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Determination of valence states of Iron in glass and of Uranium in Calcium fluoride single crystals
Mnadytica Chimlca A c t a Elsevier Publishing Company, Amsterdam
495
Prirttcci in. T h e N e t h e r l a n d s
DETERMINATION OF VALENCE STATES OF OF UIZANIUM IN CALCIUM FLUORIDE SINGLE
IRON IN GLASS CIZYSTALS
AND
U. A : B E D L~wrence R a d i a t i o n Laboratory, U.niversity of California, Berkeley, Calif. 94720 ( ( f l . S . A . ) ( R e c e i v e d Ditty 2 6 t h , 1969)
D u r i n g s t u d i e s in t h i s l a b o r a t o r y , it b e c a m e n e c e s s a r y t o d e t e r m i n e t i l e i r o n ( I I ) a n d i r o n ( I I I ) o x i d e c o n t e n t of s o d i u m d i s i l i c a t e g l a s s e s w h i c h h a d b e e n u s e d in h i g h t e m p e r a t u r e e l e c t r o c h e m i s t r y e x p e r i m e n t s . A w e a l t h of p u b l i c a t i o n s deals w i t h t h e d e t e r m i n a t i o n of i r o n ( I I ) . A m o n g o t h e r s , CHENG 1 d i s c u s s e s v a r i o u s m e t h o d s for t h e d e t e r m i n a t i o n of i r o n ( I I ) o x i d e in s o m e s o l i d s a n d , s t a t i n g t h e l i m i t a t i o n s for his p u r p o s e , d e v e l o p e d a p r o c e d u r e for d e t e r m i n i n g i r o n ( I I ) i n ferrites. H o w e v e r , h i s a p p r o a c h is u n s u i t a b l e for t h e d e c o m p o s i t i o n of glass. A m e t h o d d e s c r i b e d b y CLOSE et al." f o r i r o n ( I I ) in glass w a s s e l e c t e d . T h e y r e c o m m e n d a h y d r o f l u o r i c - s u l f u r i c acic[ m i x t u r e for t h e d i s s o l u t i o n of g l a s s u n d e r a n i n e r t a t r n o s p h e r e , f o l l o w e d b y t i t r a t i o l x of t h e l i b e r a t e d i r o n ( I I ) w i t h c e r i u m ( I V ) . T h e i r o n ( I I ) r e s u l t s o b t a i n e d b y t h i s p r o c e d u r e in t h i s l a b o r a t o r y w e r e w i d e l y s c a t t e r e d , a n d a t t e m p t s to m o d i f y t h e method did not improve the precision. T h e m e t h o d p r e s e n t e d h e r e is b a s e d on t h e f a c t t h a t c e r i u m ( I V ) is s t a b l e for a n e x t e n d e d p e r i o d o v e r t h e t e m p e r a t u r e r a n g e 2 o - I o o ° in t h e h y d r o f l u o r i c - s u l f u r i c a c i d m i x t u r e . T h i s p e r m i t s t h e i n s t a n t a n e o u s o x i d a t i o n of t h e r e l e a s e d i r o n ( I I ) b y a k n o w n excess of s t a n d a r d c e r i u m ( I V ) s o l u t i o n d u r i n g t h e d i s s o l u t i o n of t h e g l a s s a n d t h u s o b v i a t e s t h e n e e d for a n i n e r t a t m o s p h e r e . T h e r e s u l t s o b t a i n e d o n g l a s s s a m p l e s b y t h i s p r o c e d u r e a r e p r e c i s e a n d t h e a c c u r a c y of t h e d e t e r m i n a t i o n o n s i m u l a t e d s a m p l e s w a s w i t h i n 1 % . T h e m e t h o d is also a p p l i c a b l e t o t h e d e t e r m i n a t i o n of i r o n ( I I ) o x i d e in m a g n e s i u m o x i d e . T h e f o r m a l o x i d a t i o n p o t e n t i a l s for t h e c e r i u m ( I V ) - c e r i u m ( I I I ) c o u p l e a n d for t h e i r o n ( I I I ) - i r o n ( I I ) c o u p l e are e s t i m a t e d i n t h e g l a s s d i s s o l v i n g a c i d m i x t u r e a n d t h e i r i m p o r t a n c e is d i s c u s s e d . T h e p r o c e d u r e w a s f u r t h e r e m p l o y e d in d e t e r m i n i n g v a l e n c e s t a t e s of s e m i - l n i c r o q u a n t i t i e s of u r a n i u m i n c a l c i u m f l u o r i d e single c r y s t a l s . :EXPERIMENTAL
Apparatus T e f l o n b e a k e r s w i t h p o u r i n g lips, 3.4 c m o.d., 2.7 c m i.d., a n d 4.6 c m h i g h , w i t h a c a p a c i t y of 30 m l , w e r e m a c h i n e d f r o m COlmnercial r o d s t o c k a n d w e r e f i t t e d with Teflon covers. Teflon-covered magnetic stirring bars, in conjunction with M a g - M i x m a g n e t i c s t i r r e r s , w e r e u s e d t o a g i t a t e t h e g l a s s - a c i d m i x t u r e s . Micro w a s h o u t p i p e t s , g u a r a n t e e d " t o c o n t a i n " w i t h i n +o.ox~/o of t h e s t a t e d v o l u m e , w e r e used to aliquot the standard solutions and the indicator. Hydrofluoric acid was aliquoted with 2.o-ml plastic pipets. A previously described lead column reductor A ~ a l . Chim. Acla, 47 (1969) 4 9 5 - 5 o ~
496
u. ABED
was u s e d in d e t e r m i n i n g t h e t o t a l u r a n i u m ~ a n d t h e t o t a l i r o n 4. T h e p o t e n t i a l m e a s u r e m e n t s w e r e m a d e w i t h a D i g i - T e c d i g i t a l d,c. v o l t m e t e r .
Reagents All c h e m i c a l s u s e d were r e a g e n t g r a d e u n l e s s o t h e r w i s e specified. S u f f i c i e n t c e r i u m (IV) a m m o n i u m n i t r a t e was d i s s o l v e d in s u l f u r i c a c i d to g i v e , on final d i l u t i o n , a s t o c k s o l u t i o n o . I 114 in c e r i u m ( I V ) a n d I M in s u l f u r i c a c i d ; o . o r M c e r i u m ( I V ) s o l u t i o n s w e r e p r e p a r e d b y d i l u t i o n of t h e s t o c k s o l u t i o n while m a i n t a i n i n g a s u l f u r i c a c i d c o n c e n t r a t i o n of l O % b y v o l u m e . T h e o.I M s o l u t i o n w a s s t a b l e for a t l e a s t 2 y e a r s , a n d t h e o . o i M d i l u t i o n was s t a b l e for a t l e a s t 3 w e e k s . A s t a n d a r d o . o o r M i r o n ( I I ) a m m o n i u m s u l f a t e s o l u t i o n , l O % b y v o l u m e in s u l f u r i c a c i d , was p r e p a r e d d a i l y b y d i r e c t w e i g h i n g . S u f f i c i e n t i r o n w i r e for s t a n d a r d i z a t i o n w a s d i s s o l v e d w i t h h y d r o c h l o r i c acid t o give a s o l u t i o n of o.I M i r o n ( I I I ) o n d i l u t i o n . A x:2o d i l u t i o n of the c o m m e r c i a l l y a v a i l a b l e I , I o - p h e n a n t h r o l i n e i r o n ( I I ) sulfo.te (ferroin) i n d i c a t o r , o.o25 M , f r o m G. F. S m i t h C h e m i c a l C o m p a n y v)as e m p l o y e d . C o n c e n t r a t e d s u l f u r i c a c i d a n d 4 8 % h y d r o f l u o r i c a c i d w e r e p u r i f i e d w i t h p e r m a n g a n a t e as d e s c r i b e d p r e v i o u s l y 2 a n d w e r e u s e d t h r o u g h o u t t h e p r o c e d u r e for i r o n . N.B.S. u r a n i u m d i o x i d e , o.I M i r o n ( I I I ) s u l f a t e solution, a n d a c a l c i u m f l u o r i d e single c r y s t a l w e r e u s e d in t h e u r a n i u m d e t e r m i n a t i o n . P o t e n t i a l measureme~tts T h e f o r m a l o x i d a t i o n p o t e n t i a l m e a s u r e m e n t s of t h e c e r i u m ( I V ) - c e r i u m ( I I I ) c o u p l e w e r e c o n d u c t e d in a I o o - m l p o l y e t h y l e n e cell, w i t h a. p l a t i n u n l w i r e a n d a L i n g a n e - t y p e s a t u r a t e d c a l o m e l e l e c t r o d e (SCE) c o m b i n a t i o n . D i f f u s i o n of t h e p o t a s s i u m c h l o r i d e i n t o t h e cell a n d c o n t a c t of t h e glass e l e c t r o d e w i t h h y d r o f l u o r i c a c i d is n o t d e s i r a b l e , t h e r e f o r e t h e e l e c t r i c a l c o n t a c t t h r o u g h t h e cell w a s a c c o m p l i s h e d b y a l l o w i n g t h e SCE b r i d g e t o dip i n t o a 5 M a m m o n i u m n i t r a t e soaution, a n d b y b r i d g i n g f r o m t h e r e i n t o t h e cell b y a bees' w a x - c o a t e d U - t u b e w i t h a n t t p t u r n e d tip. T h e a g a r a g a r s a l t b r i d g e w a s a v o i d e d b e c a u s e s t r o n g o x i d a n t s are k n o w n t o a t t a c k its. T h e e n t i r e cell a n d a s s o c i a t e d p a r t s w e r e i m m e r s e d in a z5.o ° +_o.I ° c o n s t a n t t e m p e r a t u r e bath. T h e s o l u t i o n u s e d c o n s i s t e d of I.OO m l of o.o992 M c e r i u m ( I V ) a n d I.OO m l of o.o99z 3/I c e r i u m ( I I I ) , b o t h in I /W s u l f u r i c acid, xo m l of h y d x o f l u o r i c a c i d , IO m l of s u l f u r i c acid, a n d 20 m l of w a t e r . T h e m i x t u r e w a s s t i r r e d cor~tinuously w i t h a m a g n e t i c s t i r r e r w h i l e p o t e n t i a l m e a s u r e m e n t s w e r e m a d e at 5 - m i n i n t e r v a l s . T h e m e a s u r e m e n t of tlae iron(III)-iron(II) f o r m a l o x i d a t i o n p o t e n t i a l was m a d e ill t h e s a m e cell as d e s c r i b e d a b o v e . I n this c a s e t h e b r i d g e s o l u t i o n w a s s a t u r a t e d p o t a s s i u m s u l f a t e , since c o n t a c t of a n i r o n ( I I ) s o l u t i o n w i t h a s t r o n g n i t r a t e s o l u t i o n m i g h t r e s u l t in o x i d a t i o n of t h e i r o n ( I I ) . "1"he i r o n ( I I I ) - i r o n ( I I ) p o t e n t i a l w a s m e a s u r e d o n a s o l u t i o n s i m i l a r t o t h e o n e above, b u t c o n t a i n i m g I.OO ml of 0.0988 NI i r o n ( I I I ) a n d x.oo m l of o.o999 / F / i r o n ( I I ) i n s t e a d of c e r i u m . B e f o r e a l i q u o t i n g t h e i r o n i n t o t h e a c i d - w a t e r solution, t h e m i x t u r e w a s p u r g e d of o x y g e n w i t h a c h i p of D r y Ice. C a r b o n d i o x i d e gas w a s d i r e c t e d o v e r t h e s u r f a c e of ~he s o l u t i o n d u r i n g t h e time the potential measurements were made. S t a n d a r d i z a t i o n o f o . o z M eerie sulfate D e l i v e r a 3 - m l a l i q u o t of t h e o.I M s t a n d a r d i r o n s o l u t i o n i n t o a 3 o - m l p l a t i n u m A n a l , C h i m . A c t a , 47 0 9 6 9 ) 495-5o2
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c r u c i b l e a n d f u m e a l m o s t t o d r y n e s s w i t h x m l of s u l f u r i c a c i d a n d 2 m l of h y d r o f l u o r i c a c i d . T r a n s f e r t h e s a m p l e t o a 5 o - m l b e a k e r , a d d 5 ml of 4 M h y d r o c h l o r i c acid, a n d d i l u t e t o ~-5 ml. W a s h t h e irop. t h r o u g h a l e a d c o l u m n r e d u c t o r w i t h s i x 9-5-ml p o r t i o n s of o.8 M h y d r o c h l o r i c a c i d . R e c e i v e t h e e l u e n t in a 5 o o - m l E r l e n m e y e r f l a s k w h i c h c o n t a i n s IO g of b o r i c a c i d a n d s u f f i c i e n t D r y I c e to p r o v i d e an i n e r t a t m o s p h e r e t h r o u g h o u t t h e s u b s e q u e n t t i t r a t i o n . A l i q u o t 4 m l of s u l f u r i c a c i d a n d I ml of I :~-o f e r r o i n s o l u t i o n i n t o t h e s a m p l e flask. W h i l e stirring, t i t r a t e w i t h t h e o.ox / V / c e r i u m (IV) solution to the end-point. D e t e r m i n e indicator and reagent blanks and a p p l y t h e a p p r o p r i a t e titer corrections to the results.
D e t e r m i n a t i o n o f iron ( I I ) G r i n d a glass s a m p l e in a D i a m o n i t e m o r t a r t o p a s s IOO m e s h . W e i g h x o o m g of t h e glass t o g i v e o . 4 - 1 . o m g of iron(II) oxide. T r a n s f e r t h e s a m p l e t o a T e f l o n b e a k e r a n d a l i q u o t z m l of o . o i M s t a n d a r d c e r i u m ( I V ) s o l u t i o n , z m l of h y d r o f l u o r i c a c i d , a n d I ml of s u l f u r i c a c i d i n t o t h e b e a k e r . S t i r t h e m i x t u r e magn. e t i c a l l y u n t i l t h e glass h a s d i s s o l v e d . S o m e s a m p l e s r e q u i r e h o t a c i d s t o effect d i s s o l u t i o n . T h e y m a y b e h e a t e d for 24 h OF m o r e in a w a t e r b a t h at i o o ° w i t h o u t d e s t r o y i n g t h e o x i d a n t . B l a n k s are t r e a t e d s i m i l a r l y . A d d IO g of b o r i c a c i d t o t h e d i s s o l v e d s a m p l e a n d s t i r f o r a n a d d i t i o n a l 5 rain. T r a n s f e r t h e s a m p l e s o l u t i o n t o a ~-5o-ml ] ~ r l e n m e y e r f l a s k a n d a l i q u o t 4 m l of s u l f u r i c a c i d a n d I m l of 1 : 2 o f e r r o i n s o l u t i o n i n t o t h e s a m p l e c o n t a i n e r . D i l u t e t o IOO ml a n d , w h i l e s t i r r i n g , t i t r a t e w i t h s t a n d a r d o . o o i M iron(II) a m m o n i u m s u l f a t e t o t h e e n d - p o i n t . U p to IO m g of iron(II) o x i d e c a n b e d e t e r m i n e d b y e m p l o y i n g t h e s t a n d a r d c e r i u m ( I V ) s t o c k s o l u t i o n a n d a s t a n d a r d o . o i M iron(II) ammonium sulfate titrant. D e l e r m i n a t i o n o f total i r o n W e i g h 5O-lOO m g of t i l e I o o - m e s h glass s a m p l e t o g i v e o . 5 - I . o m g of Fe20:3. T r a n s f e r t h e s a m p l e t o a 3 o - m l p l a t i n u m c r u c i b l e a n d t r e a t t h e g l a s s as d e s c r i b e d a b o v e for t h e s t a n d a r d i z a t i o n of t h e c e r a t e s o l u t i o n . W h e n t h e s a m p l e h a s d i s s o l v e d , p r o c e e d w i t h t h e c o l u m n r e d u c t i o n , lZeceive t h e e l u e n t in a 5 o o - m l E r l e n m e y e r f l a s k w h i c h c o n t a i n s a ~-ml a l i q u o t o f t h e o . o i M s t a n d a r d c e r i u m ( I V ) s o l u t i o n a n d IO g of b o r i c acid. M a g n e t i c a l l y s t i r t h e c e r i u m ( I V ) - b o r i c a c i d m i x t u r e w h i l e r e c e i v i n g t h e e l u e n t . A d d 4 m l of s u l f u r i c a c i d a n d I m l o f 1:2o f e r r o i n s o l u t i o n . T i t r a t e t h e e x c e s s of s t a n d a r d c e r i u m ( I V ) w i t h s t a n d a r d o . o o i m i r o n ( I I ) a m m o n i u m s u l f a t e t o t h e e n d - p o i n t . U p t o I o m g of t o t a l i r o n can b e d e t e r m i n e d b y e m p l o y i n g t h e s t a n d a r d cerium(IV) s t o c k s o l u t i o n a n d a s t a n d a r d o . o i M iron(II) a m m o n i u m s u l f a t e titrant. Valence d e t e r m i n a t i o n o f u r a n i u m G r i n d a c a l c i u m f l u o r i d e - u r a n i u m s a m p l e in an a g a t e m o r t a r t o pas.'.; IOO m e s h . W e i g h lOO-2OO m g t o g i v e o . I - I . O m g of u r a n i u m . W e i g h IOO-2OO nag of a f i n e l y g r o u n d c a l c i u m f l u o r i d e single c r y s t a l , w h i c h s e r v e s as p a r t of t h e b l a n k . T r a n s f e r t h e s a m p l e s t o 2 5 o - m l E r l e n m e y e r f l a s k s a n d a l i q u o t into e a c h 3 ml of o . o i M s t a n d a r d c e r i u m ( I V ) s u l f a t e s o l u t i o n , x m l of iron(III) s u l f a t e s o l u t i o n and, a f t e r t h e a d d i t i o n of 2.5 g of b o r i c acid, I m l of p e r c h l o r i c acid. S u s p e n d t h e flasks in a b o i l i n g w a t e r b a t h and stir the solutions magnetically. When the samples have dissolved, dilute t h e m t o 15o m l w i t h d i s t i l l e d w a t e r , a d d i n g 5 m l of s u l f u r i c a c i d a n d o n e d r o p o f Anal. Chim. Aata, 47 (I969) 495-502
498
u. ABED
o.o25 M f e r r o i n i n d i c a t o r . T i t r a t e t h e e x c e s s of c e r i u m ( I V ) w i t h s t a n d a r d o . o o i M iron(II) ammonium sulfate. A n i n d e p e n d e n t d e t e r m i n a t i o n for t o t a l u r a n i u m m u s t b e m a d e on a n o t h e r p o r t i o n of t h e s a m p l e i n o r d e r t o c a l c u l a t e t h e c h a n g e in v a l e n c e . DISCUSSION
Iron(iI) and ( I I I ) T h e i n s t a n t a n e o u s o x i d a t i o n of i r o n ( I I ) r e l e a s e d u p o n d i s s o l u t i o n of a g l a s s sample has obvious benefits. However, the strong oxidant selected must be stable w i t h r e s p e c t to l i g h t , t i m e , a n d t e m p e r a t u r e , a n d m u s t b e c o m p a t i b l e w i t h t h e h i g h l y a c i d i c g l a s s - d i s s o l v i n g m i x t u r e . D i c h r o m a t e a n d p e r m a n g a n a t e p r o v e d useless. O n t h e o t h e r h a n d , s u l f a t o c e r a t e , in m o l a r s u l f u r i c acid, is s t a b l e t o l i g h t ; it h a s an e x c e l l e n t , l o n g - t e r m s t a b i l i t y , a n d it c a n b e b o i l e d for s e v e r a l h o u r s w i t h o u t s i g n i f i c a n t d e c o m p o s i t i o n 0 , % Also, d a t a o b t a i n e d in t h i s l a b o r a t o r y i n d i c a t e t h a t it is s t a b l e in t h e h y d r o f l u o r i c - s u l f u r i c a c i d m i x t u r e , e m p l o y e d in t h e r e c o m m e n d e d p r o c e d u r e , for at l e a s t s i x d a y s at r o o m t e m p e r a t u r e a n d for m o r e t h a n 24 h a t xoo °. W h e n s u l f a t o c e r a t e is a d d e d to a s o l u t i o n c o n t a i n i n g h y d r o f l u o r i c a c i d , t h e familiar yellow disappears. Fluoride complexes cerium(IV) and probably decreases t h e o x i d a t i o n p o t e n t i M of t h e s y s t e m . I t w a s t h o u g h t , t h e r e f o r e , to be of v a l u e t o e s t i m a t e t h e f o r m a l o x i d a t i o n p o t e n t i a l . A r a n g e of v a l u e s f r o m 0.7 V to 0. 9 V w a s o b t a i n e d for t h e o x i d a t i o n p o t e n t i a l of t h e c e r i u m ( I V ) - c e r i u m ( I I I ) c o u p l e a t 25 °. Several problems were attendant: the ceriam(III) fluoride gradually forms a gelatinous p r e c i p i t a t e w h i c h c o a t s t h e p l a t i n u m wire, r e s u l t i n g in v a r y i n g p o t e n t i a l r e a d i n g s . T h e p o t e n t i a l o b t a i n e d is n o t s t r i c t l y a " f o r m a l o x i d a t i o n p o t e n t i a l " since b o t h t h e o x i d i z e d a n d t h e r e d u c e d f o r m s do n o t r e m M n in s o l u t i o n . H o w e v e r , t h e p o t e n t i a l o b t a i n e d is s u f f i c i e n t l y p o s i t i v e to o x i d i z e i r o n ( I I ) u n d e r t h e s a m e c o n d i t i o n s . A d d i t i o n of IO g of boric a c i d r e s u l t s in d i s s o l u t i o n of t h e c e r i u m ( I I I ) f l u o r i d e a n d in a m a r k e d i n c r e a s e in p o t e n t i a l , u p to a s t a b l e 1.31 V, d u e to r e l e a s e of c e r i m n ( I V ) ion b y b o r a t e - f l u o r i d e c o m p l e x i n g . F u r t h e r a d d i t i o n of b o r i c a c i d d o e s n o t a f f e c t t h e r e a d i n g s . T h e v a l u e r e p o r t e d h e r e is l o w e r t h a n t h e c o m m o n l y s t a t e d v a l u e o f 1.44 V a n d n l a y i n d i c a t e s o m e r e s i d u a l c e r i u m ( I V ) - f l u o r i d e c o m p l e x i n g , a l t h o u g h t h e solut i o n m e a s u r e d is s a t u r a t e d w i t h b o r i c acid. T h e v a l u e s p r e s e n t e d a r e n o t c o r r e c t e d for t h e j u n c t i o n p o t e n t i a l . T h e s t r o n g f l u o r i d e c o m p l e x i n g of i r o n ( I I I ) , b u t n o t t h a t of t h e i r o n ( I I ) , is well k n o w n . T h e r e f o r e , t h e low f o r m a l o x i d a t i o n p o t e n t i a l of o.51 V o b t a h l e d u n d e r t h e recommended conditions was expected. When the fluoride was masked with boric acid, a p o t e n t i a l of o.69. V w a s o b t a i n e d . Since i r o n ( I I I ) is c o m p l e x e d b y s u l f a t e (log f l a = 5 . 2 ) , t h e v a l u e r e p o r t e d here, a l t h o u g h l o w e r t h a n t h a t o b t a i n e d in 1 M sulfuric a c i d (0.68 V), is a c c e p t a b l e . T h e o x i d a t i o n p o t e n t i a l of o x y g e n ( I . 2 2 9 V) is c o n s i d e r a b l y m o r e p o s i t i v e t h a n t h e v a l u e s r e p o r t e d for t h e i r o n ( I I I ) - i r o n ( I I ) c o u p l e in e i t h e r f l u o r i d e or s u l f a t e m e d i a a n d , t h e r e f o r e , o x y g e n m u s t b e e x c l u d e d . A s t u d y w a s m a d e to c o r r e l a t e t h e p a r t i c l e size of a c o m m e r c i a l glass w i t h t h e time required for dissolution, and to deternfine whether there was any relationship b e t w e e n t h e p a r t i c l e size a n d t h e i r o n ( I I ) c o n t e n t f o u n d . T h e g l a s s w a s g r o u n d in a D i a m o n i t e m o r t a r a n d s i e v e d t o g i v e > 20 m e s h , < 20 m e s h , < 4.8 m e s h , < 80 m e s h , a n d < xoo m e s h . A p p r o x i m a t e l y IOO m g of e a c h m e s h size w a s d i s s o l v e d in d u p l i c a t e A~zal. Gldm. Aata, 47 (1969) 4 9 5 - 5 o 2
DETERMINATION
OF
VALENCE
STATES
OF
l~e AND
499
U
f o r 15o m i n i n t h e h y d r o f l u o r i c - s u l f u r i c a c i d a n d c e r i u m ( I V ) m i x t u r e t o e s t a b l i s h t h e a m o u n t of i r o n ( I I ) p r e s e n t . T h e d i s s o l u t i o n t i m e w a s t h e n s h o r t e n e d w i t h d e c r e a s i n g p a r t i c l e size. T r i p l i c a t e a n d q u a d r u p l i c a t e r e s u l t s were s e c u r e d in m o s t cases. T h e m i n i m u m t i m e r e q u i r e d for d i s s o l v i n g tile p a r t i c u l a r g l a s s a t h a n d w a s : < IOO m e s h , IO r a i n ; < 8 o m e s h , 20 rain; <.48 m e s h , 45 r a i n ; < 2 o m e s h , IOO rain; > 2 0 m e s h , I2O r a i n . T h e i r o n ( I I ) c o n t e n t w a s i n d e p e n d e n t of t h e l e n g t h of t i m e of g r i n d i n g . E v i d e n t l y , n o o x i d a t i o n of i r o n ( I I ) o c c u r r e d d u r i n g p r o l o n g e d g r i n d i n g (5 d a y s ) or d u r i n g e x p o s u r e to air of t h e finely g r o u n d s a m p l e , s u p p o r t i n g t h e v i e w s of HILLEBRAND 8 a n d DENSEM 9. T h e a v e r a g e v a l u e of 35 c o m p l e t e l y d i s s o l v e d s a m p l e s w a s 0 . 3 7 4 % i r o n ( I I ) , c o v e r i n g t h e r a n g e f r o m o . 3 5 5 % to o . 3 9 1 ° , w i t h a s t a n d a r d d e v i a t i o n of o . o i % . T h e b a s i s U p o n w h i c h d i s s o l u t i o n w a s j u d g e d to be c o m p l e t e w e r e t h e v a l u e s o b t a i n e d for all m e s h sizes a f t e r 15o rain of d i s s o l v i n g . B a s e d on t h e f o r e g o i n g f i n d i n g s , s o d i u m d i s i l i c a t e glasses, w h i c h h a d b e e n u s e d in h i g h - t e m p e r a t u r e electrochemistry experiments, were analyzed according to the recommended proced u r e . R e p r o d u c i b l e r e s u l t s a r e r e p r e s e n t e d b y : S a m p l e A, I9.Xz+o.5~/o i r o n ( I I ) (5 d e t e r m i n a t i o n s ) a n d , S a m p l e 1B, 2 5 . 9 o + o . 1 5 % i r o n ( I I ) (3 d e t e r m i n a t i o n s ) . A p o t e n t i o m e t r i c d e t e r m i n a t i o n of m i c r o a m o u n t s of i r o n ( I I ) d e s c r i b e d in t h e l i t e r a t u r O 0 s e e m e d t o h a v e s e v e r a l d r a w b a c k s ; in p a r t i c u l a r , t h a t t h e g l a s s e s s u b m i t t e d for a n a l y s i s c o u l d n o t be d i s s o l v e d w i t h i n 5 r a i n as c o u l d t h o s e cited. T h e p r e s e n t m e t h o d w a s t h e r e f o r e t e s t e d o n t h e s e m i - m i c r o scale. S t a n d a r d glasses are n o t a v a i l a b l e a n d h a d to be s i m u l a t e d b y u s i n g i r o n - f r e e q u a r t z wool a n d k n o w n q u a n t i t i e s of s t a n d a r d i r o n ( I I ) a m m o n i u m s u l f a t e . T h e a m o u n t of i r o n ( I I ) f o u n d w a s w i t h i n 1 % o f t h e a m o u n t a d d e d (Table I). T a b l e I I i l l u s t r a t e s t h e p r e c i s i o n o b t a i n e d TABLE
I
SEMI-MICRO ANALYSIS OF I R O N ( [ I ) AMI~ION'IUM SULFAT~ AND QUARTZ ~.VOOL
mmoles Fe(II)
% Error
,,1 dded
_l;'ound
0.01003 0.01003 o.oxoo 3 o.oo5o I 0.00501
0.00990 0.00995 0.00995 o. 0 0 4 9 9
-- r .3 --0.8 --0.8 -- o.4
0.00504
+0.6
TABLE ANALYSIS
II OF INDUSTRIAL
5;am#le #e(II) (%)
Quoted
GLASSES
Found
No. of deters.
Std. dev. (%)
Range (%)
x
o.=8i
0.306
8
4-o.ooz
0.302-0.309
= 3
0-546 0.350
0-573 I.I9
9
8
4-0.008 4-0.003
0.56o-0.587 I.I7--I.26
0.322 0.588 1.19
0-424 0.650 x.4z
5 4 4
-4-O.Oll .-I- o . 0 2 o 4-0.060
o.413-o.442 0.635--0.685 1.36-x.48
T o t a l iron ( % ) x :Z 3
A ~ a l . Chim. A c t a , 47 (1959) 4 9 5 - 5 0 2
500
U. A B E D
for a n a l y s i s of i n d u s t r i a l glasses c o n t a i n i n g x ~o or less of i r o n ( I I ) . T h e a n a l y t i c a l d a t a q u o t e d b y t h e m a n u f a c t u r e r for i r o n ( I I ) a n d for t o t a l i r o n w e r e u s u a l l y l o w e r t h a n the results obtained with the proposed method. F o r t h e d e t e r m i n a t i o n of t o t a l iron, a n i n e r t a t m o s p h e r e w a s e l i m i n a t e d b y r e c e i v i n g t h e r e d u c e d e l u e n t in a n e x c e s s of s t a n d a r d c e r i u m ( I V ) , w h i c h was b a c k t i t r a t e d w i t h s t a n d a r d i r o n ( I I ) a m m o n i u m sulfate. T h e t i t r a t i o n e n d - p o i n t c o u l d be o b s e r v e d m o r e c a r e f u l l y w i t h o u t t h e D r y I c e , s p l a s h i n g of t h e s a m p l e s o l u t i o n w a s a v o i d e d , a n d t h e s o l u t i o n s d i d n o t h a v e to b e t i t r a t e d i m m e d i a t e l y . T h e a c c u r a c y o b t a i n e d w i t h a series of s i m u l a t e d s a m p l e s w a s w i t h i n 0 . 3 % of t h e a m o u n t of t o t a l iron present. F u r t h e r m o r e , r a t i o s of i r o n ( I I ) t o i r o n ( I I I ) w e r e d e t e r m i n e d in m a g n e s i u m o x i d e c r y s t a l s w h i c h w e r e u s e d in e l e c t r o n p a r a m a g n e t i c r e s o n a n c e s t u d i e s . T h e r a t i o s o b t a i n e d b y t h e r e c o m m e n d e d p r o c e d u r e , b u t o m i t t i n g h y d r o f l u o r i c a n d b o r i c acid, • vere in g o o d a g r e e m e n t w i t h t h e t h e o r e t i c a l v a l u e s . T h e m e t h o d a p p l i e s t o glasses a n d t o m a t e r i a l s w h i c h d o n o t c o n t a i n r e d u c i n g s u b s t a n c e s o t h e r t h a n i r o n ( I I ) a n d w h i c h can. b e d i s s o l v e d at IOO ° or less. I t s h o u l d b e f e a s i b l e to d e t e r m i n e m i c r o a m o u n t s of i r o n ( I I ) b y a s l i g h t m o d i f i c a t i o n of t h e p r o p o s e d m e t h o d i n w h i c h t h e final t i t r a t i o n w i t h i r o n ( I I ) a m m o n i u m s u l f a t e is s u b s t i t u t e d b y a s p e c t r o p h o t o m e t r i c d e t e r m i n a t i o n of t h e excess of c e r i u m ( I V ) a t 35o n m . The suggested procedure has the following advantages over existing methods for t h e F e O d e t e r m i n a t i o n in glass: (I) b e t t e r p r e c i s i o n , (2) e l i m i n a t i o n of a n i n e r t a t m o s p h e r e for t h e i r o n ( I I ) as well as for t h e to~al i r o n d e t e r m i n a t i o n , (3) s t a b i l i t y of ~he o x i d a n t a t xoo °, a n d (4) s i m p l i c i t y of o p e r a t i o n w i t h c o m m o n , i n e x p e n s i v e l a b o ratory equipment. Many samples may be determined simultaneously during a working day. Ura~um T h e p r i n c i p l e of a n i n s t a n t a n e o u s o x i d a t i o n w a s a p p l i e d t o t h e d e t e r m i n a t i o n of t h e o x i d a t i o n s t a t e of u r a n i u m in c a l c i u m f l u o r i d e single c r y s t a l s , t h e p r o p e r t i e s of w h i c h are b e i n g s t u d i e d b y o p t i c a l s p e c t r o s c o p y . T h e s e c r y s t a l s c o n t a i n e d o.x-o.8~/o of u r a n i u m b e l i e v e d to b e i n t h e + 3 o r t h e + 4 o x i d a t i o n s t a t e . A n i r o n ( I I I ) c a t a l y s t was required to hasten the oxidation of uranium(IV) to uranium(VI) by cerium(IV). Preliminary tests were made with simulated samples, using N.B.S. uranium d i o x i d e a n d r e a g e n t - g r a d e c a l c i u m f l u o r i d e . T h e r e a g e n t b l a n k for IOO m g of c a l c i u m f l u o r i d e , c o m b i n e d w i t h t h e acids a n d t h e i n d i c a t o r u s e d in t h e r e c o m m e n d e d p r o c e dure, c o n s u m e d 4 o % of t h e a d d e d s t a l x d a r d c e r i u m ( I V ) . I n v i e w of a d e s i r e d o v e r a l l a c c u r a c y of 4-xo~/o i n t h e v a l e n c e d e t e r m i n a t i o n , a 4 0 % b l a n k c o u l d n o t b e t o l e r a t e d . I n s t e a d , a f i n e l y g r o u n d c a l c i u m f l u o r i d e s i n g l e c r y s t a l w a s u s e d in s u b s e q u e n t w o r k . T h i s c r y s t a l w a s g r o w n f r o m s p e c i a l l y p u r i f i e d r e a g e n t s for o p t i c a l s t u d i e s . T h e v a l u e of t h e b l a n k d e c r e a s e d t o x o % of t h e a d d e d s t a n d a r d c e r i u m ( I V ) . I t w a s p r o v e d t h a t t h i s b l a n k w a s "h~ot d u e t o t h e c a l c i u m f l u o r i d e , b u t e x c l u s i v e l y t o t h e a c i d s a n d indicator. I t h a s b e e n s t a t e d ix t h a t c a l c i u m f l u o r i d e c a n b e r e a d i l y d i s s o l v e d i n h o t h y d r o c h l o r i c a c i d i n t h e p r e s e n c e of f l u o r i d e - c o m p l e x i n g c a t i o n s . A n i n v e s t i g a t i o n showed that hydrochloric acid was not an efficient solvent, and that cerium(IV) a p p a r e n t l y o x i d i z e d c h l o r i d e t o c h l o r i n e . P e r c h l o r i c a c i d w a s c h o s e n for t h e reA~al. Ghi~r~. Acta, 47 (x969) 495-502
DETERMINATION
OF VALENCE
STATES
OF
Fe A N D
U
5o1
c o m m e n d e d p r o c e d u r e b e c a u s e it d i s s o l v e d t h e c a l c i u m f l u o r i d e c r y s t a l s w i t h i n s e v e r a l h o u r s j u s t b e l o w IOO ° a n d d i d n o t i n t e r f e r e w i t h t h e o x i d a n t .
Acc,~racy T h e m e t h o d w a s a p p l i e d t o s i m u l a t e d s a m p l e s c o n s i s t i n g of a c a l c i u m f l u o r i d e s i n g l e c r y s t a l t o w h i c h k n o w n q u a n t i t i e s of N . B . S . u r a n i u m d i o x i d e w e r e a d d e d . A p p r o x i m a t e l y IOO m g of c a l c i u m f l u o r i d e w e r e c o m b i n e d w i t h a p p r o x i m a t e l y 2.5 m g of u r a n i u m d i o x i d e . T h e r e s u l t s o b t a i n e d b y t i t r a t i n g t h e e x c e s s of c e r i u m ( I V ) w e r e low b y a n a v e r a g e of 1o% . A l e a d c o l u m n r e d u c t i o n of k n o w n m i x t u r e s of u r a n i u m d i o x i d e (2.5 rag) a n d c a l c i u m f l u o r i d e (IOO ing) in perclfioric a c i d , o x i d i z e d f i r s t t o t h e + 6 v a l e n c e s t a t e w i t h h y d r o g e n p e r o x i d e , g a v e a 4 % p o s i t i v e e r r o r for t h e d e t e r m i n a t i o n of t o t a l u r a n i u m . A p i n k s i n g l e c r y s t a l , c o n s i s t i n g of c a l c i u m f l u o r i d e a n d u r a n i u m in t h e + 3 o x i d a t i o n s t a t e as e v i d e n c e d b y t h e c h a r a c t e r i s t i c color, w a s a n a l y z e d i n q u a d r u p l i ca're. T h e p r e c i s i o n wm~ + o . 1 3 % . N o t e n o u g h m a t e r i a l w a s a v a i l a b l e t o p e r m i t t h e d e t e r m i n a t i o n of t o t a l u r a n i u m a n d t h e r e f o r e , t h e i n i t i a l v a l e n c e c o u l d n o t be confirmed. A g r e e n s i n g l e c r y s t a l , h o w e v e r , w a s a n a l y z e d for t o t a l u r a n i u m b y t w o ind e p e n d e n t m e t h o d s . N e u t r o n a c t i v a t i o n a n a l y s i s in d u p l i c a t e g a v e o . 7 o % a n d 0 . 8 2 % u r a n i u m . A s p e c t r o p h o t o m e t r i c d e t e r m i n a t i o n in d u p l i c a t e 12 r e s u l t e d in o . 8 1 % a n d o . 8 0 % u r a n i u m . T h e d e t e r m i n a t i o n of t h e c h a n g e in o x i d a t i o n s t a t e of t h e u r a n i u m b y c e r i u m ( I V ) t i t r a t i o n to u r a n i u m ( V I ) g a v e a v a l u e of 2.06 ( 4 - 5 % ) , i n d i c a t i n g t h e p r e s e n c e of u r a n i u m ( I V ) in t h e c r y s t a l ( T a b l e hi). O b v i o u s l y , t h e m e t h o d c a n n o t be u s e d w i t h o u t m o d i f i c a t i o n if m i x t u r e s of s e v e r a l v a l e n c e s a n d / o r r e d u c i n g s u b s t a n c e s are p r e s e n t . A d d i t i o n a l i n v e s t i g a t i o n s of t h e v a r i o u s o x i d a t i o n s t a t e s of u r a n i u m in c a l c i u m f l u o r i d e a n d in o t h e r s o l i d m a t e r i a l s a r e in p r o g r e s s . TABLE
III
S~l~i%tI-l~tlCRO D I ~ T E I , I % I I N ' A T I O N OI," U R A N I U M
meq. zo-5 fot~nd
m m o l e s . IO-r" U found
6.57
3.32 = 3.44 = 3.36b 3.4 ob
6.88 6.92 7.I8 7.3t
ilv. 3.38 2ffeutron activation b Spcctrophotometry.
IN CALCIUI~I FLUORIDID
Oxidation change 1.94 2.04 2.05 2,12 2.16 av. 2.06
analysis.
SUMMARY
T h e i n s t a n t a n e o u s o x i d a t i o n of m a c r o a n d s e m i - m i c r o a m o u n t s of iron(II) in v a r i o u s t y p e s of glasses, of i r o n ( I I ) in m a g n e s i u m o x i d e , a n d of s e m i - m i c r o q u a n t i t i e s o f u r a n i u m ( I I I ) o r u r a n i u m ( I V ) in c a l c i u m f l u o r i d e s i n g l e c r y s t a l s , b y excess of c e r i u m ( I V ) p r e s e n t in t h e s o l v e n t s y s t e m , f o l l o w e d b y b a c k - t i t r a t i o n w i t h i r o n ( I I ) A ~ a l . Chim. A v t a , 47 ( 1 9 6 9 ) 4 9 5 - 5 0 2
502
U. A B E D
ammonium s u l f a t e , is t h e b a s i s f o r a s i m p l e , a c c u r a t e m e t h o d w h i c h , f u r t h e r m o r e , obviates the need for an inert atmosphere. Formal oxidation potentials of the Ce(IV)/ Ce(III) couple and the Fe(III)/Fe(II) c o u p l e in t h e h y d r o f l u o r i c - s u l f u r i c acid glassdissolving mixture were estimated. REFERENCES i I £ . L , CHENG, A ~ I .
C h e m . , 3 6 (I967) i666.
2 P . CLOSE, H . ~V[. SHEPHERD AND C. H . DRUMMOND, A n t . C e r a m . S o c . B u l l . , 41 (~958) 455.
W . ]). CO0K~, F . HAZEL AND W. M. MCNABB, / l n a l . C h e m . , 22 (195o) 654. W. D. TRI~ADWELL~ Helv. Chim. Acta, 5 (I9z2) 8o6. L. MEI'rES, Polt~rographic Techniques, z n d E d n . , I n t e r s c i e n c e , N e w Y o r k , 1965, p. 388. G. F . SMITH, Cerate Oxidimetry, G. F r e d e r i c k S m i t h C h e m . Co., C o l u m b u s , Ohio, 1942. I-[. A. LAITXNEN, Chemical A n a l y s i s , McGrztw-I-Iill B o o k Co., N e w Y o r k , 196o. W. F. HXLL~BRAND, jr. A m . Chem. See., 3o (I9o8) z i 2 o . N. E . DI~NS~M, J . Sea. Glass 7"ethanol., 27 (1936) 303. IO P . CLOSE, E . J . I"IORNYAK, T. ~BAA.K AND J . F . TILLI~IAN, .IWicrochem. f . , lO (x966) 333. I I A. ~I~UDR~VATOV, S'IIF l*analyse du f l u o r u r e de calcium (i,~z J~rench), C o m p t . r e n d . A c a d . Sci., U R S S , 4 (I934) 42. x2 F. G. SI.IERIB"AI~ID A. IV[. A~VAD, ./lnal. C h i m . . : l e t a , 26 (196z) 235. 3 4 5 6 7 8 9
A*~al. C h i m . Acta, 47 (x969) 495-502
495
Prirttcci in. T h e N e t h e r l a n d s
DETERMINATION OF VALENCE STATES OF OF UIZANIUM IN CALCIUM FLUORIDE SINGLE
IRON IN GLASS CIZYSTALS
AND
U. A : B E D L~wrence R a d i a t i o n Laboratory, U.niversity of California, Berkeley, Calif. 94720 ( ( f l . S . A . ) ( R e c e i v e d Ditty 2 6 t h , 1969)
D u r i n g s t u d i e s in t h i s l a b o r a t o r y , it b e c a m e n e c e s s a r y t o d e t e r m i n e t i l e i r o n ( I I ) a n d i r o n ( I I I ) o x i d e c o n t e n t of s o d i u m d i s i l i c a t e g l a s s e s w h i c h h a d b e e n u s e d in h i g h t e m p e r a t u r e e l e c t r o c h e m i s t r y e x p e r i m e n t s . A w e a l t h of p u b l i c a t i o n s deals w i t h t h e d e t e r m i n a t i o n of i r o n ( I I ) . A m o n g o t h e r s , CHENG 1 d i s c u s s e s v a r i o u s m e t h o d s for t h e d e t e r m i n a t i o n of i r o n ( I I ) o x i d e in s o m e s o l i d s a n d , s t a t i n g t h e l i m i t a t i o n s for his p u r p o s e , d e v e l o p e d a p r o c e d u r e for d e t e r m i n i n g i r o n ( I I ) i n ferrites. H o w e v e r , h i s a p p r o a c h is u n s u i t a b l e for t h e d e c o m p o s i t i o n of glass. A m e t h o d d e s c r i b e d b y CLOSE et al." f o r i r o n ( I I ) in glass w a s s e l e c t e d . T h e y r e c o m m e n d a h y d r o f l u o r i c - s u l f u r i c acic[ m i x t u r e for t h e d i s s o l u t i o n of g l a s s u n d e r a n i n e r t a t r n o s p h e r e , f o l l o w e d b y t i t r a t i o l x of t h e l i b e r a t e d i r o n ( I I ) w i t h c e r i u m ( I V ) . T h e i r o n ( I I ) r e s u l t s o b t a i n e d b y t h i s p r o c e d u r e in t h i s l a b o r a t o r y w e r e w i d e l y s c a t t e r e d , a n d a t t e m p t s to m o d i f y t h e method did not improve the precision. T h e m e t h o d p r e s e n t e d h e r e is b a s e d on t h e f a c t t h a t c e r i u m ( I V ) is s t a b l e for a n e x t e n d e d p e r i o d o v e r t h e t e m p e r a t u r e r a n g e 2 o - I o o ° in t h e h y d r o f l u o r i c - s u l f u r i c a c i d m i x t u r e . T h i s p e r m i t s t h e i n s t a n t a n e o u s o x i d a t i o n of t h e r e l e a s e d i r o n ( I I ) b y a k n o w n excess of s t a n d a r d c e r i u m ( I V ) s o l u t i o n d u r i n g t h e d i s s o l u t i o n of t h e g l a s s a n d t h u s o b v i a t e s t h e n e e d for a n i n e r t a t m o s p h e r e . T h e r e s u l t s o b t a i n e d o n g l a s s s a m p l e s b y t h i s p r o c e d u r e a r e p r e c i s e a n d t h e a c c u r a c y of t h e d e t e r m i n a t i o n o n s i m u l a t e d s a m p l e s w a s w i t h i n 1 % . T h e m e t h o d is also a p p l i c a b l e t o t h e d e t e r m i n a t i o n of i r o n ( I I ) o x i d e in m a g n e s i u m o x i d e . T h e f o r m a l o x i d a t i o n p o t e n t i a l s for t h e c e r i u m ( I V ) - c e r i u m ( I I I ) c o u p l e a n d for t h e i r o n ( I I I ) - i r o n ( I I ) c o u p l e are e s t i m a t e d i n t h e g l a s s d i s s o l v i n g a c i d m i x t u r e a n d t h e i r i m p o r t a n c e is d i s c u s s e d . T h e p r o c e d u r e w a s f u r t h e r e m p l o y e d in d e t e r m i n i n g v a l e n c e s t a t e s of s e m i - l n i c r o q u a n t i t i e s of u r a n i u m i n c a l c i u m f l u o r i d e single c r y s t a l s . :EXPERIMENTAL
Apparatus T e f l o n b e a k e r s w i t h p o u r i n g lips, 3.4 c m o.d., 2.7 c m i.d., a n d 4.6 c m h i g h , w i t h a c a p a c i t y of 30 m l , w e r e m a c h i n e d f r o m COlmnercial r o d s t o c k a n d w e r e f i t t e d with Teflon covers. Teflon-covered magnetic stirring bars, in conjunction with M a g - M i x m a g n e t i c s t i r r e r s , w e r e u s e d t o a g i t a t e t h e g l a s s - a c i d m i x t u r e s . Micro w a s h o u t p i p e t s , g u a r a n t e e d " t o c o n t a i n " w i t h i n +o.ox~/o of t h e s t a t e d v o l u m e , w e r e used to aliquot the standard solutions and the indicator. Hydrofluoric acid was aliquoted with 2.o-ml plastic pipets. A previously described lead column reductor A ~ a l . Chim. Acla, 47 (1969) 4 9 5 - 5 o ~
496
u. ABED
was u s e d in d e t e r m i n i n g t h e t o t a l u r a n i u m ~ a n d t h e t o t a l i r o n 4. T h e p o t e n t i a l m e a s u r e m e n t s w e r e m a d e w i t h a D i g i - T e c d i g i t a l d,c. v o l t m e t e r .
Reagents All c h e m i c a l s u s e d were r e a g e n t g r a d e u n l e s s o t h e r w i s e specified. S u f f i c i e n t c e r i u m (IV) a m m o n i u m n i t r a t e was d i s s o l v e d in s u l f u r i c a c i d to g i v e , on final d i l u t i o n , a s t o c k s o l u t i o n o . I 114 in c e r i u m ( I V ) a n d I M in s u l f u r i c a c i d ; o . o r M c e r i u m ( I V ) s o l u t i o n s w e r e p r e p a r e d b y d i l u t i o n of t h e s t o c k s o l u t i o n while m a i n t a i n i n g a s u l f u r i c a c i d c o n c e n t r a t i o n of l O % b y v o l u m e . T h e o.I M s o l u t i o n w a s s t a b l e for a t l e a s t 2 y e a r s , a n d t h e o . o i M d i l u t i o n was s t a b l e for a t l e a s t 3 w e e k s . A s t a n d a r d o . o o r M i r o n ( I I ) a m m o n i u m s u l f a t e s o l u t i o n , l O % b y v o l u m e in s u l f u r i c a c i d , was p r e p a r e d d a i l y b y d i r e c t w e i g h i n g . S u f f i c i e n t i r o n w i r e for s t a n d a r d i z a t i o n w a s d i s s o l v e d w i t h h y d r o c h l o r i c acid t o give a s o l u t i o n of o.I M i r o n ( I I I ) o n d i l u t i o n . A x:2o d i l u t i o n of the c o m m e r c i a l l y a v a i l a b l e I , I o - p h e n a n t h r o l i n e i r o n ( I I ) sulfo.te (ferroin) i n d i c a t o r , o.o25 M , f r o m G. F. S m i t h C h e m i c a l C o m p a n y v)as e m p l o y e d . C o n c e n t r a t e d s u l f u r i c a c i d a n d 4 8 % h y d r o f l u o r i c a c i d w e r e p u r i f i e d w i t h p e r m a n g a n a t e as d e s c r i b e d p r e v i o u s l y 2 a n d w e r e u s e d t h r o u g h o u t t h e p r o c e d u r e for i r o n . N.B.S. u r a n i u m d i o x i d e , o.I M i r o n ( I I I ) s u l f a t e solution, a n d a c a l c i u m f l u o r i d e single c r y s t a l w e r e u s e d in t h e u r a n i u m d e t e r m i n a t i o n . P o t e n t i a l measureme~tts T h e f o r m a l o x i d a t i o n p o t e n t i a l m e a s u r e m e n t s of t h e c e r i u m ( I V ) - c e r i u m ( I I I ) c o u p l e w e r e c o n d u c t e d in a I o o - m l p o l y e t h y l e n e cell, w i t h a. p l a t i n u n l w i r e a n d a L i n g a n e - t y p e s a t u r a t e d c a l o m e l e l e c t r o d e (SCE) c o m b i n a t i o n . D i f f u s i o n of t h e p o t a s s i u m c h l o r i d e i n t o t h e cell a n d c o n t a c t of t h e glass e l e c t r o d e w i t h h y d r o f l u o r i c a c i d is n o t d e s i r a b l e , t h e r e f o r e t h e e l e c t r i c a l c o n t a c t t h r o u g h t h e cell w a s a c c o m p l i s h e d b y a l l o w i n g t h e SCE b r i d g e t o dip i n t o a 5 M a m m o n i u m n i t r a t e soaution, a n d b y b r i d g i n g f r o m t h e r e i n t o t h e cell b y a bees' w a x - c o a t e d U - t u b e w i t h a n t t p t u r n e d tip. T h e a g a r a g a r s a l t b r i d g e w a s a v o i d e d b e c a u s e s t r o n g o x i d a n t s are k n o w n t o a t t a c k its. T h e e n t i r e cell a n d a s s o c i a t e d p a r t s w e r e i m m e r s e d in a z5.o ° +_o.I ° c o n s t a n t t e m p e r a t u r e bath. T h e s o l u t i o n u s e d c o n s i s t e d of I.OO m l of o.o992 M c e r i u m ( I V ) a n d I.OO m l of o.o99z 3/I c e r i u m ( I I I ) , b o t h in I /W s u l f u r i c acid, xo m l of h y d x o f l u o r i c a c i d , IO m l of s u l f u r i c acid, a n d 20 m l of w a t e r . T h e m i x t u r e w a s s t i r r e d cor~tinuously w i t h a m a g n e t i c s t i r r e r w h i l e p o t e n t i a l m e a s u r e m e n t s w e r e m a d e at 5 - m i n i n t e r v a l s . T h e m e a s u r e m e n t of tlae iron(III)-iron(II) f o r m a l o x i d a t i o n p o t e n t i a l was m a d e ill t h e s a m e cell as d e s c r i b e d a b o v e . I n this c a s e t h e b r i d g e s o l u t i o n w a s s a t u r a t e d p o t a s s i u m s u l f a t e , since c o n t a c t of a n i r o n ( I I ) s o l u t i o n w i t h a s t r o n g n i t r a t e s o l u t i o n m i g h t r e s u l t in o x i d a t i o n of t h e i r o n ( I I ) . "1"he i r o n ( I I I ) - i r o n ( I I ) p o t e n t i a l w a s m e a s u r e d o n a s o l u t i o n s i m i l a r t o t h e o n e above, b u t c o n t a i n i m g I.OO ml of 0.0988 NI i r o n ( I I I ) a n d x.oo m l of o.o999 / F / i r o n ( I I ) i n s t e a d of c e r i u m . B e f o r e a l i q u o t i n g t h e i r o n i n t o t h e a c i d - w a t e r solution, t h e m i x t u r e w a s p u r g e d of o x y g e n w i t h a c h i p of D r y Ice. C a r b o n d i o x i d e gas w a s d i r e c t e d o v e r t h e s u r f a c e of ~he s o l u t i o n d u r i n g t h e time the potential measurements were made. S t a n d a r d i z a t i o n o f o . o z M eerie sulfate D e l i v e r a 3 - m l a l i q u o t of t h e o.I M s t a n d a r d i r o n s o l u t i o n i n t o a 3 o - m l p l a t i n u m A n a l , C h i m . A c t a , 47 0 9 6 9 ) 495-5o2
DETERMINATION
OF V A L E N C E
STATES OF
Fe
AND U
497
c r u c i b l e a n d f u m e a l m o s t t o d r y n e s s w i t h x m l of s u l f u r i c a c i d a n d 2 m l of h y d r o f l u o r i c a c i d . T r a n s f e r t h e s a m p l e t o a 5 o - m l b e a k e r , a d d 5 ml of 4 M h y d r o c h l o r i c acid, a n d d i l u t e t o ~-5 ml. W a s h t h e irop. t h r o u g h a l e a d c o l u m n r e d u c t o r w i t h s i x 9-5-ml p o r t i o n s of o.8 M h y d r o c h l o r i c a c i d . R e c e i v e t h e e l u e n t in a 5 o o - m l E r l e n m e y e r f l a s k w h i c h c o n t a i n s IO g of b o r i c a c i d a n d s u f f i c i e n t D r y I c e to p r o v i d e an i n e r t a t m o s p h e r e t h r o u g h o u t t h e s u b s e q u e n t t i t r a t i o n . A l i q u o t 4 m l of s u l f u r i c a c i d a n d I ml of I :~-o f e r r o i n s o l u t i o n i n t o t h e s a m p l e flask. W h i l e stirring, t i t r a t e w i t h t h e o.ox / V / c e r i u m (IV) solution to the end-point. D e t e r m i n e indicator and reagent blanks and a p p l y t h e a p p r o p r i a t e titer corrections to the results.
D e t e r m i n a t i o n o f iron ( I I ) G r i n d a glass s a m p l e in a D i a m o n i t e m o r t a r t o p a s s IOO m e s h . W e i g h x o o m g of t h e glass t o g i v e o . 4 - 1 . o m g of iron(II) oxide. T r a n s f e r t h e s a m p l e t o a T e f l o n b e a k e r a n d a l i q u o t z m l of o . o i M s t a n d a r d c e r i u m ( I V ) s o l u t i o n , z m l of h y d r o f l u o r i c a c i d , a n d I ml of s u l f u r i c a c i d i n t o t h e b e a k e r . S t i r t h e m i x t u r e magn. e t i c a l l y u n t i l t h e glass h a s d i s s o l v e d . S o m e s a m p l e s r e q u i r e h o t a c i d s t o effect d i s s o l u t i o n . T h e y m a y b e h e a t e d for 24 h OF m o r e in a w a t e r b a t h at i o o ° w i t h o u t d e s t r o y i n g t h e o x i d a n t . B l a n k s are t r e a t e d s i m i l a r l y . A d d IO g of b o r i c a c i d t o t h e d i s s o l v e d s a m p l e a n d s t i r f o r a n a d d i t i o n a l 5 rain. T r a n s f e r t h e s a m p l e s o l u t i o n t o a ~-5o-ml ] ~ r l e n m e y e r f l a s k a n d a l i q u o t 4 m l of s u l f u r i c a c i d a n d I m l of 1 : 2 o f e r r o i n s o l u t i o n i n t o t h e s a m p l e c o n t a i n e r . D i l u t e t o IOO ml a n d , w h i l e s t i r r i n g , t i t r a t e w i t h s t a n d a r d o . o o i M iron(II) a m m o n i u m s u l f a t e t o t h e e n d - p o i n t . U p to IO m g of iron(II) o x i d e c a n b e d e t e r m i n e d b y e m p l o y i n g t h e s t a n d a r d c e r i u m ( I V ) s t o c k s o l u t i o n a n d a s t a n d a r d o . o i M iron(II) ammonium sulfate titrant. D e l e r m i n a t i o n o f total i r o n W e i g h 5O-lOO m g of t i l e I o o - m e s h glass s a m p l e t o g i v e o . 5 - I . o m g of Fe20:3. T r a n s f e r t h e s a m p l e t o a 3 o - m l p l a t i n u m c r u c i b l e a n d t r e a t t h e g l a s s as d e s c r i b e d a b o v e for t h e s t a n d a r d i z a t i o n of t h e c e r a t e s o l u t i o n . W h e n t h e s a m p l e h a s d i s s o l v e d , p r o c e e d w i t h t h e c o l u m n r e d u c t i o n , lZeceive t h e e l u e n t in a 5 o o - m l E r l e n m e y e r f l a s k w h i c h c o n t a i n s a ~-ml a l i q u o t o f t h e o . o i M s t a n d a r d c e r i u m ( I V ) s o l u t i o n a n d IO g of b o r i c acid. M a g n e t i c a l l y s t i r t h e c e r i u m ( I V ) - b o r i c a c i d m i x t u r e w h i l e r e c e i v i n g t h e e l u e n t . A d d 4 m l of s u l f u r i c a c i d a n d I m l o f 1:2o f e r r o i n s o l u t i o n . T i t r a t e t h e e x c e s s of s t a n d a r d c e r i u m ( I V ) w i t h s t a n d a r d o . o o i m i r o n ( I I ) a m m o n i u m s u l f a t e t o t h e e n d - p o i n t . U p t o I o m g of t o t a l i r o n can b e d e t e r m i n e d b y e m p l o y i n g t h e s t a n d a r d cerium(IV) s t o c k s o l u t i o n a n d a s t a n d a r d o . o i M iron(II) a m m o n i u m s u l f a t e titrant. Valence d e t e r m i n a t i o n o f u r a n i u m G r i n d a c a l c i u m f l u o r i d e - u r a n i u m s a m p l e in an a g a t e m o r t a r t o pas.'.; IOO m e s h . W e i g h lOO-2OO m g t o g i v e o . I - I . O m g of u r a n i u m . W e i g h IOO-2OO nag of a f i n e l y g r o u n d c a l c i u m f l u o r i d e single c r y s t a l , w h i c h s e r v e s as p a r t of t h e b l a n k . T r a n s f e r t h e s a m p l e s t o 2 5 o - m l E r l e n m e y e r f l a s k s a n d a l i q u o t into e a c h 3 ml of o . o i M s t a n d a r d c e r i u m ( I V ) s u l f a t e s o l u t i o n , x m l of iron(III) s u l f a t e s o l u t i o n and, a f t e r t h e a d d i t i o n of 2.5 g of b o r i c acid, I m l of p e r c h l o r i c acid. S u s p e n d t h e flasks in a b o i l i n g w a t e r b a t h and stir the solutions magnetically. When the samples have dissolved, dilute t h e m t o 15o m l w i t h d i s t i l l e d w a t e r , a d d i n g 5 m l of s u l f u r i c a c i d a n d o n e d r o p o f Anal. Chim. Aata, 47 (I969) 495-502
498
u. ABED
o.o25 M f e r r o i n i n d i c a t o r . T i t r a t e t h e e x c e s s of c e r i u m ( I V ) w i t h s t a n d a r d o . o o i M iron(II) ammonium sulfate. A n i n d e p e n d e n t d e t e r m i n a t i o n for t o t a l u r a n i u m m u s t b e m a d e on a n o t h e r p o r t i o n of t h e s a m p l e i n o r d e r t o c a l c u l a t e t h e c h a n g e in v a l e n c e . DISCUSSION
Iron(iI) and ( I I I ) T h e i n s t a n t a n e o u s o x i d a t i o n of i r o n ( I I ) r e l e a s e d u p o n d i s s o l u t i o n of a g l a s s sample has obvious benefits. However, the strong oxidant selected must be stable w i t h r e s p e c t to l i g h t , t i m e , a n d t e m p e r a t u r e , a n d m u s t b e c o m p a t i b l e w i t h t h e h i g h l y a c i d i c g l a s s - d i s s o l v i n g m i x t u r e . D i c h r o m a t e a n d p e r m a n g a n a t e p r o v e d useless. O n t h e o t h e r h a n d , s u l f a t o c e r a t e , in m o l a r s u l f u r i c acid, is s t a b l e t o l i g h t ; it h a s an e x c e l l e n t , l o n g - t e r m s t a b i l i t y , a n d it c a n b e b o i l e d for s e v e r a l h o u r s w i t h o u t s i g n i f i c a n t d e c o m p o s i t i o n 0 , % Also, d a t a o b t a i n e d in t h i s l a b o r a t o r y i n d i c a t e t h a t it is s t a b l e in t h e h y d r o f l u o r i c - s u l f u r i c a c i d m i x t u r e , e m p l o y e d in t h e r e c o m m e n d e d p r o c e d u r e , for at l e a s t s i x d a y s at r o o m t e m p e r a t u r e a n d for m o r e t h a n 24 h a t xoo °. W h e n s u l f a t o c e r a t e is a d d e d to a s o l u t i o n c o n t a i n i n g h y d r o f l u o r i c a c i d , t h e familiar yellow disappears. Fluoride complexes cerium(IV) and probably decreases t h e o x i d a t i o n p o t e n t i M of t h e s y s t e m . I t w a s t h o u g h t , t h e r e f o r e , to be of v a l u e t o e s t i m a t e t h e f o r m a l o x i d a t i o n p o t e n t i a l . A r a n g e of v a l u e s f r o m 0.7 V to 0. 9 V w a s o b t a i n e d for t h e o x i d a t i o n p o t e n t i a l of t h e c e r i u m ( I V ) - c e r i u m ( I I I ) c o u p l e a t 25 °. Several problems were attendant: the ceriam(III) fluoride gradually forms a gelatinous p r e c i p i t a t e w h i c h c o a t s t h e p l a t i n u m wire, r e s u l t i n g in v a r y i n g p o t e n t i a l r e a d i n g s . T h e p o t e n t i a l o b t a i n e d is n o t s t r i c t l y a " f o r m a l o x i d a t i o n p o t e n t i a l " since b o t h t h e o x i d i z e d a n d t h e r e d u c e d f o r m s do n o t r e m M n in s o l u t i o n . H o w e v e r , t h e p o t e n t i a l o b t a i n e d is s u f f i c i e n t l y p o s i t i v e to o x i d i z e i r o n ( I I ) u n d e r t h e s a m e c o n d i t i o n s . A d d i t i o n of IO g of boric a c i d r e s u l t s in d i s s o l u t i o n of t h e c e r i u m ( I I I ) f l u o r i d e a n d in a m a r k e d i n c r e a s e in p o t e n t i a l , u p to a s t a b l e 1.31 V, d u e to r e l e a s e of c e r i m n ( I V ) ion b y b o r a t e - f l u o r i d e c o m p l e x i n g . F u r t h e r a d d i t i o n of b o r i c a c i d d o e s n o t a f f e c t t h e r e a d i n g s . T h e v a l u e r e p o r t e d h e r e is l o w e r t h a n t h e c o m m o n l y s t a t e d v a l u e o f 1.44 V a n d n l a y i n d i c a t e s o m e r e s i d u a l c e r i u m ( I V ) - f l u o r i d e c o m p l e x i n g , a l t h o u g h t h e solut i o n m e a s u r e d is s a t u r a t e d w i t h b o r i c acid. T h e v a l u e s p r e s e n t e d a r e n o t c o r r e c t e d for t h e j u n c t i o n p o t e n t i a l . T h e s t r o n g f l u o r i d e c o m p l e x i n g of i r o n ( I I I ) , b u t n o t t h a t of t h e i r o n ( I I ) , is well k n o w n . T h e r e f o r e , t h e low f o r m a l o x i d a t i o n p o t e n t i a l of o.51 V o b t a h l e d u n d e r t h e recommended conditions was expected. When the fluoride was masked with boric acid, a p o t e n t i a l of o.69. V w a s o b t a i n e d . Since i r o n ( I I I ) is c o m p l e x e d b y s u l f a t e (log f l a = 5 . 2 ) , t h e v a l u e r e p o r t e d here, a l t h o u g h l o w e r t h a n t h a t o b t a i n e d in 1 M sulfuric a c i d (0.68 V), is a c c e p t a b l e . T h e o x i d a t i o n p o t e n t i a l of o x y g e n ( I . 2 2 9 V) is c o n s i d e r a b l y m o r e p o s i t i v e t h a n t h e v a l u e s r e p o r t e d for t h e i r o n ( I I I ) - i r o n ( I I ) c o u p l e in e i t h e r f l u o r i d e or s u l f a t e m e d i a a n d , t h e r e f o r e , o x y g e n m u s t b e e x c l u d e d . A s t u d y w a s m a d e to c o r r e l a t e t h e p a r t i c l e size of a c o m m e r c i a l glass w i t h t h e time required for dissolution, and to deternfine whether there was any relationship b e t w e e n t h e p a r t i c l e size a n d t h e i r o n ( I I ) c o n t e n t f o u n d . T h e g l a s s w a s g r o u n d in a D i a m o n i t e m o r t a r a n d s i e v e d t o g i v e > 20 m e s h , < 20 m e s h , < 4.8 m e s h , < 80 m e s h , a n d < xoo m e s h . A p p r o x i m a t e l y IOO m g of e a c h m e s h size w a s d i s s o l v e d in d u p l i c a t e A~zal. Gldm. Aata, 47 (1969) 4 9 5 - 5 o 2
DETERMINATION
OF
VALENCE
STATES
OF
l~e AND
499
U
f o r 15o m i n i n t h e h y d r o f l u o r i c - s u l f u r i c a c i d a n d c e r i u m ( I V ) m i x t u r e t o e s t a b l i s h t h e a m o u n t of i r o n ( I I ) p r e s e n t . T h e d i s s o l u t i o n t i m e w a s t h e n s h o r t e n e d w i t h d e c r e a s i n g p a r t i c l e size. T r i p l i c a t e a n d q u a d r u p l i c a t e r e s u l t s were s e c u r e d in m o s t cases. T h e m i n i m u m t i m e r e q u i r e d for d i s s o l v i n g tile p a r t i c u l a r g l a s s a t h a n d w a s : < IOO m e s h , IO r a i n ; < 8 o m e s h , 20 rain; <.48 m e s h , 45 r a i n ; < 2 o m e s h , IOO rain; > 2 0 m e s h , I2O r a i n . T h e i r o n ( I I ) c o n t e n t w a s i n d e p e n d e n t of t h e l e n g t h of t i m e of g r i n d i n g . E v i d e n t l y , n o o x i d a t i o n of i r o n ( I I ) o c c u r r e d d u r i n g p r o l o n g e d g r i n d i n g (5 d a y s ) or d u r i n g e x p o s u r e to air of t h e finely g r o u n d s a m p l e , s u p p o r t i n g t h e v i e w s of HILLEBRAND 8 a n d DENSEM 9. T h e a v e r a g e v a l u e of 35 c o m p l e t e l y d i s s o l v e d s a m p l e s w a s 0 . 3 7 4 % i r o n ( I I ) , c o v e r i n g t h e r a n g e f r o m o . 3 5 5 % to o . 3 9 1 ° , w i t h a s t a n d a r d d e v i a t i o n of o . o i % . T h e b a s i s U p o n w h i c h d i s s o l u t i o n w a s j u d g e d to be c o m p l e t e w e r e t h e v a l u e s o b t a i n e d for all m e s h sizes a f t e r 15o rain of d i s s o l v i n g . B a s e d on t h e f o r e g o i n g f i n d i n g s , s o d i u m d i s i l i c a t e glasses, w h i c h h a d b e e n u s e d in h i g h - t e m p e r a t u r e electrochemistry experiments, were analyzed according to the recommended proced u r e . R e p r o d u c i b l e r e s u l t s a r e r e p r e s e n t e d b y : S a m p l e A, I9.Xz+o.5~/o i r o n ( I I ) (5 d e t e r m i n a t i o n s ) a n d , S a m p l e 1B, 2 5 . 9 o + o . 1 5 % i r o n ( I I ) (3 d e t e r m i n a t i o n s ) . A p o t e n t i o m e t r i c d e t e r m i n a t i o n of m i c r o a m o u n t s of i r o n ( I I ) d e s c r i b e d in t h e l i t e r a t u r O 0 s e e m e d t o h a v e s e v e r a l d r a w b a c k s ; in p a r t i c u l a r , t h a t t h e g l a s s e s s u b m i t t e d for a n a l y s i s c o u l d n o t be d i s s o l v e d w i t h i n 5 r a i n as c o u l d t h o s e cited. T h e p r e s e n t m e t h o d w a s t h e r e f o r e t e s t e d o n t h e s e m i - m i c r o scale. S t a n d a r d glasses are n o t a v a i l a b l e a n d h a d to be s i m u l a t e d b y u s i n g i r o n - f r e e q u a r t z wool a n d k n o w n q u a n t i t i e s of s t a n d a r d i r o n ( I I ) a m m o n i u m s u l f a t e . T h e a m o u n t of i r o n ( I I ) f o u n d w a s w i t h i n 1 % o f t h e a m o u n t a d d e d (Table I). T a b l e I I i l l u s t r a t e s t h e p r e c i s i o n o b t a i n e d TABLE
I
SEMI-MICRO ANALYSIS OF I R O N ( [ I ) AMI~ION'IUM SULFAT~ AND QUARTZ ~.VOOL
mmoles Fe(II)
% Error
,,1 dded
_l;'ound
0.01003 0.01003 o.oxoo 3 o.oo5o I 0.00501
0.00990 0.00995 0.00995 o. 0 0 4 9 9
-- r .3 --0.8 --0.8 -- o.4
0.00504
+0.6
TABLE ANALYSIS
II OF INDUSTRIAL
5;am#le #e(II) (%)
Quoted
GLASSES
Found
No. of deters.
Std. dev. (%)
Range (%)
x
o.=8i
0.306
8
4-o.ooz
0.302-0.309
= 3
0-546 0.350
0-573 I.I9
9
8
4-0.008 4-0.003
0.56o-0.587 I.I7--I.26
0.322 0.588 1.19
0-424 0.650 x.4z
5 4 4
-4-O.Oll .-I- o . 0 2 o 4-0.060
o.413-o.442 0.635--0.685 1.36-x.48
T o t a l iron ( % ) x :Z 3
A ~ a l . Chim. A c t a , 47 (1959) 4 9 5 - 5 0 2
500
U. A B E D
for a n a l y s i s of i n d u s t r i a l glasses c o n t a i n i n g x ~o or less of i r o n ( I I ) . T h e a n a l y t i c a l d a t a q u o t e d b y t h e m a n u f a c t u r e r for i r o n ( I I ) a n d for t o t a l i r o n w e r e u s u a l l y l o w e r t h a n the results obtained with the proposed method. F o r t h e d e t e r m i n a t i o n of t o t a l iron, a n i n e r t a t m o s p h e r e w a s e l i m i n a t e d b y r e c e i v i n g t h e r e d u c e d e l u e n t in a n e x c e s s of s t a n d a r d c e r i u m ( I V ) , w h i c h was b a c k t i t r a t e d w i t h s t a n d a r d i r o n ( I I ) a m m o n i u m sulfate. T h e t i t r a t i o n e n d - p o i n t c o u l d be o b s e r v e d m o r e c a r e f u l l y w i t h o u t t h e D r y I c e , s p l a s h i n g of t h e s a m p l e s o l u t i o n w a s a v o i d e d , a n d t h e s o l u t i o n s d i d n o t h a v e to b e t i t r a t e d i m m e d i a t e l y . T h e a c c u r a c y o b t a i n e d w i t h a series of s i m u l a t e d s a m p l e s w a s w i t h i n 0 . 3 % of t h e a m o u n t of t o t a l iron present. F u r t h e r m o r e , r a t i o s of i r o n ( I I ) t o i r o n ( I I I ) w e r e d e t e r m i n e d in m a g n e s i u m o x i d e c r y s t a l s w h i c h w e r e u s e d in e l e c t r o n p a r a m a g n e t i c r e s o n a n c e s t u d i e s . T h e r a t i o s o b t a i n e d b y t h e r e c o m m e n d e d p r o c e d u r e , b u t o m i t t i n g h y d r o f l u o r i c a n d b o r i c acid, • vere in g o o d a g r e e m e n t w i t h t h e t h e o r e t i c a l v a l u e s . T h e m e t h o d a p p l i e s t o glasses a n d t o m a t e r i a l s w h i c h d o n o t c o n t a i n r e d u c i n g s u b s t a n c e s o t h e r t h a n i r o n ( I I ) a n d w h i c h can. b e d i s s o l v e d at IOO ° or less. I t s h o u l d b e f e a s i b l e to d e t e r m i n e m i c r o a m o u n t s of i r o n ( I I ) b y a s l i g h t m o d i f i c a t i o n of t h e p r o p o s e d m e t h o d i n w h i c h t h e final t i t r a t i o n w i t h i r o n ( I I ) a m m o n i u m s u l f a t e is s u b s t i t u t e d b y a s p e c t r o p h o t o m e t r i c d e t e r m i n a t i o n of t h e excess of c e r i u m ( I V ) a t 35o n m . The suggested procedure has the following advantages over existing methods for t h e F e O d e t e r m i n a t i o n in glass: (I) b e t t e r p r e c i s i o n , (2) e l i m i n a t i o n of a n i n e r t a t m o s p h e r e for t h e i r o n ( I I ) as well as for t h e to~al i r o n d e t e r m i n a t i o n , (3) s t a b i l i t y of ~he o x i d a n t a t xoo °, a n d (4) s i m p l i c i t y of o p e r a t i o n w i t h c o m m o n , i n e x p e n s i v e l a b o ratory equipment. Many samples may be determined simultaneously during a working day. Ura~um T h e p r i n c i p l e of a n i n s t a n t a n e o u s o x i d a t i o n w a s a p p l i e d t o t h e d e t e r m i n a t i o n of t h e o x i d a t i o n s t a t e of u r a n i u m in c a l c i u m f l u o r i d e single c r y s t a l s , t h e p r o p e r t i e s of w h i c h are b e i n g s t u d i e d b y o p t i c a l s p e c t r o s c o p y . T h e s e c r y s t a l s c o n t a i n e d o.x-o.8~/o of u r a n i u m b e l i e v e d to b e i n t h e + 3 o r t h e + 4 o x i d a t i o n s t a t e . A n i r o n ( I I I ) c a t a l y s t was required to hasten the oxidation of uranium(IV) to uranium(VI) by cerium(IV). Preliminary tests were made with simulated samples, using N.B.S. uranium d i o x i d e a n d r e a g e n t - g r a d e c a l c i u m f l u o r i d e . T h e r e a g e n t b l a n k for IOO m g of c a l c i u m f l u o r i d e , c o m b i n e d w i t h t h e acids a n d t h e i n d i c a t o r u s e d in t h e r e c o m m e n d e d p r o c e dure, c o n s u m e d 4 o % of t h e a d d e d s t a l x d a r d c e r i u m ( I V ) . I n v i e w of a d e s i r e d o v e r a l l a c c u r a c y of 4-xo~/o i n t h e v a l e n c e d e t e r m i n a t i o n , a 4 0 % b l a n k c o u l d n o t b e t o l e r a t e d . I n s t e a d , a f i n e l y g r o u n d c a l c i u m f l u o r i d e s i n g l e c r y s t a l w a s u s e d in s u b s e q u e n t w o r k . T h i s c r y s t a l w a s g r o w n f r o m s p e c i a l l y p u r i f i e d r e a g e n t s for o p t i c a l s t u d i e s . T h e v a l u e of t h e b l a n k d e c r e a s e d t o x o % of t h e a d d e d s t a n d a r d c e r i u m ( I V ) . I t w a s p r o v e d t h a t t h i s b l a n k w a s "h~ot d u e t o t h e c a l c i u m f l u o r i d e , b u t e x c l u s i v e l y t o t h e a c i d s a n d indicator. I t h a s b e e n s t a t e d ix t h a t c a l c i u m f l u o r i d e c a n b e r e a d i l y d i s s o l v e d i n h o t h y d r o c h l o r i c a c i d i n t h e p r e s e n c e of f l u o r i d e - c o m p l e x i n g c a t i o n s . A n i n v e s t i g a t i o n showed that hydrochloric acid was not an efficient solvent, and that cerium(IV) a p p a r e n t l y o x i d i z e d c h l o r i d e t o c h l o r i n e . P e r c h l o r i c a c i d w a s c h o s e n for t h e reA~al. Ghi~r~. Acta, 47 (x969) 495-502
DETERMINATION
OF VALENCE
STATES
OF
Fe A N D
U
5o1
c o m m e n d e d p r o c e d u r e b e c a u s e it d i s s o l v e d t h e c a l c i u m f l u o r i d e c r y s t a l s w i t h i n s e v e r a l h o u r s j u s t b e l o w IOO ° a n d d i d n o t i n t e r f e r e w i t h t h e o x i d a n t .
Acc,~racy T h e m e t h o d w a s a p p l i e d t o s i m u l a t e d s a m p l e s c o n s i s t i n g of a c a l c i u m f l u o r i d e s i n g l e c r y s t a l t o w h i c h k n o w n q u a n t i t i e s of N . B . S . u r a n i u m d i o x i d e w e r e a d d e d . A p p r o x i m a t e l y IOO m g of c a l c i u m f l u o r i d e w e r e c o m b i n e d w i t h a p p r o x i m a t e l y 2.5 m g of u r a n i u m d i o x i d e . T h e r e s u l t s o b t a i n e d b y t i t r a t i n g t h e e x c e s s of c e r i u m ( I V ) w e r e low b y a n a v e r a g e of 1o% . A l e a d c o l u m n r e d u c t i o n of k n o w n m i x t u r e s of u r a n i u m d i o x i d e (2.5 rag) a n d c a l c i u m f l u o r i d e (IOO ing) in perclfioric a c i d , o x i d i z e d f i r s t t o t h e + 6 v a l e n c e s t a t e w i t h h y d r o g e n p e r o x i d e , g a v e a 4 % p o s i t i v e e r r o r for t h e d e t e r m i n a t i o n of t o t a l u r a n i u m . A p i n k s i n g l e c r y s t a l , c o n s i s t i n g of c a l c i u m f l u o r i d e a n d u r a n i u m in t h e + 3 o x i d a t i o n s t a t e as e v i d e n c e d b y t h e c h a r a c t e r i s t i c color, w a s a n a l y z e d i n q u a d r u p l i ca're. T h e p r e c i s i o n wm~ + o . 1 3 % . N o t e n o u g h m a t e r i a l w a s a v a i l a b l e t o p e r m i t t h e d e t e r m i n a t i o n of t o t a l u r a n i u m a n d t h e r e f o r e , t h e i n i t i a l v a l e n c e c o u l d n o t be confirmed. A g r e e n s i n g l e c r y s t a l , h o w e v e r , w a s a n a l y z e d for t o t a l u r a n i u m b y t w o ind e p e n d e n t m e t h o d s . N e u t r o n a c t i v a t i o n a n a l y s i s in d u p l i c a t e g a v e o . 7 o % a n d 0 . 8 2 % u r a n i u m . A s p e c t r o p h o t o m e t r i c d e t e r m i n a t i o n in d u p l i c a t e 12 r e s u l t e d in o . 8 1 % a n d o . 8 0 % u r a n i u m . T h e d e t e r m i n a t i o n of t h e c h a n g e in o x i d a t i o n s t a t e of t h e u r a n i u m b y c e r i u m ( I V ) t i t r a t i o n to u r a n i u m ( V I ) g a v e a v a l u e of 2.06 ( 4 - 5 % ) , i n d i c a t i n g t h e p r e s e n c e of u r a n i u m ( I V ) in t h e c r y s t a l ( T a b l e hi). O b v i o u s l y , t h e m e t h o d c a n n o t be u s e d w i t h o u t m o d i f i c a t i o n if m i x t u r e s of s e v e r a l v a l e n c e s a n d / o r r e d u c i n g s u b s t a n c e s are p r e s e n t . A d d i t i o n a l i n v e s t i g a t i o n s of t h e v a r i o u s o x i d a t i o n s t a t e s of u r a n i u m in c a l c i u m f l u o r i d e a n d in o t h e r s o l i d m a t e r i a l s a r e in p r o g r e s s . TABLE
III
S~l~i%tI-l~tlCRO D I ~ T E I , I % I I N ' A T I O N OI," U R A N I U M
meq. zo-5 fot~nd
m m o l e s . IO-r" U found
6.57
3.32 = 3.44 = 3.36b 3.4 ob
6.88 6.92 7.I8 7.3t
ilv. 3.38 2ffeutron activation b Spcctrophotometry.
IN CALCIUI~I FLUORIDID
Oxidation change 1.94 2.04 2.05 2,12 2.16 av. 2.06
analysis.
SUMMARY
T h e i n s t a n t a n e o u s o x i d a t i o n of m a c r o a n d s e m i - m i c r o a m o u n t s of iron(II) in v a r i o u s t y p e s of glasses, of i r o n ( I I ) in m a g n e s i u m o x i d e , a n d of s e m i - m i c r o q u a n t i t i e s o f u r a n i u m ( I I I ) o r u r a n i u m ( I V ) in c a l c i u m f l u o r i d e s i n g l e c r y s t a l s , b y excess of c e r i u m ( I V ) p r e s e n t in t h e s o l v e n t s y s t e m , f o l l o w e d b y b a c k - t i t r a t i o n w i t h i r o n ( I I ) A ~ a l . Chim. A v t a , 47 ( 1 9 6 9 ) 4 9 5 - 5 0 2
502
U. A B E D
ammonium s u l f a t e , is t h e b a s i s f o r a s i m p l e , a c c u r a t e m e t h o d w h i c h , f u r t h e r m o r e , obviates the need for an inert atmosphere. Formal oxidation potentials of the Ce(IV)/ Ce(III) couple and the Fe(III)/Fe(II) c o u p l e in t h e h y d r o f l u o r i c - s u l f u r i c acid glassdissolving mixture were estimated. REFERENCES i I £ . L , CHENG, A ~ I .
C h e m . , 3 6 (I967) i666.
2 P . CLOSE, H . ~V[. SHEPHERD AND C. H . DRUMMOND, A n t . C e r a m . S o c . B u l l . , 41 (~958) 455.
W . ]). CO0K~, F . HAZEL AND W. M. MCNABB, / l n a l . C h e m . , 22 (195o) 654. W. D. TRI~ADWELL~ Helv. Chim. Acta, 5 (I9z2) 8o6. L. MEI'rES, Polt~rographic Techniques, z n d E d n . , I n t e r s c i e n c e , N e w Y o r k , 1965, p. 388. G. F . SMITH, Cerate Oxidimetry, G. F r e d e r i c k S m i t h C h e m . Co., C o l u m b u s , Ohio, 1942. I-[. A. LAITXNEN, Chemical A n a l y s i s , McGrztw-I-Iill B o o k Co., N e w Y o r k , 196o. W. F. HXLL~BRAND, jr. A m . Chem. See., 3o (I9o8) z i 2 o . N. E . DI~NS~M, J . Sea. Glass 7"ethanol., 27 (1936) 303. IO P . CLOSE, E . J . I"IORNYAK, T. ~BAA.K AND J . F . TILLI~IAN, .IWicrochem. f . , lO (x966) 333. I I A. ~I~UDR~VATOV, S'IIF l*analyse du f l u o r u r e de calcium (i,~z J~rench), C o m p t . r e n d . A c a d . Sci., U R S S , 4 (I934) 42. x2 F. G. SI.IERIB"AI~ID A. IV[. A~VAD, ./lnal. C h i m . . : l e t a , 26 (196z) 235. 3 4 5 6 7 8 9
A*~al. C h i m . Acta, 47 (x969) 495-502