THE ELECTROLYTIC REDITTIOX
O F POTASSIL-JI
CHLOK&ATE
BY .4DOI.I”
L. Y O E G E
JTitli tlie esceptioii of soiiie papers clealiiig with organic coi~ipouiicls,~ verj. little lias been piiblislied 011 qtiaiititati1.r electrolytic reduction,’ and there is iii coiiseqiieiice iic) satisfactor!theor!. of the subject. The object of the work to be c1escril)etl in this paper was to gather data wliicli iniglit ser1.e before loiig as a basis for a coiiiplete theory of electrol!,tic reduction. Ii‘liile the esperiiiieiits Iiave iiot been carried far enough to \\-arrant tlieoretical deductions, a iininber of interesting facts 1iax.e heeii ohsen-ed, all of wliicli will have to be acco1intcd for at some fiitiire time. I t \vas tleemetl best to stud>- tlie 1-edtictioii of 311 iiiorgaiiic conipouiid 1)ecau.e the theor!- of electi-ol!.tic dissociatioti could be appliecl to the results. Froiii a n esperimnital poiiit of x-ien t n o thiiiR-s were essential. The coiiipotiiid iiiust he oiie that is iiot readily reduced. so tliat there 11ia~.he a possiliility of tlie total yield T-ar!.ing \.sr!. iiiucli witli chaiigiiig coiiclitiuiis, anti either the original coiiipotiiid or the reduction product iiiiist be oiie that can be deteriiiiiiecl anal!ticall!. with case. Rot11 reqiiisites are satisfied in potassiiiiii chlorate, and tliis salt \\.as tliercfore take11 as the siibstaiicc to lie studied. The coiiditioiic affwtiiig this reduction are h i t little kiio\vi-n. 111 this re the most iiiiportaiit points in\-estigated \yere : the presence of ~
_..___-__ i
E l l ~ h , Jour. p r a k t . C1:em. 1 2 I 43, 39 I S ~; I: H i i i ~ , Zeit. I-clrogeiiis utilized when iio current passes, while the curl-e for the alkaline cell reaches its zero of hydrogen utilizatioii while there is still considerable current flowing. T h i s inclines oiie to the opinion that there is soiiie coiistitueiit of the cell important as a reducing factor, tlie electroiiiotiye force of polarization of which has not been reached under the conditions of the ruii until a current flowed sufficient to cause current density of 0.006 j amp ~111'. T h e aiiionnt of li!.tlrogen that should he evolved during an!. run, as calciilated froin tlie ayerage current derived from tlie copper \-oltaiiieter, n.as found to be a l ~ v a y snctnall!- less than that given off in the os!--liydrogeii yoltameter. I n the first riiii, for instance, there are 620 cc of hydrogen evolved iii tlie voltameter. Aksiiiiiing0,03738 gram of li>.clrogeii generated per ampere hour, in t v o honrs with a current of 0.672 ampere. 0.0502 grain of li>-clrogeii would be given off. ,It o0 C there are 0.0S987 gram of 11)-drogen per liter or one gram per 11.127 liters.
T h e increase i n the voliiiiie of lijdrogeii per degi-ee centigrade is 0 . 0 0 3 6 6 , aiid a i tlie teiiiperature of tlie rooiii during the run w a i about 2 2 ' , tlie iiicrea5e '11 yoliiiiie o\-er that at o 3 C is 0 . 0 8 : therefore a gram's \ oliiiiie at rooiii temperature i i I 2 . 0 2 liter\, or a liter of h!-drogeii n e i g h s 0.0S31 g . During tlie riiii of two Iioiiri, tlierefore,
0.0LiC2 ~
O.OS3I
IOOO =
606 cc of I i ~ d r o g e i slioiild i be
e\oll.ecl. T h i s discrepaiic!- between 6 2 0 aiid 606 cc is probabl! due to the iiiecliaiiical traiisfer iii tlie 1-oltaiiieter of the os!'geii liberated a t the anode lj!. tlie curreiit to the cathode tiibe. IYitli a stroiig current this plieiioiiieiioii caii lie clistiiictlj. obsen-ed. T h i s is siibstaiitiated b!- the disagreemeiit observed in tlie livdrogeii aiid ox!.geii 1-oluiiies at an\-iiistaiit iii the x-oltaiiieter, for the \.oliiiiie of li!drogeii is ai\\-a!-s iiiore tliaii tivice that of tlie o n g e i i generated. T h i s last is not coiiclusive, Iion-e\.er, as ozoiie is foriiietl to soiiie extent at the anode, aiid being triatomic it i-educes tlie 1-011iiiieof tlie os!-geii of \rhich it is foriiied lj!. oiiethird. Peroxide of li!drogeii, H ,(Iz, iiiaj- also be foriiied, tliereli!. takiiix os!.g-eii in soliitioii, aiid would also teiid to increase the \.ariaticm 1ietn.eeii tlie ohser\~edv:ilues in the iiimiier stated. Tlie cjiiaiitities of h y d r o ~ e i ie\.olved as ohser\-ed and those calciilated fi-oiii tlie current strength were plotted, and it was tlirii seeii that tliese curves n e r e botli straight lines, so that the iiiechaiiicnl transfer of os!-geii or whatel-er otlier actioii produces the disnpeeiiieiit is a function of the current, i. e. the l-oltaxe alone. -1cjiiaiititative test for the rediictioii in the forexoiiig ruiis \ra> rii:~le 1 ~ niial!.ziiig . all the soliitioiis for clilorid. T l i e iiietliotl first eiiiplo!~ed was l.)!. titratioii with sill-er nitrate, aiitl aiiiiiioiiiiiiii sulfoc!-auate. 1)otli I / I O aiid exactly eqiiivalent, ii.siiig ferric aiiiiiioiiiiiiii su1f:ite as indicator. Several tlifficiilties n e r r eiicoiiiiteretl nitli this iiietliod. Tlie titratioii iiiiist lie rapid as tlic indicator fades qiiicklj-. I t was also noticed that the c.xcesi of >il\.er iiitrate added seeiiird to change the eiicl-poiiit, thoiigli this eiitl-poilit \\-as at iio time clearl!- marked. So titratioii \\-as al~aiidoiiedand another iiirtliod resorted to. Tlii.: \vas to add a quaiitit!. of tlie silver iiitrate soliitioii to tlie soliitioii to 1)e
aiial>xed, to allow the soltitioil to cleat- and add sil\.er nitrate again, continuing this pi-ocess iiiitil one drop of sil\.er nitrate produced no cloud in a solittion nhicli has cleared coiiipletel!,. T h i s inethod proved iiiucli iiiore satisfactor!. a n d se\.eral portions of tlie saiiie solution aiial!,zed for a check agreed esactlj- whenever tried. T h e disad\-aiitage of this operation is the time it takes. T h i s inconvenience was 01-ercoiiie to a considerable degree h!. heating the solution cliiriiix tlie atialysis to xlioiit 7 5 ” C and also li!. sliakiiig tlie precipitate \.ioleiitl>. when foriiied. T h i s last ]vas accoiiiplished 11). eiiiplo!.itig a iiiacliiiie traiisforining rotational into reciprocatitig motion. 13~.tiiriiiiig a crank, a bottle coiitaiiiiiig tlie solution and precipitate, anti firmly attached to tlie reciprocating portion, \vas shaken violeiitl!. up and do\vii. I{!. using three burettes as tiiaii!- soliltions cotild lie aiinl>.zed at the same time, aiid tiine is s a \ d \vliich n o u l d otherwise lie lost iii n-aitiiig for the precipitate to settle after shaking. On analj-sis. 13). the first tiietliod liere, very siiiall qua1ititie.G of cliloricl Tvei-e found, though traces n-ere obser\-ed in all solutions, outer and inner. T h i s w a s to he expected, as tlie iiiasiiiiiiiii quaiitit!. of li!.drogeii utilized, I 2 cc, correspoiids to o.001 grain, \vliicli iiieaiis the formation of about 0.013 p-aiii of potassium clilorid. Tliis is iiiticli larger than the anal!.sii.i showed, in this iiistaiice 0.003 grani, Tvliicli kvould seein to indicate that four-fiftlis of tlie redtiction here \vas in the forination of potassium li!.poclilorite, aiid as a tiiatter of fact this latter salt, detected 11). the odor, ivas a l \ v ~ y spresent to soiiie extent. I n a11 cases, the iiiiier solutioti \vas clouded li!. the nitrate solution iiiore than the outer, but i i i t i o case did tlie efficieiic!. of the j.ielc1, i. e. the ratio of h>drogeiiutilized to the total hj-drogeii e\-ol\.ecl, rise a1ioL.e s i r perceiit. From this series of riiiis i t is e\-ideiit that liylrog-eti electrol!.ticall!- e\-ol\.ed lias little teiideiic!. at ordiiiar!. teiiiperatitres to reduce potassittiii chlorate.
TAI3I.K
I
.?ilknliiie cell Catliotic .\111]>
AI1:p
Ayerage cn1= Telrlp
I~ytlrogenev(ilwc1 Calc Ceil
l-oltalll
o,h:?
0 . io;,
,io"
620.
0.147
0.023
21
140.
0.0SCj
o.014
19
0.04Ci
0.00;
19
o.6;r 0.147
0.0s~
29"
620.
\i9,7.,i
61';..i
0.021)
21
140.
I.?,i.O
124.0
Ci.OS. at the ziiic cathode is apparent. TYitli the cadiiiiuni cathode this seems to 1iai.e little or 110 effect aiid oiie must asslime froiii this difference in lxha\.ior tliat tlie actioii of reduction in the zinc cell is different from tliat in tlie cadiiiiiiiii cell. T h i s inay be due to tlie foriiiatioii of zincate for n-liicli there is no correspondin:;. cadiiiiuiii salt. .is the surface of the zinc cathode \vas increased the zincate could more readily forin, for tlieii the K O H conld react more cliiiclil!. and before the sulfuric acid conld change it to K 2 S 0 4 . I t n i l 1 be observed tliat the increase in !.ield increases at a rapid rate as tlie xirreiit (leiisit>- decreases. I n attempting to f o l l o ~this effect further, in order to increase tlie surface of tlie cathodes, the sticks of zinc aiid catliiiium n.ere replaced by liollon c!-linders of the saiiie iiietals. 'Yo obtain these, casting \vas found necessar!-. T h e patterns \\.ere iiiade of lo\^ iiieltiiig paraffin. The>. were fornied melting- the paraffiii i t i a beaker of hot Ivater, oti the surface of ivliicli it floats i i i a liquid la>.er. In this a glass c!-liiider, kept as cool as possible is plunged aiid iiiimetIiatt.l>.u-ithdra\vii, a film of tlie paraffin solidifying 011 its surface. T h i s is repeated a iiiiniber of tiiiies until the layer of paraffiii is alioiit 0 . 2 cni. i i i thickness. T h e paraffiii is tlieii cut.
,ss
Ado@h L. 1 + g L
cent was obtained, and tlie fourth gal-e 47 percent. Froiii a fifth riiii at 60" iiistead of 65" wit11 a slightly higher current deiisitj-. both tencliiig to decrease j.ield, 42 perceiit was obtained. From these resnlts it is e\-icleiit t h a t casting had some effect on the outer ,surface of tlie 211, ~ l i i c l igradually \yore awaj.. Tliougli cast in cli-y sand \\-liicli had lieeii baked to inelt t h e ~iaraffiii,tlie surface n-as pi-obaljly cliilled to sniiie esteiit and resisted iiiucli iiiore tlie action of tlie acid, dne to the formation of siiialler crystals in tlie metal. Froiii tlie chip broken off of tlie c!.liiicler after tlie fifth riiii, this formation of small crj-stals near tlie siirface and larger oiies nitliiii \\-as still noticeable. T o test this effect iiiore tliorouglil!- two sticks of ziiic were ciit i n tivo pieces: one piece of each stick laid aside, and the otlier piece cast iii the same foriii. One of the pieces n-as cast in cold moist :and i i i order to harden ; the otlier in a liollo\v 111-asscylinder wliich was first cut loii~itudinallyand then the two halves joined and wrapped with asbestos and wire and heated. 1 he foriner nietliod, lion-ever, was found to produce a iniicli harder castiiig than the latter. T h i s coiild scarcely be clue to aiij- actioii of tlie hrnss in for1iiii.g ai1 nllo!-. as, i n ponriiig, the ziiic liad n-eldetl nitli the tirass, and, 011 reiiioviiig tlie lirass, a la!-er of zinc adliered to i t ? surface. Had ai1 alloy been forinecl. the teiideiic!. \\-auld ha\-e beeii to soften tlie casting. The results o1)taiiiecl \\-ere p r o h a l i l ~dne ~ to tlie different temperatiires of the ziiic lien poiiretl. Aipliotograpli, slion.iiig tlie effect of the differeiit conditions iiiider \\-liich tlie electrcdes were cast 011 the crystallization of tlie metal, ivas taken lxit is not reproduced iii this article.' Runs 1vei-e iiiatie ivitli these tv-o cast pieces and the tn-o 1111cast ones all iised as cathodes and aiiialgaiiiated, froin nhicli the folloIviiig- data n.erc olitaiiied : T.IBI,E117 f ?
.\~er;ige .Atiii> ~~
~~
~~
~
Yield
Kerlncerl yieltl
0.4235
0.032
64.,io
72.3
-,~,.6 -
I
0.42,Tj
0.029
0.40~?~i
0.02s
64.4 66.3
O.+0
