16 GENERAL METHODS 



be changed from the lower to the higher state by the commonly 

 employed oxidizing agents, KMnO 4 , I 2 or K 2 Cr 2 O7. 



10FeS0 4 +2KMnO 4 +8H 2 SO 4 



- 5Fe(SO 4 ) 3 +K 2 SO 4 +2MnSO4+8H 2 O. 



In a similar manner, many organic compounds yield readily to 

 decomposition. 



5H 2 C 2 O 4 + 2KMn0 4 + 3H 2 SO 4 



= 10CO 2 +8H 2 O+K 2 SO 4 +2MnSO 4 . 



CO(NH 2 ) 2 +3I 2 +6NaOH = CO 2 +N 2 +6NaI+5H 2 0. 



It is apparent that if the strength of the oxidizing solution is 

 known (that is, if the oxidizing solution is standardized) and the 

 volume used up in the reaction noted, we can calculate from these 

 equations the quantity of the substance oxidized or decomposed. 

 In this way standardized oxidizing solutions find a wide use in the 

 quantitative determination of oxidizable compounds. 



Oxidizing Agents. The common oxidizing agents employed 

 are KMnO 4 , I 2 , and K 2 Cr 2 Oy. We shall consider only the first 

 two. KMn0 4 gives up its oxygen directly. 



2KMnO 4 = K 2 O 2MnO 50. 



This reduction is always carried on in the presence of H 2 SO4 in 

 order to dissolve the K 2 and the colored MnO. 



K 2 0+2MnO+50+3H 2 S0 4 = K 2 SO 4 +2MnSO 4 +3H 2 O+5O. 



(Keep in mind that 2 molecules of KMnO 4 yield 5 atoms. of 

 Oxygen.) 



Iodine yields oxygen indirectly. 



I 2 +H 2 O = 2HI+O. 



(Keep in mind that 2 atoms of Iodine yield 1 of Oxygen.) 

 The Normal Solution. Although these reactions are complex, 

 the strength of the reagents may nevertheless be expressed in simple 



