Abstract: Mean activity Coefficients of HCl in concentrated hydrochloric acid solutions are determined by measuring emf′s of following cells (A). Ag-AgCl/HCl(m)/H_2(P)/Pt(black) (B). Ag-AgCl/HCl(m)/pH-glass electrode for HCl molalities from 0.01844 to 15.02 tool kg~(-1) at 25 ℃. Using observed emf data of ceils (A) and (B), mean activity coefficients of HCl are calculated, and their deviations are less than 1.2%. Within this molality range, “standard potential” E_G~0 of pH-glass electrode is a constant and its standard deviation is equal to 0.016%. The pH-glass electrode used has good reproducibility. Therefore, it is possible to determine the activity coefficients in high concentrated hydrochloric acid solution by using pH-glass electrode.
For concentrated hydrochloric acid in molality range 0.1844—15.02 mol kg~(-1) at 25 ℃, the lograrithm of activity coefficients of HCl can be expressed adquately by the equation:
logγ±=-0.5115/(1+1.471)+0.1069 m+7.412×10~(-3) m-6.637×10~(-4) m~3
+1.586×10~(-5) m~4
where m is the HCl concentration in molality, γ± is its activity coefficients. Using this equation, activities of solvent H_2O have been calculated.