Question

1. Use the diagram below (results of reduction kinetics of methylene blue) to help you answer question i)-vi) pdo gainst [Asc) Kpseudo VS [HCI] 500 05 0.1 500 y-10352x-624.82 R 0.4968 1000 1500 [HCIl mol 1 b) i Determine the order of reaction of a) b) and c) ii) Use the slope of the graphs from (a) and (b) above as well as the fixed concentrations of the other reactants to determine the rate constants of the uncatalyzed (k) and Catalyzed (K.) reactions. Use the formulae below to help you with. dk dk pseuda H,O d[Asc] ii) Combine your results from i) and ii) to give the overall rate law for the reduction of methylene blue by ascorbic acid under acidic conditions. iv) Why was it important to collect data until the absorbance had fallen to less than 1/8 of its initial v) Briefly discuss how this experiment could be improved to obtain a more accurate value for the rate constants. vi) Briefly describe how this experiment could be modified to determine the activation energy for the reaction.

Answer 1

(i)

The graph (a) shows the 2^nd order reaction as direction of uncatalyzed reaction (red) is following the catalysed reaction and its slope decreases

The graph (b) shows the 0 order reaction as direction of uncatalyzed reaction is following the catalysed reaction in a curve

The graph (c) shows the 1^st order reaction as direction of uncatalyzed reaction is following the catalysed reaction.

(ii)

For graph (a), 2^nd order reaction is present

Where, [Asc] is concentration of ascorbic acid after time t

[Asc₀] is initial concentration of ascorbic acid

For graph (b), 0^nd order reaction is present

The given equation is

On relating with the standard y = mx + c

Slope is equivalent to rate constant = 10352

Thus, rate constant will be equal to 10352 mol /L /s

(iii)

Rate law for graph (a)

Rate law for graph (b)

R = K

Rate law for graph (c)

(iv) The absorbance indicates the working or absorption of ascorbic acid to follow the catalysed reaction. After getting falling further by 8^th concentration, it get impossible for the detector to caliberate the concentration of the dosage and not give the correct measurement of rate constant.