IJBAF, January, 2013, 1(1): ISSN:

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1 : ISSN: COLORIMETRIC DETERMINATION OF MOLYBDENUM (III) BY KCNS PANDYA AV AND CHAUHAN JS Department of Biochemistry and Chemistry, C U SHAH Science College Ahmadabad, Gujarat, India ajit1sujit@yahoo.com ABSTRACT A colorimetric method for the determination of Mo (III) in acidic solution is developed. The metal ion forms a reddish colored complex with CNS ligand in acidic medium. The complex formation is complete within few seconds. The complex is stable for four hours in acidic medium at room temperature but dissociates on heating. The complex shows maximum absorbance at 500 nm. The beer s law is obeyed in the range of 100 to 500 gs of Molybdenum. The molar absorptivity (E) is found to be l mole 1 cm 1. Synthetic samples are prepared and the method has been applied successfully. Keywords: Molybdenum (III), Colorimetric Method, KCNS INTRODUCTION Molybdenum forms compounds in all by moist air. The molybdenum trichloride is oxidation states from 2 to +6 [1]. insoluble in water, dilute hydrochloric acid, However, very little is known about some acetone, carbon tetrachloride and benzene. of the low oxidation states i.e. 2, 1, +1, +2, +3 etc. of molybdenum. Although, in this area some of the unusual properties of The compound is completely soluble in nitric acid, but is oxidized to higher oxidation states. It is slightly soluble in transition metals are found. The ether, alcohol and pyridine. molybdenum metal and other transition metals play important role in catalysis. Mo (III) forms blue coloured specis known as isopoly molybdates whose structure has been determined recently [2]. Molybdenum (III) chloride is a dark red compound which is gradually hydrolysed as well as oxidized Molybdenum is found in high strength steel alloys. It is also found in trace amounts in plants and animals. Excess molybdenum can be toxic in some animals. There are 35 known isotopes of molybdenum ranging from atomic mass from 83 to 117 which attracts the research interest 43

2 A number of spectrophotometric methods have been developed in recent years for the determination of molybdenum. An improved method for the determination of Mo (VI) by thiocynate method has been reported [3]. Polarographic examination of the Mo (V) thiocynate complex in diethyl ether has been reported [4]. A method for the selective extraction of Mo (V) thiocynate with n-benzylaniline has been reported [5]. A spectrophotometric method for the determination of Molybdenum from steel with thiocynate and nitron has been reported [6]. A method for the determination of trace amount of molybdenum from soil by the use of long chain alkylamines for pre concentration of Mo by atomic absorption spectroscopy has been developed [7]. A new spectrophotometric method for the determination of molybdenum by dithio oxamide has been reported [8]. Complexes of molybdenum (III) with 2, 2 Bipyridyl have been studied [9]. Its structure has been assigned on the basis of analytical, spectroscopic, magnetic and conductance data. Binuclear molybdenum (III) complex halides i.e. [Mo 2 Cl 9 ] 3 has been studied [10]. The octahedral complex of molybdenum (III) i.e. [Mo(CN) 6 ] 3 and Cyno-Bridged [Mo 2 (CN) 11 ] 5 has been synthesized [11]. The species [Mo(CN) 8 ] 4 has been studied and assigned the spectra [12]. The complex of molybdenum (III) of the type MoX 3 (NH 3 ) 3 has reported where X = Cl, Br, I [13]. Molybdenum (III) chloride (MoCl 3 ) reacts with halide ions to form octahedral complex [14] MoCl3 when reacts with nitriles at room temperature gives MoCl 2 3 NCR complex [15]. The complex of Mo (III) with ethylene diamine (en) has been reported [16]. The pyridine complexes of MoCl 3 Py 3 can be made by heating molybdenum (III) chloride and pyridine in a sealed tube at 270 C [17]. According to recent reports, when MoCl 3 is heated in aniline or piperidine at 70 0 C, complexes of the type MoCl 3 L 3 are obtained [18]. The crystal and molecular structure of MoCl 3 (C 5 H 5 N) 3 has been reported [19, 20]. MATERIALS AND METHODS A colorimeter (Model No.EQ-652) was used for colorimetric measurement. The ph measurements were made with an ELICOLI 120 ph meter. The reagent used was KCNS. The substance was dissolved in minimum amount of dilute HCl and the solution was used. MO (III) Solution: A 0.01 M stock solution was prepared by dissolving appropriate substance in Con. HCl (11 M). Working solutions were prepared by diluting the stock solutions to an appropriate volume. All the chemicals used were of A.R. grade. In each set of different 50 ml standard are flasks, various volumes of Mo (III) and reagent solution were taken and made up to 44

3 the mark with Con. HCl. The absorbance was measured at 500 nm against colourless reagent blank. The calibration curve was prepared by plotting absorbance against the amount of molybdenum. RESULTS AND DISCUSSIONS Determination of the Wavelength and Maximum Absorption The absorption spectra of red coloured complex solution were recorded in the wavelength region nm as Shown in the Table 1. It was observed that the complex showed maximum absorbance at 500 nm where as the reagent blank is colorless solution which does not absorb in the visible region. This is shown in Figure 1. Hence the analysis was carried out at 500 nm. Absorption decreases on either side of wavelength 500 nm indicates bell-shaped pattern of absorption. Effect of Time The complex formation is complete within the time of mixing the Molybdenum (III) solution and ligand KCNS. The complex dissociates after four hours. Effect of ph The complex is stable only at strong acidic ph. It dissociates when ph is increased and the complex dissociates completely above the ph of 1.5 as shown in Table 2 and Figure 2. Effect of Temperature The complex shows maximum stability only at room temperature i.e. at 25 0 C 35 0 C. It dissociates at higher temperature as shown in Table 3 and Figure 3. The Effect of Reagent Concentration (KCNS) on the Complex The complex formation requires six fold concentration of the ligand. Therefore it seems that the ion association must be 1:6. The complex may have the following structure (Figure 4). Results of effect of ligands have been shown in Table 4 Figure 5. The beer s law is obeyed in the concentration range gms of Mo (III). The molar absroptivity of the complex at 500 nm (in acidic medium) is 20.0 l mole 1 cm 1. The Effect of Foreign Ions The effect of various anions and cations on the determination of Mo (III) under optimum conditions was studied. It was noticed that metals such as Fe (III), Ni (II), Hg (II), Cr (III), Cr (VI), V (III) etc. strongly interfere even when present in very low concentrations. Ions such as Cl Br, SO4, F, Na +, K, NH 4 + does not interfere even when present in large excess. Determination of Mo (III) from Synthetic Samples A number of synthetic samples were prepared for the analysis. Colorimetric determination was carried out by the proposed method. The results are given in the Table 5. 45

4 Table 1: Absorption Spectra S. No. Wavelength nm Absorbance nm nm nm nm nm nm nm nm nm 0.10 Figure 1: Absorption Spectra Table 2: Effect of ph S. No. ph Absorbance AT 500 nm

5 Figure 2: Effect of ph Table 3: Effect of Temperature S. No. Temp 0 C Absorbance AT 500 nm C C C C C C C 0.01 Figure 3: Effect of Temperature 47

6 CNS CNS Mo SCN CNS CNS Figure 4: Complex SCN Table 4: Effect of Metal Ligands S. No. Metal : Legand (0.01 M) (0.01 M) Absorbance AT 500 nm 1. 1 : : : : : : Figure 5: Effect of Metal Ligands Sample Synthetic Sample 1 Synthetic Sample 2 Synthetic Sample 3 Table 5: Determination of Mo (III) from Synthetic Samples Mo (III) taken gs Abs. Average Mo (III) found gs Relative error %

7 CONCLUSION The proposed method may be improved by using more sensitive instruments. The complex can be extracted into organic solvents and further it may be characterized and identified by latest techniques. The stability and the structural characteristics can be studied at different levels. ACKNOWLEDGEMENTS The authors are thankful to C.U. Shah Science College for providing laboratory facilities. REFERENCES [1] Advanced Inorganic chemistry by F.A. Cotton and G. Wilkinson : Interscience second Ed., 1966, Chapter 30. [2] Karl-Heinz Tytko and Oskar Glemser Anorganisch chemisches Institute der Universitat Gottingen, Gottingen, West Germany. [3] Yatriranjan V and Jaswant R, Microchemica Acta., 62 (4), DOI: 10, 10071/BFL; [4] Afghan BK and Dagnall RM, Talanta, 14 (2), 1967, [5] Khosla MML and Rao SP, Analytica Chimica acta., 57 (2), 1971, [6] Thomas JK and Gordon AP, Analytica Chimica Acta., 113 (2), 1980, [7] Kim CH, Alexander PW and Smythe LE, Talanta, 23, (3), 1976, [8] Williams DA, Holcomb IJ and Boltz DF, Anal. Chem. 1975, 47(12), [9] Carmichael WM, Edwards DA and Walton RA, J. Chem. Soc. A, 1966, DOI: 1039/J [10] Lewis J, Nyholm RS and Smith PW, J. Chem. Soc. A., 1969, 57-60, DOI: /J [11] Laurance G, Beauvais and Jeffrey R, Long, Department of Chemistry; University of California, Berkeley; California J/A/C/S Communications. [12] Xin-Yi Wang, Mathew G, Hilfiger AP and Kim R, Dunbar Chem. Commun., 2010, 46, DOI -10, 1039/COCC00399, A First published on web 13 may [13] Michel B, Claus J, Jacobsen H, Camilla MJ and Iver Schmidt, Inorganica Chemica Acta, 247 (2), 1996, [14] Chillesotti A and Atti R. Accad Linacei, V-12, 1903, 67. [15] Smith PW and Wedd AG, J. Chem. Soc., (A), 1966, 231. [16] Adwards DA, Fowles GWA and Walton RA, J. Inorg. Nucl. Chem., 27,

8 [17] Rosenheim A, Abel G and Lewy R, Z. anorg. Allgem. Chem., 197, 189, [18] Ikramov KU, Kushakbaev A, Purpierv NA and Yunusoval NM and Khim ZHU, 15(5), 27 (1971), C. A b. [19] Zeitschrist Fiir anorganische and allgemeine chemie., 403 (2), 1974, [20] Brencic JV, Zeitschrift fiir anorganische and allgemeine chemie, 403 (2), 1974,