1809
V O L U M E 2 6 , NO. 1 1 , N O V E M B E R 1 9 5 4 Table IV.
Belknap, E. L., I d . M c d . a d Sicig., 21, 305 (1952). Bersin, Th., and Schwars, H., S c h w i z . M e d . Wochsciii.., 33, 765
Effect of Different Acids on Absorbance
(1953).
Deviation Absorbance, .4cid UsedQ .4bsorbance (Absorbance) % Acetic, (407,) 0 60 . .. 100 Sulfuric 0 28 -0 32 46 7 Sitric 0 20 - 0 40 33 3 Hvdrochloric 0 24 - 0 36 40 0 Pdrchloric 0 31 -0.29 31 7 Phosphoric 0.44 -0.16 73 4 Acetic-HaPOa (1 : 1) 0 59 -0.01 98.4 Acetic-Hap04 (3: 1 ) 0 61 +o. 01 101.6 f0.02 103.2 .kcetic-HzSO4 ( 3 : 1) 0 62 Acetic-HC1 ( 3 : 1) 0 62 +0.02 103 2 12 Acidity of all solutions u-as 1.0.V and arsenious acid concentration \\*as
Bessman, S. P., Reid, H., and Itubii:. 11.. M e d , A W L . Dipf, Columbia. 21, 312 (1952). Darhey, h.,A N ~ LCHEM., . 24, 3 7 3 ( 1 9 5 2 ~ . Foreman, H., Vier. AI., and Magee, .\I.. J . H i d . C'ltem., 203, 1 0 G (1953).
Plumb, 11. C., Martell, -4.E., arid Reriworth, F. C . , J . P / i / s . "2 Colloid Chern., 54, 1208 (1950).
Popovici, .4.,Geschichter, C . I:., and Rutin. 11..Bull. Grorgc~ O / C / LL7nia. M e d . C'ejder. 5, 108 (1951). I'fibil, I{., and Kluhaloi-a, ,J., Collection C'zcchosZor. C ' h e m . C'om/ ~ C ( I ? L . T . . 15, 42 (1950). Suby, FI. I...J, CroZ., 6 8 , 9 0 (1952). Suhy. H I.. Alhright, F., Wayne. J.. and Denipsey, E.. l t j j d , ,
0.7.v. b
Based on acetic acid solution absorbance as 1007c.
prmence of mixed and variable amounts of several of the anions makes acetic acid appe:tr t o be the best choice.
6 6 , 527 (195%). Till, H. S.. B r o w n , 13. H., Zlntki*, .X.. Zak, B., 11yer3, ( + , 13.. and Bol-le. 1.*I.. A ? r a . J . C'Zirb. Path.. 23. 1226 119531. (13) Kishinsky, H., IVeiiihcrg, T., Prevoqt, E. AI.. Buagiii, H.. and AIiller, 31. J.. J . La/,, C l i r ~ .M e d . , 42, 530 (1953). ~I
ACKNOWLEDG31 ENT
The ethylenediaminetetraacetic acid used in this esperimcntation was 1-ersene, supplied by the BersTvorth Co., Framinpham, Mass. LITERATC-RE CITED (1)
Bauer, R . O., Iiollo. E'. lt., Spooner, C., and Woodman, E., Federation Proc., 1 1 , 3 2 1 (1952).
R E C E I V E for D review April 2 2 , 1854. Accepted d l i g r i e t 6. 1954. Presented before the Division of Biological Chemistry a t the 124th AIeeting of the AMERICANC H E M I C ASOCIETY, L Chicago, Ill. Work slipported in part by the Receiving Hospital Research Corp., t h e Detroit Cancer Institute, a n d in part by institutional grants t o tlie Detroit Institute of Cancer Research and Wayne University College of Medicine from t h e .kmrrican Cancer Society, Southeastern Michigan Dirision.
Standardization of Titanous Solutions against Potassium Dichromate RAYMOND H. PIERSON and E. ST. CLAIR GANTZ A n a l y t i c a l Chemistry Branch,
U.S. N a v a l O r d n a n c e
Test Station, Inyokern, China Lake, Calif.
Coniniercial supplies of titanous solutions usually conConsequently, if such solutain iron as an inipurit? tions are standardized against strong oxidants, the , d u e for titanous content will be in error. -4 con\enient method f o r determining the iron content and making the necessar? corrections has been de?eloped. The use of titanium h>dride, which has a negligible iron content, is ad\ocated for preparing titanous solutions. On the basis of the present findings, potassium dichromate is re-established as a convenient and valid reagent for standardization of titanous solutions.
.
T
I T B S O C S solutions are po~vcrfulreducing agents widely used in titrimetric analysis (1-10). They have been preparcd and standardized in numcrous ways. The purposes of this paper are: to advocate the use of titanium hj,clride, TiH, (obtairi:i~blefrom 31etal IIydrides, Inc., Beverly, Mass.), for preparation of t,itanous solutions; to describe a convenient and accurate method for determining the iron content of titanous solutions; t o furnish a correction procedure based 011 tlie determination, t l i c x h y nxiking tlie direct standardization against dirhrom:ite valid; arid to readvocate the use of pot,assium dichromatc in st:tndardizing titanous solutions. Preparation of titatiou? solutions from titanium hydride [as previously recomnicndcd ( 6 , I O ) ] offers two advantages over the use of commcrcially available solutions-much lower cost and frrrdoiii from iron contc'n-which greatly outweigh the slightly greatcr time rcquired in ni:tkiiig the standard titanous solutions from the hydride. ond atlvant~ngc~ has probably not been as widely rrcogiiized a s the first. For example, Lamond recent1)- reported ( 4 ) t h a t d l *upplic,.s of titmious chloride or sulfate tested i n his laboratories c.ontainrii significaut amounts of iron. However, in the 1almrator:- in which the a,uthorsare eniploved, so hit ion^ prepared
from the hydride have cont:iiiied extremely small, actual1)- insignificant amounts of iron. For some kiiida of work the presence of a moderate amount of iron in the titanous solution would not be objectionable; in othcr caws it would be. If a titanous solution t h a t contains a siyiiificaiit amount of iron must be used the role played by tht: ferrous ions determines the method chosen for standardization. Depending on the I I I R I ~ I I C I ' i j i which the titanous solution is to be used, these ferrous ions ma!- be eit,her active or inactive. The determiriation of nitroglycerin in propellants ( 1 1 furnishes x gaod csample of the latter case which is the onc usually encountered. Sitivglycerin is reduce:l by an excess of ferrous solutidn to j.ield ferric ions, which arc then tit,ratetl by the standard titanous solution. The ferrous content of the titanous solution is inactive, so that a standardization i? required which yields a value of the titsnous solution excluding its ferrous content. I t is on the basis of the above situation t h a t Lamond has niised olljections to the usc of potaisium dicliromate in the (direct) standardization of t:tanous solutions. He gives three altcrnativei for avoiding the error due t o iron: ( l i preparation of ironfree titanous solution; ( 2 ) standartlizing "against potsssium dichromate through ferrous ammonium sulfate" using ammonium thiocyanate as indicator; and ( 3 ) standardization against some standard other than dichromxtP. Purifications of titanous solutions (made from impure rengeriti) as described by Lamond are time-consuming arid are believed l)y the authors of this paper t o be unwarrant,ed as long as titanium hydride of high quality is available. Corrections for iron content are either negligihle or very small when thc hydride is used. ADVANTAGES O F POTASSIU3I DICHRO3IATE IN STAVD.ARDIZISC. TITANOUS SOLUTIONS
Daily, rapid, and accurate :tandardization is essential for many itpplirntions of titanous roliition, I)crauie its strength gradually
1810
decreases even though i t be stored under a protective inert gas. (Carbon dioxide is commonly used because of its low cost, availability, and freedom from toxic or explosive hazards.) If the analyst uses a time-consuming standardization each day, his useful output will be reduced drastically as compared with that achieved when the titanous solution is rapidly evaluated. Titanous solutions have been standardized against iron wire, iron ore, ferrous ammonium sulfate, p-nitroaniline, ferric solutions, and potassium dichromate. The latter has been recommended ( 2 , 3,5 , 8) and in the authors’ opinion is to be preferred. Iron, iron ore, and ferrous ammonium sulfate must be oxidized, and succeeding steps may lead either to retention of some of the oxidant-e.g., hydrogen peroxide-or t o loss of some iron (by volatilization) when the solutions are boiled to remove the last traces of the oxidant. Furthermore, these procedures are unnecessarily time-consuming. Ferrous ammonium sulfate is not a sufficiently reliable primary standard because of its uncertain water content. Pure p-nitroaniline may be satisfactory, but is not so widely used as the Bureau of Standards potassium dichromate, nor so generally available. The ferric solution requires standardization by means of other secondary and primary standards. Some laboratories standardize the titanous solution daily against a standard ferric solution which was previously standardized against a freshly standardized titanous solution. This system is rapid, but requires maintenance of the secondary standard. Other laboratories dispense with the secondary standard altogether and use only the primary standard, potassium dichromate, with a suitable indicator such as sodium diphenyl benzidine sulfonat,e. Standardization against potassium dichromate is accurate and very rapid. It can be done directly if due consideration is given t o iron content of the titanous solution, or it can be done “against dichromate through ferrous ammonium sulfate” (Laniond’s second suggestion). This latter procedure consists simply of adding the standard potassium dichromate in accurately known amount t o a slight excess of acidified ferrous ammonium sulfate solution (free from ferric iron or correct,ed for ferric iron content by a blank determination) and titrating the resultant ferric solution with the t,itanous solution, using ammonium thiocyanate as indicator. T h a t there is no significant difference in normalities of titanous solutions determined directly ( n i t h due allowance for iron impurities) and those “against dichromate through ferrous ammonium sulfate” has been repeatedly demonstrated in t,he author’s laboratory and confirmed by members of the Joint Army Navy Air Force Analytical Chemistry Pane! in conjunction with round robin determinations of nitroglycerin. This is evidence that for the use cited no discrepancy is found in using sodium diphenyl benzidine sulfonate as indicator in one case and ammonium thiocyanate in the other. Lamond (4) gives data which show t h a t for iron-free titanous chloride the o-phenanthroline end point of a direct standardization also checks with the ammonium thiocyanate end point of the indirect procedure. STANDARDIZATION OF 0.2N TITANOUS SOLUTION AGAIXS? POTASSIUM DICHROMATE
Prepare exactly 0.2000N potassium dichromate solution by weighing out 9.8080 grams of Bureau of Standards dichromate KO.136 (which has been dried for 2 hours at 100” C. and st’ored in a desiccator), dissolving the crystals in distilled wat’er, and making the final volume exactly 1000 ml. This solution is stable, b u t some laborat,ories assign 2 weeks as a maximum time limit for remaking this primary standard. Pass a current of carbon dioxide into a 300-ml. titration flask (equipped with a small side-arm inlet for the gas) for 5 minutks. Add from a buret 40.00 ml. of the 0.2000-N potassium dichromate and then 80 ,ml. of 10% sulfuric acid solution. Tit,rate with tit’anous solution, adding 4 drops of 0.5% aqueous solution of sodium diphenylbenzidine sulfonate (indicator obtainable from G. Frederick Smith Chemical Co., Columbus, Ohio) near the end point’. The color change sequence should be dark brownish purple to lighter purple or bluish purple to green. The end point is exceedingly sharp. A reversal to light purple or bluish purple \Till t.ake place
ANALYTICAL CHEMISTRY when the end point has not quite been reached. Then with the addition of very small droplets the reversal speed decreases until finally (and very sharply) the green is permanent as judged after a 30-second waiting period. Once this point is reached, reversal does not occur even when the waiting period is extended to several minutes. The final green color is due to the reduced chromium salt, and has sometimes been inaccurately described as blue or blue-green. Other indicators have been useddiphenylamine, barium diphenylamine sulfonate, diphenylaminesulfonic acid, o-phenanthroline ferrous sulfate, phenylanthranilic acid, etc.-but do not appear to offer advantages over the indicat’or discussed. Comparisons made in the authors’ laboratory show that diphenylaminesulfonic acid and phenylanthranilic acid (G. F. Smith reagent 168) give color sequences similar to those of the sodium diphenylbenzidine sulfonate and in the application cited yield end points agreeing precisely with t h a t obtained wit’h sodium diphenylbenzidine sulfonate. ?r’ormalit,y, N , of the titanous solution is calculated as follows:
N
0.2
x
T’d
= ___
v
f
where Vd equals volume in milliliters of the dichromate solution and Vi equals volume in milliliters of the titanous solution, or for 40.00 ml. of the dichromat,e solut,ion, *V = 8 / V t . DETERMINATION OF IRON CONTENT OF TITANOUS SOLUTION
Replace the air in a 300-ml. titration flask provided with a small side arm by passing a st,ream of inert gas-e.g., carbon dioxide-through t.he side arm for 5 minutes and continue passing t,he gas into the flask during all subsequent steps. Add to t,his flask 40.00 ml. of the t,it,anoussolut.ion and 80 ml. of 10% sulfuric acid. Then add a moderate excess of potassium permanganate solut’ion (approximately 0.1N) and let the reagents stand for a few seconds. Next’ add 20% ammonium thiocyanate solution until the excess of permanganate is destroyed (usually only a feT7 drops are required) and then add 3 ml. more of the ammonium t>hiocyanate. Titrate the ferric iron produced in the above s t e p with the tit,anous chloride solution being standardized, the thiocyanate serving as indicator. The color changes are easily followed: The pink or purple titanous solut’ion becomes colorless upon gradual addition of the potassium permanganate and then an excess of permanganate yields the characteristic purple color of the added reagent; a feiv drops of thiocyanate dispel the purple color of the permanganate and then produce the charact’eristic blood red color due to reaction of additional thiocyanate with ferric iron, provided t,hat iron in significant amount was prrsrnt originally in the titanous solution. Also t,it,ratea 40.00-ml. portion of standard dichromate solution dirrctly with the titanous solution, using sodium diphenyl benzidine sulfonate as indicat,or. The ferrous content of the impure solution may be calculated as follows (no ferric iron will be present in the titanous reagent): 1,et
normality of titanous portion of the impure tit’anous solution .V, = normality of ferrous portion of the impure tit’anous solution .Vd = normality of standard K2Cr20?solution Trri = nil. of standard KzCr20,solution ITl = nil. of impure t,itanous solution used in the direct tit.rat,ion against standard &Cr?Oi, using sodium diphenyl benzidine sulfonate indicator IT2 = ml. of sample of impure titanous solution taken for oxidation with K M n 0 4 = ml. of impure titanous solution required to t,itrate the ferric iron from 1‘2 .\-(
=
From the titration against dichromate using sulfonate indicat,or
Vd
x
X d =
Vl(.Yt
+Si)
This equation rearranges to (vd
x
Ivd)
-
(VI
x
-I-/) = T1’ xN
t
From the titration of ferric iron with impure titanous solution using ammonium thiocyanate indicator Tz’
x
N, =
T72
x
LVt
By solving the simultaneous equations
1811
V O L U M E 2 6 , NO. 1 1 , N O V E M B E R 1 9 5 4 S , provides the desired measure of the ferrous iron content of the impure titanous solution, each miiiiliter cont,aining S J X 55.8 mg. of ferrous iron. CORRECTION FOR IRON CONTENT AZiD CALCULATION OF EFFECTIVE KORMALITY O F TITANOUS SOLUTION
.Ytns defined above is the effective normality of the impure titanous solution Lvhen employed in a ferrous-titanous procedure such as the nitroglycerin determination ( 1 ) . It is readily calculated by subtracting N , from the uncorrected normality of the impure titanous solution found bj- the direct titration :igainPt potassium dichromate with sodium diphenyl 1)riizidinc. sulfon:tte as indicator.
.\-b
=
;Vu - S J = 0.2222 - 0.0033
=
0.2189
This example is illustrative of a solution t h a t contains an appreciable amount of iron. Generally the corrections for solutions prepared from titanium hydride are negligible. ACKNOWLEDGMENT
This paper is published v i t h the permission of FY. B. AIc1,ean. technical director, U. P.S a v a l Ordnance Test Station. LITERATURE CITED
Becker, W ,'A7,,IKD.EKG.CHEM.,ANAL.ED.,5, 1.52 (1933). Rreit, J . E., J . Assoc. Ofic. A g i . Chemists, 31, 573 (1948); 32, 589 (1949). Butts, P. G., Rleikle, W. J., Shovers, J., Kouba, D. L., and ASAL. C"af., 20, 947 (1948). Becker, W.W., Laniond, J. J., Anal. Chiin. Acta, 8, 217 (1953). Rodden, C. J., and Goldbeck. C . G . , AZTAL.CHEM., 24, 102 (1952). Shacfer, W.E., and Becker, W.K , Ibid., 2 5 , 1226 (1953). Siggia, Sidney, "Quantitative Organic ..inalysis via Functional Groups,'' p. 82, Xew York, John Wiley B. Sons, 1949. Stenger, \'. A,, h . 4 1 , . CHEM.,2 3 , 1540 (1951). Sternglanz, P. D., Thon~pson,11. C., and Savell, W.L., I b i d . , 2 5 , 1111 (1953). Wagner, C. D., Smith, I
