ediled by ROD O'CONNOR
Texas ABM Universilq College Station. TX 77843
Setting High Standards H. I.Felnsteln' George Mason Unlversilq Fairlax. VA 22030
For a n u m h e r of reasons i n c l u d i n e a v a i l a h i l i t v in t h e p u r e state, stability, h i g h e q u i v a l e n t w e k h t , a n d r a p i d a n d s t n i c h i l l m e t r i c r e a c t i o n w i t h s t r o n g bases, p n t a s s i u m h y d r o g e n p h t h a l a t e i s w i d e l y u s e d as a p r i m a r y s t a n d a r d in a r i d i m e t r v - a l k a l i m e t r v.. A o r i m a r v s t a n d a r d i s o n e t h a t c a n he used d i r e r t l y t n s l a n d a r d i z e o t h e r reagents a n d snlutions. A p o t a s s i u m h y d r o g e n p h t h a l a t e c e r t i f i e d by t h e N a t i o n a l B u r e a u of S t a n d a r d s was used to s t a n d a r d i z e a s o l u t i o n o f s o d i u m hydroxide. T h e standard soluticm of s t d i u m h y d r n x i d e was t h e n used t o assay a gocd commercial sample o f potassium halfh v d r n r e n n h t h a l a t e . T h e l a t t e r h a d been p r e p a r e d IIV n k u t r a i i z s i i o n of p u r e p h t h a l i c a c i d with pn&ssium hydroxide. a n d t h e p r o d u c t dried.
.
H02C-ICsH~l-CO2H
+ KOH
-
+ HrO
H02C-(C6H4)-COrK
Suppose t h a t a s a m p l e of t h e dried p o t a s s i u m h y d r o g e n p h t h a l a t e ( f o r m u l a w e i g h t 204.22) contained 0.10% hv w e i g h t nf u n r e a c t e d p h t h a l i c a c i d ( m o l e c u l a r w e i g h t 166.13) as t h e only impurity. W h a t w o u l d t h i s c o m m e r c i a l p r n d u c t assay in t e r m s of p o t a s s i u m h y d r o g e n p h t h a l a t e 15 s i g n i f i c a n t figures)?
HOrC-(CfiH4)-C02K
+ NaOH
H02C-GH,I-COIH
+ 2 NaOH
-
+ H2O
N~OC-(C~HI)-CO,K
+ 2H20
Na02C-(C6H,,-CO?Na
Answer:
100.15% as p o t a s s i u m h y d r o g e n p h t h a l a t e
' P r e w n l address: 1041 1Forest Avenue. Fairlax. VA 22030
q~nstionsrelating lo practical applications will tingle y w r brains and those of your studnnt~in this monlhly minifeature. Contributions to this feature are welcome and should be addressed lo the lealure editoc. who will also send detailed solutions upon req-I. Rod O'Conn.31 received his BS from Southn~stMisour1 State Collean in 1955
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First +ear Chemistry Programs. he held faculty poailionial the University o i Omaha. Montana State. Kent State. and the University of Arlzona Dr. O'Conna's wwk in chemical educalim is widely known. He is I h e a w of I w e l ~ e books. h e most recent beina the second edition of 'Fundamentals programs on tecnnlque5 01 organic chcm slry lor #heAmer Can Chsmm Soc e h m rece red lne l97? e n 01 - eb ,. an0 - - a comolste color le e v w m c o ~ s w Wesl Award in i&uctional televtsion. He isthereci~lienlofa Tour Speaker al me vear Award lrom the Amer can Chemca Soc cly and ol Ive leach ng auardr. mclulmga 1978 MRo~lacrbrng Chem sls Arsocml on natmona Calalr91' .,-~ Award - - am - - a- 1979 0 -~rl m u shed Acn evemenl Awara lrom lne Fomer Slujent~Association 01 ex& ABM Univer5ity. He received an Alumni i Universihl Achievement Award in 1978 lmm southeast ~ i r r o u rSlate ~
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Volume 58
Number 7
July 1981
567
