Reaction Between Persulphate And Iodide Ions Biology Essay

answer Between Persulphate And Iodide Ions Biology EssayPersulphate (S2O82-) is reduced to sulphate (SO42-) in presence of iodide ions (I-) in aqueous solution. While persulphate is being reduced, iodide is being modify to tincture of iodine. The general reaction equation beingS2O82- + 2I- 2SO42- + I2On the other hand, iodine throne be converted to iodide in presence of thiosulphate (S2O32-) as followsI2 + 2S2O32- S4O62- + 2I-If iodine indicator is added to the solution a blue emblazon of the starch-based iodine indicator complex develops after all thiosulphate has been consumed. This is because the starch-based iodine indicator complex is very stable in high concentrations of iodine. The charges transfers and the energy level spacings in the resulting complex check out to absorptions in the visible part of the spectrum blue. The bearing of the resulting blue colour depends on the amount of iodine present.Therefore, the development of the blue colour is useful as it indic ates a eonian point in the put across of the reaction which can be taken as being representative of the end of the reaction (Practical Booklet p.37).Several energizing parameters can be easily analysed and laid if those reactions are timed as they progress from start to end, hence the importance of the component time (t) in kinetic studies.By adding a known amount of thiosulphate and iodine indicator, the reaction rate can be determined as it obeys the following rate equationAIMSThis experiment was undertaken to determine the reaction rate, the order of reaction with respect to both iodide and persulphate, and the effect of summercater in noodle strength on the rate constant quantity of this reaction.EXPERIMENTAL Methods ProceduresAn exact copy of the methods provided in the practical booklet is attached to this document as no deviations were made from those given.RESULTSReactionTime t (minsec)Tim t (seconds)11932117229455853958598425201520533302010 give in Timing of reactio n from the exact time of mixing to the time of the blue colour appearanceTreatment of resultsReactionSolution ASolution B ( + 0.5g iodine indicator)KI ( molee cm-3)Na2S2O3 (mol cm-3)KCl (mol cm-3)K2S2O8 (mol cm-3)H2O (cm3)10.050.00050.1000.00425.020.100.00050.0500.00422.530.050.00050.0880.00815.640.050.00050.0500.00427.550.050.00050.0000.00430.0Table Concentrations of all substances in the final reaction mixture and water volume to account for dilution to a 50cm-3 final volume.From the rate equation of this reactionInterpreting the above results, doubling I- while keeping S2O82- constant duplicate the rate of reaction halves t (time of appearance of the blue colour). Doubling S2O82- while keeping I- constant, also multiply the rate of reaction.The below equation gives the relationship of the variation of rate constant (k) with dome strength (I)This equation is of type , where k0 is the limiting value of the rate constant at zero ionic strength. where zA and zB are the charges of the two ions involved in the rate-determining step at low ionic strengths.Since I- remains constant during each kinetic run, the integrated rate equation iswhere a and (a-x) represent S2O82- at times t = 0 and t = t respectively.Making k the subjectHence, for reactions 1, 4 and 5Per 2 moles of S2O32- consumed 1 mole of S2O82- oxidises iodide because any iodine produced is converted back to iodide until all thiosulphate is consumed. Therefore, adding a known amount of thiosulphate sanctions to determine the concentration of persulphate at the end of the reaction, when t=t.From 0.0005 mol cm-3 of S2O32- consumed, 0.0005/2 = 0.00025 mol cm-3 of S2O82- were consumed. Therefore the remaining persulphate at the end of reaction = 0.0040 0.00025 = 0.00375 mol cm-3For reaction 2For reaction 3At the start of this run S2O82- = 0.00800 mol cm-3 and S2O32- = 0.0005 mol cm-3. At the end of the reaction 0.0005/2 = 0.00025 mol cm-3 of S2O82- were consumed. Hence, from the initial concentratio n of S2O82- 0.00800 0.00025 = 0.00775 mol cm-3 of S2O82- were present at t=t.Rate Constant DeterminationThe value of k can now be calculated for each mixture. The values were calculated and recorded in the table belowReactionRate Constant (k) / mol cm-3s-112345Table Values of k constant for each reaction mixtureCalculation sampleFor reaction 1t = 1172 sIonic Strength DeterminationThe contribution of each electrolyte to the organic ionic strength is given byTaking into account the dilution of the final volume to 50 cm3 of all electrolytes, and knowing that for 11 electrolytes, I=concentration, and for 21 electrolytes, I= 3 x concentration. Hence, for these mixturesThe ionic strength was calculated and recorded in the table belowReactionIonic Strength (I) / mol cm-310.16420.16430.16440.11450.0635Table Ionic Strength per each reactionSample calculationCalculation of B and k0In order to determine B and k0 a plot of v.s. logk was plotted.Reactionk(mol cm-3s-1)Logk(mol cm-3s-1)I(mol cm-3)1-2.960.1640.2882-2.960.1640.2883-2.970.1640.2884-3.070.1140.2525-3.190.06350.201Table k constant and ionic strength for each reactionGraph Correlation between logk and ionic strengthThe correlation is given as being y = 2.6305x 3.7229.HencelogK0= -3.72 mol cm-3 s-1k0= mol cm-3 s-1k0= mol dm-3 s-1B = 2.63H S CalculationDISCUSSION (Questions)As stated above(..) doubling I- while keeping S2O82- constant doubles the rate of reaction halves t (time of appearance of the blue colour). Doubling S2O82- while keeping I- constant, also doubles the rate of reaction. Hence, in the rate equationx= 1 and y=1. The reaction is of first order with respect to and with respect to . As a result, the overall rate of reaction is x+y=2.The overall rate of reaction is of second order in which the rate determining step isS2O82- + I- IS2O83-This is consistent with the rate observed experimentally by comparing mixtures 1 to 2 and 1 to 3.The value of B (2.63) is rather high in comparison with the t heoretical value but of same magnitude.As stated above, B is given by where zA and zB are the charges of the two ions involved in the rate-determining step. Hence, theoretically .The value of k0 determined experimentally is rather low in comparison to the print value.k0= mol dm-3 s-1Published value mol dm-3 s-1Some source of error must have influenced this result. Perhaps wrong timing and contaminated glassware would allow a rather faster/slower reaction which results in a different rate constant (k).(Answer to Q1 above.)The ionic strength is the same for reactions 1, 2 and 3. Reaction 4 shows a characteristic ionic strength for the concentrations of ions present in the mixture (Table 2). Accordingly, reaction 5 with no KCl added shows a rather low ionic strength as expected.A variation of Ionic strength vs. Rate constant is notable. With reference to table 5, a decrease in ionic strength accompanies a decrease in the rate constant the lower the ionic strength of a reaction the lo wer its rate constant (k).It is important to pertain that the ionic strength of each mixture remains constant up to time t (appearance of blue colour). This is perfectly understandable because the rate of production of anions is play off to the rate of their expenditure, hence manifesting a constant ionic strength. However, when all thiosulphate has been consumed the ionic strength decreases because an interruption in their equilibrium causes the consumption of iodine to stop.In other wordsWhen the reactions reaches tS2O82- + 2I- 2SO42- + I2I2 + 2S2O32- S4O62- + 2I-Thus, at t there is an increase in the amount of I2 and a drastic decrease in the amount of I-. ThereforeAt t,which results in a low ionic strength.(Answer to Q2 above)For this experiment, the value of calculated is rather low but positive. All systems tend to progress in a electric charge of increasing information and because an increase in the disorder of the system in question.For this bimolecular reaction in sol ution at 25C, the entropy of activation of the rate determining step is positive meaning the final starch-based iodine indicator complex is rather stable because increases in entropy correspond to irreversible changes in a system. This is because the amount of work the system can do is limited because most of the energy was wasted as heat therefore this reaction is thermodynamically irreversible reaction.(Answer to Q3 above)A reaction which proceeds more slowly with increasing ionic strength isCONCLUSIONAims were accomplished.All kinetic parameters were determined although some major sources of error were present during this experiment.Possible sources of error may include difficult or inappropriate timing (non-digital watches were used). Difficulty to quickly get the end point of the reaction (development of blue colour) as the rate of reaction to some of the mixtures was very slow contamination of glassware could also contribute for such errors.Nevertheless, the order of reactio n with respect to both iodide and persulphate was determined precisely and the effect of decreasing ionic strength is known to decrease the rate of reaction.