quantity should not imply a particular choice of unit (e.g., "molar amount," "moleaee"). Of all the sueeestions that have been made, I think much the best is ~ i o r g eGorin's "chemical amount" (J.Chem. Educ. 1982,59,508; 1983.60. 782). This isdescriptive, easy tosay, uses familiar ~ o r d s , ~ a n d does not require a major change in IUPAC recommendations. Indeed, IUPAC can continue to recommend "amount" as the abbreviated name; i t has only to allow this to he amulified to "chemical amount" wherever confusion with "amount" in the ordinary sense is liable to occur. A further difficulty that students have is differentiating between the relative mass of an entity, M, (= 18.02 for HzO), and its molar mass, M (= 18.02 glmol for HzO). T o overcome this problem, Frazer and Servant suggested that only the latter quantity be taught in schools. However, this is not an ideal solution, since the quantity that is actually measured is relative atomic mass, and i t is this quantity that is tabulated in atandard texts. An alternative solution is to give t o relative mass the more distinct and rational symbol m, (m is the standard symbol for mass), and to formulate the relationship between molar mass and relative mass explicitly as ~~
~~
Abbrevlate Recomblnent "rt" To the Editor: We have been concerned for some time about the tendency to misuse the abbreviation "rDNA" for recombinant DNA, rather than ribosomal DNA. We, therefore, were dismaved to see this usaee annear nrominentlv in a recent article [Parsons, K. A. f h i s jhurnai 1988,65, &5]. Although other abbreviations have been orooosed (I).one of our correspondents, R.C. King, hassuggestkd ..rt'; bd used toabbreviate "recombinant" (2). We suooort this abhreviation as the least confusing (3).We ask thatyour assistants, authors, and referees require "rt" he used for recombinant DNA (rtDNA) or RNA (rtRNA), when helpful, and that ?DNA, rRNA, and rProtein" be strictly reserved for ribosomal species. Your assistance in correc& this confusing terminolo& will be appreciated by studenta and teachers alike, who must learn and teach ahout both rDNA and rtDNA. Llterature Clted
M = M%,
Terry L. Helser
where M e = 1 glmol. The latter is equal to the product of the Avogadroconstant and the unified atomic mass constant ( = 1/12th of the massof a "C acorn) and is called hy IUPAC the "standard molar mass" (Quantities, Units and S>mbols, p %).This formulation is particularly useful when M has to be in kglmol, as in some physicochemical calculations, since the need to insert a value for M e (in this case 0.001 kglmol) helps to ensure the appropriate units are used. 1 have out theabovesurvestions to Mills, and he i s s n m a thetic to-them, provided-that they receive support from a sufficient number of chemists throughout the world. I should be very grateful thereforeif readers who wouldlike to see such changes would write to Mills a t the University of Reading, England, to express their support for them. If they can promote them in other ways, I should appreciate this also. I believe that these changes would greatly facilitate the teaching of stoichiometry, especially a t an introductory level. P. G. Nelson Unlverslty of Hull Hull HUB 7RX England
Depanrnenl of Chem stry State Jn verrity College Oneonta. NY 13820
Carol A. Ryder Depanment of Biology State Univenlty College Oneonta, NY 13820
Redllch-Klster-De To the Editor:
Faclo Standard
The article of F. R. Hilgeman and G. H. Richter in "The Computer Bulletin Board", [J. Chem. Educ. 1988 65, A 9 6 971 is valuable in showing how useful a commercial spreadsheet can be for least-squares fitting of data. Unfortunately, they have taken one of the Redlich-Kister equations m-2
@ = X U - X)
1A,(-1
+ 2X)J
1-0
and converted back t o the unsymmetrical Margules form m-2
Avold Misleading the Students To the Editor:
@=X(i-X)lBjXj j=o
Chemists have a long-standing habit, misleading a t least to students, of saying that strong bases produce acids (instead of anions or salts) in various reactions. We thus show aspirin plus NaOH yielding salicylic acid (I) instead of (sodium) salicylate, or cyanuric chloride plus NaOH yielding cyanuric acid (2) instead of (sodium) cyanurate. Why not use correct statements, which would he only slightly longer, or even shorter, than the misleading ones? The transformation of the salt into the actual acid sometimes can be omitted or is not even desired; other times it ought to he made explicit anyway. Llterature Clted 1. Street, K. W J I J. Chsrn.Edue. L988,65.915 2. Clyde, D.D. J.Chem. Educ. 1988.65,912.
Ronald L. Rich Campus Box 7905 Depanment of Chemical Engineering NCSU Raleigh. NC 27695-7905
This is unnecessary since one can calculate spreadsheet columns as X ( l - X)(-1+2X)j almost as easily as Xi - Xif1. The ability t o compare values with workers using reverse numbering of the components is sufficient reason for the Redlicb-Kister form t o have become a de facto standard in the analysis of thermodynamic data for binary systems. More nhvsical chemistrv teachers should become familiar with tiis'form, and the &ple equations for the calculation of oartial mold auantities (8,- 6h0 and 8 9 - 0 9 ' ) with the same set of codfficients (see ~ i d l i c h ;~ f s t e r f - ~ u r n q u i s t . Chem. Eng. Progr., Symp Ser. 1952,48 (2), 49-61 or nearly any chemical engineering textbook). I t is also simple to pro=am the temperature and pressure deaendence of Redlichin a modern spreadsheet and to use the ~ i s t e coefficients r spreadsheet to calculate the excess quantitv and both partial mold quantities a t any concentration. Reed A. Howald Momma State University Boreman. MT 59717
Volume 67 Number 7 July 1990
629
