• R K Chaturvedi

Articles written in Proceedings – Section A

• Potentiometric studies on the dissociation of gallic acid

Dissociation of gallic acid at different temperatures in the range 300–380 Å was investigated using glass and calomel electrodes. Applying modified Debye-Huckel equation the thermodynamic dissociation constantK was calculated. The variation ofK with temperatureT appeared to follow:—$$- lnK = \frac{A}{T} + B + CT$$ where the constantsA, B andC for gallic acid were 84·11, 5·59 and 14·29 ×10−3 respectively. From these, the thermodynamic functionsΔF,ΔH,ΔS andΔCp were computed. The effect of substitution of three hydroxyl groups in the nucleus of benzoic acid onpK andΔF was discussed. The radius of the anion of gallic acid was computed from the calculated values ofΔH; it corresponded to 0·78 Å.

• Conductometric determination of a few physico-chemical constants of murexide

Conductance measurements of murexide or ammonium purpurate solutions were made at 30° + 0.05°C. using a Serfass conductivity bridge. Ostwald’s dilution law was found to be inapplicable; equivalent conductance at infinite dilution and the classical and thermodynamic dissociation constants were computed by various methods applicable for systems involving ion association. The following physico-chemical constants of murexide were calculated :-

Thermodynamic dissociation constant.

Ionic mobility of purpurate ion.

Ionic rasius.

Diffusion coefficient.

•