752
JOURNAL OF CHEMICAL EDUCATION
APFZL,1932
The final equation is balanced by using the number of atoms in (I), (2) and (4). Very truly yours, OBER SLOTTERBECK CHARDON COMMUNITY PUBLICSCHOOLS CHARDON. OHIO
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DEAR EDITOR: Many students and many teachers of chemistry make hard work of balancing equations of oxidation and reduction. As was pointed out in the Correspondence Section of the December, EDUCATION (p. 2453), the 1931, number of the JOURNALOF CHEMICAL algebraic method is purely mechanical and affords little insight into the nature of the chemical reactions considered. It is not worthy of consideration. I have never seen any more simple method of balancing oxidation and reduction equations than the rule originated by Professor 0. C. Johnson of the University of Michigan in 1880 (Chem. News, 42, 51). Professor R. J. Carney substitutes the term, "oxidation number," for bond. The oxidation number or bond in most cases will be the same number as the valence. The valence or oxidation numbef is determined by the following simple + rules: *
(a) Hydrogen has a valence or oxidation number of + I . ( b ) Oxygen has a valence or oxidation number of -2, except in H202 and peroxides. (6) Free elements have a valence or oxidizing number of zero. ( d ) The sum of the valencies or oxidation numbers of the elements in a compound is zero. This simple rule will balance all equations of oxidation and reduction: THE TOTAL GAIN IN VALENCE OR OXIDATION NUMBER FOR ALL OF THE ATOMS I N ONE MOLECULE OF THE REDUCING AGENT IS THE NUMBER OF MOLECULES OF THE OXIDIZING AGENT TO BE TAKEN; THE TOTAL LOSS I N VALENCE OR OXIDATION NUMBER FOR ALL O F THE ATOMS IN ONE MOLECULE OF THE OXIDIZING AGENT IS THE NUMBER OF MOLECULES OF
After obtaining these two numbers the rest of the equation can be balanced by inspection. The equations that students often have difficulty with in any method are those in which a part of the oxidizing agent or reducing agent also
THE REDUCING AGENT TO BE TAKEN.
*Modified from "Outline of the Methods of Qualitative Chemical Analysis," by R . J. Carney, University of Michigan, p. 32.
VOL.9. NO. 4
753
CORRESPONDENCE
enters into combination without being oxidized or reduced, and those in which all the elements oxidized or reduced are present in the same molecule. 8HN03 ---t 3Cu(NOa)x The first is illustrated in the equation 3Cu 2NO 4H20. Inspection shows that only part of the nitric acid acts as an oxidizing agent. This reactiou is explained in many ways but I think the simplest method is to write the acid twice as follows:
+
+
+
The total change in valence of the reducing agent (Cu) is two; hence according to the rule take two molecules of the oxidizing agent (HNOa) and the total change in valence of the oxidizing agent is three, therefore take three molecules of the reducing agent (copper). . The numbers 3 and 2, fixed by the rule, decide the number of molecules of Cu(NO& and NO in the balanced equation. Inspection shows that six molecules of nitric acid are needed to enter into combination with the copper. The second difficult kind is illustrated in the equation: ti
2HC10s (oxidizing)
+ HCIOs (reducing) --+ HCIOl + 2C102 + H1O +7
+6
+4
The oxidizing HC103 changes to ClOz, the reducing to HClOa. I think the above method of explaining the action of nitric acid on copper is simpler than that given by Prokssor Earl Otto in the February, EDUCATION (pp. 361-3) and 1932, numb- oI Lhe JOURNAL OF CHEMICAL J emphasizes the double action of nitric acid. Attention should be called to an error in the products formed in one of the equations given by Professor Otto (p. 363). HaAsOl is formed instead of A S ( N O ~when ) ~ nitric acid acts on AS&.
Very truly yours, BERTW. PEET
* * * * * * DEAREDITOR: The objection to the algebraic method of balancing chemical equations which Nicholas Dietz, Jr., gives in your issue of February, 1932 (p. 361), is correct as far as it goes, but he has overlooked the fact that one cannot divorce chemistry completely from mathematics in using the latter in many chemical calculations. The statement to the effect that there must be a t least (n - 1) different elements involved in a chemical equation of n substances before this equation can be balanced by the algebraic method,
