This dissertation has been 64-1265 microfilmed exactly as received HENNE, Mary Tashdjian, 1931- POLAROGRAPHY OF HYDROGEN PEROXIDE IN LANTHANUM SOLUTIONS. The Ohio State University, Ph.D., 1963 Chemistry, analytical University Microfilms, Inc., Ann Arbor, Michigan POLAROGRAPHY OF HYDROGEN PEROXIDE IN LANTHANUM SOLUTIONS DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Mary Tashdjian Henne> B. A.» M. S. ****** The Ohio S ta te U n iv ersity 1963 Approved by — U/> Adviser bartment of Chemistry TO MY HUSBAND ALBERT L. HENNE FOR HIS LOVE AND ENCOURAGEMENT ACKNOWLEDGMENT I wish to express my gratitude to the Staff of the department for giving me an integrated understanding of chemistry, and to Dr. Justin W. Collat who originated the subject of this problem and supplied the needed guidance through the intricacies of the re se a rc h . i i TABLE OF CONTENTS Page PREFACE........................................................................................................................ i i LIST OF TABLES....................................................................................................... iv LIST OF ILLUSTRATIONS ........................................................ v I . INTRODUCTION............................................................................................. 1 I I . LITERATURE SURVEY.................................................................................... 2 Polarography of Hydrogen Peroxide Catalytic Decomposition of Hydrogen Peroxide Properties of Lanthanum Compounds H I . EXPERIMENTAL......................................... 21 Equipment Procedures IV. RESULTS............................ 30 Polarography in Lanthanum Nitrate Solutions The Lanthanum Hydroxide Effect Solution-Electrode Interaction Oscillography V. CONCLUSION.................................... 128 LIST OF REFERENCES ............................................................................; . 131 AUTOBIOGRAPHY................................................................................................................138 i i i LIST OF TABLES Table Page 1 * Ienic concentrations .............................................................................. 48 2. Ionic concentrations ........................................................ 49 3* Decomposition of hydrogen peroxide on the mercury surface in lanthanum nitrate and sodium nitrate so lu tio n s ............................................................ 102 iv LIST OF ILLUSTRATIONS Figure Page 1* Oscilloscopic circu it ...............................................................................22 2. Cell No. 1 .................................................................................................... 24 3* Supporting electrolytes ...................................................................... 31 4. Hydrogen peroxide concentration effect in perchlorate solutions .................................................................. 33 5* Hydrogen peroxide concentration effect in chloride solutions ................................................................. 35 6 . Hydrogen peroxide concentration effect in lanthanum nitrate solutions .................................. 39 7. Hydrogen peroxide concentration effect in dilute lanthanum n itra te ...................................................... **1 8 . Current versus hydrogen peroxide concentration ..... 43 9* Nitrate ion concentration effect ............................................... 50 10* Cation effect ............. ...................... .. 54 11. Effect of mercury pressure» low hydrogen peroxide concentration ................................................................. 58 12. Current versus effective pressure for Figure 11 . 6l 13. Effect of mercury pressure* high hydrogen peroxide concentration ........ .................... ... 63 14. Current versus effective pressure for Figure 13 .... 63 15. The effect of lanthanum hydroxide on the reduction of hydrogen peroxide .................................... 68 16 • Tests for lanthanum peroxide .................................................... • 71 17* Factors influencing the formation of lanthanum peroxide ................................................................. 75 18. The anion effect in the formation of lanthanum peroxide .......................................................................79 ▼ LIST OF ILLUSTRATIONS (contd.) Figure Page 19* Hydrogen peroxide cfecomposition in the absence o f lanthanum h y d r o x i d e ......................................................................82 20. Hydrogen peroxide decomposition on the presence of mercury and lanthanum n itr a te ................................................87 21. Respective importance of mercury and lanthanum n itra te ....................................................... 91 22. The effect of low ionic strength ................................................... 9^ 23. The e ff e c t o f high io n ic stre n g th ............................................ 97 2k» The effect of very low lanthanum n itra te ................................100 25. Potential-pH diagram for the hydrogen peroxide-mercury system ................................................... 106 26. Oscillograms of hydrogen peroxide in 10 mM lanthanum nitrate ........................................................... 113 27. Oscillograms of hydrogen peroxide in 1 mM lanthanum n itr a te ................................................................... 116 28. Oscillograms of hydrogen peroxide in 100 mM lanthanum n itr a te ............................................... 119 29. Oscillograms of hydrogen peroxide in ammonium n i t r a t e ......................... 121 vi I . INTRODUCTION The electrode reduction of hydrogen peroxide is a problem of great versatility; it has been studied in alkali electrolytes* in standard buffers* and in the presence of heavy or transition cations. This has been reviewed in detail in the Literature Survey. The present study investigates the reduction of hydrogen peroxide at the dropping mercury electrode* D.M.E.* in neutral, unbuffered lan­ thanum salt solutions, mostly nitrates. A systematic search was made for experimental conditions which would insure dependable* reproducible results. The procedures adopted controlled the preparation and age of the lanthanum solutions, standardized the deaeration period* and mini­ mized the length of contact with mercury. With all conditions strictly normalized* the factors affecting the polarography were investigated. This involved a study of the concentration effects and of the specificity of lanthanum hydroxide in the electrode process. It also required an examination of the chemical reactions which occur by mere contact of the solutions with mercury surface and an oscillographic study of the elec­ trode reduction process at minimum contact with mercury. In the presence of lanthanum, a pronounced positive shift of the hydrogen peroxide reduction wave preceded by an isolated current peak was observed. Interpretation of the experimental results led to the con­ clusion that this behavior can be explained as an autocatalyzed reduction involving the formation of soluble lanthanum peroxide intermediates. I I . LITERATURE SURVEY A. Polarography of Hydrogen Peroxide 1. Polarography in alkali electrolytes and buffered solutions The oxidation-reduction reactions of hydrogen peroxide have been studied at the dropping mercury electrode, D. M. E., and at other inert metal electrodes* in the presence and in the absence of air. The present survey is restricted to electrode reactions at D.M.E.* and almost entirely concerned with reduction; it briefly reviews oxidation only for the sake of completeness. The reduction of oxygen in alkali, electrolytes was first described by Heyrovsky (1*2) as a process represented by two waves of equal heights. The first wave between O.Ov. and -0.2v. is the reduction of oxygen to hydrogen peroxide* (1) Og + 2H+ + 2e -* HgOg (ac id medium) (2) Og + 2HgO + 2e -• HgC^ + 20H (n e u tra l o r a lk a lin e medium) w hile the second wave a t - 0 .8v. is the reduction of hydrogen peroxide to water or hydroxyl ion, (3) HgOg + + 2e -♦ 2 Hg 0 (acid medium) (b) HgOg + 2e -• 2 OH” (alkaline medium) with all voltages referred to the standard calomel electrode, S.C.E. Heyrovsky (1*2) reported the reduction potential of hydrogen peroxide as - 0 .8v. in acid solutions and -l.lv. in alkaline solutions. He also observed a linear relationship between limiting current and concentration when he added constant increments of hydrogen peroxide to air saturated solutions. Similar studies were made in air saturated solutiorS of potassium chloride or Clark and Lubs buffer* at pH's ranging from 2 to 10 by Kolthoff and M iller (3) who established the irrevers­ ibility of the electrode process when they recorded a constant E = -»93v. vs. S.C.E. for the whole range and established that the plot4 . log - id - "1— versus E was not rectilinear. The upper lim it of workable concentration was set by Giguere (4) a t 0 . 15 $, where an appreciable decomposition of hydrogen peroxide to oxygen occurred at the mercury surface* and where the linear relation between the limiting current and the concentration ceased to prevail. At concentrations smaller than 0.05#> hydrogen peroxide did not oxidize mercury. The lowest lim it for the detection of hydrogen peroxide was - set at 0.00356 by Pellequer ( 5 ) • B ockris ( 6 )