University of Utah soit Late City, 84112
I
oxidation-~edurfonReaction
A number of papers have recently been published in which the student is asked to investigate a reaction whose stoichiometry is unknown to him, and on the basis of his data write an appropriate equation or determine one of the products of the reaction.' The experiment described here is similar in many respects to that described by Child and R ~ m e t t e , ~ although i t has the advantage that a primary standard solution can be used as titrant. In this case, hydra~inesulfate is titrated at 65'C with standard bromate in the presence of sodium rn~lybdate.~ The student is faced with the problem of identifying not only the hydraziue oxidation product (NJ through the stoichiometry but also the bromate reduction product (bromide) through the use of some elementary qualitative analysis. He is also offered a chance to speculate on the actual mechanism for the reaction
which involves the reductiou molybdenum(V1) to molybdenum(V) (blue) by hydrazine and oxidation of molybdenum(V) by bromate. He can see graphically the effectof heating the solution too hot-the end point then is not colorless, but yellow, because Br2is produced. The equation for the reaction is 3NzH,
+ 2Br03-
-
3NI
+ 2 B r + 61310
and the average N2HI:BrQ- mole ratio reported for the determination ranges between 1.21 and 1.68. The grand average for these students (n = 31) was 1.46. Interested readers may obtain a copy of the directions given the student by request to the author. TIETZE, H. R., J. CHEM.EDUC. 40, 345 (1963); CHILD,W. C., JR., AND RAYETTE, R. W., J. CHEM.EDEC.44,109 (1967). ' Second reference in footnote one. SZABELLEDY, L., AND \I.\DIE,\I.,J f i k v x h i m . .4cla 2, >i (1937).
Volume 44, Number 9, September 1967
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537
