US EPA

1451744 

Journal Article 

Effect of Ionic Strength on the Kinetics of Oxidation of Ascorbic Acid by Methylene Green in Aqueous Methanol System 

Saeed, R; Khan, SR; Ashfaq, M 

2012 

Yes 

Asian Journal of Chemistry
ISSN: 0970-7077
EISSN: 0975-427X 

24 

8 

3745-3750 

WOS:000305034200099 

The effect of ionic strength and temperature on the
kinetics of the reaction between methylene green and ascorbic acid was studied in presence of
iodine by spectrophotometric method. The oxidation of ascorbic acid was carried out in 10, 15,
20, 25 and 30 % aqueous methanol and decrease in the values of rate of reaction was observed with
decrease in dielectric constant of solvent. The absorbance data was collected at 656 nm at
different ionic strength and temperature ranges from 2.7063 x 10(-4) mol dm(-3) to 8.9604 x 10(-
4) mol dm(-3) and 298 to 318 K with the difference of 5 K respectively. It was observed that with
the increase in ionic strength and temperature the rate of the reaction also increased. The
presence of iodine enhances the rate of chemical reaction. The reaction follows first order
kinetics with respect to ascorbic acid and fractional order with respect to methylene green. The
overall reaction is pseudo first order. Energy of activation (E-a*) was calculated with the help
of kinetic data by using Arrhenius relationship. Thermodynamic parameters such as enthalpy change
of activation (Delta H*), Gibbs free energy change of activation (Delta G*) and entropy change of
activation (Delta S*) were also evaluated. 

Kinetics; Oxidation; Methylene Green; Ascorbic acid; Iodine