GUEST AUTHORS
Textbook Errors,
0. Bostrup, K. Demand!, and K. 0. Hansen Frederiksborg Statsskolel Hillerod, Denmark
The Thermal Decomposition of KCIO,
In almost every textbook of chemistry2 i t is stated that potassium chlorate liberates oxygen and forms potassium chloride when heated to 400°C. Since the rate of this reaction is impractically slow a t lower temperatures, it is generally recommended that a small amount of suitable catalyst be added to cause the reaction to proceed a t a convenient rate a t 150°C.
150DC
2KClOs
MnO,
2KC1
47
+ 301
But this is not the whole truth. We are here not thinking of the temporary formation of perchlorate, which eventually decomposes, hut refer to the fact that Suggestions of material mitable for this column and guest columns suitahle for publie&ion directly are eagerly solicited. They should be sent with as many details as possible, and particularly with references to modem textbooks, to Karol J. Mysels, Departre ment of Chemistry, University of Southern California, Los Angeles 7, ~alifornia. EDITOR'SNOTE: It might not be clear to the non-Danish resder that this is a hieh school in which Mr. Bastrun teaches. As he points out, it is n&worthy that "It is possible fa; students a t the secondary level to discover and to investigate failures in their textbooks!' K. J. M. q i n c e the purpose of this column is to prevent the spread and continuation of errors and not to evaluate individual texts, the source of errors discussed will not be cited. To be presented, the error must occur in at least two independent standard books.
when the catalyst is present, chlorine-containing gases (CL and C102)form alongside the o ~ y g e n . ~ Our attention was drawn to this peculiar fact by Kirsten Sorensen, one of the students here; she observed during one of the standard class experiments with oxygen that the gas had a very remarkable smell. We examined the problem further and found in agreement with earlier investigations that pure potassium chlorate when heated in a crucible over a Bunsen burner is converted quantitatively (within 0.2%) to the chloride. When manganese(1V) oxide or iron(II1) oxide is added, i t is easy to show that chlorine-containing gases are formed. Our experiments showed that as much as 3% of the gases generated may be chlorine or chlorine(IV) oxide. Assuming that most of the impurities in the oxygen was Clr, we estimated the amountin two ways: (1) The impure oxygen is passed through a solution of K I in water and the liberated iodine was titrated with standard thiosulfate solution. (2) The impure oxygen gas was passed through a solution of AgN03and HNOa in water. The amount of AgCl formed was estimated nephelemetrically by visual comparison with standards based on an HCl solution. a
G ~ L I N.'Handbuch , der anorganischo Chemie," System Xo.
6, Chlor., Berlin, 1927, pp. 342-343.
Volume 39, Number 1 1 , November 1962
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