142 SMITH'S INTERMEDIATE CHEMISTRY 



8 atoms of chlorine thereby made available, leaving 5C1 to be 

 liberated. Since this chlorine is obtained as C1 2 , it is necessary 

 to double our quantities throughout. 



Balanced: 2KMnO 4 + 16HC1 -4 8H 2 O + 2KC1 + 2MnCl 2 + 5C1 2 . 



This action is an oxidation of the hydrogen chloride by the per- 

 manganate. The potassium permanganate, which supplied the 

 oxygen, is called the oxidizing agent. Since the permanganate 

 lost oxygen, it was itself reduced. In all oxidations one substance 

 is oxidized and another reduced. 



Deacon's process (p. 140) is also an oxidation of hydrogen chlo- 

 ride (by free oxygen). The oxygen is reduced to water. 



Chlorine may be prepared by using other substances to oxidize 

 hydrochloric acid. Amongst those which are suitable are man- 

 ganese dioxide Mn0 2 , potassium chlorate KC10 3 and red lead 

 Pb 3 4 . 



Manganese Dioxide and Hydrogen Chloride. The action 

 of manganese dioxide upon hydrochloric acid is an instructive one. 

 It is a general rule, of which we shall meet many applications, that 

 when an acid interacts with an oxide of a metal, there are two 

 constant features in the result, namely: (1) The oxygen of the 

 oxide combines with the hydrogen of the acid to form water, and 

 (2) the metal of the oxide combines with the acid radical of the 

 acid. Here the skeleton equation should be Mn0 2 + HC1 

 H 2 + MnCh. With O 2 , to form water, 4HC1 is required, and 

 the product is 2H 2 O. Hence the equation is 



Balanced: MnO 2 + 4HC1 -> 2H 2 O + MnCl 4 . 



This is, undoubtedly, what happens in the first place. The prod- 

 ucts actually obtained on heating the mixture, however, are 

 water, manganous chloride MnCl 2 and chlorine. We owe the 

 chlorine to the fact that the tetrachloride is unstable. At low 

 temperatures it decomposes into manganese trichloride (MnCla) 



