- Email: [email protected]
Reduction of permanganate by iodide in a neutral medium
Notes
179
conductivity after the break corresponds to the addition of the alkali showing no neutralisation process is taking place after the break.
Acknowledgement--The authors express their sincere gratitude to Professor R. P. MITRA for his interest in this work.
Department of Chemistry University of Delhi Delhi, India
D . V . S . JAIN A. K. BANErOEE
Reduction o f p e r m a n g a n a t e by iodide in a neutral m e d i u m
(Received 12 December 1960; in revisedform 30 January 1961) IODIDE acts as a strong reducing agent (1~ towards permanganate in an alkaline medium with reduction from Mn(VII) to Mn(VI) ; in a neutral medium reduction is to Mn(IV). Analytical measurements have been made to determine the oxidation state of iodine which is formed in the latter case. Potassium permanganate and potassium iodide were allowed to react until manganese dioxide separated, leaving a colourless supernatant liquid. The precipitate was filtered and washed in a measuring flask; 25 ml aliquots of the filtrate were analysed for iodate and iodide. ¢2~ Manganese dioxide was determined iodometrically. 25 ml samples were also titrated against a standard solution of oxalic acid to determine the liberated alkali. Table 1 shows the results obtained. It was found that manganese was in the Mn(IV) state, retaining only two fifths of its original TABLE I.--KMnO4 = 0.2 N; KI = 0.2 N; TOTALVOLUME
=
KMnO4 ml 10 10 10 10 10 5 5 5 5 5 2"5 2'5 2'5 2'5
KI ml
1 2 4 6 8 0-5 1'0
1-25 2.50 5.00 0.25 0.50 0.75
1-25
MnO2 found as ml of K M n O ,
Oxidant in filtrate as ml of KMnO4
4"05 4"04 4"04 4"05 4-07 1"98
598 5'98 597 5.98 596 3.00 3-00 3.00 3.00 3.00 1.502 1.502 1.51
1 "98 1'99 1 "99 1 '99 0"995 0"995 0"995 0"995
1-50
Remaining KI, found ml 0
50ml Remaining KI, calculated ml
3"007 4.948
0 1.00 3.00 5.00
0 0.508 0-766 2.014
0 0.500 0.75 2.00
0 0.266 0.508 1"017
0 0.25 0-50 1.00
1.017
oxidising capacity; three fifths of the latter is imparted to the filtrate. The latter is colourless and contains no iodine, hydrogen peroxide or potassium hypoiodite, but responds to tests for potassium iodate. ~3~ The minimum concentration of iodide required for the reduction of permanganate is 0.1 equivalent per equivalent of permanganate, and determination of the unused iodide in the filtrate ~1~y. K. GUPTA, Bull.polon. Sci. (Poland), 8, 79 (1960). ~z~W. W. Sco'r-r, Standard Methods of Chemical Analysis, 454, D. Van Nostrand and Co., Inc., New York (1958). cal A. I. VOGEL,A Textbook of Macro- and Semimicro Quantitative Inorganic Analysis, p, 372. Longmans Green and Co., London, 4th Edition, 1959.
180
Notes
shows that in all the experiments 0"1 equivalent of iodide is oxidised by one equivalent of permanganate according to the equation 2 M n O c + I - + H 2 0 = IO3- + 2MnOz + 2OH-. This estimation of iodide in presence of the oxidant, assumed to be iodate, provides strong support for the presence of iodate in the filtrate; the amount of iodide was calculated on the basis of the reaction, IO3- + 5I- + 6H + = 312 + 3HzO. The amount of alkali determined was found to be irregular and to decrease with time. Experiments were also performed using amounts of iodide less than 0'1 equivalent of the original permanganate, and the excess permanganate was estimated colorimetrically at 524 m/* after separating the manganese dioxide by centrifuging. The results are tabulated in Table 2. TABLE 2.--REACTION MIXTURE50 ML
KMnO~ N
KI N
Optical density of remaining KMnO4 (10 times diluted)
0"05 0"05 0"05 0"04 0"04 0"02
0.004 0.002
0"48 1"39
0.001
1'90
0.002
0"93 1 '42 0"48
0.001 0.001
KMnO4 from Beer's law graphically N 0"001 0"00297 0-00405 0'00197 0"00302 0'001
I JI Remaining [ KMnO4 N
!
0"01 0"0297 0'0405 0"0197 0"0302 0'01
Expected remaining KMnO, N 0"01 0"03 0"04 0'02 0"03 0'01
The results obviously point to the formation of iodate when permanganate is reduced to manganese dioxide by potassium iodide.
Department of Chemistry D.S.B. Government College Nainital, India
Y . K . GLrpTA
D e r Reaktionsdruck des Indium(I)sulfids (Received 30 January 1961) DAS Zustandsdiagramm des Systems Indium/SchwefeF 1~enthiilt keine Hinweise fiJr die Existenz des festen oder geschmolzenen Indium(I)sulfids. Es ist jedoch bekannt, ~ dass sich bei der Einwirkung von Schwefelwasserstoff auf Indium-Metall bei 1000°C gasffrmiges In2S bildet, welches sich im Vakuum absublimieren 1/isst und im kiihleren Teil der Apparatur als schwarzer Spiegel erscheint. In Zusammenhang mit unseren friiheren Untersuchungen fiber Gallium(I)sulfid ta~ schien es uns yon Interesse, den Reaktionsdruck von In~S fiber Schmelzen der Bruttozusammensetzung InS + In und In2S3 -4- 4 In zu messen. Die Ergebnisse der Messungen zwiscben 1000 ° und 1200°C zeigen die Tab. 1 und 2. Innerhalb des untersuchten Temperaturintervalles zeigen die Messwerte der Tab. 1 im lg p -- T -1 Diagramm keine merkliche Abweichung yon einer Geraden, d.h. Alia ist in diesem Bereich im Rahmen der Messgenauigkeit temperaturunabh~ingig. Es ist daher gerechtfertigt, die Messungen durch eine Dampfdruckgleichung mit nur zwei Parametern zu beschreiben. Nach der Methode der kleinsten Fehlerquadrate erhlilt man 9 320'3 lg pi%s(Torr) T + 7.9212 (1) Der Gleichgewichtsdruck yon In~S fiber Indiumsulfid-Phasen mit hinreicbend grosser Indiumaktivit/it ist unabhiingig von der Art der ursprtinglich eingesetzten festen Indiumsulfide. Der Reaktionsdruck von In2S fiber Schmelzen der Bruttozusammensetzung In2Sa + 4 In stimmt also iiberein tl~ M. F. STUBBS,J. A. SCHUFLE,A. J. THOMPSONand J. M. DUNCAN,J. Amer. Chem. Soc. 74, 1441 (1952) tt~ E. GASTINGER,Z. Naturf. 10B, 115 (1955) ~a~H. SPANDAUund F. KLANBERG,Z. anorg, allg. Chem. 295, 300 (1958)
179
conductivity after the break corresponds to the addition of the alkali showing no neutralisation process is taking place after the break.
Acknowledgement--The authors express their sincere gratitude to Professor R. P. MITRA for his interest in this work.
Department of Chemistry University of Delhi Delhi, India
D . V . S . JAIN A. K. BANErOEE
Reduction o f p e r m a n g a n a t e by iodide in a neutral m e d i u m
(Received 12 December 1960; in revisedform 30 January 1961) IODIDE acts as a strong reducing agent (1~ towards permanganate in an alkaline medium with reduction from Mn(VII) to Mn(VI) ; in a neutral medium reduction is to Mn(IV). Analytical measurements have been made to determine the oxidation state of iodine which is formed in the latter case. Potassium permanganate and potassium iodide were allowed to react until manganese dioxide separated, leaving a colourless supernatant liquid. The precipitate was filtered and washed in a measuring flask; 25 ml aliquots of the filtrate were analysed for iodate and iodide. ¢2~ Manganese dioxide was determined iodometrically. 25 ml samples were also titrated against a standard solution of oxalic acid to determine the liberated alkali. Table 1 shows the results obtained. It was found that manganese was in the Mn(IV) state, retaining only two fifths of its original TABLE I.--KMnO4 = 0.2 N; KI = 0.2 N; TOTALVOLUME
=
KMnO4 ml 10 10 10 10 10 5 5 5 5 5 2"5 2'5 2'5 2'5
KI ml
1 2 4 6 8 0-5 1'0
1-25 2.50 5.00 0.25 0.50 0.75
1-25
MnO2 found as ml of K M n O ,
Oxidant in filtrate as ml of KMnO4
4"05 4"04 4"04 4"05 4-07 1"98
598 5'98 597 5.98 596 3.00 3-00 3.00 3.00 3.00 1.502 1.502 1.51
1 "98 1'99 1 "99 1 '99 0"995 0"995 0"995 0"995
1-50
Remaining KI, found ml 0
50ml Remaining KI, calculated ml
3"007 4.948
0 1.00 3.00 5.00
0 0.508 0-766 2.014
0 0.500 0.75 2.00
0 0.266 0.508 1"017
0 0.25 0-50 1.00
1.017
oxidising capacity; three fifths of the latter is imparted to the filtrate. The latter is colourless and contains no iodine, hydrogen peroxide or potassium hypoiodite, but responds to tests for potassium iodate. ~3~ The minimum concentration of iodide required for the reduction of permanganate is 0.1 equivalent per equivalent of permanganate, and determination of the unused iodide in the filtrate ~1~y. K. GUPTA, Bull.polon. Sci. (Poland), 8, 79 (1960). ~z~W. W. Sco'r-r, Standard Methods of Chemical Analysis, 454, D. Van Nostrand and Co., Inc., New York (1958). cal A. I. VOGEL,A Textbook of Macro- and Semimicro Quantitative Inorganic Analysis, p, 372. Longmans Green and Co., London, 4th Edition, 1959.
180
Notes
shows that in all the experiments 0"1 equivalent of iodide is oxidised by one equivalent of permanganate according to the equation 2 M n O c + I - + H 2 0 = IO3- + 2MnOz + 2OH-. This estimation of iodide in presence of the oxidant, assumed to be iodate, provides strong support for the presence of iodate in the filtrate; the amount of iodide was calculated on the basis of the reaction, IO3- + 5I- + 6H + = 312 + 3HzO. The amount of alkali determined was found to be irregular and to decrease with time. Experiments were also performed using amounts of iodide less than 0'1 equivalent of the original permanganate, and the excess permanganate was estimated colorimetrically at 524 m/* after separating the manganese dioxide by centrifuging. The results are tabulated in Table 2. TABLE 2.--REACTION MIXTURE50 ML
KMnO~ N
KI N
Optical density of remaining KMnO4 (10 times diluted)
0"05 0"05 0"05 0"04 0"04 0"02
0.004 0.002
0"48 1"39
0.001
1'90
0.002
0"93 1 '42 0"48
0.001 0.001
KMnO4 from Beer's law graphically N 0"001 0"00297 0-00405 0'00197 0"00302 0'001
I JI Remaining [ KMnO4 N
!
0"01 0"0297 0'0405 0"0197 0"0302 0'01
Expected remaining KMnO, N 0"01 0"03 0"04 0'02 0"03 0'01
The results obviously point to the formation of iodate when permanganate is reduced to manganese dioxide by potassium iodide.
Department of Chemistry D.S.B. Government College Nainital, India
Y . K . GLrpTA
D e r Reaktionsdruck des Indium(I)sulfids (Received 30 January 1961) DAS Zustandsdiagramm des Systems Indium/SchwefeF 1~enthiilt keine Hinweise fiJr die Existenz des festen oder geschmolzenen Indium(I)sulfids. Es ist jedoch bekannt, ~ dass sich bei der Einwirkung von Schwefelwasserstoff auf Indium-Metall bei 1000°C gasffrmiges In2S bildet, welches sich im Vakuum absublimieren 1/isst und im kiihleren Teil der Apparatur als schwarzer Spiegel erscheint. In Zusammenhang mit unseren friiheren Untersuchungen fiber Gallium(I)sulfid ta~ schien es uns yon Interesse, den Reaktionsdruck von In~S fiber Schmelzen der Bruttozusammensetzung InS + In und In2S3 -4- 4 In zu messen. Die Ergebnisse der Messungen zwiscben 1000 ° und 1200°C zeigen die Tab. 1 und 2. Innerhalb des untersuchten Temperaturintervalles zeigen die Messwerte der Tab. 1 im lg p -- T -1 Diagramm keine merkliche Abweichung yon einer Geraden, d.h. Alia ist in diesem Bereich im Rahmen der Messgenauigkeit temperaturunabh~ingig. Es ist daher gerechtfertigt, die Messungen durch eine Dampfdruckgleichung mit nur zwei Parametern zu beschreiben. Nach der Methode der kleinsten Fehlerquadrate erhlilt man 9 320'3 lg pi%s(Torr) T + 7.9212 (1) Der Gleichgewichtsdruck yon In~S fiber Indiumsulfid-Phasen mit hinreicbend grosser Indiumaktivit/it ist unabhiingig von der Art der ursprtinglich eingesetzten festen Indiumsulfide. Der Reaktionsdruck von In2S fiber Schmelzen der Bruttozusammensetzung In2Sa + 4 In stimmt also iiberein tl~ M. F. STUBBS,J. A. SCHUFLE,A. J. THOMPSONand J. M. DUNCAN,J. Amer. Chem. Soc. 74, 1441 (1952) tt~ E. GASTINGER,Z. Naturf. 10B, 115 (1955) ~a~H. SPANDAUund F. KLANBERG,Z. anorg, allg. Chem. 295, 300 (1958)