Predicting Inorganic Reactions - ACS Symposium Series (ACS

Chapter 3

Predicting Inorganic Reactions The Development of an Expert System James P. Birk

Downloaded by CORNELL UNIV on October 18, 2016 | http://pubs.acs.org Publication Date: September 1, 1989 | doi: 10.1021/bk-1989-0408.ch003

Department of Chemistry, Arizona State University, Tempe, AZ 85287-1604

An expert system has been developed, using PROLOG, to predict products of inorganic chemical reactions. The expert system was designed to model predictive approaches used by a number of chemists, using the simplest rules possible. After the user inputs chemical formulas of one or two reactants, the formulas are parsed to determine the component elements and to recognize any significant polyatomic groups. Oxidation numbers are then assigned to the elements. This information, in addition to a limited database, i s used to place the reactants into classifications which w i l l fire rules for various kinds of chemical reactions. The expert system can make predictions for combination reactions, decomposition reactions, single displacement reactions, double displacement reactions (including oxidation-reduction, acid-base, and precipitation reactions), and complex ion formation reactions. Computer use in the educational process has become commonplace, ranging from drill-and practice, tutorials, and simulations to word processing and spreadsheets. Software for computer-assisted instruction (CAI) has undergone a substantial change in character over the past 20 years. Starting out as a calculation-aid, software has evolved into drill-and-practice and tutorial aids, along with a number of other more specialized types of instructional aid (J_). However, most software does not offer the student an opportunity to study a subject in the truly individualized manner that would be consistent with the one-on-one situation existing when a student sits in front of a computer terminal (2). Most present software i s computer-controlled rather than student-controlled. The computer generally guides the student through the subject matter. Although the student may be able to make selections from a menu, the computer is not very responsive to the student's needs. 0097-6156/89/O408-O020$06.00/0 o 1989 American Chemical Society

Hohne and Pierce; Expert System Applications in Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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BIRK

Predicting Inorganic Reactions

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I n t e l l i g e n t T u t o r i n g Systems Now, w i t h t h e i n c r e a s i n g a v a i l a b i l i t y o f f a s t e r p r o c e s s o r s and more memory, t h e n a t u r e o f i n s t r u c t i o n a l computing i s on t h e verge o f s u b s t a n t i a l change. The o p p o r t u n i t y t o p l a c e t h e s t u d e n t i n charge of a c o m p u t e r - a s s i s t e d l e a r n i n g e x p e r i e n c e i s o f f e r e d by t h e a p p l i c a t i o n o f e x p e r t systems and a r t i f i c i a l i n t e l l i g e n c e developments t o i n s t r u c t i o n a l computing (3.). I n t h e s e systems, t h e u s u a l q u e s t i o n and answer format t y p i c a l o f CAI t u t o r i a l programs w i l l no l o n g e r p r e v a i l . The program w i l l no l o n g e r drag t h e s t u d e n t a l o n g i n i t s wake. R a t h e r , t h e program w i l l become a t o o l and a d v i s o r f o r t h e s t u d e n t , p r o v i d i n g a l e a r n i n g environment w i t h much l e s s p r e d e t e r m i n e d s t r u c t u r e than i s now common, w i t h t h e s t u d e n t r a t h e r than t h e computer i n c o n t r o l . S t u d e n t s w i l l i n t e r a c t w i t h the program, a s k i n g q u e s t i o n s , a s k i n g f o r h e l p o r a d v i c e , a s k i n g f o r examples. The program w i l l respond i n t e l l i g e n t l y t o s t u d e n t q u e r i e s , p r o v i d i n g answers t o q u e s t i o n s , e x p l a i n i n g answers, and e x p l a i n i n g how answers were determined. The program may a l s o ask q u e s t i o n s t o guide t h e s t u d e n t and t o t e s t the s t u d e n t , i f so r e q u e s t e d , b u t then w i l l a l s o be a b l e t o e x p l a i n why t h e s t u d e n t ' s answer was e i t h e r c o r r e c t o r i n c o r r e c t . Such q u e s t i o n s w i l l be formulated at a l e v e l appropriate t o the student's previous performance. Systems t h a t have t h e s e c a p a b i l i t i e s a r e c a l l e d i n t e l l i g e n t t u t o r i n g systems. A f u l l i n t e l l i g e n t t u t o r i n g system i s made up o f s e v e r a l p a r t s (3.). The knowledge domain i s a database o f f a c t s t h a t p r o v i d e t h e b a s i s f o r knowledge i n t h e p a r t i c u l a r s u b j e c t . The e x p e r t system c o n s i s t s of a s e t o f r u l e s t h a t makes use o f t h e database t o p r o v i d e e x p e r t i s e i n t h e s u b j e c t a r e a (j\). The user i n t e r f a c e p r o v i d e s f o r communication between t h e program and t h e s t u d e n t i n such a way t h a t the s t u d e n t can ask q u e s t i o n s o f the program. A g o a l i n many i n t e l l i g e n t t u t o r i n g systems i s n a t u r a l language communication, i n which i n t e r a c t i o n can t a k e p l a c e i n E n g l i s h s e n t e n c e s . The t e a c h i n g model p r o v i d e s t h e p e d a g o g i c a l approaches, e x p l a n a t i o n s , t u t o r i n g , q u e s t i o n s , s i t u a t i o n s , e t c . t h a t would g e n e r a l l y be p r o v i d e d by a t e a c h e r , a f t e r j u d g i n g t h e p r o g r e s s o f t h e s t u d e n t . The s t u d e n t model m a i n t a i n s a p a s t h i s t o r y o f s t u d e n t use and r e s p o n s e s . This i n f o r m a t i o n i s used by t h e t e a c h i n g model t o s e l e c t a p p r o p r i a t e c h a l l e n g e s and e x p l a n a t i o n s f o r each s t u d e n t . E x p e r t Systems C e n t r a l t o an i n t e l l i g e n t t u t o r i n g program i s an e x p e r t system, which i s a program t h a t c o n s i s t s o f a compendium o f knowledge ( f a c t s and r u l e s ) about a p a r t i c u l a r t o p i c . T h i s e x p e r t system s h o u l d have enough knowledge t o a l l o w t h e computer t o answer q u e s t i o n s o r make p r e d i c t i o n s i n a g i v e n knowledge area w i t h t h e a c c u r a c y o f a human e x p e r t (5). The development o f an e x p e r t system r e q u i r e s a u n d e r s t a n d i n g o f t h e f u n c t i o n i n g and t h i n k i n g p a t t e r n s o f a human e x p e r t . Such an u n d e r s t a n d i n g o f t e n e l u d e s even t h a t e x p e r t . To be an e x p e r t , a p e r s o n must be so f a m i l i a r w i t h a knowledge a r e a t h a t p r e d i c t i o n s o r s o l u t i o n s t o problems seem t o f l o w from t h a t person w i t h l i t t l e v i s i b l e e f f o r t . This i s i n fact a c h a r a c t e r i s t i c of college


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E X P E R T SYSTEM APPLICATIONS IN CHEMISTRY


i n s t r u c t o r s t h a t undoubtedly dismays many s t u d e n t s . By v i r t u e o f such i n t i m a t e and l o n g - s t a n d i n g f a m i l i a r i t y w i t h a s u b j e c t , an e x p e r t o f t e n does not c o n s c i o u s l y u n d e r s t a n d t h e p r o c e s s by which answers o r s o l u t i o n s a r e g e n e r a t e d . However, t o c o n v e r t t h e computer i n t o an e x p e r t , such a n a l y s e s o f t h i n k i n g p r o c e s s e s must be made i n c o n s i d e r a b l e d e t a i l . Thus, development of an e x p e r t system p r o v i d e s i n s i g h t i n t o t h e methodology used i n t h e s u b j e c t a r e a . P r e f e r a b l y , an i n s t r u c t i o n a l e x p e r t system s h o u l d model t h e approaches used by e x p e r t s t o r e a c h c o n c l u s i o n s t h a t a r e n o t o n l y a c c u r a t e b u t a l s o p e d a g o g i c a l l y sound. I n t h i s way, when t h e e x p e r t system i s i n v e r t e d , t o be a b l e t o e x p l a i n i t s own p r o c e s s i n g o f a q u e s t i o n , t h e e x p l a n a t i o n s w i l l match t h o s e t h a t would be g i v e n by an a s t u t e t e a c h e r . Descriptive Inorganic

Chemistry

PIRExS. There has been widespread i n t e r e s t i n i n c r e a s i n g t h e coverage of d e s c r i p t i v e i n o r g a n i c c h e m i s t r y i n t h e g e n e r a l c h e m i s t r y c u r r i c u l u m ( 6 - 1 3 ) . The manner i n which t h i s i s t o be a c c o m p l i s h e d e f f e c t i v e l y has not y e t been c l e a r l y d e l i n e a t e d , however. W i t h support from P r o j e c t SERAPHIM, an attempt i s underway t o develop computer s o f t w a r e which w i l l h e l p t e a c h d e s c r i p t i v e i n o r g a n i c c h e m i s t r y . We w i l l d e s c r i b e here work i n v o l v e d i n t h e development of an i n t e l l i g e n t t u t o r i n g system t o t e a c h d e s c r i p t i v e i n o r g a n i c r e a c t i o n c h e m i s t r y . The i n i t i a l e f f o r t s on t h i s p r o j e c t have r e s u l t e d i n an e x p e r t system c a l l e d PIRExS ( P r e d i c t i n g I n o r g a n i c R e a c t i v i t y E x p e r t System), w r i t t e n i n PROLOG f o r t h e IBM PC and o t h e r c o m p a t i b l e microcomputers. T h i s e x p e r t system c a n make p r e d i c t i o n s o f t h e p r o d u c t s o f i n o r g a n i c r e a c t i o n s , as w e l l as e x p l a i n t h e manner i n which t h o s e p r e d i c t i o n s were made. Thus, t h i s system comprises p o r t i o n s o f t h e i n t e l l i g e n t t u t o r i n g system t h a t s h o u l d u l t i m a t e l y r e s u l t from t h i s work. A l a r g e number o f d i f f e r e n t t y p e s of r e a c t i o n s can be handled s u c c e s s f u l l y by t h i s e x p e r t system. The program w i l l make p r e d i c t i o n s w i t h a s u c c e s s r a t e o f about 95? on t h e t y p e s o f r e a c t i o n s shown i n T a b l e I . The s u c c e s s r a t e was determined by s e l e c t i n g about 1000 r e a c t i o n s used i n g e n e r a l c h e m i s t r y and i n o r g a n i c c h e m i s t r y t e x t b o o k s . The program was c o n s i d e r e d t o be s u c c e s s f u l i f i t c o u l d r e p r o d u c e t h e r e a c t i o n as w r i t t e n i n t h e t e x t , even though t h e program would u s u a l l y come up w i t h more t h a n one p o s s i b l e r e a c t i o n . Expert System Development. The development o f t h i s e x p e r t system was i n i t i a t e d by g a t h e r i n g a group o f eminent i n o r g a n i c c h e m i c a l e d u c a t o r s t o d i s c u s s the manner i n which e x p e r t s make p r e d i c t i o n s . Two p o s s i b i l i t i e s were c o n s i d e r e d : E i t h e r an e x p e r t c a l l s upon a l a r g e , perhaps s u b c o n s c i o u s , database o f known r e a c t i o n s and p r e d i c t s by analogy w i t h known r e s u l t s , o r an e x p e r t u n d e r s t a n d s t h e b a s i c p r i n c i p l e s and r u l e s g o v e r n i n g c h e m i c a l r e a c t i v i t y and a p p l i e s these r e s u l t s , a g a i n perhaps s u b c o n s c i o u s l y , t o a g i v e n s i t u a t i o n . The r e a l mode o f o p e r a t i o n o f an e x p e r t may w e l l be a c o m b i n a t i o n o f these approaches. S e v e r a l c o n c l u s i o n s a r o s e from t h i s meeting. A database approach was c o n s i d e r e d u n s a t i s f a c t o r y s i n c e t h e p o s s i b l e c o m b i n a t i o n s o f t h e more than 100,000 known i n o r g a n i c c h e m i c a l s would r e q u i r e a massive c o m p i l a t i o n o f known r e a c t i o n s . T h i s


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approach would a l s o p r o v i d e l i t t l e p e d a g o g i c a l a s s i s t a n c e s i n c e no s t u d e n t would w i l l i n g l y a c c e p t t h e t a s k o f memorizing such l a r g e numbers o f r e a c t i o n s . F u r t h e r , t h e absence o f a r e a c t i o n from t h e database would not a l l o w a s t u d e n t t o d i s t i n g u i s h between two possibilities: E i t h e r t h e r e a c t i o n does not t a k e p l a c e , o r t h e r e a c t i o n was o v e r l o o k e d o r o m i t t e d f o r some r e a s o n by t h e database creator.


T a b l e I . Types o f R e a c t i o n s P r e d i c t e d by PIRExS d i s p r o p o r t i o n a t i o n o f elements d i s p r o p o r t i o n a t i o n of s i m p l e i o n s d i s p r o p o r t i o n a t i o n of compounds d i s p r o p o r t i o n a t i o n of oxo i o n s i n t e r n a l redox o f i o n i c compounds t h e r m a l d e c o m p o s i t i o n r e a c t i o n s o f compounds: h y d r i d e s , h y d r a t e s , m e t a l h y d r o x i d e s , ammonium s a l t s , p e r o x i d e s , o x i d e s , h a l i d e s , t h i o s u l f a t e s , m e t a l oxo s a l t s , p r o t o n a t e d m e t a l oxo s a l t s b i n a r y c o m b i n a t i o n r e a c t i o n s of elements redox r e a c t i o n s o f e l e m e n t s , i o n s , and i o n i c compounds i n a c i d i c solution d i s p l a c e m e n t o f H from w a t e r , steam, o r a c i d s by elements o x i d a t i o n o f a compound by m o l e c u l a r oxygen redox r e a c t i o n s between gaseous nonmetal o x i d e s d i s p l a c e m e n t o f an element i n a compound by another element d i s p l a c e m e n t o f an element i n a compound by c a r b o n monoxide o x i d e d i s p l a c e m e n t r e a c t i o n s between o x i d e s and oxo s a l t s o x i d e d i s p l a c e m e n t r e a c t i o n s between o x i d e s and o x o a c i d s ionic p r e c i p i t a t i o n reactions a c i d - b a s e r e a c t i o n s between o x i d e s hydrolysis of various i o n i c species h y d r o l y s i s o f c o v a l e n t compounds, e s p e c i a l l y h a l i d e s acid-base n e u t r a l i z a t i o n reactions complex i o n s u b s t i t u t i o n r e a c t i o n s covalent o x i d a t i v e - a d d i t i o n reactions reactions of concentrated s u l f u r i c a c i d 2

A r u l e - b a s e d system i s c l e a r l y s u p e r i o r from a p e d a g o g i c a l viewpoint. Such a system would be more open-ended s i n c e i t c o u l d use p e r i o d i c r e l a t i o n s t o e x t r a p o l a t e t o r e l a t e d r e a c t i o n s . A rulebased system a l s o has t h e c a p a b i l i t y o f b e i n g i n v e r t e d t o be a b l e t o e x p l a i n i t s answers, a n e c e s s i t y i f t h e e x p e r t system i s t o be developed i n t o an i n t e l l i g e n t t u t o r i n g system. However, a r u l e based system i s a l s o e x p e c t e d t o have l i m i t a t i o n s i n t h e number o f p r e d i c t i o n s i t can make, s i n c e r u l e s must be f o r m u l a t e d t o c o v e r many d i f f e r e n t t y p e s o f r e a c t i o n s . F i n a l l y , a l t h o u g h o u t group o f e x p e r t s c o u l d make p r e d i c t i o n s w i t h ease, v e r b a l i z i n g t h e e x a c t approach and r u l e s used t o make t h e p r e d i c t i o n s was not an easy t a s k . As e x p l a i n e d e a r l i e r , t h i s i s c o n s i s t e n t w i t h t h e n a t u r e of an e x p e r t , so i t i s not a s u r p r i s i n g r e s u l t . The answers developed by t h e group a l s o made i t c l e a r t h a t numerous approaches c o u l d l e a d t o s u c c e s s f u l p r e d i c t i o n s . I n s p i t e


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o f t h i s v a r i a b i l i t y i n approach, a common t h r e a d appeared. V i r t u a l l y a l l p r e d i c t i o n s were made by f i r s t c a t e g o r i z i n g the r e a c t a n t s i n t o one or more r e a c t a n t c l a s s e s , then examining t h o s e r e a c t i o n t y p e s t h a t would be a p p r o p r i a t e f o r t h o s e r e a c t a n t c l a s s e s . E x p e r t System Design. The e x p e r t system d e s i g n was based on the g e n e r a l approaches used by our group of e x p e r t s . A f t e r f o r m u l a s of two r e a c t a n t s (sometimes o n l y one r e a c t a n t ) a r e i n p u t , the f o r m u l a s are parsed t o i d e n t i f y component elements and r e c o g n i z a b l e p o l y a t o m i c groups, then o x i d a t i o n numbers and i o n i c charges are a s s i g n e d , and f i n a l l y the r e a c t a n t s p e c i e s are checked as p o s s i b l e examples of a v a r i e t y of r e a c t a n t c l a s s e s . T h i s i n f o r m a t i o n i s then used t o t r i g g e r r u l e s f o r r e a c t i o n t y p e s a p p r o p r i a t e t o t h o s e r e a c t a n t c l a s s e s . Use was made o f PROLOG'S b a c k t r a c k i n g c a p a b i l i t i e s t o search f o r a l l p o s s i b l e r e a c t i o n s f o r the r e a c t a n t s t h a t were i n p u t . Database. The e x p e r t system c o n s u l t s a database t o get the i n f o r m a t i o n r e q u i r e d t o a s s i g n a r e a c t a n t t o the v a r i o u s p o s s i b l e r e a c t a n t c l a s s e s . S u r p r i s i n g l y l i t t l e i n f o r m a t i o n i s needed i n t h i s database e i t h e r t o a s s i g n r e a c t a n t c l a s s e s or t o make p r e d i c t i o n s of c h e m i c a l r e a c t i v i t y . The i n f o r m a t i o n t h a t was p l a c e d i n the database i s l i s t e d i n T a b l e I I . Reactant C l a s s e s . In o r d e r t o make p r e d i c t i o n s of c h e m i c a l r e a c t i v i t y , i t i s n e c e s s a r y t o check whether a r e a c t a n t i s a member of about 30 d i f f e r e n t r e a c t a n t c l a s s e s . These r e a c t a n t c l a s s e s a r e l i s t e d i n T a b l e I I I . In a d d i t i o n , f o r ease i n programming, groups of r e a c t a n t c l a s s e s were d e f i n e d . These groups c o n t a i n as members those r e a c t a n t c l a s s e s t h a t w i l l undergo s i m i l a r r e a c t i o n s . The r e a c t a n t c l a s s groups are l i s t e d i n T a b l e IV. The d e f i n i t i o n s of r e a c t a n t c l a s s e s were u s u a l l y f a i r l y s i m p l e , i n v o l v i n g m o s t l y i n f o r m a t i o n about the c o m p o s i t i o n o f the substance. For example, the d e f i n i t i o n of an o x o a c i d can be g i v e n by the f o l l o w i n g s t a t e m e n t , which p a r a p h r a s e s the PROLOG p r e d i c a t e : A s u b s t a n c e i s an o x o a c i d i f the s u b s t a n c e c o n t a i n s t h r e e components, and the s u b s t a n c e c o n t a i n s hydrogen and oxygen, and the s u b s t a n c e c o n t a i n s another nonmetal, and the s u b s t a n c e i s uncharged. Another example i s p r o v i d e d by the d e f i n i t i o n of a i o n i c compound: A s u b s t a n c e i s an i o n i c compound i f the substance c o n t a i n s two or more components, and the one component i s a m e t a l , and another component i s a nonmetal, and the s u b s t a n c e i s uncharged. Some of the common d e f i n i t i o n s were found not t o be o p e r a b l e , s i n c e they r e q u i r e some knowledge o f r e a c t i v i t y i n o r d e r t o be a b l e t o c l a s s i f y the r e a c t a n t . For example, the u s u a l d e f i n i t i o n of a Bronstead a c i d i n d i c a t e s t h a t an a c i d i s a s u b s t a n c e which w i l l donate a p r o t o n t o another s u b s t a n c e . However, t h i s means t h a t we must know whether the p r o t o n d o n a t i o n p r o c e s s o c c u r s b e f o r e we can d e c i d e whether the s u b s t a n c e i s an a c i d . S i n c e we must know whether


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BIRK


Table I I .

Database f o r PIRExS


General i n f o r m a t i o n : Elemental Information: name, symbol, atomic number, group number, p e r i o d number, metallic character, electronegativity I o n i c Radius: v a l u e s f o r a l l the s i m p l e monatomic i o n s of the elements Reduction P o t e n t i a l : E° v a l u e s f o r c o n v e r s i o n s between a d j a c e n t and non-adjacent oxidation states Synonyms: p r e f e r r e d c h e m i c a l f o r m u l a s and a l t e r n a t i v e f o r m u l a s t h a t might be i n p u t by a user or be c r e a t e d by the program Some a c i d and base d i s s o c i a t i o n c o n s t a n t s B o i l i n g p o i n t s of nonmetal o x i d e s I n f o r m a t i o n S p e c i f i c t o the C u r r e n t

Reactants:

Compound: f o r m u l a and charge Components: elements and t h e i r numbers number of p o l y a t o m i c groups c o n t a i n i n g t h e element O x i d a t i o n Numbers: o x i d a t i o n numbers of a l l the component elements Count: t o t a l number of d i f f e r e n t elements i n the r e a c t a n t P o l y a t o m i c Group: f o r m u l a and charge o f r e c o g n i z a b l e p o l y a t o m i c groups Acid: f o r m u l a , c h a r g e , and p K o f any a c i d and i t s c o n j u g a t e Base: f o r m u l a , c h a r g e , and p K o f any base and i t s c o n j u g a t e Strongest Acid: f o r m u l a , c h a r g e , and p K o f the s t r o n g e s t a c i d p r e s e n t S t r o n g e s t Base: f o r m u l a , c h a r g e , and p K of the s t r o n g e s t base p r e s e n t Complex I o n : i d e n t i t y o f the metal and i t s o x i d a t i o n number i d e n t i t y of t h e l i g a n d s , t h e i r number and charge Free Ligand: f o r m u l a and charge o f any s p e c i e s t h a t i s a p o t e n t i a l l i g a n d a

b

a

b


25

26


T a b l e I I I . Reactant None Water (H 0) Ammonium H y d r o x i d e (NHj^OH) M e t a l Oxide (CuO) T e r n a r y C o v a l e n t Compound ( C H F ) P o l y a t o m i c A n i o n S a l t (KNCS) S t r o n g Oxoacid (HClOjj) Binary Ionic S a l t (Na 0) Compound (NaCl) P r o t o n a t e d NonMetal S a l t (NaHS) B a s i c Compound ( N a S ) Oxoanion S a l t ( N a ^ O ^ ) Simple Ion ( C l ~ ) Anion (HS") Oxoanion (CO^ ) P r o t o n a t e d Oxoanion (HSO^") 2

2

2


2

T a b l e IV. Binary S a l t : binary ionic s a l t binary acid Ionic Species: ion i o n i c compound binary acid oxoacid ammonium s a l t Oxo I o n : oxoanion oxocation Base: b a s i c compound basic anion ammonia ammonium h y d r o x i d e

2

C l a s s e s and Examples Element (Cu) Ammonia (NH3) NonMetal Oxide (NO?) C o v a l e n t Compound ( C 0 ) I o n i c Oxo S a l t (Na C0g) Oxoacid (H^O^) I o n i c Compound ( N a S ) A c i d (H S) Ammonium S a l t (NH^Cl) P r o t o n a t e d Oxoanion S a l t (NaHSO^) M e t a l H y d r o x i d e (NaOH) Ion ( N a ) Cation ( C u ) B a s i c Anion (S ") Oxocation ( V 0 ) 2

2

2

2

+

2 +

2 +

Groups o f R e a c t a n t

Classes

Oxide S p e c i e s : nonmetal o x i d e metal oxide metal h y d r o x i d e Redox S p e c i e s i o n i c compound ion oxoacid element Polyatomic S a l t polyatomic anion s a l t oxoanion s a l t p r o t o n a t e d nonmetal s a l t ammonium s a l t Acid: acid nonmetal o x i d e

a s u b s t a n c e i s an a c i d b e f o r e we can d e c i d e whether a p r e d i c t i o n of a proton donation r e a c t i o n i s a l i k e l y p o s s i b i l i t y , t h i s d e f i n i t i o n i s c i r c u l a r i n terms of t h e d e s i r e d use. To c i r c u m v e n t t h i s p o s s i b i l i t y , we use a d e f i n i t i o n i n terms of c o m p o s i t i o n : A s u b s t a n c e i s an a c i d i f the substance c o n t a i n s two or more components, and the substance c o n t a i n s hydrogen and t h e s u b s t a n c e c o n t a i n s another nonmetal, or the substance i s the hydrogen i o n .



3.

BIRK


27

T h i s d e f i n i t i o n w i l l be t r u e f o r a number of s u b s t a n c e s t h a t we g e n e r a l l y do not c o n s i d e r t o be a c i d s , however. For example, methane, h y d r o x i d e i o n and amide i o n would be a c i d s by t h i s d e f i n i t i o n . Of c o u r s e , a knowledge o f the a c i d s t r e n g t h s would p r o v i d e a c r i t e r i o n f o r e l i m i n a t i n g s u b s t a n c e s such as t h e s e . S i n c e we a l s o wanted i n f o r m a t i o n about acid, s t r e n g t h s i n o r d e r t o make p r e d i c t i o n s about t h e most l i k e l y r e a c t i o n s , i t was n e c e s s a r y t o refine this definition. I n e s s e n c e , r u l e s had t o be d e f i n e d f o r the s t r e n g t h of each d i f f e r e n t c l a s s of a c i d (and b a s e ) , so t h a t d e f i n i t i o n s a c t u a l l y had t o be developed f o r a l l t h e s e c l a s s e s as w e l l . A l t h o u g h t r e n d s i n a c i d s t r e n g t h of b i n a r y a c i d s can be p r e d i c t e d w i t h i n a g i v e n p e r i o d or group of the p e r i o d i c t a b l e , t h e r e does not appear t o be any r e a s o n a b l y s i m p l e way t o p r e d i c t v a l u e s of the a c i d d i s s o c i a t i o n c o n s t a n t s f o r t h e s e s p e c i e s . In t h i s c a s e , r e f e r e n c e i s made t o a database of v a l u e s . For o x o a c i d s , i t i s p o s s i b l e t o make o r d e r - o f - m a g n i t u d e p r e d i c t i o n s of the a c i d d i s s o c i a t i o n c o n s t a n t v a l u e s , based on the o x i d a t i o n number of t h e c e n t r a l atom, the number of oxygen atoms, and the number of hydrogen atoms (V\). I t i s a l s o p o s s i b l e t o p r e d i c t v a l u e s of the a c i d d i s s o c i a t i o n c o n s t a n t s of aquometal i o n s , based on the c h a r g e , r a d i u s and e l e c t r o n e g a t i v i t y of t h e m e t a l i o n ( 1 5 - 1 6 ) . Bases can be d e f i n e d i n a s i m i l a r manner. Bases i n c l u d e b a s i c compounds (uncharged s p e c i e s c o n t a i n i n g two or more components, i n c l u d i n g a m e t a l and a n o n m e t a l ) , b a s i c a n i o n s ( n e g a t i v e l y c h a r g e d s p e c i e s c o n t a i n i n g one or more components, i n c l u d i n g at l e a s t one n o n m e t a l ) , ammonia, and ammonium h y d r o x i d e . As w i t h a c i d s , t h i s d e f i n i t i o n w i l l r e c o g n i z e s u b s t a n c e s such as NaCl or B r " , w h i c h are not v e r y b a s i c . Thus, i t i s a l s o n e c e s s a r y t o d e v e l o p a s e r i e s of r u l e s or database t a b l e s ( t h e same as t h o s e f o r b i n a r y a c i d s , w i t h pK =* Hi - p K ) t o e s t a b l i s h the magnitude of the base s t r e n g t h . T h i s p r o v i d e s c r i t e r i a t o e l i m i n a t e p o t e n t i a l bases which a r e t o o weak t o be c o n s i d e r e d meaningfully. Thus, the s i m p l e d e f i n i t i o n s of a c i d s and bases t h a t are most o f t e n used had t o be expanded i n t o q u i t e a l a r g e number of d e f i n i t i o n s and r u l e s t o be u s e f u l f o r p r e d i c t i n g r e a c t i o n s between a c i d s and b a s e s , a r e a c t i o n c l a s s which i s u s u a l l y c o n s i d e r e d t o be f a i r l y simple. S i m i l a r r e s u l t s were found t h r o u g h o u t t h i s p r o j e c t . M a t e r i a l which i s c o n s i d e r e d t o be f a i r l y s i m p l e and s t r a i g h t f o r w a r d when we t r y t o t e a c h i t t o our s t u d e n t s , o f t e n i s found t o be much more complex when we t r y t o t e a c h i t t o t h e computer, s i n c e we cannot expect the " s t u d e n t " t o make the major i n t e l l e c t u a l l e a p s t h a t we seem t o e x p e c t of our human s t u d e n t s . T h i s has proved h e l p f u l i n u n d e r s t a n d i n g some o f the problems s t u d e n t s have i n l e a r n i n g m a t e r i a l t h e way i t i s commonly t a u g h t . W r i t i n g a s e t of r u l e s and t e s t i n g them w i t h a v a r i e t y of examples i s a u s e f u l way of d e f i n i n g t h e l i m i t a t i o n s of v a r i o u s i n s t r u c t i o n a l approaches. b

a

Reaction Classes. Once the r e a c t a n t s can be i d e n t i f i e d as members of v a r i o u s r e a c t a n t c l a s s e s , i t i s p o s s i b l e t o make a p r e d e t e r m i n a t i o n of the r e a c t i o n c l a s s e s t h a t s h o u l d be examined.


28

E X P E R T SYSTEM APPLICATIONS IN

CHEMISTRY


T h i s a l l o w s us t o e l i m i n a t e r e a c t i o n c l a s s e s which are not p o s s i b l e . For example, i f the r e a c t a n t s c o n s i s t of two e l e m e n t s , t h e r e i s no need t o examine a c i d - b a s e r e a c t i o n s , or r e a c t i o n s between elements and w a t e r , or d e c o m p o s i t i o n r e a c t i o n s , e t c . R e a c t i o n s w i t h One R e a c t a n t . I f t h e r e i s o n l y one r e a c t a n t , t h e r e are a l i m i t e d number of p o s s i b l e r e a c t i o n t y p e s . I n aqueous s o l u t i o n , a d i s p r o p o r t i o n a t i o n r e a c t i o n i s p o s s i b l e f o r an element, an oxo i o n ( T a b l e I V ) , a s i m p l e i o n , or a compound. A compound can a l s o undergo a d e c o m p o s i t i o n r e a c t i o n of v a r i o u s t y p e s , as l i s t e d i n T a b l e I . An i o n i c compound can undergo an i n t e r n a l redox r e a c t i o n , i n which the o x i d a n t and r e d u c t a n t are c h e m i c a l l y combined i n a single reactant. An i o n i c s p e c i e s ( T a b l e IV) or a p o l y a t o m i c s a l t (or p o l y a t o m i c a n i o n ) can undergo h y d r o l y s i s i n aqueous s o l u t i o n . A l l o t h e r r e a c t i o n c l a s s e s are c o n s i d e r e d o n l y i f t h e r e are two reactants. R e a c t i o n s w i t h Two R e a c t a n t s . Numerous r e a c t i o n t y p e s (see T a b l e I ) are p o s s i b l e i n the case o f two r e a c t a n t s . I n some c a s e s , s e v e r a l r e a c t i o n c l a s s e s need t o be c o n s i d e r e d f o r two r e a c t a n t s . Consider the case of FeFo and C r ( H C 0 g ) t which may be an i m p r o b a b l e s e t of r e a c t a n t s but which i l l u s t r a t e s n i c e l y the o p e r a t i o n of the e x p e r t system. S i n c e t h e s e are i o n i c compounds and, t h e r e f o r e , redox s p e c i e s ( T a b l e I V ) , the e x p e r t system w i l l check f o r redox r e a c t i o n s , u s i n g r e d u c t i o n p o t e n t i a l s f o r each c o m b i n a t i o n of component elements from the two r e a c t a n t s t o d e c i d e whether any redox w i l l o c c u r . Iron(III) w i l l o x i d i z e c h r o m i u m ( I I | i n t h i s system. P a r s i n g f o r a c i d s and bases i d e n t i f i e s t h e i r o n ( I I I ) i o n as an a c i d w i t h pK of 5.01, the f l u o r i d e i o n as a base w i t h pK of 10.85, the c h r o m i u n u l l ) i o n as an a c i d w i t h p K of 11.4, and b i c a r b o n a t e i o n as an a c i d w i t h p K of 7.3 and as a base w i t h pK of 11.2. Based on t h e s e r e s u l t s , p r e d i c t i o n s are made of the e x t e n t of h y d r o l y s i s of each of t h e s e i o n s . P i c k i n g the s t r o n g e s t a c i d ( s m a l l e s t p K ) and s t r o n g e s t base ( s m a l l e s t pK^) from t h e s e s p e c i e s , the e x p e r t system p r e d i c t s t h a t aqueous i r o n ( I I I ) i o n w i l l r e a c t w i t h aqueous f l u o r i d e i o n t o form i r o n ( I I I ) h y d r o x i d e and h y d r o f l u o r i c a c i d w i t h a pK of 1.86. S i n c e the r e a c t a n t s are b o t h i o n i c s p e c i e s , the e x p e r t system w i l l check f o r aqueous p r e c i p i t a t i o n r e a c t i o n s . In t h i s case, using s o l u b i l i t y r u l e s , the e x p e r t system p r e d i c t s l o g i c a l l y , but i n c o r r e c t l y , t h a t i r o n ( I I I ) c a r b o n a t e w i l l p r e c i p i t a t e from t h e solution. I n f a c t , i f a p r e c i p i t a t e i s formed, i t i s more l i k e l y t o be i r o n ( I I I ) h y d r o x i d e , s i n c e i r o n ( I I I ) i o n and c a r b o n a t e i o n are b o t h r a t h e r s u s c e p t i b l e t o h y d r o l y s i s . R u l e s have not y e t been e s t a b l i s h e d t o p r e d i c t when h y d r o l y s i s of the components w i l l override p r e c i p i t a t e formation. P a r s i n g f o r complex i o n s i n d i c a t e s t h a t the s o l u t i o n w i l l c o n t a i n h e x a a q u a i r o n ( I I I ) i o n and hexaaquachromium(II) i o n as complex i o n s , w h i l e the f l u o r i d e i o n and water are p o s s i b l e l i g a n d s . The p r e s e n c e of a complex i o n and a f r e e l i g a n d i n d i c a t e s t h a t complex i o n s u b s t i t u t i o n r e a c t i o n s are p o s s i b l e . S i n c e b o t h chromium(II) i o n and f l u o r i d e i o n are h a r d , f l u o r i d e i o n s h o u l d s u b s t i t u t e i n a s t e p w i s e manner f o r the bound water m o l e c u l e s on the 2

b

a

a

b

a


3.

BIRK

29


hexaaquachromium(II) i o n , f o r m i n g a s e r i e s of f l u o r o c h r o m i u m ( I I ) complexes. Not a l l examples w i l l g e n e r a t e t h i s many p o s s i b l e r e a c t i o n s , but i n a l l c a s e s , the r e a c t a n t s are examined t o see i f they f a l l i n t o r e a c t a n t c l a s s e s f o r which r e a c t i o n s of a l l the t y p e s l i s t e d i n T a b l e I are p o s s i b l e . The r e a c t a n t c l a s s e s and t h e i r p o s s i b l e r e a c t i o n s are summarized i n T a b l e V. R u l e s f o r R e a c t i v i t y P r e d i c t i o n . R u l e s f o r p r e d i c t i n g r e a c t i v i t y of g i v e n c h e m i c a l s p e c i e s were developed as s i m p l y as p o s s i b l e , i n o r d e r t h a t they would be a p p r o p r i a t e f o r l a t e r p e d a l o g i c a l use. The use of r e d u c t i o n p o t e n t i a l s f o r the p r e d i c t i o n of redox r e a c t i o n s has a l r e a d y been mentioned, as has the use of p K and pK v a l u e s t o s a t i s f y the r u l e t h a t the s t r o n g e s t a c i d w i l l r e a c t w i t h the s t r o n g e s t base t o undergo a c i d - b a s e n e u t r a l i z a t i o n r e a c t i o n s . Some of the r e a c t i v i t y r u l e s make use o n l y of the r e a c t a n t c l a s s i f i c a t i o n s d e s c r i b e d e a r l i e r . An example i s t h e nonaqueous r e a c t i o n between o x i d e s : oxide r e a c t i o n i f one r e a c t a n t i s a metal o x i d e , and t h e o t h e r r e a c t a n t i s a nonmetal o x i d e , then a m e t a l o x o a n i o n s a l t i s formed, oxide r e a c t i o n i f one r e a c t a n t i s a m e t a l h y d r o x i d e , and t h e o t h e r r e a c t a n t i s a nonmetal o x i d e , then a m e t a l oxoanion s a l t i s formed, oxide r e a c t i o n i f one r e a c t a n t i s a m e t a l o x i d e , and the o t h e r r e a c t a n t i s w a t e r , then a m e t a l h y d r o x i d e i s formed, oxide r e a c t i o n i f one r e a c t a n t i s a nonmetal o x i d e , and t h e o t h e r r e a c t a n t i s w a t e r , then an o x o a c i d i s formed, oxide r e a c t i o n i f b o t h r e a c t a n t s are nonmetal o x i d e s , and t h e nonmetals have o x i d a t i o n s t a t e s , one h i g h e r and one lower than the i n i t i a l s t a t e s , and the r e d u c t i o n p o t e n t i a l s t o these new o x i d a t i o n s t a t e s combine t o g i v e a p o s i t i v e v a l u e , t h e n two new nonmetal o x i d e s a r e formed by r e d o x . Many r u l e s make use o f p e r i o d i c i t y , as e x e m p l i f i e d by the r e a c t i o n of elements w i t h w a t e r . The r u l e s f o r t h i s c l a s s of r e a c t i o n s can be summarized as f o l l o w s : v i g o r o u s r e a c t i o n w i t h c o l d water i f the element i s a m e t a l , and t h e m e t a l i s i n group 1 or group 2, and the m e t a l i s i n the t h i r d p e r i o d and h i g h e r , then a m e t a l h y d r o x i d e and m o l e c u l a r hydrogen a r e formed, m i l d r e a c t i o n w i t h c o l d water i f the element i s a m e t a l , and the m e t a l i s b e r y l l i u m , o r magnesium, or i n group 3, or a l a n t h a n i d e , then a metal h y d r o x i d e and m o l e c u l a r hydrogen are formed.


a

b



30

EXPERT SYSTEM APPLICATIONS IN CHEMISTRY

no r e a c t i o n w i t h c o l d water i f the element i s any o t h e r m e t a l , or t h e element i s a nonmetal o t h e r than a h a l o g e n , o x i d a t i o n o f water i f the element i s f l u o r i n e , t h e n hydrogen f l u o r i d e and m o l e c u l a r oxygen a r e formed, disproportionation i f the element i f a h a l o g e n , then h y d r o h a l i c a c i d and hypohalous a c i d a r e formed, r e a c t i o n w i t h steam i f the element i s a m e t a l , and t h e r e d u c t i o n p o t e n t i a l from the l o w e s t o x i d a t i o n s t a t e i s l e s s t h a n -.414 V, then a m e t a l o x i d e and m o l e c u l a r hydrogen a r e formed, reaction with acid i f the element i s a m e t a l , and t h e r e d u c t i o n p o t e n t i a l from the l o w e s t o x i d a t i o n s t a t e i s l e s s t h a n 0.0 V, then a m e t a l i o n and m o l e c u l a r hydrogen a r e formed. R u l e s f o r some o t h e r r e a c t i o n s make use o f i n f o r m a t i o n from a d a t a b a s e . For example, sodium s u l f i t e w i l l r e a c t w i t h s i l i c o n d i o x i d e a t h i g h t e m p e r a t u r e s t o form sodium s i l i c a t e and s u l f u r d i o x i d e . T h i s example f o l l o w s t h e g e n e r a l r u l e : nonmetal o x i d e d i s p l a c e m e n t i f one r e a c t a n t i s a metal o x o a n i o n s a l t , and t h e o t h e r r e a c t a n t i s a nonmetal o x i d e , and t h e d i s p l a c e d nonmetal o x i d e i s more v o l a t i l e t h a n t h e r e a c t a n t nonmetal o x i d e . The r e l a t i v e v o l a t i l i t y i s determined from the b o i l i n g p o i n t s o f t h e nonmetal o x i d e s , which a r e s t o r e d i n a d a t a b a s e . P r o p e r t i e s such as charge o r o x i d a t i o n s t a t e , which a r e determined by a f o r m u l a p a r s e r f o r t h e c u r r e n t r e a c t a n t s , may be a d e t e r m i n i n g f a c t o r i n o t h e r r u l e s , such as the h y d r o l y s i s o f halides: h a l i d e compound h y d r o l y s i s i f the compound i s a nonmetal h a l i d e , and t h e compound i s not a c a r b o n t e t r a h a l i d e , and t h e compound i s not a n i t r o g e n t r i h a l i d e , and t h e compound i s not s u l f u r h e x a f l u o r i d e , and t h e second r e a c t a n t i s w a t e r , then a nonmetal o x i d e and hydrogen h a l i d e a r e formed, h a l i d e compound h y d r o l y s i s i f the compound i s a m e t a l h a l i d e , and t h e second r e a c t a n t i s w a t e r , and t h e m e t a l has an o x i d a t i o n s t a t e o f +4 o r g r e a t e r , then a m e t a l o x i d e and hydrogen h a l i d e a r e formed, or a m e t a l o x o i o n and hydrogen h a l i d e a r e formed. The oxometal f o r m u l a ( o x i d e or o x o i o n ) i s determined by t h e common form o f t h a t m e t a l i n t h e a p p r o p r i a t e o x i d a t i o n s t a t e i n aqueous s o l u t i o n . The l a t t e r i s determined by a n o t h e r s e t o f r a t h e r comprehensive r u l e s .


3.


BIRK


T a b l e V.

31

R e a c t a n t s and P o s s i b l e R e a c t i o n s

Reactant 1

Reactant 2

Reaction Class

none element simple i o n compound i o n i c compound compound oxo i o n element redox s p e c i e s element compound oxide species nonmetal o x i d e c o v a l e n t compound

none none none none none none none element redox s p e c i e s water oxygen oxides species nonmetal o x i d e 0 or h a l o g e n

nonmetal o x i d e nonmetal h a l i d e element carbon carbon carbon monoxide i o n i c oxo s a l t oxoacid cone. H S0i|

halogen halogen compound metal h y d r o x i d e oxoanion s a l t compound nonmetal o x i d e nonmetal o x i d e element, b i n a r y ionic salt, ionic oxo s a l t , p o l y atomic a n i o n s a l t c o v a l e n t compound none water ionic species base s p e c i e s ionic species free ligand

no r e a c t i o n disproportionation d i s p r o p o r t i onat i on disproportionation i n t e r n a l redox thermal decomposition d i s p r o p o r t i onat i on binary combination i o n i c redox hydrogen d i s p l a c e m e n t o x i d a t i o n by 0 oxide acid-base o x i d e redox o x i d a t i o n of covalent oxide or h a l i d e o x i d a t i v e a d d i t i o n of halogen o x i d a t i v e a d d i t i o n of halogen displacement displacement displacement displacement oxide displacement oxide displacement r e a c t i o n s o f h o t , cone. sulfuric acid ( a c i d - b a s e or redox)

2

water ionic species ionic species ionic species acid species ionic species complex i o n

2

2

hydrolysis hydrolysis hydrolysis hydrolysis acid-base n e u t r a l i z a t i o n precipitation complex i o n s u b s t i t u t i o n



32


The E x p l a n a t i o n F a c i l i t y In o r d e r t o c o n v e r t an e x p e r t system t o an i n t e l l i g e n t t u t o r i n g system, the e x p e r t system must be a b l e t o e x p l a i n i t s answers. T h i s e x p l a n a t i o n f a c i l i t y has been added t o the PIRExS program by means of amendments t o t h e r u l e s and by a d d i t i o n of d i s k f i l e s t h a t c o n t a i n a l l the r u l e s e x p r e s s e d i n n a t u r a l language ( E n g l i s h ) . Every r u l e d e f i n e d i n the program was l a b e l l e d i n t e r n a l l y by a t r a c k i n g v a r i a b l e . When the program attempts t o e x e c u t e a r u l e , t h i s t r a c k i n g v a r i a b l e i s added t o the database i d e n t i f i e d by a number t h a t i s d e f i n e d w i t h i n the r u l e . T h i s t r a c k i n g v a r i a b l e has t h e form: track(number,character) where t h e number i s a s s i g n e d s y s t e m a t i c a l l y f o r a l l t h e r u l e s and the c h a r a c t e r can be e i t h e r T or F, depending on whether the r u l e was found t o be t r u e or f a l s e . C o n s i d e r , f o r example, a r u l e numbered 9580. On e n t r y t o t h i s r u l e , t r a c k ( 9 5 8 0 , F ) i s added t o the database. I f t h e r u l e i s found t o be f a l s e , then t h e database i s l e f t as i s . However, i f the r u l e i s found t o be t r u e , t r a c k ( 9 5 8 0 , F ) i s removed from the database and t r a c k ( 9 5 8 0 , F ) i s added t o the database. In a d d i t i o n , at appropriate places r e l a t i v e t o other program o u t p u t , c a l l s a r e made t o a r o u t i n e t h a t checks the database f o r any t r a c k i n g v a r i a b l e s , l o o k s up the c o r r e s p o n d i n g messages i n the d i s k f i l e s , p r i n t s t h e s e messages, and removes t h e t r a c k i n g v a r i a b l e s from the database. I n t h i s way, a p p r o p r i a t e e x p l a n a t o r y messages are p r i n t e d a l o n g w i t h t h e r e a c t i v i t y p r e d i c t i o n s . To a i d i n r e v i e w i n g the program o u t p u t , each page of output i s saved t o the database and can be r e c o v e r e d by a page-up/page-down f u n c t i o n . Thus, an e n t i r e s e t of e x p l a n a t o r y messages can be r e v i e w e d or p r i n t e d out as needed t o understand the e n t i r e p r o c e s s of making p r e d i c t i o n s f o r a g i v e n s e t of r e a c t a n t s . P e d a g o g i c a l Uses A l t h o u g h PIRExS i s not an i n t e l l i g e n t t u t o r , i t can s t i l l be used t o t e a c h s t u d e n t s about i n o r g a n i c c h e m i c a l r e a c t i v i t y . I t does not t u t o r a s t u d e n t , but i t can e x p l a i n the l o g i c and r u l e s used t o make r e a c t i v i t y p r e d i c t i o n s . I t remains f o r a t e a c h e r t o c r e a t e an environment i n which the program can be used as a t o o l t o t e a c h i n o r g a n i c r e a c t i v i t y . The most o b v i o u s approach i s t o p r o v i d e the s t u d e n t s w i t h r e a c t i v i t y problems t o s o l v e , a l l o w i n g the use o f PIRExS as a r e s o u r c e . S y n t h e s i s pathways p r o v i d e good problems (17). For example, s t u d e n t s c o u l d be asked t o p r e p a r e chromium(III) s u l f i d e , s t a r t i n g w i t h p o t a s s i u m chromate. Another p o s s i b l e use i s the d i s c o v e r y of r e a c t i v i t y r u l e s . For example, s t u d e n t s c o u l d be asked t o develop a s e t of r u l e s t h a t would p r e d i c t t h e s t a b i l i t y w i t h r e s p e c t t o thermal d e c o m p o s i t i o n of c a r b o n a t e s . I n such an a p p l i c a t i o n , the i n s t r u c t o r would want t o e l i m i n a t e t h e e x p l a n a t i o n f a c i l i t y , s i n c e i t would p r o v i d e the answer w i t h l i t t l e s t u d e n t e f f o r t or i m a g i n a t i o n . Another f e a t u r e of PIRExS p r o v i d e s t h i s s o r t of i n s t r u c t o r f l e x i b i l i t y . A d i s k f i l e , c o n t a i n i n g keywords f o r e x p l a n a t i o n s as w e l l as f o r each of the r e a c t i o n c l a s s e s , i s r e a d i n t o the database d u r i n g program s t a r t - u p . I f an i n s t r u c t o r uses an e d i t o r t o remove or comment out any of these keywords, s t u d e n t


3. BIRK


33

a c c e s s t o t h a t f e a t u r e o f t h e program i s b l o c k e d . Thus, program c a p a b i l i t i e s can be adapted t o t h e c u r r e n t needs o f t h e s t u d e n t s o r the i n s t r u c t o r . Acknowledgments


The author i s g r a t e f u l f o r s u p p o r t i n t h e form o f a f e l l o w s h i p from P r o j e c t SERAPHIM, funded t h r o u g h t h e D i r e c t o r a t e f o r S c i e n c e and E n g i n e e r i n g E d u c a t i o n o f t h e N a t i o n a l S c i e n c e F o u n d a t i o n and t h e Fund f o r Improvement o f Post-Secondary E d u c a t i o n o f t h e Department o f E d u c a t i o n . The a u t h o r i s f u r t h e r g r a t e f u l t o John and B e t t y Moore and t h e Department o f C h e m i s t r y , E a s t e r n M i c h i g a n U n i v e r s i t y f o r t h e i r h o s p i t a l i t y d u r i n g a s a b b a t i c a l l e a v e , d u r i n g which much of t h i s work was completed.

L i t e r a t u r e Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

Moore, J. W. Acad. Comp. 1987, 2 (3), 18-21, 45-49. Duckworth, E. L. Acad. Comp. 1987, 2 (3), 6-10, 38-43, 62-63. Klopfer, L . E. J. Comp. Math. Sci. Teaching 1986, 5 (4), 16-32. Floyd, M. Turbo Technix 1988, M a r . / A p r . , 64-66. Myers, W. IEEE Expert 1986, Spring, 100-109. Basolo, F. J. Chem. Educ. 1980, 57, 45-46. Basolo, F. J. Chem. Educ. 1980, 57, 761-762. Hudson, M. J. Chem. Educ. 1980, 57, 770-772. Basolo, F.; Parry, R. W. J. Chem. Educ. 1980, 57, 772-777. Cassen, T.; DuBois, T. D. J. Chem. Educ. 1982, 59, 377-379. Beach, D. H. J. Chem. Educ. 1984, 61, 520-521. Basolo, F. J. Chem. Educ. 1984, 61, 520-521. Zuckerman, J. J. J. Chem. Educ. 1986, 63, 829-833. R i c c i , J. E. J. Amer. Chem. Soc. 1948, 70, 109. Wulfsberg, G. P r i n c i p l e s of Descriptive Inorganic Chemistry; Brooks/Cole Publishing C o . : Belmont, CA, 1987; p. 27-31. 16. Baes, C. F. Jr.; Mesmer, R. E. The Hydrolysis of Cations; WileyInterscience: New York, 1976; Chapter 18. 17. Kauffman, G. B. J. Chem. Educ. 1987, 64, 252-254.

RECEIVED June 9, 1989


Predicting Inorganic Reactions - ACS Symposium Series (ACS

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