148 ATOMS, IONS, SALTS, AND SURFACES 



concentration the values indicated are 45 per cent for cadmium chloride and less than 

 0.1 per cent for the mercuric halides. 



TABLE II 



Percentage Ionization of Acids and Bases in Water at o.i 

 Normal and 25 °C. 



Per Cent 



Sulphurous acid (into H+ and HSO3) 34 



Phosphoric acid (into H+ and H2PO4) 28 



Nitrous or hydrofluoric acid 8 



Hydrogen sulphide, carbonic acid, and hypochlorous acid. . . o. i 



Hydrocyanic acid and HBO2 o .002 



WEAK ELECTROLYTES OR SLIGHTLY IONIZED SUBSTANCES 



Slightly ionized substances follow the mass-law relation with respect to ionization 

 at small concentrations, provided strong electrolytes are not present. Thus, with 

 acetic acid (HAC), 



— — =Ai = o. 000018 . 



Chac 



The ionization constants (/v,) for a few weak electrolytes are given in Table III. 



TABLE III 



Ionization Constants at 25° C. 



Acids lo'iC 



Hydrocyanic o . 0005 



Boric (HBO,) .0017 



Hypochlorous o . 044 



Nitrous 400 



Hydrofluoric 790 



Formic 210 



Acetic 18 



Propionic 13 



n-Butyric 15 



Monochlor acetic i >SSo 



Benzoic 60 



Ortho 



Hydroxy benzoic i ,020 



Chlor benzoic 1,320 



Nitro benzoic 6, 160 



Bases 



Ammonium hydroxide 18. 



Methyl ammonium hydroxide . . 500 . 

 Phenyl ammonium hydroxide. . 0.0004 



HYDROGEN-ION CONCENTRATION AND pH 



Suppose that a primary cell consists of an electrolyte with two hydrogen elec- 

 trodes. At the electrode on the left-hand side the pressure of hydrogen is 10 atm. 

 (atmospheres), and on the right-hand side i atm. The cell is 



M+IIz (10 atm.) , Electrolyte with //+ ions , M + II2 (i atm.) . 



