CHAPTER XIX 

 OXIDIZING SUBSTANCES 



IN the preceding chapters we have encountered several rather 

 confusing oxidizing reactions. For example, in the preparation 

 of chlorine by the action of KMn0 4 on HC1 (p. 142), it was stated 

 that the hydrogen chloride was oxidized to chlorine and the potas- 

 sium permanganate reduced to manganous chloride. The student 

 may have found it difficult to understand how we can regard 

 a substance as oxidized when no oxygen is added to it. In order 

 to explain oxidations more clearly, particularly in connection with 

 the conception of valence, we must now learn more about oxida- 

 tion in general. We can do this best through the study of three 

 oxidizing substances which are of a simpler nature and are all 

 in common use. These are ozone, hydrogen peroxide, and hypo- 

 chlorous acid. 



OZONE Os 



When oxygen is blown from a small nozzle through the tip of a 

 Bunsen flame, a part of it is turned into ozone. The same thing 

 happens when a platinum wire, heated by an electric current, is 

 held under liquefied oxygen. This shows us that, to get ozone, we 

 must add energy (for example, by strong heating) to oxygen. We 

 learn, also, that the ozone must be cooled at once and kept cold. 

 If it lingers in the cooler (but not cold) region round the flame, it 

 decomposes again. 



Ozone is also obtained by the action of fluorine on water (p. 

 207). 



Preparation of Ozone. In practice electrical energy, devel- 

 oped by passing a " silent discharge " through the oxygen, is 



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