Analysis by phase-titration of three-component systems containing two mutually immiscible or partially miscible components

804

Short communications

Tshnta.1972,Vol.19,pp. 804 to 807. PcrpamonPM8.

PrinW.4in Northem Ineland

Analysis by phase-titration of three-component systems containing two mutually immiscible or partially miscible components (Received 30 August 1971. Accepted 1 November 1971) THE PRxNCIPLJ3of phase-titration8 has been used to determine the composition of a large number of binary solution8 of organic liquids. 1- 6 SurP ha8 developed a phase titration procedure for the analysis of ternary mixture8 containing two mutually immiscible or partially miscible components. The method is useful for systems where chemical determination of any of the components is difllcult. In the present communication, another phase-titration method is described, which can be used to analyse one-phase ternary mixtures containing two mutually immiscible or partially miscible cornponents, without separate determination of any component. The method involves titrating a measured amount of the ternary mixture at constant temperature with one of the immiscible components until a second phase just appears. The refractive index (a physical property which can be quickly measured) of the resultant solution on the binodal curve is then measured, and the complete composition of the ternary mixture is calculated. THEORY A ternary phase-diagram for a system containing A, B and C where B and C are mutually immiscible and A is miscible with both B and C in all proportions is shown in Fig. 1. Solutions represented by a point on or below the binodal curve are heterogeneous and turbid. At constant temperature, the position of the binodal line is fixed for a given ternary mixture, and serves as a reference line in the procedure described below. A set ofbinary solutions of A and B, richer in B and of known composition is prepared by weight and titrated with C until a permanent turbidity appears. The resultant ternary solution is then weighed to determine the weight of the titrant added. The turbid solution is clarified by adding a drop of two of A and the refractive index is measured. Two calibration curves are then drawn indicating (a) the weight of C required to produce turbidity in 1 g of the binary solution, and (b) the refractive index as a function of original binary composition. The procedure is repeated for binary solutions of A and C, richer in C, and another pair of calibration curves is drawn for B as the titrant.

FIG. I.-Ternary

miscibility

diagram

showing analysis.

regions

suitable

for phase-titration

805

Short communications

The dual set of calibrations is necessary because sometimes only one of the two titrants will give a satisfactory end-point (see below). To analyse a homogeneous mixture of A, B and C, two samples of known weight are titrated, one with B and the other with C to bring the composition on to the binodal curve.* The solution is weighed, clarified by adding a drop of A, and its refractive index measured. With C used as the titrant, a refractive index value corresponding to y% B signifies the ratio of A:B in the original ternary mixture to be (100 - y):~ (during titration with C, the ratio remains unchanged). From the calibration curve, the weight of C required to titrate 1 g of a binary mixture of A and B in the same ratio as in the sample is found (z g). This means that (1 + z) g of the turbid solution (obtained by titration with C) contains (100 - y)/lOO, y/l00 and z g of A, B and C respectively. If x g is the weight C required to titrate 1 g of the original ternary mixture to this point on the binodal curve, the composition of the sample is given by A = (100 - y)(l + x)/(1 + z)%; B = ~(1 + x)/(1 + z)%, and C = lOO(z - x)/(1 + z)%. The calculation is similar when B is used as the titrant. In some cases, the refractive index calibration plot show a maximum or minimum, so two composition values can correspond to a single refractive index value. To find which one refers to the actual composition, a small amount of B or C is added, the solution is clarified with A, and the direction of shift of refractive index is observed. Ternary solutions with composition represented by a point anywhere in areas BKCL or BKCN will yield a turbidimetric end-point on titration with B and C respectively. If the composition of the ternary lies outside BKCNML, the area defined by the tangents and the binodal curve, it will not yield any turbidimetric end-point on titration with either B or C. In such cases, a sufficient and known weight of B or C is added to a known weight of the ternary, to bring its composition into one of the &ratable regions BKCL or BKCN.O The method is illustrated for the ternary system benzene, cyclohexane and nitromethane, the system used to illustrate the method described ear1ier.O EXPERIMENTAL The solvents were purified according to established procedures. a*1 Densities and refractive index values for the liquids used are recorded in Table I along with the literature values for comparison.* The experimental details of the titration and the apparatus have been described earlier.” Calibration curves were prepared, as outlined under Theory, for benzene-nitromethane mixtures TABLEl.-SOME

PHYSICAL

PROPERTIES

OF SOLVENTS

Density, g/ml Present work

Literature valuer**

USED

AT

30°C

Refractive index Present work

Literature value’**

Benzene

O-8685

0.8685

14945

1.4948

Cyclohexane

0.7694

07690

1.4205

l-4208*

Nitromethane

1.1239

1.1245

1.3770

1.3771*

l

Values extrapolated

to 30°C.

titrated with cyclohexane, and for benzen-yclohexane mixtures titrated with nitromethane. The experimental values are given in Table II. To illustrate the method, over the entire one-phase region of the system, seven synthetic ternary mixtures were prepared and analysed. The results obtained are compared with the actual composition values in Table III. Samples 1 and 2 gave turbidimetric end-points with nitromethane, 5 and 6 with cyclohexane, 3 with both, and 4 and 7 with neither. Two sets of each of samples 4 and 7 were diluted with about the same weight of nitromethane or cyclohexane (uide ref. 7) and the resulting solutions titrated with cyclohexane or nitromethane respectively. The refractive indices of all the titrated solutions were measured and the weight ratios benzene:nitromethane in samples 3, 5, 6 and the solutions obtained by diluting samples 4 and 7 with nitromethane were computed from the calibration curves. The weight ratios benzene:cyclohexane in samples 1,2,3 and the solutions obtained by diluting samples 4 and 7 with cyclohexane were similarly calculated. * The selection of the titrant depends on the composition of the ternary to be titrated.* samples yield turbidity with B, some with C, some with both and some with neither.#

Some

806

Short communications TABLEIT.-EXPERIMENTAL DATA FOR CALIBRATION CURVES FOR THE SYSTEM C,H&,H,,-CH,NO, AT 30°C.

Solutions of benzene + nitromethane Weight % CHSNOa in original binary

titrated with cyclohexane

Weight of C,H,, required to titrate 1 g of binary

91.31 82.04 72.93 62.33 49,73

Refractive index of the resultant solution

0.0886 0.1336 0.2257 0.4200 0.7767

1.3888 1.4000 1.4096 1.4191 1.4260

Solutions of benzene + cyclohexane titrated with nitromethane Weight % CBHla in original binary

Weight of CH,NO, required to titrate 1 g of binary

94.18 8356 67.69 59.33 54.06

0.0451 0.0764 0.2186 0.4367 0.6844

Refractive index of the resultant solution 1.4235 1.4293 1.4322 1.4308 1.4283

TABLEIII.-COMPARISON OF THE ACTUAL AND ESTIMATED COMPOSITION OF THE TERNARY MIXTURE CBHa + CgHls + CH,NO,.

Cyclohexane

Nitromethene

% w/w

% w/w Titrant

Sample Present 63.2 52.6 39.3 29.8 13.7 10.7 9.2

Estimated 62.7 52.9 39.1 39.3 304 30.0 13.4 10.4 9.6 9.3

Present 12.3 13-8 32.4 16.0 62.2 43.7 14.8

Estimated 12.4 13.8 31.8 32.2 16.1 16.0 61.8 44.1 14.2 14.6

Nitromethane Nitromethane Nitromethane Cyclohexane Nitromethane Cyclohexane Cyclohexane Cyclohexane Nitromethane Cyclohexane

DISCUSSION On the whole, the agreement between the actual and determined composition values (Table III) is good. The maximum difference is - 1% when cyclohexane is used and - 3 % when nitromethane is used as the titrant. The agreement between the actual value and the two sets of determined values for samples 3, 4 and 7 are reasonably good. The method of analysis is more precise and less time-consuming than the one described earlier.6 This can be attributed to (i) the calibration curves being drawn directly from the experimental results and not needing any graphical treatment, and (ii) only one phase-titration being needed instead of the two required in the other procedure. The procedure does not involve a separate determination of any of the components by an independent method. It is extremely useful for ternary systems where chemical analysis of any of the components is difficult. The method has, however, the same limitations and errors as other phasetitrations.e S. K. Sum Chemistry Department Indian Institute of Technology New Delhi-29, India

807

Short communications Summary-A method, based on phase titration, for the analysis of ternary mixtures containing two mutually immiscible or partially miscible components is described. The method involves titrating a measured amount of the sample at constant temperature with one of the immiscible components to a turbidimetric end-point. The refractive index of the resultant solution (clarified by addition of the mutually miscible component) is determined and from the results the composition of the ternary mixture is estimated. The method is illustrated for the system consisting of benzene, cyclohexane and nitromethane. Zusammenfassnng-Beschrieben wird ein auf einer Phasentitration beruhendes Verfahren zur Analyse tern&r Gem&he, die zwei gegenseitig nicht mischbare oder teilweise mischbare Komponenten enthalten. Dabei wird eine abgemessene Menge der Probe bei konstanter Temperatur mit einer der nicht mischbaren Komponenten zum turbidimetrischen Endpunkt titriert. Der Brechungsindex der entstehenden Losung (gekliirt durch Zugabe der mischbaren Komponente) wird bestimmt und aus dem Ergebnis die Zusammensetzung des temlren Gemisches ermittelt . Das Verfahren wird an dem System Benzol-Cyclohexan-Nitromethan beispielhaft erllutert. R&utt&Gn d&it une methode basQ sur le titrage de phase pour l’analyse de melanges temaires contenant deux composants non miscibles ou partiellement miscibles pun dans l’autre. La methode comprend le titrage ii temperature constante dune quantite mesun% de l’6chantillon avec l’un des constituants non miscibles jusqu’l point de fin de dosage turbidimetrique. On determine l’indice de refraction de la solution rBsultante (clariiiee par addition du constituant mutuellement miscible) et l’on estime la composition du melange temaire ti partir des r&hats. La mdthode est illustr&e par le systemeconstitue de benzene, cyclohexane et nitromethane. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8.

C. D. Bogin, Ind. Eng. Chetn., 1924,16,380. D. W. Rogers, D. L. Thompson and I. D. Chawla, Z’&nta, 1966,13,1389 and references therein. S. I. Spiridonova, J. Anal. Chem. (U.S.S.R.), 1949,4, 169 and references therein. E. R. Caley and A. Habboush, Anal. Chem., 1961,33,1613. D. A. Dunnery and G. R. Atwood, Talanta, 1968,15, 855. S. K. Suri, ibid., 1970,17, 577. A. Weissberger, Organic Solvents, Vol. VII, 2nd Ed., Interscience, New York, 1960. J. Timmermans, Physico-Chemical Constants of Pure Organic Compounds, Elsevier, Amsterdam, 1950.

Talmta.1972,Vol. 19.pp.807to810.Pemamon Press. PrintedinNorthem Ireland

Simple spectrophotometric

method for determination of zirconium

or hafnium in selected molybdenum-base

alloys

(Received 13 September 1971. Accepted 2 November 1971) ARSANAZO III (1,8-dihydroxynaphthalene-3,6-disulpho-2,7-bis(azo-2)-phenylarsonic acid) gives marked colour reactions with a number of elements. The high stability of the metal complexes permits the elements to be photometrically determined in strongly acidic media, which eliminates partial hydrolysis of certain elements. A high degree of selectivity is attained when determining the quadrivalent elements, zirconium and hafnium, in strongly acidic media, 9M hydrochloric acid. It has been reported that no colour reactions with Arsenazo III are observed for elements having cations of radius less than 0.7-O-8 A. The ionic radii, in A, for those elements that might be components of molybdenum-base alloys are Cr 0.52, Fe 0.64, MO 0.62, Ni 0.69, Re 0.56. Ta 0.68, Ti 0.68,