126 



SMITH'S INTERMEDIATE CHEMISTRY 



delivery tube, the gas dissolves in the water as fast as it is 



formed. 



If the correct proportions of the materials are used, then, when 



the action is over, all that remains in the flask is a white solid, 



different from salt, and called sodium-hydrogen sulphate NaHSO 4 . 



A part of this may be in solution in a 

 little water, contained originally in the 

 commercial sulphuric acid, of which 

 water commonly forms from 6 to 7 per 

 cent. The equation is easy to make 

 from the formulae given, 



NaCl+H 2 S0 4 ->HClt+NaHS04, (1) 



and requires no further balancing. (An 

 arrow pointing upward is used in 

 equations to indicate that the sub- 

 stance to which it refers removes 

 itself from the reaction by escaping in the form of a gas.) 



Other Sources of Hydrogen Chloride. Chlorides of other 

 metals could be substituted for the sodium chloride in this action, 

 and all but the less soluble ones would give hydrogen chloride 

 freely. Common salt is employed because it is the cheapest of 

 the chlorides. 



While theoretically any acid would, like sulphuric acid, furnish 

 the required hydrogen, and liberate hydrogen chloride, yet in 

 practice no other acid works so well. Some, like phosphoric 

 acid H 3 PO 4 , act too slowly, because they do not dissolve sodium 

 chloride so readily. Others, like hydrofluoric acid HF, are too 

 volatile, and the heat of the action would send them over with 

 the hydrogen chloride in the form of vapor. Others, like nitric 

 acid HN0 3 , would react chemically with hydrogen chloride. Still 

 others, like hydriodic acid HI, being gases, could be used only in 

 aqueous solution, and the water would dissolve the hydrogen 

 chloride produced, and prevent its escape from the vessel. Aside 



