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An organic reagent for the volumetric determination of tin Boardman, Harold 1942-12-31

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An Organic Reagent f o r the "Volumetric D e t e r m i n a t i o n o f T i n  H a r o l d Boardman  A T h e s i s submitted i n p a r t i a l  fulfilment  of the requirements f o r the degree o f ,. MASTER OF ARTS  The U n i v e r s i t y of B r i t i s h Columbia A p r i l 1942  Foreword  The chemist i s o f t e n c a l l e d upon to perform a n a l y s e s which have i n t e r f e r e n c e s d i f f i c u l t t o overcome by inorganic- methods; the expanding f i e l d of the a p p l i c a t i o n of organic reagents t o i n o r g a n i c a n a l y s i s promises to overcome many o f these  difficulties.  T h i s work, • Intended, t o remove c e r t a i n i n t e r f e r e n c e s i n the a n a l y s i s of t i n , was done under the expert s u p e r v i s i o n of J . A l l e n H a r r i s , Ph.D., t o whom I wish to express my thanks. H. Boardman  T A B L E  OF  C O N T E N T S  Page A. General Theory o f Organic Reagents  1  B. Organic Reagents f o r T i n  2  C. Experimental Work (a) P r e p a r a t i o n of the Reagent (b) The Search f o r a V o l u m e t r i c Procedure 1. The Permanganate P r e c i p i t a t e  6 8 9  2. The Bichromate P r e c i p i t a t e  12  3. T r i p h e n y l n a p t h y l arsonium Shloride  15  4 . The T h i o s u l p h a t e P r e c i p i t a t e  IB  (c) The D e t e r m i n a t i o n of T i n  19  D. C o n c l u s i o n s and Suggestionf f o r F u r t h e r Work 20 E. B i b l i o g r a p h y  ,-  22  An Organic Reagent f o r the Y o l u m e t r i c D e t e r m i n a t i o n of T i n  General Theory o f Organic Reagents  Organic reagents are extremely u s e f u l i n the three f i e l d s of q u a n t i t a t i v e a n a l y s i s - g r a v i m e t r i c , v o l u m e t r i c , and c o l o r i m e t r i o d e t e r m i n a t i o n s - where t h e i r use supplants t e d i o u s o r i n a c c u r a t e i n o r g a n i c methods* Organic reagents which r e a c t w i t h o n l y one element are termed s p e c i f i c and reagents which r e a c t w i t h a l i m i t e d number o f elements are termed s e l e c t i v e .  Often a s e l e c t i v e  reagent may be made s p e c i f i c f o r a given element  ina  mixture by i n a c t i v a t i n g o t h e r components by means of a masking r e a g e n t . Feig|k (1,2) has done much i n c l a r i f y i n g the theory of the' a c t i o n of o r g a n i c r e a g e n t s .  By f a r the l a r g e s t  group  of o r g a n i c reagents are those t h a t form the s o - c a l l e d i n n e r complex compounds.  The a b i l i t y o f these reagents t o form  inner-complex s a l t s i s due t o  c e r t a i n s a l t forming  a c i d i c atomic groupings which are l a r g e l y : s u l p h o n i c (SO^H), s u l f i n i c ( S 0 H ) . c a r b o x y l , h y d r o x y l , s u l f h y d r y l (SH), 2  Oxime (N0H=J, and imine (= NH).  The hydrogen atoms are  r e p l a c e a b l e by one e q u i v a l e n t o f m e t a l .  1  The molecule must  be so c o n s t i t u t e d , however, that the metal may  also  coordinate  w i t h some other atom (thus s a t u r a t i n g the secondary of the m e t a l atom). sulphur.  The  valences  T h i s atom o f t e n i s oxygen, n i t r o g e n or  r i n g t h u s formed, c o n t r i b u t e s to the  stability  of the r e s u l t i n g compound. The important  s o l u b i l i t y of the compound i s , of  course,  i n g r a v i m e t r i c and v o l u m e t r i c a n a l y s i s .  Solubility  i s o f t e n i n f l u e n c e d by other atomic groupings present molecule.  i n the  In g e n e r a l , the s o l u b i l i t y i s g r e a t e r the more  s i m i l a r the molecules of the- s o l u t e and s o l v e n t are.  Thus  the presence of h y d r o x y ! groups i n the molecule i n c r e a s e s s o l u b i l i t y of a compound i n water.  The  the  s u l f o n i c a c i d group  has a l s o the a b i l i t y to b i n d water and hence i n c r e a s e  the  solubility. Another important the s o - c a l l e d "weighting the molecular  p o i n t as r e g a r d s s o l u b i l i t y i s  effect".  In g e n e r a l , the  weight the l e s s i s the s o l u b i l i t y .  Evidently  i n s o l u b i l i t y should be as great as p o s s i b l e s i n c e i n c r e a s e s the  greater  this  sensitivity.  Organic Reagents f o r T i n  The  experimental  work c o n s i s t e d of a search f o r a  volumetric method f o r t i n t h a t would be a c c u r a t e , q u i t e r a p i d , and a p p l i c a b l e to the a n a l y s i s of o r e s , e t c *  The  existent  methods f o r t i n depend upon the o x i d a t i o n faromtthesstannous to the s t a n n i c c o n d i t i o n .  Controversy  has c e n t r e d around the  i n i t i a l r e d u c t i o n of t i n and the q u e s t i o n o f a i r o x i d a t i o n . V a r i o u s r e d u c i n g agents have been used, among the l a t e s t being powdered an'imony or. aluminum.  With powdered antimony  i t i s u s u a l to b o i l the s o l u t i o n , which has a h i g h a c i d 'concentration,, f o r f o r t y - f i v e minutes to ensure complete reductions  A i r o x i d a t i o n e x e r c i s e s a c o n s i d e r a b l e e f f e c t on t  the t i t r a t i o n .  Apparatus has been d e v i s e d f o r the e x c l u s i o n  of a i r by CO ( 3 ) . Another method i n use i n many l a b o r a t o r i e s i s t o reduce the t i n i n a l a r g e Erlenmeyer, add s o l i d NaHGOg, to the a c i d s o l u t i o n , cork and c o o l .  A f t e r the f l a s k i s c o o l  the cork i s removed and the s o l u t i o n i s t i t r a t e d as r a p i d l y as p o s s i b l e w i t h an i o d i n e s o l u t i o n of s u i t a b l e c o n c e n t r a t i o n . Blanks.have to be r u n a l s o .  D i s c r e p a n c i e s sometimes o c c u r ,  which are undoubtedly due t o the method o f r e d u c t i o n o r t h e e f f e c t of a i r o x i d a t i o n . A method f o r d e t e r m i n i n g t i n - i n , the s t a n n i c c o n d i t i o n wofild be f r e e o f both these e r r o r s . There i s no method f o r the v o l u m e t r i c d e t e r m i n a t i o n o f t i n i n the s t a n n i c c o n d i t i o n by i n o r g a n i c r e a g e n t s . Cupferron w i l l p r e c i p i t a t e t i n ( 4 ) . A 10% s o l u t i o n of c u p f e r r o n i s added; w i t h v i g o r o u s ' s t i r r i n g t h e ; p r e c i p i t a t e becomes compact and b r i t t l e (50-45 min.).  With i t ,  tetra-  v a l e n t t i n can be separated from a r s e n i c and antimony i n a c i d s o l u t i o n ( 6 ) . H i l l e b r a n d and L u n d e l l ' s book covers the uses of c u p f e r r o n . A v o l u m e t r i c method f o r the d e t e r m i n a t i o n of s m a l l amounts o f t i n i n ores has been developed  by A l i m a r i h and  S.M.Peuzner ( 5 ) . T h i s i s based upon the r e d u c t i o n and  4  decomposition o f methyl orange by t i n i n a c i d s o l u t i o n t o s u l f a n i l i c a c i d and dimethyl-P-phenylenediamine.  The t i n i n  a 15-20fo HC1 s o l u t i o n i s heated f o r 50-60 minutes i n a GOg atmosphere and then t i t r a t e d w i t h 0.01 o r 0.05% s o l u t i o n of methyl-orange. interfere.  Sb, As, B i , Cu, Cd,.Pb, Fe do n o t .  T i , V, Mo, and I do. A e o l o r i m e t r i c method f o r d e t e r m i n i n g t i n has been  worked on by R.E.D.Glark (7).- The method uses s u b s t i t u t e d 1:2 dimercapto benzenes.  The unknovm s o l u t i o n i s d i l u t e d  a f t e r a d d i t i o n of a drop o f t h i o g l y c o l l i c a c i d u n t i l the conc e n t r a t i o n of t i n l i e s between 1.5 and 6 p.p.m.  A standard  s o l u t i o n o f t i n . c o n t a i n i n g about 10 p.p.m. t o g e t h e r w i t h about 0.2 g. o f t h i o g l y c o l l i c a c i d p e r l i t e r i s d i l u t e d i n a measuring c y l i n d e r u n t i l a c o l o u r match i s o b t a i n e d i n the f o l l o w i n g manner.  Two t e s t tubes c o n t a i n i n g  identical  volumes (5-10 ml.) o f the two s o l u t i o n s a r e t r e a t e d w i t h 0.5 cc o f HG1 f o l l o w e d by an equal q u a n t i t y o f 4 - c h l o r o - l : 2 d i mercaptobenzene  i n a 2% S o l u t i o n of NaOH.  T h i s causes the  p r e c i p i t a t i o n of a white suspension of the mercaptan.  The  tubes are. immersed i n ' b o i l i n g water f o r 10 sec. b f t w h i c h time the p i n k c o l o u r has developed f u l l y and the two c o l o u r s a r e compared d i r e c t l y by r e j e c t e d l i g h t .  Accuracy «• 10$.  S a l t s o f Fe may i n t e r f e r e a t or above 2$. The p r e p a r a t i o n of t h e reagent i s g i v e n ( 8 ) . Another c o l o r i m e t r i c method f o r t i n i s a m o d i f i c a t i o n o f the molybdenum blue method recommended by F e i g t ( 9 ) . M  The method was developed by B". S t r a f f o r d (ID). The t i n i s  5  reduced  t o the stannous c o n d i t i o n by b o i l i n g the a c i d i f i e d  a o l u t i o n w i t h a l i t t l e aluminum i n an atmosphere o f COg. To the cooled s o l u t i o n i s added an a c i d molybdate s o l u t i o n , and a f t e r standing a minute a measured amount of amyl a l c o h o l (10 ml) is*added;  t h i s e x t r a c t s the whole o f the blue  c o l o u r e d compounds.  The amyl a l c o h o l s o l u t i o n i s separated; made  at t h i s stage i t i s s l i g h t l y t u r b i d , but may be/quite b r i g h t by the a d d i t i o n o f 1 ml o f e t h y l a l c o h o l . i s then measured i n the Lovibond  The blue s o l u t i o n  Tintometer  Gacotheline i s used f o r the d e t e c t i o n of t i n only (11).  The t e s t s o l u t i o n i s made a l k a l i n e w i t h NaOH and  r e d u c i n g agents are removed.  Then i n a c i d s o l u t i o n c a c o t h e l i n e  g i v e s a p u r p l e c o l o u r which i s e a s i l y d e s t r o y e d by a i r oxidation. A few other o r g a n i c reagents f o r t i n a l s o e x i s t . I n p a s s i n g i t might be w e l l t o mention a method f o r s e p a r a t i n g s t a n n i c oxide (the u s u a l form i n which t i n occurs i n ores) from v a r i o u s other o x i d e s ( 1 2 ) . furnace i s r e q u i r e d , the temperature t r o l l e d to. w i t h i n 5 degrees.  An e l e c t r i c  crucible  of which can be con-  H e a t i n g SnOg w i t h HH^I a t about  425° C a f f o r d s a means of s e p a r a t i n g the SnOg from the F e 0 2  and GuO which a r e t h e common SnOg -v 4MH I 4  -s> S n l  4  3  contaminants: 4-  A. method which promised  4HH -V- 2HgO 3  a means o f d e t e r m i n i n g t i n i n  the s t a n n i c c o n d i t i o n w i t h p o s s i b l e a p p l i c a t i o n to ores e t c . was g i v e n by W i H a r d and Smith (13)* c h l o r i d e i s the r e a g e n t .  Tetraphenyl  arsonium  T h i s i s an o r g a n i c iiba^iarI s i m i l a r to  the organic ammonium liases such as t e t r a e t h y l ammonium hydroxide.  The phenyl groups, o f course, g r e a t l y weaken i t s  b a s i c p r o p e r t i e s , but i t i s q u i t e s o l u b l e i n water and w i l l combine w i t h the complex m e t a l l i c a c i d s o f mercury, z i n c , cadmium, bismuth and t i n , as w e l l as many other radicles.  inorganic  I n other words, i t i s by no means a s p e c i f i c  reagent but r a t h e r a reagent which i s s e l e c t i v e f o r c e r t a i n a c i d i c groups.  I t s a p p l i c a t i o n t o the a n a l y s i s o f t i n w i l l  depend upon the method o f g e t t i n g t i n i n t o s o l u t i o n whereby i n t e r f e r i n g elements are absent.  The r e s e a r c h i n t h i s  l a b o r a t o r y was concerned w i t h t h i s reagent and another s i m i l a r d e r i v a t i v e t h a t was prepared.  E x p e r i m e n t a l Work  P r e p a r a t i o n o f the Reagent The method used f o r t h e p r e p a r a t i o n of the reagent wa's  that of B l i c k e , .WiHard and Taras (14).  t r i p h e n y l a r s i n e was obtained  Commercial  from Eastman and from t h i s  t r i p h e n y l a r s i n e oxide was made (15).  The t r i p h e n y l a r s i n e  (20 g.) i s d i s s o l v e d i n an excess o f g l a c i a l a c e t i c a c i d . T'tisn bromine i s added (14g.) s l o w l y and w i t h s t i r r i n g . Concentrated  NH4OH  i s then added s l o w l y i n e x c e s s , u n t i l the  t r i p h e n y l a r s i n e h y d r o x i d e has p r e c i p i t a t e d .  This i s f i l t e r e d  on a Buchner f u n n e l and washed w i t h water; the p r e c i p i t a t e i s d i s s o l v e d w i t h warming i n t h e s m a l l e s t p o s s i b l e amount of e t h y l a l c o h o l and r e p r e c i p i t a t e d by adding an excess o f water,  whereby f i n e white c r y s t a l s o f the h y d r o x i d e are o b t a i n e d . These are d e s s i c a t e d i n vacuo over c o n c e n t r a t e d s u l p h u r i c a c i d f o r s e v e r a l days whence water i s l o s t , l e a v i n g t r i p h e n y l arsine oxide. (C H ) As 6  5  3  -v Br 2  (C H ) AsBr 6  5  3  2  (G H ) As(0H) 6  5  3  —»  (C H ) AsBr  -s- 2NH 0H 4  2  6  5  3  2  2NH Br + (C H5 ) As(0H) 4  6  -> H 0 + (G Hg) As = 2  6  Then phen$tlmagnesium  3  3  0  bromide i s made from 15g o f Mg,  68 c c . of bromobenzene and 300 c c . o f dry ether i n a l i t e r f l a s k equipped w i t h a r e f l u x condenser and s t i r r e r .  After  r e a c t i o n i s complete ( s t a r t e d by adding a l i t t l e i i o d i n e and warming) 500 c c . o f d r y benzene i s poured i n and 60 g. o f t r i p h e n y l a r s i n e oxide, i s added, a l i t t l e a t a time (over f o u r hours) w i t h s t i r r i n g .  Then s t i r r i n g i s c o n t i n u e d f o r three  more hours u n t i l a l l the o x i d e has d i s a p p e a r e d . The ether-benaene l a y e r i s decanted o f f from the v i s c o u s o i l and $ 500 c c . o f water i s added s l o w l y w h i l e t h e oil  i s s t i r r e d with a s t i r r i n g rod.  t  A f t e r thorough t r i t u r a -  t i o n abopt 150 c c . o f cone. HG1 a r e added u n t i l a l l the white s o l i d t h a t appears d i s s o l v e s .  The m i x t u r e i s a l l o w e d t o , s t a n d  u n t i l the o i l on the bottom has c r y s t a l l i z e d . filtered.  This i s  The f i l t r a t e i s n e u t r a l i z e d w i t h NaOH and a l i t t l e  NaCl i s added t o r e c o v e r any t e i r a p h e n y l arsonium c h l o r i d e i n solution.  The crude t e t r a p h e n y l arsonium c h l o r i d e i s p u r i f i e d  by d i s s o l v i n g i n 800 c c . o f hot water and a d d i n g 150 g. N a C l , c o a l i n g and f i l t e r i n g .  8  GgHgBr -v Mg  G H MgBr 5  5  C H MgBr v ( G H ) A s = 0 6  5  6  5  ( C g H ) A s - 0 - MgBr  3  5  ( G H ) A s - 0 - MgBr + HOH 6  5  4  ( G H ) A s O H + HGl 6  5  4  HgO  4  ~ M C g H ) As0H 4- MgBr OH 5  4  +• ( C g H ) A s C l 5  I n the l a t e r work a new  4  d e r i v a t i v e was prepared  t r i p h e ' n y l j n a p t h y l arsoniumn c h l o r i d e .  -  T h i s was made i n e x a c t -  l y the same manner - except that n a p t h y l magnesium bromide was' used i n s t e a d of phenylmagnesium bromide. (The same molar p r o p o r t i o n s were used.) The Search f o r a v o l u m e t r i c Procedure Although t e t r a p h e n y l arsonium c h l o r i d e p r e c i p i t a t e s w i t h t i n , some method of determining i s necessary.-  the reagent v o l u m e t r i c a l l y  The reagent g i v e s p r e c i p i t a t e s w i t h i o d i n e  ( i n presence of k l ) , molybdate, diohromate, permanganate and other ions:.  W i l l a r d and Smith used i o d i n e to determine the  reagent, a p o t e n t i o m e t r i c t i t r a t i o n being employed.  The  p r e c i p i t a t e i s of a r u s t y brown c o l o u r , d i f f i c u l t to f i l t e r ; i t s composition (G H ) As 6  n  5  5  4  shows i t to be the p e r i o d i d e : +  I  G  + I  (C H ) AsI 6  5  4  3  - 10 ml. of the water s o l u t i o n (0.01 - 0.03  M)  are  measured and d i l u t e d to n e a r l y 100 c c . w i t h water or s a t u r a t e d NaGl s o l u t i o n .  The r e f e r e n c e and i n d i c a t o r e l e c t r o d e s are  immersed i n t h i s s o l u t i o n w h i l e standard i o d i n e s o l u t i o n of about the same c o n c e n t r a t i o n c o n t a i n i n g 6 - 8 added s l o w l y w i t h constant  stirring.  g.KI / l . i s  As the i o d i n e i s added  9  the p o t e n t i a l decreases to a min. v a l u e .  When t h i s minimum  i s reached the i o d i n e i s added dropwise and  time a l l o w e d f o r  the system to reach e q u i l i b r i u m . When an e q u i v a l e n t q u a n t i t y of i o d i n e has been added, there i s a sudden i n c r e a s e i n p o t e n t i a l . * Near the' end p o i n t the s o l u t i o n must be  completely  s a t u r a t e d with s a l t before the t i t r a t i o n i s completed." I n a t e s t of t h i s t i t r a t i o n the E.^.F. dropped to a minimubYand stayed t h e r e .  I t was not v e r y a p p l i c a b l e to  the d e t e r m i n a t i o n of any range of reagent; t h i s was method i n v e s t i g a t e d f o r t i t r a t i n g the reagent.  the only  Three r e a c t i o n s  were s t u d i e d : w i t h KMnO , K C r 0 , and NagSgO^. 2  2  7  The •Permanganate Prec i p i t a t e Tetraphenyl  arsonium permanganate i s a dark r e d  i n s o l u b l e s a l t which removes any p o s s i b i l i t y of t i t r a t i n g reagent w i t h KMn0 u s i n g an i n d i c a t o r . 4  The  the  p r e c i p i t a t e forms  i n n e u t r a l or a c i d s o l u t i o n s , but not i n b a s i e s o l u t i o n s , p o s s i b l y because of the f o r m a t i o n of t e t r a p h e n y l arsonium a .7  hydroxide.  Tjie pure s a l t i n water g i v e s a Ph of fe§ showing  t h a t h y d r o l y s i s takes p l a c e .  Below i s l i s t e d a t a b l e of the  p r o p e r t i e s of the p r e c i p i t a t e . P r o p e r t i e s of (CgHg^AsMnO^ 1. Ph of a s a t u r a t e d s o l u t i o n 2. F a i r l y s o l u b l e i n a s o l u t i o n made a c i d w i t h a c e t i c . 3. I n s o l u b l e i n a b o v e . s o l u t i o n i f NH^Cl i s p r e s e n t . • 4 . I n s o l u b l e i n a s o l u t i o n made b a s i c w i t h NH^OH (once formed). Decomposes upon b a i l i n g . 5. S e n s i t i v i t y - w i l l not p r e c i p i t a t e w i t h l e s s than 3 ml. of  10 of 0.01 M. reagent i n a volume of 60 m l . 6. The p r e c i p i t a t e d i s s o l v e s t o a c l e a r s o l u t i o n when b o i l e d w i t h a s o l u t i o n o f sodium o x a l a t e a c i d i f i e d w i t h H S 0 . g  The  4  l a s t mentioned p r o p e r t y ©an be used t o d e t e r -  mine t h e reagent p r o v i d e d adequate p r e c a u t i o n s are taken w i t h r e s p e c t to r e a c t i o n o f permanganate w i t h H61 and organic matter. To determine  the composition o f the p r e c i p i t a t e  an excess of standard KMnQ^ s o l u t i o n was added t o 5 m l . o f reagent.  The p r e c i p i t a t e was f i l t e r e d through a weighed  gooch c r u c i b l e and washed w i t h water. the f i l t r a t e was determined solution.  The excess KMnO i n  w i t h a standard sodium o x a l a t e  R e s u l t s are t a b u l a t e d f o r d u p l i c a t e samples. N o r m a l i t y o f K 3 I n ^ = ^ . 101 "  " Na C 0 2  2  4  - 0.307  .  Volume of reagent i n each ease was;.5 ml;, t o which 10 m l . o f KMh0  4  were added.  5 ml. of Na Gg0 2  4  s o l u t i o n was  added t o the f i l t r a t e and the excess Na 0 0 back t i t r a t e d / 2 2 4 w i t h KMn0 . 4  .1. EMn0 back t i t r a t i o n - 9.4 m l . 4  Weight o f p r e c i p i t a t e =0.0375 g. 2. KMn0  4  back t i t r a t i o n = 9^4-ml.  Weight of p r e c i p i t a t e =0.0365 g. Assuming the composition o f the p r e c i p i t a t e to be ( G H ) A s M n 0 , weight of p r e c i p i t a t e c a l c u l a t e d 6  5  4  4  Percentage  s  0.0424 g.  e r r o r - 11.5%, p r o b a b l y a r i s i n g from the  e x p e r i m e n t a l c o n d i t i o n s , ( W a t e r was used f o r washing i n which  11  the p r e c i p i t a t e i s a l i t t l e s o l u b l e due to hydrolysis,,) Since the s e n s i t i v i t y of the p r o c e s s i s n o t very g r e a t i t was abandoned. Hbte that h y d r o l y s i s of the s a l t can take p l a c e because t e t r a p h e n y l arsonium hydroxide i s a weak, and, i n the presence of NaOH, a somewhat i n s o l u b l e base.  An attempt  was made to f i n d the approximate s t r e n g t h o f the base: KB  = &G6H5)4As]  [OH]  [(C H ) AS0H} 6  5  -  4  I n the h y d r o l y s i s of the c h l o r i d e we (C H ) As 6  5  4  +. H 0  II*  ( C H ) AsOH -V-  2  6  -  KH-  5  4  rtG6H5) AsOH} [ l l ] [(C6H ) As-»J 4  "  KB  have:  5  K H - — 1 - h  4  where h  degree of h y d r o l y s i s  Gh=£H*} =  |I.C H ) ASGH] §  5  4  which  can be found by measuring the Pg of. the s o l u t i o n . KH  ^  III G  4  -£H 3  0.3355 g. o f pure t e t r a p h e n y l arsonium c h l o r i d e was weighed and d i s s o l v e d i n e x a c t l y 80 ml. of water t o make a 0.01 m o l a l s o l u t i o n .  The  >*• U *"3 ~ ' H  KH„  2 24  x  of t h i s s o l u t i o n was  10  "  6  5.02 X l O ^ 0.0& - 2.24 X  3  0.647 I 10  - 3  10"  5  2.65,  The Piohrornate P r e c i p i t a t e TetEa phenyl arsenium c h l o r i d e g i v e s a y e l l o w f l o c e u l e n t p r e c i p i t a t e w i t h potassium dichromate i n a c i d solution.  The Pg of water c o n t a i n i n g the dichromate i s 1.5  showing t h a t c o n s i d e r a b l e h y d r o l y s i s takes p l a c e .  The  p r e c i p i t a t e i s p r a c t i c a l l y insoluble i n a c i d s o l u t i o n at o r d i n a r y temperatures s i n c e the f i l t e r e d s o l u t i o n t h a t has been i n c o n t a c t w i t h the s o l i d f o r some time g i v e s no p r e c i 4  p i t a t e w i t h Pb "  i n acetic acid solution.  However, f e r r o u s  ammonium sulphate completely d i s s o l v e s the p r e c i p i t a t e i n a s o l u t i o n a c i d i f i e d w i t h HGl, showing that t h e r e are enough G±g0  7  i o n s i n s o l u t i o n to a l l o w t h i s r e a c t i o n to go on.  Furthermore, the p r e c i p i t a t e i s completely temperature o f b o i l i n g water. . The composition  s o l u b l e a t the  • '  o f the p r e c i p i t a t e i s  as shown by the f o l l o w i n g r e s u l t s . of the dichromate was prepared decantation.  Some  and washed t h o r o u g h l y by  The p r e c i p i t a t e was d r i e d and 0.1 g. weighed.  T h i s was d i s s o l v e d i n b o i l i n g water, a c i d i f i e d w i t h a c e t i c a o i d and t r e a t e d w i t h l e a d a c e t a t e . ; Weight of P b C r 0 = 0.0666- g. 4  T h e o r e t i c a l weight of C r 0 2  Experimental  - 0.1 X 216.02 646.44  7  =  0.022 g.  weight o f C r 0 = 0.0666 X 216.02 - 0.022 646.44 2  7  13  The dichromate i s i n s o l u b l e whereas the chromate i s s o l u b l e at o r d i n a r y temperatures.  Making the s o l u t i o n b a s i c  immediately d i s s o l v e s the p r e c i p i t a t e by forming the chromate ion and removing the t e t r a p h e n y l arsonium i o n from s o l u t i o n as hydroxide". To determine the reagent w i t h potassium dichromate a direct titration  o r a d e t e r m i n a t i o n o f excess dichromate  a f t e r f i l t e r i n g o f f the p r e c i p i t a t e can be used. f i l t e r i n g i s to be avoided. a method f o r t i t r a t i n g  I f possible,  An attempt was made t o develop  the reagent d i r e c t l y .  The i n d i c a t o r  f i r s t s e l e c t e d c o n s i s t e d o f one or two m l . of a 1% K I s o l u t i o n a l o n g w i t h s t a r c h s o l u t i o n , t h e ' i d e a being t h a t when an excess o f G^gG^  i o n s were p r e s e n t these would s e t  f r e e I g from the K I , thus g i v i n g the s t a r c h b l u e end p o i n t * The K I had t o be a weak s o l u t i o n , otherwise I  g  was s e t f r e e  before the end p o i n t and t e t r a p h e n y l arsonium p e r i o d i d e was p r e c i p i t a t e d , ' A s a t u r a t e d NaCl s o l u t i o n seemed t o be necessary and a c c u r a t e c o n t r o l o f the a c i d c o n c e n t r a t i o n . The volume o f the s o l u t i o n had to be kept down t o a minimum. The f o l l o w i n g t a b l e shows some t i t r a t i o n ( M o l a l i t y of reagent approx. of Rea£jent K C r 0  Vol.  s  1 ml 2 2  3 3 4  rr  » ii it it  2  7  t e s t s that„were made.  0.01).  t i t e r Vol.  No p r e c i p i t a t e 1.3 m l . 1.3 «  of  Reagent K C r 0 2  5 ml. 6 " 6  »  2.2  "  7 "  2.2 2.8  «! "  10 !»  9  "  2  7  titer  4 . 0 ml. 4.0 n  4.9 6.2 6.6  7.3  t, ri it it  14  Although r e s u l t s are r e p r o d u c i b l e , the t i t r a t i o n f o r h i g h e r volumes becomes h i g h e r showing t h a t a blank would have to be s u b t r a c t e d ; c a r e f u l c o n t r o l o f PH i s a l s o necessary.  W i t h h i g h e r volumes o f reagent the y e l l o w c o l o u r  of the highly  f l o c c u l e n t p r e c i p i t a t e completely obscures the  end point» A redox i n d i c a t o r was t r i e d - o r t h o and.also diphenylamine.  phenanthfoline  The same d i f f i c u l t y was found.  Blank d e t e r m i n a t i o n s were made w i t h O-phenanthtoline a t d i f f e r e n t BaGl and HOI c o n c e n t r a t i o n s .  The b l a n k v a r i e s  with both these c o n c e n t r a t i o n s from 9.3 t o 2.6 m l . o f dichromate s o l u t i o n .  With these d i f f i c u l t i e s i n view the.  process was abandoned. T i t r a t i o n of excess It Or 0_ w i t h f e r r o u s ammonium 2 e~- I sulphate c o u l d be used, but the f i l t r a t i o n of the p r e c i p i t a t e i s tedious.  Shown below are two s t a n d a r d i z a t i o n s o f the  reagent Using t h i s method.  The p r e c i p i t a t e i s washed w i t h  water c o n t a i n i n g HOI. 1 ml. FeS0  4  -  ><t  .58 m l . K C r 0 2  2  7  1. 5 m l . o f reagent; 7.1 m l . o f K 0 r 0 2  Excess K C r 0 7 2  g. 10 a  2  2  added.  7  - 4.7 X *58 = 2.7 m l .  ,\ 4.3 m l . r e a c t e d .  2. 10 ml o f reagent; 14.0 m l . o f K C r G 2  Excess K C r 0 2  .%  2  7  -  9.5  2  7  X .58 — 5 . 5 m l .  8.5 m l . r e a c t e d .  15  The  only p r a c t i c a l a p p l i c a t i o n would be  s m a l l amounts of dichromate g r a v i m e t r i c a l l y .  determining  Two cases are  c i t e d to show the r e p r o d u c i b i l i t y of r e s u l t s .  To 5 ml. of  Reagent i n a volume of 60 ml. c o n t a i n i n g NaCl and HOI excess of K - C r 0 g  2  7  was  an  added w*tk the p r e c i p i t a t e was  filtered  and washed. 1. Weight of p r e c i p i t a t e , 2. Weight of p r e c i p i t a t e T r i p h e n y l n a p t h y l arsonium  - 0.0700 g. -  0.0704 g.  chloride  A t t h i s stage of the r e s e a r c h i t was decided t r y to prepare a reagent of d i f f e r e n t s t r u c t u r e  to  to see what  e f f e c t i t would have upon the p r e c i p i t a t e s mentioned.  The  p r e p a r a t i o n o f t h i s d e r i v a t i v e has a l r e a d y been d e s c r i b e d T r i p h e n y l n a p t h y l arsonium c h l o r i d e forms a p r e c i p i t a t e w i t h dichromate s i m i l a r to the t e t t a p h e n y l . d e r i v a t i v e , except t h a t once c r y s t a l l i z e d i t i s not  readily  s o l u b l e i n b a s i c s o l u t i o n , nor w i t h . f e r r o u s ammonium sulphate in acid solution.  I t d i s s o l v e s i n b o i l i n g water,  the dichromate g i v e s a P H of 3.2 tetraphenyl d e r i v a t i v e .  as compared to 1.5  Hence the n a p t h y l i s l e s s  i n water, f o r the hydrolyzed.  The•permanganate p r e c i p i t a t e of the n a p t h y l d e r i v a t i v e i s a l s o s i m i l a r to t h a t of the t e t r a p h e n y l d e r i v a t i v e . i t g i v e s a PH of 4.5 derivative.  as compared to 2.7  F u r t h e r work; Mas  f o r the  s i t i o n of t h i s new  tetraphenyl  c a r r i e d out w i t h the  d e r i v a t i v e , because of i t s g r e a t e r s e n s i t i v i t y .  In water,  The  napthyl compo-  reagent has not been determined; i t i s  16  j u s t assumed that the s t r u c t u r e i s t h a t given^because of the method of p r e p a r a t i o n . The T h i o s u l p h a t e P r e c i p i t a t e I t had been observed that sodium t h i o s u l p h a t e completely  d i s s o l v e d t e t r a p h e n y l arsonium p e r i o d i d e l e a v i n g  a white p r e c i p i t a t e i f excess t h i o s u l p h a t e was added.  The  t h i o s u l p h a t e p r e c i p i t a t e o f the new d e r i v a t i v e was i n v e s t i gated.  T h i s i s a white c r y s t a l l i n e s a l t , formed i n s l i g h t l y  a c i d s o l u t i o n but q u i t e i n s o l u b l e even i n b a s i c s o l u t i o n once formed.  H a l f a ml. each o f 0.005 11 N a S g 0 and reagent w i l l g  3  give a p r e c i p i t a t e i n 60.ml. o f s o l u t i o n . d i s s o l v e even i f the s o l u t i o n i s b o i l e d .  T h i s w i l l not Water that has been  i n c o n t a c t w i t h the s a l t f o r some time w i l l not d e c o l o r i z e a l i t t l e very weak i o d i n e s o l u t i o n which confirms insolubility.  i t s complete  A l s o , i n w a t e r t h i s s a l t g i v e s a PH o f 7 s  showing that no h y d r o l y s i s tkkes p l a c e . T h i s l e d t o an exact method f o r t i t r a t i n g t h e reagent.; The i d e a was t o add an excess o f Ha. S O  solution  C> £i Q  ^  to a g i v e n volume of reagent and back t i t r a t e w i t h an I s o l u t i o n , u s i n g s t a r c h as an i n d i c a t o r . experiments gave the f o l l o w i n g r e s u l t s :  Preliminary  g  17 l..:ml. I .  1.1 m l . NagSgOg V o l . Of Reagent  Total v o l . .of S o l n .  5 10 . 20 10 ( I 20  100 m l . 200 ml.  ml ml ml ml ml  V o l . of , I . NapSoO^ •• 5 8 5 5 5  Titer  ml ml ml ml ml  3.8 5.6 1. 3 2.8 1.0  N a  ml ml ml ml ml  S  2 2°3 Reacted 0.8 1.8 3.6 1.9 3.7  ml ml ml ml ml  The t a b l e shows the r e p r o d u c i b i l i t y o f r e s u l t s and t h a t the method i s q u i t e q u a n t i t a t i v e . To i n v e s t i g a t e the c o n d i t i o n s necessary f o r t i t r a t i o n the potentiometer was used.  I t was found t h a t  when an excess o f NagSgOg was added i t took a l i t t l e time f o r E t o come to a steady value - corresponding to the time necessary f o r the completion of r e a c t i o n . to f i f t e e n minutes u s u a l l y .  Then as the I  This took from t e n g  s o l n . i s added  the. E drops s l o w l y , u n t i l at the end p o i n t i t drops q u i t e r a p i d l y . , An example i s g i v e n : 8 ml o f t h i o s u l p h a t e were added to 5 ml o f reagent and when I? was steady the s o l u t i o n was t i t r a t e d w i t h 12 s o l n . ( a u t o m a t i c a l l y s t i r r e d ) . IVol. o f I 1  1  0 ml' 0.2 ml 0055 " 0.7 '« 0.8 " 1*0 » 1.2 »  0  V o l . o f I-j, ' •. :  . E . 3.4 3.7 3.8 3.85 3.90 • 3.90 3.85  1.4 m l . 1.5 " 1.7 •« 1.8 " •1.9 »» 2 2 2.3 " 9  E.  '•3.8 . • 3,72 ••! 3.62 3.60 . 3.55 2.9 drops r a p i d l y  The t i t r a t i o n was c a r r i e d on f a i r l y s l o w l y i n the above d e t e r m i n a t i o n .  F u r t h e r t i t r a t i o n s were made u s i n g  the potentiometer and having the s t a r c h i n d i c a t o r i n s o l u t i o n a t the same time.  The r e s u l t s are as f o l l o w s :  5 ml. of. r e a g e n t , 8 ml. of t h i o s u l p h a t e I n d i c a t o r end p o i n t - 5.7 ml. t h i o s u l p h a t e r e a c t e d . Potentiometer  end p o i n t  "  n  "  2. 6 ml. of r e a g e n t , 10 ml. of t h i o s u l p h a t e Indicator  end p o i n t - 7 ml. t h i o s u l p h a t e  • Potentiomenter  n  n  - 6.9  "  "  reacted "  3. 10 ml. of reagent, 15 ml. of t h i o s u l p h a t e Indicator  end p o i n t - 11.4  Potentiometer .'  The  "  "  -  "  ml. r e a c t e d "  B  end p o i n t appears q u i c k l y but does not  very l o n g , probably  due  last  to a d s o r p t i o n o f Ig from s o l u t i o n  by the p r e c i p i t a t e ; 0.1 ml. w i l l r e s t o r e the c o l o u r . JHirther t e s t s u s i n g 0.005 N s o l u t i o n s of N a S g 0 g  3  and Ig showed t h a t to get best r e s u l t s the t h i o s u l p h a t e must be added drop by drop w i t h automatic s t i r r i n g . ml. of HG1. and a l i t t l e NaCl must be  Two  or  three  present.  With l a r g e r volumes of reagent l e s s t h i o s u l p h a t e appears to r e a c t w i t h the reagent.  T h i s i s probably  because  too l a r g e a volume of i o d i n e i s used because of a d s o r p t i o n . The f a d i n g end p o i n t would seem to c o n f i r m t h i s ;  the  a n a l y s i s of t i n s o l u t i o n s g i v e s the same r e s u l t s ( q . v . ) . The 101m P r e c i p i t a t e Both d e r i v a t i v e s used g i v e a white c r y s t a l l i n e p r e c i p i t a t e w i t h t i n , p r o v i d i n g the s o l u t i o n i s s a t u r a t e d w i t h NaCl and c o n t a i n s a l i t t l e HCl.  The purpose of the  N a C l i s to form sodium c h l o r o s t a n n a t e  and keep the r e s u l t i n g  t e t r a p h e n y l arsonium c h l o r o s t a n n a t e  (or t r i p h e n y l n a p t h y l  19  arsonium c h l o r o s t a n n a t e )  i n s o l u b l e . The -pmepose of the HOI  i s t o prevent h y d r o l y s i s . inv;water.  .  The p r e c i p i t a t e s s l o w l y d i s s o l v e  '  Tin Determination W i l l a r d and Smith g i v e the d i r e c t i o n s f o r p r e c i p i t a t i n g t e t r a p h e n y l arsonium c h l o r o s t a n n a t e a s :  "2 c c . o f  HC1 and enough NaGl are added to give a 2.5 to 3,0 M conc e n t r a t i o n of NaGl i n a f i n a l volume of 60 M l . "  I t was  found that the t e t r a p h e n y l arsonium c h l o r i d e would not g i v e a p r e c i p i t a t e w i t h I mg. o f t i n under these c o n d i t i o n s but t h a t the new d e r i v a t i v e d i d .  Furthermore the s o l u t i o n must  be s a t u r a t e d w i t h NaGl and i n washing the p r e c i p i t a t e a s a t u r a t e d s o l u t i o n o f NaGl must a l s o be used. A t i n s o l u t i o n was made by d i s s o l v i n g t i n i n HG1 and complete e x i d a t i o n t o the s t a n n i c c o n d i t i o n was ensured. T h i s was s t a n d a r d i z e d w i t h an i o d i n e s o l u t i o n and found t o c o n t a i n .9 mg. of t i n p e r 10 m l .  A g i v e n volume of the t i n  s o l u t i o n was measured, one or two m l . o f HC1 added and the s o l u t i o n was made up to 60 ml. and s a t u r a t e d w i t h N a C l .  The  s o l u t i o n s t e s t e d below were allowed t o stand f o r an hour or two, a f t e r a d d i t i o n o f an excess o f reagent,, then f i l t e r e d  through  number 40 Whatman and washed w i t h s a t u r a t e d NaCl u n t i l f r e e of r e a g e n t , ( t e s t i n g f i l t r a t e w i t h I g s o l n . ) .  The p r e c i p i t a t e  was washed w i t h a stream o f water from a wash b o t t l e i n t o a 150 m l , beaker.  A few ml. o f HGl and a l i t t l e NaGl were  added then a measured volume o f NagSgOgw^nej* by drop, w i t h stirring.  The excess Na2S20g was then back t i t r a t e d  with  21  Suggestions f o r f u r t h e r work The composition of the t h i o s u l p h a t e p r e c i p i t a t e and new d e r i v a t i v e must be known f o r c e r t a i n . The c o n d i t i o n s necessary f o r determining  larger  q u a n t i t i e s o f reagent (and t h e r e f o r e o f t i n ) must be mare f u l l y investigated». The p r o p e r t i e s of a h i g h e r d e r i v a t i v e could be compared w i t h the o t h e r s . I g . t r i n a p t h y l , a r s i n e can be made ( 1 7 ) ; i t may be p o s s i b l e t o prepare t r i n a p t h y l phenyl arsonium c h l o r i d e or t e t r a n a p t h y l arsonium c h l o r i d e .  The  arsonium compounds could a l s o be compared to the stibonium, phosphonium and ammonium compounds.  To t h i s end t r i p h e n y l  s t i b i n e was obtained but time has not p e r m i t t e d g a t i o n along  an i n v e s t i -  these l i n e s .  The reagent r e a c t s w i t h the t h i o c y a n a t e of c o b a l t and i r o n .  complexes  I t may be p o s s i b l e to use i t f o r c o b a l t  i f the i n t e r f e r e n c e of i r o n could be removed.  Apparently  i r o n g i v e s a great d e a l of t r o u b l e i n determining  Co i n ores,  with a - nitroso B - napthol. The reagent a l s o p r e c i p i t a t e s gold and p l a t i n u m i n presence o f H C l , p r o b a b l y the e h l o r o a u r a t e i n a t e being p r e c i p i t a t e d . property  and c h l o r o p l a t -  I t may be p o s s i b l e t o use t h i s  i n qualitative analysis.  20  an Ig solution. Normality of NagS 0„ sol'n. - 0.0052 p  1 ml. of I< - 0.96 ml. of Ka„S 2 g03 c  Vol. of Sn soln. 1. 2 ml. 2. 4 ml. 3. 5 ml. 4. 7 ml. 5..8 ml. 6. 10ml. ;  Na„S •acTdid  Ig t i t e r  Na S 0 Reacted  5.1 ml. 10.5 ml. 13.4 ml. 13.5 ml. 16.0 ml. 18.3 ml.  2.4 4.8 7.2 3.7 4.4 6.1  2.8 ml. 5.9 mlo 6.5 ml. 10.0 ml. 11.8 ml. 12.4 ml.  0  ml. ml. ml. ml. ml. ml.  ?  g  Tin Found  Error  1.7 ml. 3.6 ml, 4.1 ml, 6.2 ml. 7.3 ml. 7.7 ml.  -0.1 mg. 0.0 mg. -0.4 mg, -0.1 mg, •fO.l mg. -1.3 mg.  It can not be emphasized too much that a saturated solution of NaCl must be used.  Saturation must always be tested by adding a  l i t t l e HG1 to the NaCl solution whence some solid salt w i l l precipitate. When higher volumes of t i n were used, results were low: thus for 12.6 mg. of t i n , only 10.3 mg. were found.  Conclusions 1. A method has been described for determining small amounts of t i n i n the stannic conditions this may be applied to larger amounts of t i n i f adsorption effects can be overcome, (thus, 10 ml of cone. HC1 prevents a fading end-point.) 2. The error due to atmospheric oxidation of stannous t i n i s thus removed. 3. The time required for analysis i s shortened by s t i r r i n g .  B I B L I O G R A P H Y 1 . S p e c i f i c & S p e c i a l R e a c t i o n s , F. F e i g l - Nordeman. 2.  Ind. &,Eng. Chem.., A n a l . E d . , 8 ,  3.  J..  4.  I n d . & Eng. Chem.,. 1 2 , 3 4 4 , 1 9 2 0 .  Ind. Eng. Chem.,  1922,  , 1 5 , 1 0 7 1  11,  (1923)  (1936).  - G. L u n d e l l & J . Schener.  14,427  5. J . A p p l i e d Chem. (U.S.S.R.), 6. Ind. Eng. Ghem.  401-410,  1366,  -  Furman,  77  (1938).  JN.H.  7 . Tech. Pub. of I n t e r n a t i o n a l T i n Research and Development C o u n c i l - Sec. A, no. 4 0 . 8 . J . Ghem. S o c ,  1936, 175.  Chem. Z t g . 4 7 ,  9.  561,  (1923).  1 0 . The I n s t , of Ghem. o f Great B r i t a i n and I r e l a n d , ^The 1  D e t e c t i o n and D e t e r m i n a t i o n o f S m a l l Amounts o f  I n o r g a n i c Substances by C o l o r i m e t r i c Methods."  11.  H e l v . Chim. A c t a ,  .12.  Ind. & Eng. Ghem. A n a l . Ed. ( V o l . 8 , p . 1 1 4 , 3 6 ) -Caley & B u r f o r d .  13.  "  14.  "  12,  R  »  720  •«  J . A. Chem. Soc* -  (1929)  "  61,  88  - G u t z e i t , G.  11,186-8  (1939).  (1939).  1 5 . Berichte, 1 9 , 1 0 3 2 - Philips. 1 6 . O x i d a t i o n Reduction  I n d i c a t o r s - Ghem. Reviews, Y o l . 2 9 ,  no. 1 , page 6 9 , Aug. 1 9 4 1 . 1 7 . Organic Compounds of A r s e n i c and Antimony; Longmans, G i l b e r t T. Morgan.  

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