The method of potentiometric titration was used to determine
the yield of chlorides radiolytically produced 1n solution of chlorobenzene
inn-hexane. The results obtatned suggest that this method
is convenient for the determination of chlorides present in nonaqueous
solution and could be applied particularly in chemic.al
dosimetry

M. Bonifačić

M. Vlatković

S. Musić

English

Hrčak - Portal of scientific journals of Croatia

CROATICA CHEMICA ACTA CCACAA 46 (2) 89-92 (1974) CCA-824 YU ISSN 0011-1643 545.37 Note Potentiometric Determination of Chlorides Formed by Radiolysis of Chlorobenzene in n-Hexane S. Music, M. BonifaCic, and M . Vlatkovic Institute »Ruder Boskovi c«, 41000 Zagreb, Croatia, Yugoslavia Received September 12, 1973 The method of potentiometric titration was used to determine the yield of chlorides radiolytically produced 1n solution of chloro-benzene inn-hexane. The results obtatned suggest that this method is convenient for the determination of chlorides present in non-aqueous solution and could be applied particularly in chemic.al dosimetry. Hydrochloric acid is one of the radiolytical iproducts in irradiaited orgainic so~utions containililg a chlor.inated hydrocarbon. Those systems are of interest in radiation chem~stry since at a sufficiently hi1gh concentration of chlorinated compounds the yield of hydrochloric acid may correspond to the y;ield of electrons formed in the system through the absorption of high energy rndia-tion. Also, chlorinated hydrocarbons are an essential component of dosimetric systems proposed1-a. The concentration of radiolytically produced hydrochloric acid could be determined by measurements of either H ' or c1- ions and the methods used so far include spectrophotometry4, colorimetry5, potentiomet ric pH measu-rements6, oscillometry7, and alkalimetric or mercudmet ric titrations3. The sensitivity and accuracy of the analytical method are particularly important in establishing the usefulness of the system for dosimetric appli-cation. The well known potentiometric chloride titratio:rus seem to be the most accurate, sensitive and easiest to perform even in cases of non-aqueous dosimetric systems. The purpose of the present communica11Jion is to illustrate the determination of radiolytically produced c1- ions by ,potentiometric titration carried out wirth an Ag/ Ag"S indicator electrode. The inadiaited model system used was the solution of chlorobenzene i:n n-hexane. EXPERIMENTAL Materials All chemicals were of analytical grade purity with exception of chlorobenzooe (Riedel de Haen, tech.) which was distilled twice on a 170 cm column packed with glas,s spirals and the fraction boiling at 131.6 °c was collected. The solution of AgN03 1Ln ethanol used in all titrations was standardized at approximately 1 X 10-3 M by use of a standard NaCl solution. Preparation and irradiation of samples The solution of 1.956 X 10-3 M C6H5Cl in n -hexane was prepared volumetrically. 2 ml-samples were dried with P20 5 and degassed by a few cycles of freezing, evacuation and thawing, before being sealed off in Pyrex ampoules. 90 S. MUSIC ET AL. Irradiations were performed on a 66Co source. The dose rate was determined by ferrous sulphate dosimetry and from these determinations the dose rate in n-hexane solution was calculated by applying corrections for electron density. After irradiation the samples were kept in liquid air until the time of analysis. Emf. measurements Emf. measurements were carried out by means of the cell8 A,g/AgBr I O.Ql M KBr I 0.001 M KN03 I test solution I Ag/Ag2S and a potentiometer (Derritron Instruments Ltd.) coupled with a galvanometer (Mul-tiflex, Lange) of maximal sensitivity 6 X 10-10 A/mm and resistance o.f 7000 Q. It is possible to use instead any of the commercial types of Ag/ Ag2S electrode or any reference electrode, e. g. a calomel electrode pro·vided with a double junction in order to prevent the contamination of the sample solution with chloride ions. Analysis for HCl 2 ml of aqueous solution of 0.3 M H2S04 were added after the ampoule containing the frozen sample was opened. When the sample solution reached room temperature the two layers were vigorously agitated by shaking in order to ensure complete extraction of HCl from the organic layer. Then 1 ml of aqueous acidic solution was transferred to a beaker containing 10 ml of ethanol aµd then titrated with standardized 1 X 10-3 M AgN03 by means of a microdosimeter which made it possible to add 0.001 ml of the reagent with a fair degree of accuracy. During the titration the solution wars stirred by a magnetic stirrer. RESULTS AND DISCUSSION The production of hydrochloric acid as a function of radiation dose is shown in Fig. 1 for 1.965 X 10-a M chlorobenzene in n-hexane. Each poiint represents the mean of 2-4 independent measurements. The deviation from the mean was ± 1.5 per cent or less for chloride concentration above 1 X 10-4 M. The lowest concen.tra:tion determined in the irradiated sample was approxi-mately 5 X 10-5 M .of chloride. The equivalence point ~n each single titration was established by Gran's methodn. Obviously, the high precision and sens~tivity of potentiometric titration made it posible to measure even small changes .in HCl radiation yieJd. Consequently two straight lines should be plotted through the experimental points for the doses up to 7 X 1019 eV/g. Two radiation yields G1 (HCl) and G:, (HCl) which were estimated frnm two slopes amounted to 1.00 •and 0.82, respectively. This probably reflects the influence of some secondary products on the process of HCl formation already in th~s iniJtial pe:r;iod of radiolysis. However, at higher total doses (> 7 X 1019 eV/g) a continuous decrease in HCl yield normally occurs because of the substantial decrease in CGH5Cl concentTation. Preliminary determinations of G (Ci-) as a funC'tion of initial C0H;5Cl concentration have shown thait in the range from 0.982 M to 0.982 X X 10-3 M of chlorobenzene this value changes from 3.41 to 0.61. Experience gained in this work suggests the suitability of potentiometric determination of chlorides in non-aqueous irradiated systems, ·particularly for the purpose of chemical dos~metry. Acknowledgement. We wish to express our gratitude to Dr. I. Dvornik for helpful discussion. DETERMINATION OF CHLORIDES 91 -3 . 0 6 1.965 · 10 M c6t-\fl in n-hexane / 5 0/ / :L ~ /0 'o ~ '"-=' 11/G u 3 I .____, 2 I 0 I 0 d 0 0 2 3 4 5 6 7 8 DOSE/1019 eVg1 Fig. 1. Production of HCl as function of radiation dose during the radiolysis of 1.965 X 10-• M CsHsCl solution in n -hexane. REFE R E NCE S 1. S. G. S i go 1 off, Selected Topics in Radiation Dosimetry (Proc. Symp. Vienna 1960), IAEA, Vienna 1961, p . 337. 2. D . G. 0 t t, W. H. Schweitz er, J. A. Saye g, and P. S. Harris, Health Phys. 7 (1961) 20. 3. I. D v or n i k in: N. W. Ho 1 m an d R. J. Berry (Eds.) , Manual on Radiation Dosimetry, New York 1970, p . 345. 4. S. U. Cho i and J . E. W i 11 a rd, J. Phys. Chem. 66 (1962) 1041. 5. I. D v or n i k, U. Z e c, A. An i c, and F. Ran o g a j e c, Solid State and Chemical Dosimetry in Medicine and Biology (Proc. Symp. Vienna 1966), IAEA, Vienna 1967, p. 237. 6. J. Wende n burg and A. Heng 1 e in, Z. Naturforsch. 17b (1962) 590. 7. Zs. Horvath, E. Ban ya i and G. F 61 di a k, Radiochim. Acta 13 (1970) 150. 8. S. Music, M. Sc. Thesis, University of Zagreb, Zagreb 1972. 9. G. Gran, Analyst 77 (1952) 661. 92 S. MUSIC ET AL. SAZETAK Potenciometrijsko odredivanje klorida nastalih radiolizom klorbenzena u n-heksanu s. Music, M . Bonifacic i M. Vlatkov ic Metodom potenciometrijske titracije odredivan je prinos klorida nastalih radio-lizom otopine klorbenzena u n-heksanu. Dobiveni rezultati ukazuju na prikladnost opi.sane metode za odredivanje klorida u bezvodnom mediju, posebno u kemijskoj dommetriji. INSTITUT »RUDER BOSKOVIC« 41000 ZAGREB Primlj e no 12. ruj n a 1973 . 

Potentiometric Determination of Chlorides Formed by Radiolysis of Chlorobenzene in n-Hexane

Abstract

Similar works

Full text

Available Versions

Hrčak - Portal of scientific journals of Croatia