62 Preparation of Substances 



centimeters of sulfuric acid would be necessary to 

 contain the number of grams found under 2. 



4. What volum of nitrogen oxids was given off in 

 this experiment? To solv this problem it will be 

 necessary to establish the relationship between the 

 weight of copper used and the volum of gas given off. 

 The gas given off is the colorless nitric oxid wliich 

 changes to the brown nitrogen dioxid without change 

 in volum upon exposure to the air. The following 

 equatioQ shows the decomposition of nitric acid as it 

 takes place in the experiment, 



4HXO3 = 2H2O + 3O2 + 4N0. 



The change from the colorless to the brown oxid is 

 simple, 



2N0 +02= 2NO2, 



and the quantities 2N0 and 2NO2 bear out the state- 

 ment that there is no change in volum in the oxida- 

 tion of nitric oxid to nitrogen dioxid. The relation of 

 the nitrogen dioxid to the copper must be sought thru 

 the oxygen which unites w^th the copper, 



Cu + = CuO. 



The copper being once oxidized we lose interest in it, 

 for the purposes of this calculation, as it reacts with 

 the sulfuric acid without changing its relationship to 

 the oxygen, 



CuO + H2SO4 • aq. = CUSO4 • aq. 



Now it is possible to establish the relationship of the 

 copper to the nitrogen dioxid thru the oxj^gen as fol- 

 lows: One Cu unites with one O, hence 6Cu unites 

 wath 3O2 and, from the first equation, the produc- 

 tion of 3O2 is accompanied by the evolution of 4N0 

 which goes to 4NO2 without change in volum. Then 

 6Cu are accompanied by the production of 4NO2 



