Computerized Data Acquisition of a Second Order Reaction
Computerized Data Acquisition of a Second Order Reaction
Abstract
Introduction
The rates at which reactions occur depend on the composition and the temperature of the reaction mixture. Usually the rate of reaction is found to be proportional to the concentrations of the reactants raised to a power.1 There are many reactions that have a rate law in the form of:
(1) v = k[A]a[B]b
According to reference1 the power to which the concentration of a species (product or reactant) is raised in a rate law of this nature is the order of the reaction with respect to that species. In equation (1) first order with respect to [A] and first order with respect to [B]; however, the overall reaction is the sum of the individual orders. Thus we have a second order reaction. In this experiment a hexacyanoferrate(III) ion ([Fe(CN)6]3-) oxidizes ascorbic acid (C6H8O6) by the following reaction:
(2) 2[Fe(CN)6]3- + C6H8O6 = 2[Fe(CN)6]4- + C6H6O6 + 2H+
The reaction above is of a first order reaction at room temperature with respect to individual reactants; therefore the reaction stoichiometry and rate law at time t are:
(3) aA + bB products and (4) -d[A] = k[A] [B]
where [A] represents the concentration of ascorbic acid and [B] represents the concentrations of [Fe(CN)6]3- at time t. For this experiment we will use an integrated rate law in the form of:
(5) ln [A] = b [A]0 - a [B]0 kt + ln [A]0
where [A]0 and [B]0 are the initial concentrations of C6H8O6 and [Fe(CN)6]3- and a=1 and b=2. From equation (5), it is possible to calculate the second-order rate constant k by plotting ln [A]/[B] against time (find slope of line where b=2 and a=1). EDTA in this experiment is used as a masking agent to hide metal ions that would normally interfere with the analysis in this reaction. Thus the absorbance of [Fe(CN)6]3- at time t is given by:
(6) Absorbance = 1012 [Fe(CN)6]3-
The oxidation of C6H8O6 by [Fe(CN)6]3- involves a mechanism that
Abstract
Introduction
The rates at which reactions occur depend on the composition and the temperature of the reaction mixture. Usually the rate of reaction is found to be proportional to the concentrations of the reactants raised to a power.1 There are many reactions that have a rate law in the form of:
(1) v = k[A]a[B]b
According to reference1 the power to which the concentration of a species (product or reactant) is raised in a rate law of this nature is the order of the reaction with respect to that species. In equation (1) first order with respect to [A] and first order with respect to [B]; however, the overall reaction is the sum of the individual orders. Thus we have a second order reaction. In this experiment a hexacyanoferrate(III) ion ([Fe(CN)6]3-) oxidizes ascorbic acid (C6H8O6) by the following reaction:
(2) 2[Fe(CN)6]3- + C6H8O6 = 2[Fe(CN)6]4- + C6H6O6 + 2H+
The reaction above is of a first order reaction at room temperature with respect to individual reactants; therefore the reaction stoichiometry and rate law at time t are:
(3) aA + bB products and (4) -d[A] = k[A] [B]
where [A] represents the concentration of ascorbic acid and [B] represents the concentrations of [Fe(CN)6]3- at time t. For this experiment we will use an integrated rate law in the form of:
(5) ln [A] = b [A]0 - a [B]0 kt + ln [A]0
where [A]0 and [B]0 are the initial concentrations of C6H8O6 and [Fe(CN)6]3- and a=1 and b=2. From equation (5), it is possible to calculate the second-order rate constant k by plotting ln [A]/[B] against time (find slope of line where b=2 and a=1). EDTA in this experiment is used as a masking agent to hide metal ions that would normally interfere with the analysis in this reaction. Thus the absorbance of [Fe(CN)6]3- at time t is given by:
(6) Absorbance = 1012 [Fe(CN)6]3-
The oxidation of C6H8O6 by [Fe(CN)6]3- involves a mechanism that