The Electromotive-Force of Cells Containing Stannous Sulphate and Stannic Oxide Citation Miller, Palmer (1924) The Electromotive-Force of Cells Containing Stannous Sulphate and Stannic Oxide. Bachelor's thesis, California Institute of Technology. doi:10.7907/H0XD-1T68. https://resolver.caltech.edu/CaltechETD:etd-06142004-145236 Abstract No Abstract. Item Type: Thesis (Bachelor's thesis) Subject Keywords: Chemistry Degree Grantor: California Institute of Technology Division: Chemistry and Chemical Engineering Major Option: Chemistry Thesis Availability: Public (worldwide access) Research Advisor(s): Smith, David F. Thesis Committee: None, None Defense Date: 1924 Record Number: CaltechETD:etd-06142004-145236 Persistent URL: https://resolver.caltech.edu/CaltechETD:etd-06142004-145236 DOI: 10.7907/H0XD-1T68 Default Usage Policy: No commercial reproduction, distribution, display or performance rights in this work are provided. ID Code: 2580 Collection: CaltechTHESIS Deposited By: Imported from ETD-db Deposited On: 15 Jun 2004 Last Modified: 03 Oct 2019 23:18 Thesis Files Preview PDF - Final Version See Usage Policy. 571kB Repository Staff Only: item control page

The Electronotive-Force of Cells Containing Stannous Sulphate and Stannic Oxide. A Thesis by Palmer Miller. In partial fulfillment of the requirements for the degree of. Bachelor of Science in Chemistry. California Institute of Technology. 1933. Object of this Research and Review of Previous Work. The objects of this research were to determine: (1) The free energy of Sn0Og. (2) The difference between the free energy of - SnSO4(s) and of Hg2S804(s). (3) The heat of formation of SnSO,. . It had been hoped to use these data in connection with measurements of the equilibrium in the reaction, SnS04(s) = Sn0o(s) +S03(g). | but complications have prevented the obtaining of the latter measurements so that the results of the following work are presented in advance as a separate contribution to our knowledge of the compounds of tin. Apparently neitser the free energy nor the heat of formation of SnS04(s) have been determined. However the equilibrium between Sn0g, Sn, SnO, Ho, and H20, was deter-—- ‘mined by Wehler and Balz, : eeZeitachrift flr Elektrochemie. 27, 414, (1911).** but the results seem to be in error. Thus, the heat effect of the reaction calculated from the temperature coefficient of the equilibrium is several thousand calories different from that obtained from thermochemical data. Also experi- ments made by Mr. P. L. Magill in this laboratory seem to lead to different results. It was thought desirable, there- fore, to get at least an approximate value for the free energy of Sn, at room temperature and avoid uncertainty in extrapolation from high temperatures. It was proposed to measure the electromotive- force of cells containing Hg, HgO, Sn0s, and Sn; and He, Hg2804, SnS04, and Sn. One of the hardest problems was the preparation of materials of sufficient purity. In _ this connection the author wishes to acknowledge his indebtedness to Mr. V. Kalichevsky for the preparation of the HgO and the solution of NapgSnSz for plating the electrodes; and.to Mr. F. A. Hough for the preparation of the SnS0Oq. This research was carried on under the direction of Dr. David F. Smith to whom the author is indebted for much valuable advice and aid both in the laboratory work and in the writing of this report. Preparation of Materials. Alcohol: The absolute alcohol was made by refluxing 94% alcohol with a large quantity of lime and anhydrous KOH ‘for two days. It was then distilled into a flask which contained finely powdered lime and anhydrous KOH. This mixture was refluxed for two days and distilled. The first ten cubic-centimeters were discarded and the remainder was caught in 350 cc. flasks which were then sealed off. KOH: The KOH ueged in the oxide cell was prepared by fusing KOH ina polished iron crucible. The resulting mass was powdered, was shaken with absolute alcohol, and was” filtered owt of contact with air. The filtrate was placed in a vacumn dessicator over CaCl, and the air exhausted. Upon standing the solution firat became brown and then crystals of KOH appeared. These were was hed with absolute ether. | | “Sn0g: The Sn0, was prepared by igniting sn804. The product was a light yellow powder. 7 | Hg: This was made by heating the nitrate, HgNOz. Tin: The tin was prepared by boiling a solution of Sn6l5 with a strong solution of NaOH. The precipitate of metallic tin was washed until it gave a neutral washing which showed no test for chlorides. It was then placed in a tube, evacuated, dried, and finally melted to a button of pure metallic tin. This tin was powdered py filing with a clean new file. SnSO,: A solution of pure SnCl2g of commerce was treated wits NaOH and the Sn(OH)9 washed with water until free from chlorides. The Sn(OH)z was dissolved in dilute HoS04 and from this solution the SnSO, was precipitated by adding alcohol. This product was dissolved in dilute HsS04 and was shaken with finely powdered tin for several days. The solution was then filtered and the SnS04 precipitated With alcohol. This product was washed with alcohol and ether and dried ina va 7umn dessicator. The SnSO4 prepared by this method was used in the solubility measurenents and, after shaking with tin, was used in the alcohol-H39804 cells. For the cell containine the analgam the SnSO, was dis- solved in dilute H2504 and was shaken with finely powdered tin for three days. It was then re-precipitated py adding eighteen normal HgS04 until tse solution was approximatly ten normal. After washing tue Sn50, with alcohol it was dried in a dessicator. The final product was a fine white powder. All the above processes were carried on in an atmosphere of COg to prevent oxidation. Hg_80,: This was prepared by the method desoribed by G. A. Hulett using two crystallizing dishes and an auto- matie stirrer. **Physical Review 32, 261, (1911).** The HggS04 was shaken several times with the cell solution before using. | . Hg: The méroury used; in the cells, in the prepara— tion of the HggS04, and in the amalgam, was purified by @lectrolizing and distilling. . Mercury amalgam: The amalgam of approximately 0.6 weight percent tin was prepared by weighing out the required quantities and sealing them in an exhausted tuvoe. Upon heating, the tin completely dissolved. Sn0lg: A solution of pure SnClg of commerce was shaken with tin for three days. This solution, after being filtered, was concentrated and was cooled in a vacumn dessicator. The SnClg, which crystallized out in large needle like crystals, was dissolved in water. This solution was shaken with tin for three days and was then filte wd and sealed until used. | | NagSn8z: This solution, which was used to plate the tin electrodes was made as follows: Chlorine gas was passed over comercial tin at a temperathre below 100°. The SnCl4 thus obtained was distilled and tne fraction boiling at 114° was collected. It was then diluted four times ite volume with water and a concentrated solution of NaS added until the precipitate re-dissolved, after whicha fifty percent excess was added, The plating of the electrodes was done with a current of from 0.08 to 0.03 amperes. Tin is precipitated quanti- tatively in this way without occlusion of impurities in the deposite#, and is a white closeiy adhering mass. **Berichte. 81, 3, 2900.** **J, A. Ch. S. Trans. 1915, CVII, 71.** Apparatus. The cells were of the common "H" type with the electrodes at the vottom. | The oil thermostats, one of which was at 359 and the Other at 45°, were both regulated to keep the temperature Constant to 0.029. The electromotive-force measurements were made with a Leeds and Northrup potentiometer against a Weston standard cell. | For shaking the various solutions a motor driven revolving wheel was enployed. The Oxide Cell. The oxide cell is represented in the following manner; Sn(s)+Sn09(s), sol'n. of KOH in absolute alcohol, Hg0(s)+ Hg(1). Alcoholic KOH was used to prevent hydration of the 8n0z and also to cut down the OH” ion concentration and thus prevent the reaction @KOH+ KgSn0zg+Sn = 2Ko8n09g+ H30- which proceeds in aqueous alkaline solutions. The cell ' reaction when four faradays are passed theough the cell from left to rfght, is Sn(s)+8Hg0(s) = Sn09(s)+ 2Hg(1). In setting up this cell two bottles were filled with the absolute alcohol KOH solution. The stoppers were waxed in after some HgO and Hg was placed in one and Sn0g and Sn in the other. The two bottles were then shaken for two days. After the cell was cleaned, dried, and filled with nitrogen, the suspensions were poured in the respective sides of the cell up to the connecting tube. When the suspensions had settled tne rest of the cell was filled with the original solution. The glass stoppers were then waxed in and the cell placed in the 25° thermostat. Data. Temperature 325° E.M.F. 190867 volts. For six days the measured electromotive-force of this cell was not different from the value 1.0267 by moré than three millivolts and was within 0.1 millivolt of this value the last three days. Results and Calculations. ~ AFg50= ENF = 94,758. calories. 2(Fupo)=Fsndg -AF. Fgn0g = -288 ,374 calories , assuming the value of -13808 calories for the free energy of HgO given oy Lewis and Randall. **Lewis and Randall, "Thermodynamics" .** The Sulphate Cell. In order to deternine the concentration of sulphuric acid necessary to cause the soluvility of SnS0, to fall to such a value as would not appreciably effect the activity . of the H580,, tne solubility of Sns80, in various solutione pi H2eS04 was determined. The total stannous tin concentra- tion was determined by titration with standard iodine, and these values, after being calculated to moles per Kg. of solution, were plotted against the respective normalities of the sulphuric acid, The saturation point was approached merely from the unsaturated side and may be in error by a few percent. While the solubility of Snso, was being determined the cell was set up three times with alcohol-.80, solutions in which $nS0, is but slightly soluble. Two celle were set up with a solution of equal volumes of eight normal S04 and alcohol, and one with equal volumes of eighteen normal HjS0, and alcohol. The cell in these casés is represented in the following manner: _ Hg(1)+Hg804(s), sol'n. of HoS804 in alcohol; SnS04(s)+ Sn(a). The cell reaction was . Sn +HggS04 = SnSO4 +2Hg. From the solubility curve of SnSQ4gin H2804 ,it was decided that a golution of approximately ten normal or more in Ho804 would make a suitable cell solution since 10 12 the soluvility of SnSo4 in this solution is but 0.03 molail. However an acid of this concentration reacted with the metallic tin and therefore a liquid amalgam of about 0.6 weight percent of tin was used. For this cell, represented _by the expression Sng, (1)+SnS0,(s), sol'n. of 10 N. HpS04, HggSO4(e) FHg(1)., , the reaction was ‘SnHg,+ HggS04 = SnS04+2Hg +xHg. A portion of the same analgam was then placed ina cellot the type Sn, SnCl5 sol'n approximately 0.4 molal, Sng x. in order to refer the above electromotive-force to pure tin. The change in electromotive-force with the temperature was found by first letting the cell come to equilibruim at 25° and then at 45°. From these values the heat effect of the cell reaction could be calculated. Data. From the alcohol-Ilp804 cells the value for the electro- motive-force was approximately 0.855 volts. This value was not used in the calculations because the alcohol-H2S0, cells did not give as sensitimue readings nor as constant a value ag did the amalgam cells. Resuits and Calculations. (1) - (2) (3) = (1) +(2) SnHg, + Hg,S04= Sn+xHge = SnHgy Sn +Hg,S04= SnS0,+-8Hg +xlg SnS0O at 3He. Temp. E.M.F. E.M.F. EMF | 1 35° 0.85472 0.00385 0.25830 | 2 35° 0.85480 ——-0.00100 9.85580" 3 35° 0.85405 0.00120 0.85525 4 25° -- . -- 0.855 1 459 0.85364 0.00848 0.86206. Value no.l was obtained from a cell having for tae tin electrode a platinum coil plated with tin. Valmes 2 and 3 were from @ cell in which the tin electrode was a coil of platinum wire about which finely powdered tin was packed. Value number 4 is the average value for those cells containing alconol and H.S0, as the cell solution. The average of values 1,2,3,&4 is 0.856 calories. ~ ABS ENF..856 x 8 x 96494 = 3950002lories. 4.183 as = ENF = = 39788 calopies. E,_E,.4.192x(4\H) (22) T, 1,7 193988 (TT) - SH = 37000 calories. THggS04- Hgngo, 07 HgnS042212000 calories assuming the value of -175000 calories for the heat of formation of Hg9S04, taken from **Landolt Bornstein. "Tapellen".** a NO 7 | Solubility of On30., in solutions of H,S5O,, ° = Moles SnSQ).perHg.. .. ls glereste taste eter - yy Lew nineties oe te gNormality 5 0F SOx. 6... ect ee aes ao i a oe ve eae g. Patron Mutter fO The Solubility Curve of SnSO,4 in HeSo4. All the values for this diagram, except the solubility in pure water, were determined by shaking various normalities of acid with an excess of solid SnSO, and finding the con- centration of the stannous tin by titration with standard ‘fodine. The value for the solubility in pure water was taken from the value determined by Wargrac. **Comp. Rend. 45, 650, (1852).** The diagram shows the phases in equilibrium with acids of various concentrations. The point "A" represents the meta-stable equilibrium of SnSO4 in pure water. This is only a meta-stable equilibrium because upon standing the Salt hydrolizes readily and the basic salt is precipitated until equilibrium is reached. The presence of even a sual H* ion concentration seems to cahalize the hydrolysis reaction to such a degree that a meta-stable equilibrium is not attained adn any case except pure water. When the acid concentration cecomes greater than 1.6 normal the basic salt SnS04:25n8: xH20 changes to SnSO4,. Further increases in the acid concentration cause the solubility to deerease due to the common ion effect. In this connection Dr. D. F. Smith made sone calcula- tions on the activities of SnS04. 15 ESnt* H9S04 E. A Sn* A Snt calculated from E. 0.096 0.5 0.203 0.00643 0.00533. 0.0105 0.5 0.221 0.000704 0.000704 0.048 0.05 0.204 0.0104 0.00494 0.105 0.05 0.223 0.00227 00.00112 0.482 = 0.00 © 0.190 0.0335 0.0146 0.085 0.00 0.198 0.0152 0:00185 0.010 0.00 0.211 0.0040 0.00286. The activity values in the foutth column are those of CuSO, taken from Lewis and Randall. **Lewie and Randall, "Thermodynamics" .** The values in the fifth column are calculated from the measured electrozotive-forces of F. Foester and J. Yamasaki,of the cell Sn , HgS04 + SnS04,N.F., **Zeitschrift flr Elektrochemie. 17, 368, (1911).** assuming the values in the second row to be identical by the two methods . It can readily be seen that the smaller the concentration of the acid, the more the activity Calculated varies from the actual. This ig further proof of the large hydrolysis in weakly acid solutions. It showa furthermore that upon the basis of known activity values it would ve impossible to calculate t:e Sn** ion concentra- tion in any case except strongly acid golutions since the hydrolysis is so large. 16 The Electrode Potential of Tin. If the activity. of SnS04 at this concentration were known the electrode potential of tin could be calculated, Since we have all the other necessary data (ie) the €lectromotive-force of the sulphate cell containing ten normal HjS04 and the activity of Hj504 at this concentra- tion. Summary. From the electromotive force of the oxide cell and from the assumed value of -13808 calories for the free energy of HgO, the free energy of Sn0, was calculated to be -132374 calories. Since only one measurement of this electromotive force was made, it is impossible to estimate how much this value may de in error. . The free energy of SnS0, is greater than the free energy of Hg2S04 at 25° by 3@50@ calories, and at 45° by 39780 calories. It is unlikely that these values are in error by more than 100 calories, corresponding to an error of about two millivoits in the electromotive force. When the reaction Sn+Hg9S04 =SnS04+2He takes place at an average temperature of 35°, 37000 calories of heat are evolved. This value is probably in error by less than 1000 calories. Assuming the value of -175000 calories for the heat of formation of Hg=S04, the heat of formation of SnS0,4 Becomes~-212900 calories.