With C B C l / C L i C I 5 5 % ( M / M ) ,Equation 9 still held satisfactorily by substituting C L ~with C I chloride ion concentration (molality). Other Results. Known amounts (200-300 pmole) of weak bases and excess amounts of hydrochloric acid (500-700 pmole) were added to N100-ml portions of saturated lithium chloride solution which contained some solid LiCI. From the experimental PHclvalues, the degree of protonation (per cent of the base which reacted with protons to give the conjugate acid) was calculated. I n the case of 4-bromo aniline, glycine, 4-nitro aniline (pK, 3.86, 2.35, and 1.0, respectively) the degree of protonation was 100%; in the case of urea (pK, 0.1) about 30%. P H C l measurements were carried out also in concentrated (10-20 rn) sulfuric acid solutions containing small amounts of hydrochloric acid, and in concentrated (6-7M) hydrochloric acid solutions. I n sulfuric acid solutions, Relation 8 held with Conegative (acid volatile impurities) and R S D E 1 %. CONCLUSIONS
determination, validity of Satisfactory precision in values in a wide range Relation 8, and self-consistence of PHCl of experimental conditions, give reliability to the described apparatus and procedure. Paclcan be defined as a measure of the ability of a solution to give undissociated molecules of hydrogen chloride. It is a function of water activity and of the activities of hydrogen ion ( a ~ +and ) chloride ion (ac1-). HCl,,,
e HCI.,I
for gas-solution equilibrium
(10)
where a H C I is the activity of the undissociated HCl in the solution.
HCI,,l
+ n H20 e H+ + CI- in the solution,
(11)
with Hfand C1- hydrate ions, and
Then
PHcl can provide information concerning a solvent system. I n lithium chloride solutions with CL,CIconstant and with C H C L
