158 Roberts — Action of Reducing Agents on Iodic Acid. 



These results, it will be seen, are in complete accordance 

 with those obtained by the former method and indicate the 

 following reaction : 



HI0 3 + 21, + 5HC1 = 3H 2 + 5IC1 



The equation obtained above for the reaction between iodic 

 acid, potassium iodide, and hydrochloric acid, viz : 



HIO, + 2KI + 5HC1 = 3H 2 + 2KC1 + 8IC1, 



can be derived directly by a combination of the ordinary equa- 

 tion, in which iodine is set free, 



[5KI + H10 3 + 5HC1 = 3H 2 + 5KC1'+3I 2 ]2, 



with the equation just established, 



[HI0 3 + 2l 2 + 5HCl = 3H 2 + 5lCl]3, 



in which the iodine reacts upon iodic acid. This fact supports 

 the assumption that the effect of a reducing agent upon an 

 excess of iodic acid in presence of hydrochloric acid is to set 

 free iodine which then dissolves in a mixture of the two acids 

 to form iodine monochloride. 



Iodine has apparently no effect upon either acid taken singly, 

 and there is nothing in these experiments to show whether the 

 action of the iodine on the iodic acid in the mixture of the 

 two acids is in the first instance of an oxidizing or reducing 

 nature. It may be that the iodic acid is first reduced to a 

 lower oxide, as has been previously suggested, or that it is oxi- 

 dized to periodic acid. The first condition is expressed in 

 equations I, and the latter in equations II, from which it is 

 seen that either assumption agrees with the equations just 

 established. 



I. (2HI0 3 + I 2 + 2HC1 = I 4 4 + 2H 2 + 2IC1 



|I 2 4 + 3I 2 + 8HC1 = 4H 2 + 8IC1 



/ Combined : 2HI0 3 + 4l 2 -f 10HC1 = 10lCl + 6H 2 O 



II. f2HI0 3 + 2H 2 + 2l 2 =4HI + H n O + I 2 7 



J I O +4HI+10HC1 = 7H o + 6lCl + 2Cl„ I 



} 2Cl 2 + 2l 2 =4lCl f 



L Combined : 2HI0 3 + 4l 2 + 10HC1 = 1 OlCl + 6H 2 J 



In any case it is evident that the mixture of iodine and 

 iodic acid, both ordinarily oxidizing agents, is able to effect 

 the decomposition of hydrochloric acid with the formation of 

 iodine monochloride. 



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