NITRIC ACID 309 



hloridegas, condenses moisture from the 



*'" 7 O~ O O J. 



nitric acid of commerce contains 68 per cent of the acid and boils 

 at 120.5. 



Chemical Properties Decomposition of Nitric Acid. 



The acid is not very stable. It decomposes, in part, even when 

 simply distilled (86), giving a red gas, nitrogen tetroxide N0 2 , 

 water and oxygen: 



Skeleton: HNO 3 - N0 2 + 2 + H 2 O. 



Balanced: 4HNO 3 - 4N0 2 + O 2 + 2H 2 O. 



When a reducing agent is present, oxides containing less oxygen 

 than N0 2 may be formed, such as nitric oxide NO. 



Nitric Acid as an Acid. An aqueous solution of nitric acid 

 turns blue litmus red, and is a very active, highly ionized acid. 

 With bases it gives nitrates, which can be obtained from the solu- 

 tion by evaporation: 



NaOH+ HNO 3 ^ H 2 O + NaN0 3 . 

 Ca(OH) 2 + 2HN0 3 - 2H 2 + Ca(NO 3 ) 2 . 



Nitric Acid as an Oxidizing Agent. Since nitric acid gives 

 up oxygen with liberation of energy, it is 

 also active as an oxidizing agent. Glowing 

 charcoal, as a powder or in the form of a 

 stick, will burn when pure nitric acid is 

 poured upon it (Fig. 82). Carbon dioxide and red nitrogen tetr- 

 oxide N0 2 are evolved. 



Skeleton: HN0 3 + C- NO 2 + C0 2 + H 2 O. 



Balanced: 4HN0 3 + C -* 4NO 2 1 + CO 2 1 + 2H 2 O. 



Nitric acid oxidizes indigo and other colored organic compounds, 

 in the same way as do the three oxidizing agents described in 

 Chapter XIX. It also oxidizes hydrochloric acid, upon which 



