QUESTIONS AND ANSWERS 19 



Describe a method of preparing nitrogen. Compare the properties of 

 nitrogen with those of oxygen. 

 By passing a current of air over copper, heated to redness, 

 copper oxide will be formed and nitrogen isolated. 



Nitrogen and oxygen are both colorless, odorless, tasteless gases. 

 Oxygen has a great affinity for 'other elements and supports com- 

 bustion; nitrogen unites with very few elements and does not 

 support life nor combustion. 



Describe the commercial preparation of nitric acid and write the reac- 

 tion. Mention important uses of nitric acid. 

 Sodium nitrate is distilled with sulphuric acid. 

 2NaN03 + H^SO, = Na,SO^ + 2HNO3. 



Nitric acid is used in medicine as a caustic and is employed in 

 etching copper plates for engraving ; it is also important in the refin- 

 ing of precious metals and in the making of nitroglycerine, gun 

 cotton, aniline dyes, etc. 



What element constitutes four-fifths of the air? 

 Nitrogen. 



AMMONIA ^ 



What is ammonia? Give the source and uses of ammonia. 



Ammonia is a colorless gas, of a peculiar, characteristic and 

 very pungent odor. It is neither combustible nor a supporter of 

 combustion. By weight it is composed of 13.93 parts of nitrogen 

 and 3 parts of hydrogen. It is very soluble in water; caustic and 

 readily blisters the skin; strongly alkaline in reaction. Formula, 



NH3. 



Sources: Decomposition of organic matter (meat, urine, blood, 

 etc.). Decomposition of ammonium salts by the hydroxides of 

 sodium, potassium and calcium, 2(NH^C1)+ Ca(0H)2 = CaClj + 

 2H2O + 2NH3. Ammonia is obtained, commercially, from gas 

 liquor, a by-product of gas plants. 



Uses : It is used in medicine as a cardiac stimulant and general 

 stimulant, also to increase secretions. In the household it is used 

 as a general cleaning agent in the aqueous form (hartshorn). 

 Explain why the presence of free ammonia in drinking water is a sign 

 of danger. 



Because it is indicative of contamination with decomposing 



organic matter. 

 Give the composition and method of preparation of ammonium chloride. 

 It is composed of nitrogen, hydrogen and chlorine, NH^Cl. Pre- 



