Instrumental Lecture 22 Electrochem

Instrumental Lecture 22 Electrochem - C h a p t e r 2 2 : I...

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Unformatted text preview: C h a p t e r 2 2 : I n t r o d u c t i o n t o E l e c t r o a n a l y t i c a l C h e m i s t r y T w o g e n e r a l c a t e g o r i e s : 1 ) P o t e n t i o m e t r i c S y s t e m s m e a s u r e v o l t a g e ( i . e . , p o t e n t i a l ) o f a g a l v a n i c c e l l ( p r o d u c e s e l e c t r i c i t y s p o n t a n e o u s l y ) 2 ) V o l t a m m e t r i c S y s t e m s c o n t r o l p o t e n t i a l & u s u a l l y m e a s u r e c u r r e n t i n a n e l e c t r o l y t i c c e l l ( c o n s u m e s p o w e r t o c a u s e a n e l e c t r o c h e m i c a l r e a c t i o n t o o c c u r ) D e t e r m i n e c o n c e n t r a t i o n s b y m e a s u r i n g t h e p o t e n t i a l ( i . e . , v o l t a g e ) o f a n e l e c t r o c h e m i c a l c e l l ( g a l v a n i c c e l l ) T w o e l e c t r o d e s a r e r e q u i r e d 1 ) I n d i c a t o r E l e c t r o d e p o t e n t i a l r e s p o n d s t o a c t i v i t y o f s p e c i e s o f i n t e r e s t 2 ) R e f e r e n c e E l e c t r o d e c h o s e n s o t h a t i t s p o t e n t i a l i s i n d e p e n d e n t o f s o l u t i o n c o m p o s i t i o n . P o t e n t i o m e t r y M e m b r a n e E l e c t r o d e s S e v e r a l t y p e s G l a s s m e m b r a n e e l e c t r o d e- S o l i d S t a t e - L i q u i d J u n c t i o n - P e r m e a b l e M o s t i m p o r t a n t i s g l a s s e l e c t r o d e f o r p H [ H + ] = a 1 [ H + ] = a 2 s o l u t i o n 1 s o l u t i o n 2 p o t e n t i a l d e v e l o p s a c r o s s m e m b r a n e t h i n g l a s s m e m b r a n e G l a s s p H E l e c t r o d e E = K . 5 9 1 p H C o m b i n e w i t h r e f e r e n c e e l e c t r o d e a n d m e t e r H a l f c e l l v o l t a g e p r o p o r t i o n a l t o p H N e r n s t i a n s l o p e I n t e r c e p t i s K , n o E o C a l i b r a t e w i t h b u f f e r s E l e c t r i c a l c o n n e c t i o n s e a l . 1 M H C l F i l l i n g s o l u t i o n A g w i r e c o a t e d w i t h A g C l T h i n g l a s s m e m b r a n e E r r o r s i n p H M e a s u r e m e n t 1 p H m e a s u r e m e n t s a r e o n l y a s g o o d a s t h e b u f f e r s u s e d t o c a l i b r a t e A c c u r a c y g o o d t o + . 1 u n i t s * P r e c i s i o n m a y b e g o o d t o + . 1 u n i t s J u n c t i o n p o t e n t i a l d e p e n d e n t o n i o n i c s t r e n g t h o f s o l u t i o n E j m a y b e a s i g n i f i c a n t e r r o r i f t e s t s o l u t i o n h a s d i f f e r e n t i o n i c s t r e n g t h t h a n b u f f e r s * U n l e s s u s i n g s p e c i a l b u...
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Instrumental Lecture 22 Electrochem - C h a p t e r 2 2 : I...

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