Foiclulrynnan’s SOC.,58, 400 (1950). (6) Pavelka. F., Mikrochemie, 8, 345 (1930). (7) Smith, L., and West, P. W., IND.ENG.(:HEX.. A s a ~ .ED,, . 13. 271 11941).

(8) Taylor. D. F., Iizd. Eng. Chern., 42, 639 (1950). (9) TVinn. D. M.,Dow Chemical (“o,, unpublished experiments, April 15, 1949. R E C E I ~ Efor D rei4erv .Januarx 17, 1952.

lccepted July 9, 1952.

Calcium Acid Malate Hexahydrate A Suggested Versatile Primary Standard A . C . SHEAD, D e p a r t m e n t of C h e m i s t r y , Ziniiqersity of Okluhomtr. V o r m a n . Okla.

C

ALCIUM acid malate hexahydrate, CaH2CsHsO1&H20, with a molecular weight of 414.286 and a remarkably high equivalent weight of 207.143, offers exceptional advantages as a versatile primary standard of multiple applications. It can be directly applied in alkalimetry, calcium chelatometry, and the calibration of pH meters. Indirectly, by calcining in platinum to calcium oxide with subsequent solution in excess acid and residual titration with base having a k n o m ratio to the acid, it can be employed to standardize both solutions.

1x1 dried at 100” C’.> and this is its only drawback from the standpoint of conventional procedure. However, the accompanying analyses show that when i t is properly prepared and stored, the adsorbed moisture content is almost undetectable. Aspiration of dry air over the crystals for a brief period will remove evcn this trace of moisture. Chalking would immediately reveal any decomposition. This phenomenon has never heen detected in these laboratories. PREPARATION OF MATERIALS

PROPERTIES

Calcium acid malate hexahydrate is readily prepared chemically pure from abundant “sugar sand,” a by-product from the sap skimmings of the maple sugar industry. It is pure white, free flowing with no tendency to cake on storage, and, properly bottled, has proved stable to high atmospheric temperatures and low humidities for the 5-year period over which i t has been observed in these laboratories. At no time has any change been observed during weighing directly on a watch glass. I t cannot

Calcium acid malate hexahydrate ili not regularly on thr market. Crude sugar sand, calcium malate, is sieved to remove leaves, twigs, and other gross trash. The calcium content is determined. The amount of sulfuric acid to react with this is calculated for a given desired charge and the acid diluted two or three times with water to prevent charring of the charge. After the acid and charge sufficient to form malic acid and calcium sulfate have been mixed, an equal portion of the crude sugar sand is addpd to form acid calcium malate from the malic acid formed in the first reaction. After thorough mixing, enough

ANALYTICAL CHEMISTRY

1452 ~

Analyses of calcium acid malate hexahydrate prepared from "sugar sand," a crude calcium malate waste from the maple sugar industry, made in connection with a study on the utilization of this by-product, suggested its wide applicability as a versatile primary standard. The substance is easily prepared in a high degree of purity from abundant raw materials and is stable over long periods of time. It is a white crystalline, free flowing, nonhygroscopic, nonefflorescent solid, readily weighed out in an open container without appreciable gain or loss during

water is added to form a thick paste and the whole is gently heated for about a half hour with intermittent stirring t o mix thoroughly. The mixture is t.hen left overnight, preferably a t a temperature near 0" C. Especially if seeded with a little of the product, the mass should crystallize overnight. It may require vigorous stirring to start crystallization, as the product has some tendency to form supersaturated solutions. After standing overnight a t freezing temperature the crystal masses are washed with a little ice water to flush off the calcium sulfate dihydrate, which is often hard to filter. The wash water may be allowed to settle and the clear supernatant liquid decanted off t o dissolve the previously rinsed product. The crude crystalline product, is dissolved in sufficient distilled water to put i t into solution a t the boiling point, avoiding an excess. The solution is treated with char to decolorize if necessary. The clarified solution is filtered hot, first through paper and then through fritt)ed glass to remove paper fibers. The filtrate is then evaporated until it starts to bump or until crystals begin t o appear in the hot solution. The solution is then allowed t o cool and stirred intermittently or continuously t o granulate the separating crystals. During evaporation and crystallization, the product is carefully covered to protect against atmospheric dust. The separated crystals are then brought on a fritted-glass filter and sucked dry by filter pump. The crystals, covered against dust, are exposed to air of low humidity on porous biscuitware clay plates. If the air is reasonably dry, the crystals will contain no appreciable amount of adsorbed moisture. If the air is humid, artificially dried air should be cautiously drawn over the crystals. The finished crystals should be carefully inspected before packaging. Decomposition would readily be revealed by chalking of the crystals. Neither efflorescence nor hygroscopicity has been detected in t'hese laboratories. The yield is from 50.0 to 70.0y0 of the crude sugar sand of indefinite composition. .Inalysis of six samples of the calcium acid malate hexahydrate by ignition to calcium oxide yielded an average purity factor of 100.10%. Based on loss of ignition the purity factor is 99.98% Gravimetric conversion factors employed were: CaO to C ~ H $ ~ H S O , ~ . ~=H7.38873 ~O Loss on ignition to CaHzCsHs010.6H20 = 1.15662 1,oss on ignition = ((=aHzCRHsOla.fiHzO-CaO)= (414.286 56.07) = 358.216

-\I1 weighings connected with the calcium oxide determinations were made in counterpoised glass-stoppered weighing bottles to avoid contact with air during the weighing of the system. ;\nalysis of six samples of the calcium acid malate hexahydrate by neutralization methods using a 0.1210 .V base standardized against potassium acid phthalate yielded a purity factor of 99.75%. The grand average by all methods yielded a purity factor of 99.94%. The average deviation is 3~0.13%. The pH of five different saturated solutions of calcium acid malate hexahydrate was determined at. the specified temperatures. Slight impurities of the salt, moisture, insoluble siliceous residue, or calcium sulfate will not vitiate results. The instrument used was a Beckman portable pH meter Model M, which was checked with a saturated solution of acid potassium tartrate (pH 3.57 a t 25" C.) ( 2 ) and the standard buffer furnished with the instrument. In addition, t,he p H meter had been used t o check values obtained on a Hellige ..iqua Tester bI 611 and the

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the operation, and it has an unusually high equivalent weight for most applications. It can readily be employed as a primary standard in alkalimetry; in acidimetry after ignition to calcium oxide; in Versenate chelatometry by virtue of its calcium content; and in calibration of pH meters as a saturated solution, owing to its ready but limited solubility in water. It has possibilities in the standardization of the Karl Fischer reagent by reason of its constant content of water of crystallization, pending discovery of a suitable anhydrous solvent.

readings found to be concordant. A thermometer checked for concordance from a large lot was used for all temperature readings. bverage pH of five saturated solutions was a t 15" C., 3 . i 5 i 0.05: a t 20" C., 3.72 f 0.02; at 25" C., 3.66 f. 0.02; at 30" C., 3.53 i 0.02; at 35" C., 3.46 j~0.04; a t 37.5" C., 3.43 f 0.06. The saturated solutions were stahle for a t least 2 or 3 weeks. Mold was noticed in only one instance, and then only in very minor amounts. Vigorous stirring and large excess of solute are necessarJ- to break up any supersaturation in the solutions. From 5 to 10 minutes were required to produce a saturated solution of constant reading. Boiled doubledistilled water was used in making up all solutions used in this study. KO differcmw was noticed between inimrcli:ite and later readings of pH. PRIMARY STANDAHD FOR ACIDS

Good primary standards for acids are scarce. By igniting calciuni acid malate hexahydrate t o calcium oxide, in a plxtinum crucible or in a porcelain crucible lined R-cinployerl.

1453

V O L U M E 2 4 , N O . 9, S E P T E M B E R 1 9 5 2 The sample should not be ignited directly in contact with porcelain, owing to the danger of action of calcium oxide on the material of the crucible to form silicates insoluble in acid, It is unnecessary to hydrolyze the calcium oxide to calcium hydroxide before the titration, as the water present in the acid being standardized will effect this transformation. PRIMARY STANDARD FOR VERSENATE CHELATOMETRY

Calcium acid malate hexahydrate is also suggested as a primary standard for chelatometry, involving calcium disodium dihydrogen ethylenediamine tetraacetate (Versenate) solutions (1).

As in other instances cited, the acid malate is a superior primary standard for chelatometry because of its unusually high equivalent weight of 207.143. The method used followed closely those standardizing with calcium chloride derived from calcium carbonate as a primary standard. One modification consisted in including the eriochrome black T, the magnesium ion required, and buffer, ammonium hydroxide-ammonium chloride, pH 10, in a single solution, 10 nil. of which was always added to the calcium solution being titrated. This constituted a time saver and afforded a constant amount of magnesium ion for all titrations in place of the variable amount introduced if the essential magnesium ion is included Rith the versenate titrant. The blank deducted from all volumes of reagent required amounted to 0.65 ml. of titrant. The normality of the Versenate solution established by calcium carbonate standard was 0.22 A' but

owing to the small equivalent weight of the calcium carbonate, 50.037, ana the dilutions required, is believed less accurate than that established by direct weighing of calcium acid malate hexahydrate crystals. Six different samples of calcium acid malate hexahydrate were used in determining the normality of a solution of Versenate found to be 0.022 N by calcium carbonak. The normality established by the acid calcium malate hexahydrate was 0.0211 f 0.0002. CONCLCJSIOH

A method has been developed for preparing pure calcium acid malate hexahydrate from crude sugar sand, an impure calcium malate by-product of the maple sugar industry. Three different methods for establishing its purity are given. Data are offered to prove the value of the calcium acid malate hexahydrate as a primary standard in sat,urated solution for calibrating pH meters, in alkalimet,ry, in acidimetry, in calcium c helatometry with disodium dihydrogen ethylenediamine tetracet'ate dihydrate (Versenate) solutions, and its use is suggested for standardizing the Karl Fisnher rea.gent,(3). LITERATURE CITED

(1) Biedermann, W., and Sohwartzenhach, G., Ch,imiu, 2, 56 (1948). (2) Lingane, ,J. J., ANAL.CHEM.,19,810 (1947). (3) Neuss, J. D.. O'Rrien, M. G.. m r l FrPrIiani, H. A , , Ibid., 23, 1332

(1951). RECEIVED for review Dpremhor 8 , 19.51.

.\rrf,r,t,rd .Jiine 23, 19.52.

Separation of Praseodymium from Lanthanum By Fractional Carbonate Precipitation in Trichloroacetate Solution LAURENCE L. QUILL

AND

MUHRELL L. SALUTSKY

Kedaie Chemical Laboratory, Michigan State College, East Lansing, Mirh. Precipitation from homogeneous solution appeared to be a potentially rapid means of separating mixtures of the rare earth elements. The separation and purification of priseodyniium from lanthanum-praseodymium mixtures were effected by the homogeneous precipitation of rare earth carbonates in trichloroacetate solution. Praseodymiuni concentrated in the carbonate precipitates, which upon repeated fractionation yielded a final product of spectroscopic purity. The praseodymium enrichment was independent of the temperature at which the precipitation was made, but seemed to be somewhat greater in dilute solutions. The procedure was applied to the fractionation of a crude yttrium group concentrate with good results. The trichloroacetate method is simpler and more rapid than most fractional methods for separating rare earths.

P

RASEODYMIUM and lanthanum salts are difficult to separate because of their similar chemical and physical properties. Slight differences in solubilities and basicities are important criteria in such separations. Full advantage of these slight differences is not realized by ordinary fractional precipitation methods, which depend upon the immediate formation of a precipitate after addition of a reagent. Interferences caused by local action are minimized if the precipitating rcagent is formed within the solution. Precipitations of this type which have been used for the fractional separation of the rare earthe art: summarized b y Moeller and Kremers ( 5 ) in a review article on the basicity characteristics of the rare earths. Sonic of the more common ones involve the separation of cerium by oxidation to the ceric form followed by hydrolysis, and the use of rare earth nitrites phthalates, lactates, sulfites, citrates, tartrates, m-nitrobenzoates, phenoxyacetates, etc., to form basic salts. In most of these methods the desired anion Present address, Mound Laboratory. hlonssnto Chemical Co.. Miramisburg, Ohio.

is added in the form of an alkali salt,. The resulting high concentration of alkali ions in the reaction mixtures is disadvantageous because of double salt formation. Willard and Gordon (9) separated thorium and the rare eart,hs from monazite by a homogeneous precipitation procedure involving the hydrolysis of dimethyloxalate to precipitate insoluble thorium and rare earth oxalates. Recently, dimethyloxalate has also been employed for the fractional separation of 1ant.hanum and cerium(II1) and of lanthanum and praseodymium ( 2 ) . In this investigation the separation of praseodymium from lanthanum was affected kip fractional precipitation as the carbonate in trichloroacet,at,e solution, The trichloroacetate ion under the influence of heat yields, according to Verhoek (7, 8) and Hall and Verhoek (3), carbon dioxide and the strongly basic trichloromethyl ion, whirh in tnrn reacts with water to form chloroform.

c(:13c:oo-

1

CXIq-

+ HyO

-~

4

C C k -t c : o 1 CHClr

-~-+

+ OH-