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

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An Organic Reagent f o r the "Volumetric Determination of T i n Harold Boardman A Thesis submitted i n p a r t i a l f u l f i l m e n t of the requirements f o r the degree of ,. 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 often c a l l e d upon to perform analyses which have interferences d i f f i c u l t to 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 to inorganic a n a l y s i s promises to overcome many of these d i f f i c u l t i e s . This work, • Intended, to remove c e r t a i n i n t e r  ferences i n the a n a l y s i s of t i n , was done under the expert supervision of J . A l l e n H a r r i s , Ph.D., to whom I wish to express my thanks. H. Boardman T A B L E O F C O N T E N T S Page A. General Theory of Organic Reagents 1 B. Organic Reagents f o r T i n 2 C. Experimental Work (a) Preparation of the Reagent 6 (b) The Search f o r a Volumetric Procedure 8 1. The Permanganate P r e c i p i t a t e 9 2. The Bichromate P r e c i p i t a t e 12 3. Triphenyl napthyl arsonium 15 Shloride 4 . The Thiosulphate P r e c i p i t a t e IB (c) The Determination of Tin 19 D. Conclusions and Suggestionf f o r Further Work 20 E. Bibliography ,- 22 An Organic Reagent f o r the Yolumetric Determination of Tin General Theory of Organic Reagents Organic reagents are extremely u s e f u l i n the three f i e l d s of qu 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 , volumetric, and c o l o r i m e t r i o determinations - where t h e i r use supplants tedious or inaccurate inorganic methods* Organic reagents which react w i t h only one element are termed s p e c i f i c and reagents which react with a l i m i t e d number of 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 i n a mixture by i n a c t i v a t i n g other components by means of a masking reagent. Feig|k (1,2) has done much i n c l a r i f y i n g the theory of the' act i o n of organic reagents. By f a r the l a r g e s t group of organic reagents are those that form the s o - c a l l e d inner- complex compounds. The a b i l i t y of these reagents to form inner-complex s a l t s i s due to 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 : sulphonic (SO^H), s u l f i n i c (S0 2H). carboxyl, hydroxyl, s u l f h y d r y l (SH), Oxime (N0H=J, and imine (= NH). The hydrogen atoms are replaceable by one equivalent of metal. The molecule must 1 be so c o n s t i t u t e d , however, that the metal may also coordinate with some other atom (thus s a t u r a t i n g the secondary valences of the metal atom). This atom often i s oxygen, nit r o g e n or sulphur. The r i n g thus formed, contributes to the s t a b i l i t y of the r e s u l t i n g compound. The s o l u b i l i t y of the compound i s , of course, important i n gravimetric and volumetric a n a l y s i s . S o l u b i l i t y i s often influenced by other atomic groupings present i n the molecule. In general, the s o l u b i l i t y i s greater the more s i m i l a r the molecules of the- solute and solvent are. Thus the presence of hydroxy! groups i n the molecule increases the s o l u b i l i t y of a compound i n water. The s u l f o n i c a c i d group has also the a b i l i t y to bind water and hence increase the s o l u b i l i t y . Another important point as regards s o l u b i l i t y i s the s o - c a l l e d "weighting e f f e c t " . In general, the greater the molecular weight the l e s s i s the s o l u b i l i t y . E v i d e n t l y 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 since t h i s increases the s e n s i t i v i t y . Organic Reagents f o r T i n The experimental work consisted of a search f o r a volumetric method f o r t i n that would be accurate, quite r a p i d , and applicable to the a n a l y s i s of ores,etc* The e x i s t e n t methods f o r t i n depend upon the o x i d a t i o n faromtthesstannous to the stannic c o n d i t i o n . Controversy has centred around the i n i t i a l reduction of t i n and the question of a i r o x i d a t i o n . Various reducing 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 usual to b o i l the s o l u t i o n , which has a high acid 'concentration,, f o r f o r t y - f i v e minutes to ensure complete reductions A i r ox i d a t i o n exercises a considerable e f f e c t on t the t i t r a t i o n . Apparatus has been devised f o r the excl 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 to reduce the t i n i n a large Erlenmeyer, add s o l i d NaHGOg, to the acid 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 cool 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 possible with an iodine s o l u t i o n of s u i t a b l e concentration. Blanks.have to be run a l s o . Discrepancies sometimes occur, which are undoubtedly due to the method of reduction or the e f f e c t of a i r o x i d a t i o n . A method f o r determining t i n - i n , the stannic c o n d i t i o n wofild be free of both these e r r o r s . There i s no method f o r the volumetric determination of t i n i n the stannic c o n d i t i o n by inorganic reagents. 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 cupferron i s added; with 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 , t e t r a - valent t i n can be separated from arsenic and antimony i n acid s o l u t i o n (6). H i l l e b r a n d and Lundell's book covers the uses of cupferron. A volumetric method f o r the determination of small amounts of t i n i n ores has been developed by Al i m a r i h and S.M.Peuzner (5). This i s based upon the reduction and 4 decomposition of methyl orange by t i n i n a c i d s o l u t i o n to s u l f a n i l i c acid 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 with 0.01 or 0.05% s o l u t i o n of methyl-orange. Sb, As, B i , Cu, Cd,.Pb, Fe do not. i n t e r f e r e . T i , V, Mo, and I do. A e o l o r i m e t r i c method f o r determining 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 of t h i o g l y c o l l i c acid u n t i l the con ce 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 of t i n . c o n t a i n i n g about 10 p.p.m. together with about 0.2 g. of t h i o g l y c o l l i c a c i d per l i t e r i s d i l u t e d i n a measuring cy l i n d e r u n t i l a colour match i s obtained i n the fo l l o w i n g manner. Two test tubes containing i d e n t i c a l volumes (5-10 ml.) of the two so l u t i o n s are treated with 0.5 cc of HG1 followed by an equal quantity of 4-chloro-l:2 d i - mercaptobenzene i n a 2% S o l u t i o n of NaOH. This 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. bftwhich time the pink colour has developed f u l l y and the two colours are 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$. Sa l t s of Fe may i n t e r f e r e at or above 2$. The preparation of the reagent i s given (8). Another c o l o r i m e t r i c method f o r t i n i s a modifica t i o n of the molybdenum blue method recommended by F e i g t (9). The method was developed by B". S t r a f f o r d (ID). MThe t i n i s 5 reduced to the stannous condition by b o i l i n g the a c i d i f i e d a o l ution with a l i t t l e aluminum i n an atmosphere of 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 of the blue coloured 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 of 1 ml of e t h y l a l c o h o l . The blue s o l u t i o n i s then measured i n the Lovibond Tintometer Gacotheline i s used f o r the detection of t i n only (11). The te 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 reducing agents are removed. Then i n a c i d s o l u t i o n cacotheline gives a purple colour which i s e a s i l y destroyed by a i r o x i d a t i o n . A few other organic reagents f o r t i n also e x i s t . In passing i t might be w e l l to mention a method f o r separating stannic oxide (the usual form i n which t i n occurs i n ores) from various other oxides (12). An e l e c t r i c c r u c i b l e furnace i s requi r e d , the temperature of which can be con t r o l l e d to. w i t h i n 5 degrees. Heating SnOg with HH^I at about 425° C a f f o r d s a means of separating the SnOg from the F e 2 0 3 and GuO which are the common contaminants: SnOg -v 4MH4I -s> S n l 4 4- 4HH3 -V- 2HgO A. method which promised a means of determining t i n i n the stannic c o n d i t i o n with 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 given by WiHard and Smith (13)* Tetraphenyl arsonium c h l o r i d e i s the reagent. This i s an organic 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, of course, g r e a t l y weaken i t s basic p r o p e r t i e s , but i t i s quite s o l u b l e i n water and w i l l combine with the complex m e t a l l i c acids of mercury, z i n c , cadmium, bismuth and t i n , as w e l l as many other inorganic r a d i c l e s . In other words, i t i s by no means a s p e c i f i c reagent but rather 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 to the a n a l y s i s of t i n w i l l depend upon the method of 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 research i n t h i s laboratory was concerned with t h i s reagent and another s i m i l a r d e r i v a t i v e that was prepared. Experimental Work Preparation of the Reagent The method used f o r the preparation of the reagent wa's that of B l i c k e , .WiHard and Taras (14). Commercial t r i p h e n y l a r s i n e was obtained from Eastman and from t h i s t r i p h e n y l arsine oxide was made (15). The t r i p h e n y l arsine (20 g.) i s diss o l v e d i n an excess of g l a c i a l a c e t i c a c i d . T'tisn bromine i s added (14g.) slowly and with s t i r r i n g . Con centrated NH4OH i s then added slowly i n excess, u n t i l the t r i p h e n y l arsine hydroxide 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 funnel and washed with water; the p r e c i p i t a t e i s d i s s o l v e d with warming i n the smallest 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 of water, whereby f i n e white c r y s t a l s of the hydroxide are obtained. These are dessicated i n vacuo over concentrated sulphuric ac i d for several 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 6H 5) 3As -v Br 2 — » ( C 6 H 5 ) 3 A s B r 2 ( C 6 H 5 ) 3 A s B r 2 -s- 2NH40H 2NH4Br + (C6H5 ) 3As(0H) (G 6 H 5 ) 3 A s ( 0 H ) 2 -> H 20 + (G 6Hg) 3As = 0 Then phen$tlmagnesium bromide i s made from 15g of Mg, 68 cc. of bromobenzene and 300 cc. of dry ether i n a l i t e r f l a s k equipped with a r e f l u x condenser and s t i r r e r . A f t e r r e a c t i o n i s complete (started by adding a l i t t l e i i o d i n e and warming) 500 cc. of dry benzene i s poured i n and 60 g. of 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 at a time (over four hours) with s t i r r i n g . Then s t i r r i n g i s continued f o r three more hours u n t i l a l l the oxide has disappeared. The ether-benaene l a y e r i s decanted o f f from the viscous o i l and $ 500 cc. of water i s added slowly while the o i l 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 cc. of cone. HG1 are added u n t i l a l l the white s o l i d that appears d i s s o l v e s . The mixture i s allowed to,stand 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 . This i s f i l t e r e d . The f i l t r a t e i s n e u t r a l i z e d with NaOH and a l i t t l e NaCl i s added to recover any teiraphenyl arsonium c h l o r i d e i n s o l u t i o n . The crude tetraphenyl 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 cc. of hot water and adding 150 g. NaCl, c o a l i n g and f i l t e r i n g . 8 GgHgBr -v Mg G5H5MgBr C 6H 5MgBr v (G 6H 5) 3As = 0 (CgH 5) 4As - 0 - MgBr (G 6H 5) 4As - 0 - MgBr + HOH ~MCgH 5 ) 4As0H 4- MgBr OH (G 6H 5) 4AsOH + HGl HgO +• (CgH 5) 4AsCl In the l a t e r work a new d e r i v a t i v e was prepared - triphe'nyljnapthyl arsoniumn c h l o r i d e . This was made i n exact l y the same manner - except that napthyl magnesium bromide was' used instead of phenylmagnesium bromide. (The same molar proportions were used.) The Search f o r a volumetric Procedure Although tetraphenyl arsonium c h l o r i d e p r e c i p i t a t e s with t i n , some method of determining the reagent v o l u m e t r i c a l l y i s necessary.- The reagent gives p r e c i p i t a t e s with iodine ( i n presence of k l ) , molybdate, diohromate, permanganate and other ions:. W i l l a r d and Smith used iodine to determine the reagent, a potentiometric 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 colour, d i f f i c u l t to f i l t e r ; i t s composition shows i t to be the periodide: (G 6H 5) 4As + I G + I ( C 6 H 5 ) 4 A s I 3 n5 - 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 nearly 100 cc. with water or saturated NaGl s o l u t i o n . The reference and i n d i c a t o r electrodes are immersed i n t h i s s o l u t i o n while standard iodine s o l u t i o n of about the same concentration containing 6 - 8 g.KI / l . i s added slowly with constant s t i r r i n g . As the iodine i s added 9 the p o t e n t i a l decreases to a min. value. When t h i s minimum i s reached the iodine i s added dropwise and time allowed f o r the system to reach e q u i l i b r i u m . When an equivalent quantity of iodine has been added, there i s a sudden increase i n p o t e n t i a l . * Near the' end point the s o l u t i o n must be completely saturated with s a l t before the t i t r a t i o n i s completed." In 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 there. I t was not very a p p l i c a b l e to the determination of any range of reagent; t h i s was the only method investigated f o r t i t r a t i n g the reagent. Three reactions were studied: with KMnO , K 2 C r 2 0 7 , and NagSgO^. The •Permanganate Prec i p i t a t e Tetraphenyl arsonium permanganate i s a dark red 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 the reagent with KMn04 using an i n d i c a t o r . The p r e c i p i t a t e forms i n n eutral or a c i d s o l u t i o n s , but not i n basie s o l u t i o n s , p o s s i b l y because of the formation of tetraphenyl arsonium a .7 hydroxide. Tjie pure s a l t i n water gives a Ph of fe§ showing that 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 table of the properties 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 saturated s o l u t i o n 2. F a i r l y soluble i n a s o l u t i o n made a c i d with a c e t i c . 3. Insoluble i n above.solution i f NH^Cl i s present. • 4 . Insoluble i n a s o l u t i o n made basic with 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 with l e s s than 3 ml. of 10 of 0.01 M. reagent i n a volume of 60 ml. 6. The p r e c i p i t a t e d i s s o l v e s to a c l e a r s o l u t i o n when b o i l e d with a s o l u t i o n of sodium oxalate a c i d i f i e d with H gS0 4. The l a s t mentioned property ©an be used to deter mine the reagent provided adequate precautions are taken with respect to r e a c t i o n of permanganate with H61 and organic matter. To determine the composition of 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 to 5 ml. of 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 with water. The excess KMnO i n the f i l t r a t e was determined with a standard sodium oxalate s o l u t i o n . Results are tabulated f o r duplicate samples. Normality of K 3 I n ^ = ^ . 101 " " N a 2 C 2 0 4 - 0.307 . Volume of reagent i n each ease was;.5 ml;, to which 10 ml. of KMh0 4 were added. 5 ml. of Na 2Gg0 4 s o l u t i o n was added to 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 with KMn04. .1. EMn0 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 =0.0375 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 of the p r e c i p i t a t e to be (G 6H 5) 4AsMn0 4, weight of p r e c i p i t a t e c a l c u l a t e d s 0.0424 g. Percentage e r r o r - 11.5%, probably a r i s i n g from the experimental conditions,(Water 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 soluble due to hydrolysis,,) Since the s e n s i t i v i t y of the process i s not very great i t was abandoned. Hbte that h y d r o l y s i s of the s a l t can take place because tetraphenyl 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 strength of the base: KB = &G6H5)4As] [ O H ] [ ( C 6 H 5 ) 4 A S 0 H } - In the h y d r o l y s i s of the c h l o r i d e we have: (C 6H 5) 4As +. H 20 (C 6H 5) AsOH -V- II* KH- - rtG6H5) 4AsOH} [ l l 4 ] KB " [(C6H5)4As-»J K H - — where h degree of h y d r o l y s i s 1 - h Gh=£H*} = |I.C §H 5) 4ASGH] which can be found by measuring the Pg of. the s o l u t i o n . KH ^ III G - £ H 4 3 0.3355 g. of pure tetraphenyl arsonium c h l o r i d e was weighed and d i s s o l v e d i n ex a c t l y 80 ml. of water to make a 0.01 molal s o l u t i o n . The of t h i s s o l u t i o n was 2.65, >*• UH*"3 ~ 2'24 x 10"3 K H „ 5.02 X l O ^ 6 0.647 I 10" 5 0.0& - 2.24 X 1 0 - 3 The Piohrornate P r e c i p i t a t e TetEa phenyl arsenium c h l o r i d e gives a yellow f l o c e u l e n t p r e c i p i t a t e with potassium dichromate i n a c i d s o l u t i o n . The Pg of water containing the dichromate i s 1.5 showing that considerable 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 i n s o l u b l e i n a c i d s o l u t i o n at ordinary temperatures since the f i l t e r e d s o l u t i o n that has been i n contact with the s o l i d f o r some time gives no p r e c i  p i t a t e with Pb4" i n a c e t i c a c i d s o l u t i o n . However, ferrous ammonium sulphate completely dissolves 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 with HGl, showing that there are enough G±g07 ions i n s o l u t i o n to allow 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 soluble at the temperature of b o i l i n g water. . • ' of the dichromate was prepared and washed thoroughly by decantation. The p r e c i p i t a t e was d r i e d and 0.1 g. weighed. This 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 with a c e t i c aoid and treated with lead acetate. ; Weight of PbCr0 4 = 0.0666- g. T h e o r e t i c a l weight of C r 2 0 7 - 0.1 X 216.02 = 0.022 g. The composition of 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 . Some 646.44 Experimental weight of C r 2 0 7 = 0.0666 X 216.02 - 0.022 646.44 13 The dichromate i s i n s o l u b l e whereas the chromate i s soluble at ordinary temperatures. Making the s o l u t i o n basic 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 tetraphenyl arsonium i o n from s o l u t i o n as hydroxide". To determine the reagent with potassium dichromate a d i r e c t t i t r a t i o n or a determination of 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. I f p o s s i b l e , f i l t e r i n g i s to be avoided. An attempt was made to develop a method f o r t i t r a t i n g 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 selected consisted of one or two ml. of a 1% KI s o l u t i o n along with starch s o l u t i o n , the'idea being that when an excess of G^gG^ ions were present these would set free Ig from the KI, thus g i v i n g the starch blue end p o i n t * The KI had to be a weak s o l u t i o n , otherwise I g was set fre e before the end point and tetraphenyl arsonium periodide was p r e c i p i t a t e d , ' A saturated NaCl s o l u t i o n seemed to be necessary and accurate c o n t r o l of the a c i d concentration. The volume of the s o l u t i o n had to be kept down to a minimum. The f o l l o w i n g table shows some t i t r a t i o n t e s t s that„were made. ( M o l a l i t y of reagent approx. 0.01). V o l . of Rea£ jent K s C r 2 0 7 t i t e r V o l . of Reagent K 2 C r 2 0 7 t i t e r 1 ml No p r e c i p i t a t e 5 ml. 4.0 ml. 2 rr 1.3 ml. 6 " 4.0 n 2 » 1.3 « 6 » 4 . 9 t, 3 i i 2 . 2 " 7 " 6 . 2 ri 3 it 2 . 2 «! 9 " 6 . 6 it 4 it 2 . 8 " 10 !» 7.3 it 14 Although r e s u l t s are reproducible, the t i t r a t i o n f o r higher volumes becomes higher showing that a blank would have to be subtracted; c a r e f u l c o n t r o l o f PH i s also necessary. With higher volumes of reagent the yellow colour 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 - ortho phenanthfoline and.also diphenylamine. The same d i f f i c u l t y was found. Blank determinations were made with O-phenanthtoline at d i f f e r e n t BaGl and HOI concentrations. The blank v a r i e s with both these concentrations from 9.3 to 2.6 ml. of 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_ with ferrous ammonium 2 e~- I sulphate could 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 standardizations of the reagent Using t h i s method. The p r e c i p i t a t e i s washed with water containing HOI. ><t 1 ml. FeS0 4 - .58 ml. K 2 C r 2 0 7 1. 5 ml. of reagent; 7.1 ml. of K 2 0 r 2 0 7 added. Excess K 2Cr 207 - 4.7 X *58 = 2.7 ml. g. 10 a ,\ 4.3 ml. reacted. 2. 10 ml of reagent; 14.0 ml. of K 2 C r 2 G 7 Excess K 2 C r 2 0 7 - 9.5 X .58 — 5 . 5 ml. .% 8.5 ml. reacted. 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 determining small amounts of dichromate g r a v i m e t r i c a l l y . 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. containing NaCl and HOI an excess of K g-Cr 20 7 was added w*tk the p r e c i p i t a t e was f i l t e r e d and washed. 1. Weight of p r e c i p i t a t e - 0.0700 g. , 2. Weight of p r e c i p i t a t e - 0.0704 g. Triphenyl napthyl arsonium chloride At t h i s stage of the research i t was decided to t r y to prepare a reagent of d i f f e r e n t structure 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 preparation of t h i s d e r i v a t i v e has already been described Triphenyl napthyl arsonium c h l o r i d e forms a p r e c i p i t a t e with dichromate s i m i l a r to the tettaphenyl. d e r i v a t i v e , except that once c r y s t a l l i z e d i t i s not r e a d i l y soluble i n basic s o l u t i o n , nor with.ferrous ammonium sulphate i n a c i d s o l u t i o n . I t d i s s o l v e s i n b o i l i n g water, i n water, the dichromate gives a P H of 3.2 as compared to 1.5 f o r the tetraphenyl d e r i v a t i v e . Hence the napthyl i s l e s s hydrolyzed. The•permanganate p r e c i p i t a t e of the napthyl d e r i v a t i v e i s also s i m i l a r to that of the tetraphenyl d e r i v a t i v e . In water, i t gives a PH of 4.5 as compared to 2.7 f o r the tetraphenyl d e r i v a t i v e . Further work; Mas c a r r i e d out with the napthyl derivative, because of i t s greater s e n s i t i v i t y . The compo s i t i o n of t h i s new reagent has not been determined; i t i s 16 j u s t assumed that the structure i s that given^because of the method of preparation. The Thiosulphate P r e c i p i t a t e I t had been observed that sodium thiosulphate completely d i s s o l v e d tetraphenyl arsonium periodide leaving a white p r e c i p i t a t e i f excess thiosulphate was added. The thiosulphate p r e c i p i t a t e of the new d e r i v a t i v e was i n v e s t i  gated. This 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 quite i n s o l u b l e even i n basic s o l u t i o n once formed. Half a ml. each of 0.005 11 Na gSg0 3 and reagent w i l l give a p r e c i p i t a t e i n 60.ml. of s o l u t i o n . This w i l l not 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 . Water that has been i n contact with the s a l t f o r some time w i l l not decolorize a l i t t l e very weak iodine s o l u t i o n which confirms i t s complete i n s o l u b i l i t y . A l s o , i n s w a t e r t h i s s a l t gives a PH of 7 showing that no h y d r o l y s i s tkkes place. This l e d to an exact method f o r t i t r a t i n g the reagent.; The idea was to add an excess of Ha. S O s o l u t i o n C> £i Q ^ to a given volume of reagent and back t i t r a t e with an I g s o l u t i o n , using s t a r c h as an i n d i c a t o r . P r e l i m i n a r y experiments gave the f o l l o w i n g r e s u l t s : 17 l..:ml. I . 1.1 ml. NagSgOg To t a l v o l . .of Soln. Vol. Of Reagent V o l . of . NapSoO^ , I T i t e r N a2 S2°3 Reacted 5 ml •• 5 ml 3.8 ml 0.8 ml 100 ml. 10 ml 8 ml 5.6 ml 1.8 ml . 20 ml 5 ml 1. 3 ml 3.6 ml 200 ml. ( 10 ml 5 ml 2.8 ml 1.9 ml I 20 ml 5 ml 1.0 ml 3.7 ml The table shows the r e p r o d u c i b i l i t y of r e s u l t s and that the method i s quite 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 conditions necessary f o r t i t r a t i o n the potentiometer was used. I t was found that when an excess of NagSgOg was added i t took a l i t t l e time f o r E to come to a steady value - corresponding to the time necessary f o r the completion of r e a c t i o n . This took from ten to f i f t e e n minutes u s u a l l y . Then as the I g s o l n . i s added the. E drops slowly, u n t i l at the end point i t drops quite r a p i d l y . , An example i s given: 8 ml of thiosulphate were added to 5 ml of 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 . (automatically s t i r r e d ) . IVol. of I 0 . E . V o l . of I-j, ' •. : E. 1 0 ml' 3.4 1.4 ml. '•3.8 . • 0.2 ml 3.7 1.5 " 3,72 ••! 0055 " 3.8 1.7 •« 3.62 0.7 '« 3.85 1.8 " 3.60 . 0.8 " 3.90 •1.9 »» 3.55 1*0 » • 3.90 2 9 2 2.9 1 1.2 » 3.85 2.3 " 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 slowly i n the above determination. Further t i t r a t i o n s were made using the potentiometer and having the starch i n d i c a t o r i n s o l u t i o n at the same time. The r e s u l t s are as f o l l o w s : 5 ml. of. reagent, 8 ml. of thiosulphate Indicator end point - 5.7 ml. thiosulphate reacted. Potentiometer end point " " n 2. 6 ml. of reagent, 10 ml. of thiosulphate I n d i c a t o r end point - 7 ml. thiosulphate reacted • Potentiomenter n n - 6.9 " " " 3. 10 ml. of reagent, 15 ml. of thiosulphate I n d i c a t o r end point - 11.4 ml. reacted Potentiometer " " - " " B .' The end point appears q u i c k l y but does not l a s t very long, probably due to adsorption of 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 restore the colour. JHirther t e s t s using 0.005 N s o l u t i o n s of Na gSg0 3 and Ig showed that to get best r e s u l t s the thiosulphate must be added drop by drop with automatic s t i r r i n g . Two or three ml. of HG1. and a l i t t l e NaCl must be present. With larger volumes of reagent l e s s thiosulphate appears to react with the reagent. This i s probably because too large a volume of iodine i s used because of adsorption. The f a d i n g end point would seem to confirm 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 gives 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 give a white c r y s t a l l i n e p r e c i p i t a t e with t i n , providing the s o l u t i o n i s saturated with NaCl and contains a l i t t l e HCl. The purpose of the NaCl i s to form sodium chlorostannate and keep the r e s u l t i n g tetraphenyl arsonium chlorostannate (or t r i p h e n y l napthyl 19 arsonium chlorostannate) i n s o l u b l e . The -pmepose of the HOI i s to prevent h y d r o l y s i s . The p r e c i p i t a t e s slowly dissolve inv;water. . ' Ti n Determination W i l l a r d and Smith give 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 tetraphenyl arsonium chlorostannate as: "2 cc. of HC1 and enough NaGl are added to give a 2.5 to 3,0 M con c e n t r a t i o n of NaGl i n a f i n a l volume of 60 Ml." I t was found that the tetraphenyl arsonium c h l o r i d e would not give a p r e c i p i t a t e with I mg. of t i n under these conditions but that 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 saturated with NaGl and i n washing the p r e c i p i t a t e a saturated s o l u t i o n of NaGl must also 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 to the stannic c o n d i t i o n was ensured. This was standardized with an iodine s o l u t i o n and found to contain .9 mg. of t i n per 10 ml. A given volume of the t i n s o l u t i o n was measured, one or two ml. of HC1 added and the s o l u t i o n was made up to 60 ml. and saturated with NaCl. The so l u t i o n s tested below were allowed to stand f o r an hour or two, af t e r a d d i t i o n of an excess of reagent,, then f i l t e r e d through number 40 Whatman and washed with saturated NaCl u n t i l free of reagent, ( t e s t i n g f i l t r a t e with Ig s o l n . ) . The p r e c i p i t a t e was washed with a stream of water from a wash b o t t l e into a 150 ml, beaker. A few ml. of HGl and a l i t t l e NaGl were added then a measured volume of NagSgOgw^nej* by drop, w i t h s t i r r i n g . The excess Na2S20g was then back t i t r a t e d with 21 Suggestions f o r further work The composition of the thiosulphate 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 conditions necessary f o r determining larger q u a n t i t i e s of reagent (and therefore of t i n ) must be mare f u l l y investigated». The prope r t i e s of a higher d e r i v a t i v e could be compared with the others. I g . tr i n a p t h y l , arsine can be made (17); i t may be possible to prepare t r i n a p t h y l phenyl arsonium c h l o r i d e or te t r a n a p t h y l arsonium c h l o r i d e . The arsonium compounds could also 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 permitted an i n v e s t i  gation along these l i n e s . The reagent reacts with the thiocyanate complexes of cobalt and i r o n . I t may be possible to use i t f o r cobalt i f the interference of i r o n could be removed. Apparently i r o n gives a great deal of trouble i n determining Co i n ores, with a - n i t r o s o B - napthol. The reagent also p r e c i p i t a t e s gold and platinum i n presence of HCl, probably the ehloroaurate and c h l o r o p l a t - inate being p r e c i p i t a t e d . I t may be pos s i b l e to use t h i s property i n q u a l i t a t i v e a n a l y s i s . 20 an Ig solution. Normality of NagSp0„ sol'n. - 0.0052 1 ml. of I c - 0.96 ml. of Ka„S 0 < 2 g 3 Vol. of Sn soln. Na„S •acTdid0 Ig t i t e r Na?Sg0 Reacted Tin Found Error 1. 2 ml. 2. 4 ml. 3. 5 ml. 4. 7 ml. 5..8 ml. ; 6. 10ml. 5.1 ml. 10.5 ml. 13.4 ml. 13.5 ml. 16.0 ml. 18.3 ml. 2.4 ml. 4.8 ml. 7.2 ml. 3.7 ml. 4.4 ml. 6.1 ml. 2.8 ml. 5.9 mlo 6.5 ml. 10.0 ml. 11.8 ml. 12.4 ml. 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 in 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 stirring. 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 Reactions, F. F e i g l - Nordeman. 2 . Ind. &,Eng. Chem.., Anal. E d . , 8 , 4 0 1 - 4 1 0 , ( 1 9 3 6 ) . 3 . J . . Ind. Eng. Chem., 1 9 2 2 , 1 4 , 4 2 7 - G. Lu n d e l l & J . Schener. 4 . Ind. & Eng. Chem.,. 1 2 , 3 4 4 , 1 9 2 0 . 5. J . Applied Chem. (U.S.S.R.), 1 1 , 1 3 6 6 , - 7 7 ( 1 9 3 8 ) . 6. Ind. Eng. Ghem. , 1 5 , 1 0 7 1 ( 1 9 2 3 ) Furman, J N . H . 7 . Tech. Pub. of I n t e r n a t i o n a l Tin Research and Development Council - Sec. A, no. 4 0 . 8 . J . Ghem. S o c , 1 9 3 6 , 1 7 5 . 9 . Chem. Z t g . 4 7 , 5 6 1 , ( 1 9 2 3 ) . 1 0 . The I n s t , of Ghem. of Great B r i t a i n and I r e l a n d , ^The Detection and Determination of Small Amounts of 1 Inorganic Substances by Colo r i m e t r i c Methods." 1 1 . Helv. Chim. Acta, 1 2 , 7 2 0 ( 1 9 2 9 ) - Gutz e i t , G. . 1 2 . Ind. & Eng. Ghem. Anal. Ed. ( V o l . 8 , p . 1 1 4 , 3 6 ) -Caley & Burford. 1 3 . " " R» • « " 1 1 , 1 8 6 - 8 ( 1 9 3 9 ) . 1 4 . J . A. Chem. Soc* - 6 1 , 8 8 ( 1 9 3 9 ) . 1 5 . B e r i c h t e , 1 9 , 1 0 3 2 - P h i l i p s . 1 6 . Oxidation Reduction Indicators - Ghem. Reviews, Y o l . 2 9 , no. 1 , page 6 9 , Aug. 1 9 4 1 . 1 7 . Organic Compounds of Arsenic and Antimony; Longmans, G i l b e r t T. Morgan. 

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