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Hydrazinium thiocyanate as a reagent for determination of copper
Tulmru. Vol. 26. pp. 1041 to 1042 0 Prrgamon Pros Ltd 1979. Printed in Great Britain
HYDRAZINIUM THIOCYANATE AS A REAGENT DETERMINATION OF COPPER
FOR
J. P. VITTAL,C. R. ANANTASUBRAMANIAM, R. SOIJNDARARAJAN and K. C. PAT~L
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore, 560 012 India (Received 6 March 1979. Accepted 16 April 1979)
Summary-Hydrazinium thiocyanate, N,H,SCN, has been used for the determination of copper in copper salts. The reagent reduces the copper ions to the cuprous state and precipitates cuprous thiocyanate CU~(SCN)~,quantitatively.
Recently, we reported’ a novel method for the prep aration of hydrazinium derivatives by the reaction of solid ammonium salts with hydrazine hydrate. The hydrazine content of these hydrazinium compounds was determined by titration with potassium iodate. However, it was not possible to determine the hydrazine content of N,HJ and NIH,SCN since both Iand SCN- also react with iodate, so we had to use other methods. During the course of determination of thiocyanate in NzHSSCN as Cul(SCN)2, we found that reduction of Cu2+ to Cu+ was achieved simultaneously. In the conventional method, Cu2+ is usually reduced to Cu+ by the addition of sulphurous acid,’ ammonium hydrogen sulphite,’ ascorbic acid,4 or ferrous sulphate.’ It was thought interesting to try to use hydrazinium thiocyanate as a reagent for the determination of copper in copper salts. In this communication we report the results of this investigation.
EXPERIMENTAL Preparation of hydrarinium thiocyanate
Stoichiometric quantities of ammonium thiocyanate and hydrazine hydrate were mixed. The ammonium salt dissolved instantaneously with evolution of ammonia. The resulting solution was kept over phosphorus pentoxide in a vacuum desiccator for a few days; crystals of N2H5SCN
were obtained. NH,SCN + NrH~HrO+N,H$CN
The precipitate is digested on a water-bath for about an hour, then filtered off on a porosity-3 sintered-glass crucible. The precipitate is washed with cold distilled water and finally with alcohol. The precipitate is dried to constant weight at 110-120” and weighed as Cur(SCN)2. Fe3+, Mn2+ and Cr3+ do not interfere, but Ag+ and Hg2+ do. RESULTS AND DISCUSSION The results for determination of copper in solutions containing different amounts (SO-350 mg) of it are given in Table 1. The results show good agreement. The reaction of hydrazinium thiocyanate, N2H5SCN, with Cu2+ can be written as follows:
4Cu2+ + 4N2HSSCN + 2Cu,(SCN), + 3N2H; + SH+ + N2 The stoichiometry of the reaction was checked by determination of the hydrazine content in the filtrate after the separation of Cu2(SCN),. The liberation of prot,ons accounts for the observed decrease in pH to z 2.0. This method of determination of copper is convenient, because the reduction to cuprous ions and the precipitation of cuprous thiocyanate are achieved by a single reagent. Also, the time required for the determination
is much less than for conventional
Table 1. Results of gravimetric determination of copper
+ NH, + HZ0
A 10%solution of hydrazinium thiceyanate was used. Cop per solutions were prepared by dissolving known amounts
Copper taken, g
Copper found g
Error, (%)
of copper metal in nitric acid. Experiments were also carried out with different copper salts such as the chloride, nitrate and sulphate.
0.0536 0.0717 0.0770 0.1044 0.1305 0.1750 0.1991 0.3368
0.0535 0.0715 0.0769 0.1045 0.1300 0.1754 0.1984 0.3381
-0.2 -0.3 -0.1 40.1 - 0.4 +0.2 -0.4 + 0.4
Procedure
A copper solution containing up to 0.3 g of copper is diluted to 150-200 ml in a 400-ml beaker. A 10% solution of hydrazinium thiocyanate is then added slowly with constant stirring. The solution becomes colourless, a white precipitate forms, and the supematant liquid becomes acidic. 1041
Relative standard deviation 0.13%.
1042
SHORT COMMUNICATIONS
methods.‘-’ It is interesting to note that cuprous thiocyanate is not precipitated by addition of hydrazine hydrate and thiocyanate to solutions containing Cu*+ ions. Hydrazine hydrate is known6 to reduce Cuz+ to Cu+ which either forms CuZO or is further reduced to metallic copper. Acknowledgement-The authors are grateful to Prof. C. C. Pate1 and Prof. V. R. Pai Verneker for their interest and encouragement.
REFERENCES 1.
2. 3. 4. 5. 6.
K. C. Patil, R. Soundararajan and V. R. Pai Verneker, Proc. Ind. Acad. Sci, 1978, 87A, 281. A. I. Vogel A Text Book of Quantitative Inorganic Analysis, 3rd Ed., p. 569. Longmans, London, 1975. I. M. Kolthoff and G. H. P. Van der Meens, Z. Anal. Chem., 1927, 72, 337. E. C. Stathis, Anal. Chim. Acta, 1957, 16, 21. R. Relcher and T. S. West, ibid., 1952, 6, 337. M. Valcarcel, Talanta, 1973, 20, 224.
HYDRAZINIUM THIOCYANATE AS A REAGENT DETERMINATION OF COPPER
FOR
J. P. VITTAL,C. R. ANANTASUBRAMANIAM, R. SOIJNDARARAJAN and K. C. PAT~L
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore, 560 012 India (Received 6 March 1979. Accepted 16 April 1979)
Summary-Hydrazinium thiocyanate, N,H,SCN, has been used for the determination of copper in copper salts. The reagent reduces the copper ions to the cuprous state and precipitates cuprous thiocyanate CU~(SCN)~,quantitatively.
Recently, we reported’ a novel method for the prep aration of hydrazinium derivatives by the reaction of solid ammonium salts with hydrazine hydrate. The hydrazine content of these hydrazinium compounds was determined by titration with potassium iodate. However, it was not possible to determine the hydrazine content of N,HJ and NIH,SCN since both Iand SCN- also react with iodate, so we had to use other methods. During the course of determination of thiocyanate in NzHSSCN as Cul(SCN)2, we found that reduction of Cu2+ to Cu+ was achieved simultaneously. In the conventional method, Cu2+ is usually reduced to Cu+ by the addition of sulphurous acid,’ ammonium hydrogen sulphite,’ ascorbic acid,4 or ferrous sulphate.’ It was thought interesting to try to use hydrazinium thiocyanate as a reagent for the determination of copper in copper salts. In this communication we report the results of this investigation.
EXPERIMENTAL Preparation of hydrarinium thiocyanate
Stoichiometric quantities of ammonium thiocyanate and hydrazine hydrate were mixed. The ammonium salt dissolved instantaneously with evolution of ammonia. The resulting solution was kept over phosphorus pentoxide in a vacuum desiccator for a few days; crystals of N2H5SCN
were obtained. NH,SCN + NrH~HrO+N,H$CN
The precipitate is digested on a water-bath for about an hour, then filtered off on a porosity-3 sintered-glass crucible. The precipitate is washed with cold distilled water and finally with alcohol. The precipitate is dried to constant weight at 110-120” and weighed as Cur(SCN)2. Fe3+, Mn2+ and Cr3+ do not interfere, but Ag+ and Hg2+ do. RESULTS AND DISCUSSION The results for determination of copper in solutions containing different amounts (SO-350 mg) of it are given in Table 1. The results show good agreement. The reaction of hydrazinium thiocyanate, N2H5SCN, with Cu2+ can be written as follows:
4Cu2+ + 4N2HSSCN + 2Cu,(SCN), + 3N2H; + SH+ + N2 The stoichiometry of the reaction was checked by determination of the hydrazine content in the filtrate after the separation of Cu2(SCN),. The liberation of prot,ons accounts for the observed decrease in pH to z 2.0. This method of determination of copper is convenient, because the reduction to cuprous ions and the precipitation of cuprous thiocyanate are achieved by a single reagent. Also, the time required for the determination
is much less than for conventional
Table 1. Results of gravimetric determination of copper
+ NH, + HZ0
A 10%solution of hydrazinium thiceyanate was used. Cop per solutions were prepared by dissolving known amounts
Copper taken, g
Copper found g
Error, (%)
of copper metal in nitric acid. Experiments were also carried out with different copper salts such as the chloride, nitrate and sulphate.
0.0536 0.0717 0.0770 0.1044 0.1305 0.1750 0.1991 0.3368
0.0535 0.0715 0.0769 0.1045 0.1300 0.1754 0.1984 0.3381
-0.2 -0.3 -0.1 40.1 - 0.4 +0.2 -0.4 + 0.4
Procedure
A copper solution containing up to 0.3 g of copper is diluted to 150-200 ml in a 400-ml beaker. A 10% solution of hydrazinium thiocyanate is then added slowly with constant stirring. The solution becomes colourless, a white precipitate forms, and the supematant liquid becomes acidic. 1041
Relative standard deviation 0.13%.
1042
SHORT COMMUNICATIONS
methods.‘-’ It is interesting to note that cuprous thiocyanate is not precipitated by addition of hydrazine hydrate and thiocyanate to solutions containing Cu*+ ions. Hydrazine hydrate is known6 to reduce Cuz+ to Cu+ which either forms CuZO or is further reduced to metallic copper. Acknowledgement-The authors are grateful to Prof. C. C. Pate1 and Prof. V. R. Pai Verneker for their interest and encouragement.
REFERENCES 1.
2. 3. 4. 5. 6.
K. C. Patil, R. Soundararajan and V. R. Pai Verneker, Proc. Ind. Acad. Sci, 1978, 87A, 281. A. I. Vogel A Text Book of Quantitative Inorganic Analysis, 3rd Ed., p. 569. Longmans, London, 1975. I. M. Kolthoff and G. H. P. Van der Meens, Z. Anal. Chem., 1927, 72, 337. E. C. Stathis, Anal. Chim. Acta, 1957, 16, 21. R. Relcher and T. S. West, ibid., 1952, 6, 337. M. Valcarcel, Talanta, 1973, 20, 224.