Materials and methods The chemicals used in this experiment were benzoic acid,NaOH, oxalic acid and HCl sourced from the SD Fine Chemicals Limited.
NaOH andHCL was standardized using oxalic acid(0.2N). Benzoic acid cylinder wassupported on central steel shaft which can be rotated at varying RPM controlledby digital RPM meter . A D.C Motor is connected to it can be seen in Figure 1. Benzoic Acid solid is considered pure and clay-free.
The shaft and D.C Motor have been obtained from Balaji ScientificGroup, Dombivali. Conical Flasks, beakers, burette, measuring cylinders andpipettes used in the experiment were brought from a localvendor in contract with the institution. Burette and pipette have anuncertainty of ± 0.1 ml and measuring cylinder has an uncertainty of ±1 ml.
Schematic of the experimental setup is shownin Figure 1.Figure 1.schematic diagram of experimentalsetupTo find thedissolution in the presence of reaction, we measure the dimensions of benzoic acid cylinder which was then fixed in a vertical positionwith the D.
C. motor . The cylinder was then rotated at _ RPM in aqueous NaOHsolution (300 ml) in a beaker and it was made sure that the cylinder was dippedcompletely inside the NaOH solution.
After 10 minutes the benzoic acid cylinderwas removed from the solution and the NaOH sample was titrated against HCl todetermine the unreacted NaOH concentration. The cylinder dimensions weremeasured again. For 5 different NaOHconcentrations ranging from 0.1 N to 0.5N and four different speedsbetween _RPM this procedure wasrepeated.
PhysicaldissolutionTo determinethe physical dissolution rate, the benzoic acid cylinder was rotated atsame RPM as above in 200 mL of water for30 minutes. At every 5 min intervals 5 mL samples were analyzed for benzoic acid content bytitration against 0.02N NaOH solution using phenolphthalein indicator. Everytime sample is withdrawn 5 mL of makeupwater is added .