122 SMITH'S INTERMEDIATE CHEMISTRY 



equivalent weight of a compound is that amount of it which will 

 interact with one equivalent of an element. Thus, a formula- 

 weight of hydrochloric acid HC1 (36.5 g.) is also an equivalent 

 weight, for it contains 1 g. of hydrogen, and this amount of hydro- 

 gen is displaceable by. one equivalent weight of a metal. A for- 

 mula-weight of sulphuric acid H 2 S0 4 (98 g.), however, contains 

 two equivalents of the compound, and a formula-weight of alu- 

 minium chloride Aids (133.5 g.) three equivalents. Hence 

 normal solutions of these three substances contain, respectively, 

 36.5 g. HC1, 49 g. H 2 SO 4 , and 44.5 g. A1C1 3 per liter of solution. 

 The special property of normal solutions is, obviously, that equal 

 volumes of two of them contain the exact proportions of the solutes 

 which are required for complete interaction. Solutions of this 

 kind are much used in quantitative analysis. We frequently use 

 also decinormal or one-tenth normal solutions (0.1 N or N / 10), and 

 seminormal (0.5 N or N/2), and six times normal solutions (6 N), 

 and so forth. 



A molar solution contains one mole (gram-molecular weight) 

 of the solute hi one liter of solution (not in 1 1. of solvent). When 

 molecular formulae (p. 78) are used, this means one gram-formula 

 weight per liter. In the cases cited above, the molar solution 

 contains 36.5 g. HC1, 98 g. H 2 S0 4 , and 133.5 g. A1C1 3 per liter. 



Is Dissolving a Physical or a Chemical Change ? This 

 is a question still much discussed amongst chemists. Prob- 

 ably in simple, typical cases, like dissolving paraffin in gasoline 

 or benzene, the process may be considered purely physical, and 

 the solution contains both components in unchanged chemical 

 condition. 



On the other hand, when water is used, as it is more frequently 

 than any other solvent, chemical changes undoubtedly take place. 

 The water itself, at least, is always changed. Water in the li- 

 quid state is not simply H 2 O. Its physical properties indicate that 

 it is an associated liquid, extensive combination having taken 



