Chromium(ll) Compounds To the Editor:
There is a continuing interest in the preparation of compounds of divalent chromium (I). The reader may he interested to learn that there is a compound of chromium(II), the tricyanomethanide Cr[C(CN)&, which can he prepared without elaborate precautions to ensure an oxygen-free atmosphere. I t is one of the most "stable" compounds of Cr(I1) ever discovered and can even he gently heated in air without rapid oxidation (2). Potassium tricyanomethanide, one of the starting materials, is obtainable commercially (3). Although "tricyanometbanide" is apparently correct for the C(CN):, ion, the author called it "tricyanomethide" and has seen it referred to as "tricyanomethylide".
They further comment that "the resulting equation has been left unbalanced because no solution that has ever been produced satisfies the observed results. It is quite an exercise to balance it a t all". This "exercise" provides an excellent example of the usefulness of the technique of "material balance" for balancing chemical equations, as it is not only the most fundamental and rigorous approach to the problem, but also it provides an indication as to whether the equation in question is truly a legitimate chemicalequation in the first place (1-2). Four independent equations of material balance are available involving the nine undetermined coefficients in the reaction equation:
Literature Cited I Reeva..l. C. J . ( 7 w m M u c . 19115.62.444. 2. SWei. C. I.. lnsrx.Niir1 (71ern. Lctierr 19W1, 513. :i Strem Clwmimlr. Inc., 7 Mulliken Way. Dexter Industrial Park. Newburyport, MA 0,OSii.
G. L. Sllver Monssnto Research Corporation-Mound Miamisburg. OH 45342
Unbalanced Chemical Equatlons To the Editor:
In their interesting article [1984,61, 6251 on the development of the G. Frederick Smith Chemical Company, McRride and Adams give an unhalanced chemical equation summarizing the exp&imentally observed facts for the production of perchloric acid:
A quick calculation of the degrees of freedom (fl for nine variables ( u ) and four equations ( e ) ,gives f = 5, and indicates that no single unique lowest whole number solution is possible. This is in contrast to normal chemical eauations for which f = 1(i.e., setting one coefficient a t the lowest possible whole number uniauelv determines the values of the others). The usual interpretation of the result f > 1 is that the equation in question is not that of a single unique chemical reaction, hut rather that of the sum of several simultaneous competing reactions (21, in this case probably involving the production of HC104-2H20 on the one hand, and various side reactions leading to the different nitrogen oxides on the other. Literature Clted 1. I'
