On Colloidal Electrolytes : An Attempt to Find the Dissociation Constant of Pectinic Acid

Department of Chemistry, University College of Science, Calcutta-9.

Manuscript received 5 January 1976 ; revised 22 March 1976 ; accepted 8 April 1976.

It has been shown that the values of \(p\)H of samples of pectinic acid of different CH₃O content calculated by using an equation deduced by the author agree well with those observed by Speiser, Hills and Eddy. Of one sample only (no. H 91 E) of low CH₃O content (viz. 1.70 per cent,\(\tau\)=0.90) three different concentrations have been used for titration. From the titration data of this sample (no. H 91E) its (dissociation constant) pK_s has been found to be 3.41 which is independent of the concentration of the acid and its degree of neutralisation, \(a\). As this K_\(s\) of pectinic acid of low ester content, agrees well with the intrinsic dissociation constant K_\(a\) of galacturonic acid (pK_\(a\) = 3.42), so it has been concluded that it (i.e. K_s) is identical with the intrinsic dissociation cons­tant K_\(a\) of (de-esterified) pectinic acid also.