150 SMITH'S INTERMEDIATE CHEMISTRY 



Another Example. What weight of copper will combine with 

 15.2 liters of chlorine (at and 760 mm.)? 



Cu + C1 2 -* CuCl 2 . 



63.57 g. 70.92 g. or 22.4 1. 134.49 g. 



x 15.2 liters 



The proportion is: 



22.4 : 63.57 :: 15.2 : x (= 43.14 g.). 



At Other than Standard Conditions. If the problem 

 concerns a gas at some temperature and pressure not and 760 

 mm., then correction must be made as a separate calculation. 

 For example, if the 15.2 liters of chlorine, in the foregoing illus- 

 tration, had been at 15 and 742 mm., then the volume would 

 first have to be reduced to and 760 mm. (See p. 47.) 



Questions of Volume Alone. When weights are not men- 

 tioned in the question, but volumes only, the calculation is very 

 simple. For example: What are the relative volumes of oxygen 

 and hydrogen chloride used in Deacon's process? 



4HC1 + O 2 -> 2H 2 + 2C1 2 

 Molecules: 4 122 



Volumes: 4 X 22.4 1 X 22.4 2 X 22.4 2 X 22.4 



Remembering that equal numbers of molecules occupy equal 

 volumes, and that 4HC1 = 4 molecules, 2 = 1 molecule, etc., we 

 perceive that 4 volumes of HC1 will be required for 1 volume of 

 oxygen. 



Does the volume change during the process? Yes, 4 + 1 

 volumes become 2 + 2, or 5 volumes give 4. 



Warnings. The commonest mistake made in these calcula- 

 tions is to neglect to use, in the equations, the molecular formulae. 

 We must use H 2 , 2 , C 2 H 2 (acetylene), etc., (and not H, 0, or 

 CH), because the 22.4 liters hold the weights represented by the 

 molecular formulae. 



