mnething new from the pwt Chemical Equations, Moles. and Stoichiometry Tempie University 345 Ritter Hall Philadelphia. PA 19122 T w o excellent articles a p p e a r e d in 1978 a b o u t chemical equations a n d the mole concept. "The Chemical Equation P a r t 1: Simple Reactions," Doris Kolb. J. CHKM.EIMJC.. 55.131 184 ( M a r c h 1978). Kolb stresses a t the outset that a chemical equation is unlike a mathematical.. ."expression of equality involving a t least one variable numher." "A chemical equation i s . . a concise statement describing a chemical reaction, expressed in chemical symbolism." It is indeed a shorl-hand statement afwhat hasalready happened.She begins with a short history of writing equations, gives three simple rules for writing an equation, and good examples of balancing equations starting with a simple example; going on to more complex ones. Kolh then rhows the four clas..ifirations (types) ofchemical reactions. comhination. deromposition, displacement (sinplel. and Me. tarhesis (douhle replacement). She shows how s knowledge of these four types of reactions can be used t o predict many similar types of reactions. The meaning of all the information of what a correct equation can signify is clearly shown. Thissection is followed by a section on elementary calculations based on the mole concept. Thermochemical eauations are introduced as are ionic euuations. The reader is told, "Things an equation cannot tell us!" The key point- that Doris Kolb has brought out in thisarticle can be outlined for use in handouts by teachers for their students. There is no doubt that many beginning students of chemistry will suffer far less frustrations of unnermary mysteries about balancing equations if their teacher presents this article in an outlined form to them.
.
.
~
~~
"The Mole," Doris Kolb, vember 1978).
.
~~~
J. CHEM.EDUC.,55 1111,728 (No-
This second article by Kolb is an excellent follow-up of her article cited above. As in the above article, this writer recommends strongly the use of an outline of Kolb's work in the form of handouts to the students. Kolb shows by examples, diagrams, lists, charts and other methods how to organize the mole concept clearly for the student. "How b i is~ the Auagadro number? is thequestion sooften asked. How was it determined?The teacher might be quite surprised to learn that Amedeo Avqadro never knew the constant that bears hisname. Who war Loschmidt and why do many German speaking countries use the Lwchmidt number and not the Avogadro number? The answers to these often asked questions are in Kolb's article.
"The Use of Algebra in Solving Chemical Equations," J e r r y Sears, The Science Teacher, 78 (November 1969). S e a n shows examples that indicate the usefulness of algebra in certain chemical problems. Recognizing that balancing oxidationreduction equations requires a system far more complex than the inspection method, he presents his approach. He states that his classes, after mastering his suggested technique, take great pride in balancing c?mplex equations. Sears' explanation of his algebraic 'Ms. Weerasooriya is a Teaching Asslstant. She is from Srl Lanka.
792
Journal
of
Chemical Education
Edited by: JOSEPH S. SCHMUCKLER Chairman 01 Science E d ~ ~ s t i m Temple University 345 Riner Hall PhiladBlphia. PA 19122
method of balancing redox equations is presented clearly. The reader should have nodifficulty in using the article. On page 70of the April 1970 lmue of The Science Teacher, you will find how readers resoonded toSeam'useofalaebra insulvinachemical equations. "Writing a Chemical Equation from T i t r a t i o n Data: Experim e n t for General Chemistry," Harold M. State, J. CHEM. EDUC.,39 161,297 (1962). "The quantitative significance of chemical equations can be made more real to beginning students by inverting several standard titrimetric procedures. Students are provided with solutions for which concentrations are given in grams of solute per milliliter and are asked to perform the titrations. From thevolumesaf thesolutionsused and their concentrations, the numher of gramsand the number of moles of each reactant may be calculated: from the latter the mole ratioof the reactant3 may be obtained which then permits the student to balance the chemical equation which he is given in generalized form." The example used by State requires the student to complete this equation experimentally.
+
-
+
nNaOH HIPOI Na.Hs-.PO, nHrO He discusses the results that he obtained with his classes. These are useful to you to make comparisons to your own work.
on Stoichiometry a n d Structure," R e x T. Morrison, J. CHEM.EDUC.,55 141,255 (1978).
"Emphasis
In his "View from my Classroom" article. Morrison writes of his classroom approach to teaching chemistry. Some teachers will find Morrison's ideas g d , because they do the same kinds of things, while others will find Morrisan's ideasnew and refreshina. Hedescribes his first course as having s "~toichiometr~-~enteredintroduction." In his second-year course, Morrison stresses structure as it relates to molecular behavior. He shows his students, most of whom have already studied biology, the relationship of structure to function in molecular behavior. Throughout the article, you get a good idea of Morrison the teacher and his philosophy of teaching chemistry. "Three Simple Stoichiometric Experiments for Introductory H i e h School Chemistrv." Rov Arlotto. The Science ~ G c h e r51 , (May 1974):
its will be presented in thiissue priw to when the topic is taught in a typical high
1s Currently the Joseph 5. S~hrnu~kler chairman of the Department at Education and a Professor of Chemisw at Temple University. He was tarmeriy a chemistry teacher at Haverlord Township Senior High School cn Pennsylvania where he taught ior 15 years. Dr. Schmuckier received his 85 degree in 1952. MS degree in 1954. and PhD in 1968 from !he University ol Pennsylvania. Hi5 numerous awards in recognition ot his dedication ia teaching and chemical education inci& his receipt of fhe American Chemical Society James &)'ant Comnt Award In High Schml Chemistry Teaching in 1968. Thai year he sir0 received the MCA and Chemicai lndurtrier Council awards. He is one ol the co-auihorr to the Silver Burden Company program in chemistry and was an original participant andcontributw to the CHEM Study Program lor High School Chemistry;he Mspubiishedarticier in jo~rnalsin science and science education.
.
"Simple . . lnlxratory experiments which emphasize basic "The experiments [are] . useful for chemical principles instruction a t the intmductorv level and contain sufficient food for thought for more advanced students. Their purpose is t o give the student hard experimental evidence for developing concepts of atomic mass, empirical formulas, and mole relationship between reacting species."
..."
. ..
..
Experiment 1. Synthesis of LiC11.t Experiment 2. Synthesis of CoClp(,l Experiment 3. Determining coefficients of a chemical equation. Each experiment is carefully detailed for procedures and cautions. Sample calculntions are shown for use as a guide for the teacher.
History "A Physiological B a s i s for t h e G r o u p i n g of the ElementsJ a m e s B l a k e (1815-93)." S r . M a r y A m b r o s e Devereaux, S.N.J.M.. H u g h B. D o n a h o e , K a z u o K . Kimura., J. CHEM. Enuc., 33 [ I ]340 ( J u l y 1956). "The concept cd I he grouping of the elements nn a basis of physi. ologieal srlivitv war I'ir.1 wnreivrrl l,y nn Knelish physician, dames Illnke. Hasing his r u r k on llw stwly uf the phyolc*ical activity of
inorganic caticma in living wgnnims. he was ahlr toobtain groupinas similar to I ~ I B C ihtsmed P 20 \ear< Inter h r M e n d e l m . . ." "Blake's researches n ~ m p r i s ea fascinatingchapter in the history a f t h e study of the relationship between chemical structure and physiological activity. . ..""Blake followed the recognized soneept that isomorphous elemenls were those which could replace one enather in certain crystals without affecting the structure of the crystal. Blake cnnsidered isomorphism (structural similarity) and physiological activity to he the first step t o a morescientific insight into the action of substances on living organisms." This article is a n excellent resource for a teaching example of the inlerdiseiplinary nstureof chemistry. Blake's Law, which is stillvalid. is as follows: "The reactions which take place between the elements of the living hody and inorganic compounds are not t o be explained by ordinary chemical properties of these substances but depend an certain properties they possess connected with their isomurphous relations." Blake's tshles of isomorphic groupings related t o lethal dosage isshown. Hisehart of the elements inlo physiological patterns. groups . together the elements which Mendeleev later referred to as the transition elemenis." Blake conceded that he did not forsee a periodic relationship as was emphasized Inter hy Mendeleev. T h e reader will he interested t o learn the trends of toxicity that Blake's work shows nenm perirxls and within groups. His experiments that relate chemical behavior t o chemical structure started an important series of investigations which continue today.
.
". .
Volume 58
Number 10
O c t o b e r 1981
793
