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 too power. L There are many reactions that have a rate law In the form of: (1) According to referenced 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 tit 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 headquartered(all) Ion ([Fee(CNN)6]3-) oxidized ascorbic acid (CHICHI) by the following reaction: (2) * CHICHI CHICHI + The reaction above is of a first order reaction at room temperature with respect to individual reactants; therefore the reaction geochemistry and rate law at time t are: AAA + b products and where [A] represents the concentration of ascorbic acid and [B] represents the concentrations of [Fee(CNN)6]3- at time t.
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For this experiment we will use an integrated ate law in the form of: (5) In = b [AGO – a [BIO kit + In [A]O where [A]O and [BIO are the Initial concentrations of CHICHI and [Fee(CNN)6]3- and a-I and b=2. From equation (b It Is possible to calculate the second-order rate constant k by plotting In [VA[B] against time (find slope of line where b=2 and EDIT 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 absorbency of at time t is given by: (6) Absorbency = 1012 The oxidation of CHICHI by [Fee(CNN)6]3- involves a mechanism that consists of 3 steps. In the first step, the acerbate Ion (AH-) Is rapidly formed by Unionization of the ascorbic acid. 7) AHA Following the unionization is the slow rate-determining step, the oxidation of the acerbate ion to an acerbate free radical (AH;):(8) [Fee(CNN)6]3- + AH- During the final step, an electron is rapidly transferred from the acerbate free radical to the headquartered(all) anion, producing dehydrator’s acid (A): (9) + AH- + A + According to referenced, the specific rate constant of an ionic reaction in aqueous solution depends on two factors: the ionic strength I of the solution and on the harass AZ and CB of the ionic species reacting to for the activated complex. 10) log k = log k+ 1. ZEBRA 11/2 Experimental All reagents in this experiment were of reagent grade. Mass measurements were taken on a Shimmied Libber AGE-120 analytical scale with an uncertainty of В??O. IOW . Manual data acquisition was taken with a Breasted/Turner SP-830 spectrophotometer and a stopwatch. The computerized data acquisition was completed by a Cary 50 Bio. The experiment began by preparing four solutions of 1 x 10-3 M of with vane concentrations of Nanny: 0. 025 M, 0. 5 M, 0. 1 M and 0. 2 M.
This was completed by dissolving 0. 0329245 (В??O. OOH) Goff Kef(CNN)6 with the specified concentrations of Nanny and denizen water in a 100 ml volumetric flask. A 25 ml aliquot of each solution was transferred into a 250 ml Erlenmeyer flask and the temperature of the aliquot was recorded. Next, a 500 ml 2. 5 x 10-4 M solution of ascorbic acid was prepared by using a standardized 0. 01 M HON. solution dissolved in 0. 005 Goff EDIT and denizen water. A 25 ml aliquot was transferred into each of the four 100 ml beakers by using a 25 ml pipette.
The spectrophotometer was set to 418 NM and the absorbency reading was zeroed by using denizen water as a standard. The ascorbic acid in the beaker was poured into the Kef(CNN)6 solution and the timer was immediately started. The Erlenmeyer flask was swirled for 2-3 seconds before pouring the reacting mixture into a I-CM civet. The civet was conditioned with the reacting solution 4 times before being placed into the sample holder of the spectrophotometer. An absorbency reading was taken at 30 seconds and every 30 seconds thereafter for a total of 6 minutes.
By looking at Table 1, as the molar concentration of Nanny was increased, the ionic strength of the solution increased; therefore, the rate of reaction was increased. According to the Debby- Heckle theory, this makes perfect sense. The rate determining step consists of two reagents with negative electrical charges; therefore, by increasing the ionic concentration or atmosphere, more oppositely charged ions will be present. According to literature if the reacting ions are of the same charge, then the rate of the reaction should increase as ionic strength increases.
If there were ions with opposite charges the added salt effect would slow down the rate of reaction. It is possible to tell that the rate of the reaction is not independent of the ionic strength because of the slope value (0. 00003) obtained from the plot in Figure 1. Individual temperatures were not taken for each sample prior to recording absorbency readings. All readings were based Off constant 25 co solution; therefore, as temperature directly affects any equilibrium system, the calculations may have been slightly off. It may be possible to assume that with higher temperatures the reaction ate would also increase.
Nevertheless, the manual and the computerized methods both gave similar slopes resulting from the plotting of log [CHICHI]/ [Fee(CNN)6] versus time. The two slopes had a standard deviation of only В??0. 000028, thus there was not much difference in the calculated rate constants as well.