EXPERIMENT 4: KINETICS OF THE PERSULFATE-IODIDE CLOCK REACTION

Glory Rose D.Delas Llagas Date Performed: March 11, 2014 3ChE-A Group No. 3 Date Submitted: February 4, 2014 EXPERIMENT 4: KINETICS OF THE PERSULFATE-IODIDE CLOCK REACTION I. Introduction: Harcourt-Esson reaction or the Harcourt-Essesn reaction also known as the iodine clock reaction is a classical chemical clock demonstration experiment to display chemical kinetics in action. In this experiment two colorless solutions are put together, at first there will be no visible reaction. After awhile, the solution suddenly turns to a shade dark blue. In the experiment done in the laboratory Persulfate variation of iodine clock reaction experiment was performed. In this clock reaction, sodium, potassium or ammonium persulfate was used to oxidize iodide ions to iodine. On the otherhand, sodium thiosulfate was used to reduce iodine back to iodide before iodine can complex with the starch to form the characteristic blue-black color. The reactions on the experiment are the following: Generation of Iodine: 2 I− + S2O82− → I2 + 2 SO42− Iodine removal: I2 + 2 S2O32− → 2 I− + S4O62− When all the thiosulfate is consumed the iodine may form a complex with the starch. Potassium persulfate is less soluble while ammonium persulfate has a higher solubility. Determination of rate equation: As showed in figure 1 a 10 mL of solution A was transferred in a 100 mL beaker. .1M potassium iodide were prepared. the experiment also aims to determine the rate equation and activation energy. Along the investigation. Methodology: Preparation of solutions: A 200 mL of 0. 100 mL conical flask was used to contain a 10 mL of solution D. The heating was continued until the mixture was homogenous. The produced solution was stirred until homogenous. Starch indicator was prepared by adding 0. The procedures were repeated to the different volumes of the S 2O82.The purpose of this experiment is to investigate the kinetics of the reaction between persulfate and iodide ions. B. 5 mL of solution C was added to the solution D in the flask. the effect of temperature. and the effect of ionic strength of the solution.and Isolutions specified in the laboratory manual.1M sodium thiosulfate. A drop of the starch solution was added to the transferred solution A. the effect of reactant concentration on the rate of reaction. 100 mL of 0. 100 mL of 0. and D respectively. and 200 mL of 0.1M ammonium persulfate.1M of ammonium thiosulfate. The starch solution was added to a vigorously boiling 50 mL of distilled water. C. The contents of the beaker were then poured to the flask. The prepared solutions were labeled as A. The flask was gently swirled and the time was recorded when the resulting solution turned to blue. II.5 g of starch into 10 mL distilled water. and a second solution containing 5 mL of solution (c) and 10 mL of solution (d) were added to the test tubes. . A few drops of starch. Both test tubes were put into a water bath afterwards for 10 minutes.Figure 1 Experimental set up for determining the rate constant Effect of temperature A mixture of a 10 mL of solution (a) was put in 2 large test tubes. The temperatures of the solutions in the test tubes were recoreded. as well as the time when the solution changed its color to blue. The experimental set up is illustrated in figure 2. 5128 Label A B C D Table 2 The needed volumes of the solutions to be added and the time it took for the solution to change its color Solution V of A (mL) V of B (mL) V of C (mL) V of D (mL) Time (mins) .13 298 166 Mass (g) 5. III.1 M (NH4)2SO4 with volumes of 10 mL were mixed with 5mL Na2S2O3. Data and results: Table 1 Compositions of the solutions Solution M (NH4)2S2O8 0.62 3.01 KI 0.1 (NH4)2SO4 0. The time of the appearance of the color blue was recorded.1 Starch Determination of rate equation Volume (mL) 250 500 250 200 MW 228 132.1 Na2S2O3 0.32 0.7 6.Figure 2 Experimental Set up for the determination of effect of temperature Effect of ionic Strength Solutions of (NH4)2S2O8 and 0. and 10 mL of I-.6065 0. Treatment of Results: Determination of rate constant .500 Effect of ionic strength Table 4 IV.1 2 3 4 5 6 7 8 8 8 8 8 6 4 0 2 4 6 2 4 6 7 7 7 7 5 5 5 10 8 6 4 10 10 10 3:18 4:12 7:52 8:06 1s 3:49 29:14 Effect of temperature Table 3 List of temperatures and the corresponding time when the solution changed its color to blue Solution 7 Temperature (oC) 50 Time 4:14 45 40 35 30 6:00 7:24 10:23 14:03 Solution 10 mL B Time (s) 1. 1∗(Vol A ) (total Volume) I concentration= 0. use equation from the lab manual: −¿ ln I ¿ 1 Where m and n can be ln =lnK +m ln [ S 2 O8 ] +n ¿ ∆t obtained from the graph indicated on figure 5 and 6 . computed rate constant and other computed components Solutions to complete the table: S2O8 concentration = 0.1∗(Vol D) (total Volume) To get the Rate constant K.Figure 3 The components of the solution. time of the reaction. 90 -8.50 -6.00 -3.30 -8.40 ln [I -] .90 -7.10 -8.ln dt -3.70 -6.89 R² = 0.20 -6.89x .10 -7.20 -5.50 ln [SsO8 2-] Figure 5 Graph of -ln (dt) vs ln [I -] -4.60 -ln dt f(x) = 0.40 -5.00 -5.50 -4.70 -7.4x + 34.80 -6.30 -7.50 -4.7 -5.2.00 -6.50 -7.88 .50 -6.50 -5.6 R² = 0.00 f(x) = 10.Figure 4 Graph of -ln (dt) vs ln [SsO8 2-] -4. Determining the Activation Energy. Ea plot (1/K) vs (1/T) and use the combined equation of equations 4 and 6 lnK =lnA− Ea R(x) . Arrange −Ea R . Ea In getting the activation energy. where x is equal to the equation and the slope obtained from the graph will be equal to Figure 6 Table for Activation Energy Computation 1 T . . Based on the data gathered and computed results the slope from the graph of sodium per sulfate is 10.00 f(x) = .0032 0.Figure 7 Graph of ln K vs ln (1/T) 8. Answers to Questions a. The computed over-all order of the reaction is far from the theoretical value which is 2.50 ln K 7. Comment on the effect of the reduction in ionic strength on the rate of reaction and determine whether the reactants which form the activated complex have charges of the same or different sign. And the slope from the graph of potassium iodide is 0.0031 0. Theoretical values with respect to potassium iodide and sodium persulfate are both 1.5793.00 Linear () 6.0031 0. b.0032 0.39 which is also the order of the reaction with respect to sodium per sulfate.0033 0.50 0. Adding the two the over-all order of the reaction based on the experiment was 11.82 R² = 1 7. What is the order of the reaction in terms of sodium persulfate and in terms of potassium iodide? What is the overall order of the reaction? .890 which is also the order of the reaction with respect to iodide.0034 1/T V.0033 0.48x + 25.28. . When iodide reacts with persulfate ions. . students who get their sample return the excess back to the container again. When the product is positive an increase in the rate would be expected and if the product is negative a decrease would be expected. On the other hand.Errors may be caused due to contamination of the sample solutions. c.- One factor that can affect the rate reaction is the charges of ions in the reactants presents in the sample solution. The charges of ions are also related to its ionic strength. But there is an exception . The potential causes of the contamination are the chemical reagents may not be properly sealed in the storage. and also there are students who directly put their instruments into the container of the chemical reagents. Conclusion and recommendations: Conclusion: The experiment successfully demonstrated the reaction between iodide and persulfate. If it is neutral. The amount of the thiosulfate that is added to the solution indicates how much iodine was produced through the time taken by the reaction to turn blue. then there will be no changes observed on the rate of the reaction. and the excess iodine. VI. the experiment for the rate constant k. the reaction produces iodine and sulfate. Identify sources of error in the experiment and estimate their magnitude. The product of the charges of the ions can indicate if the rate of the reaction would increase or decrease. The iodine produced is immediately consumed by the added thiosulfate ions. causes the sample to change its color from clear to blue. which the thiosulfate failed to consume. also shows that it is affected and have direct relationship with temperature. References: a. Recommendations: It is recommended to start from the last solution to check if a change in color will occur within 30 minutes time span.when zero activation energy is observed. If no changes are observed. During this circumstance the temperature does not affect the rate constant of the reaction. a decrease in the amount of (NH4)2S2O8 solution and increase of the amount of Na2S2O3 solution by 1 mL is advised. Faria (2005). Oliveira and Roberto B. Complex Kinetics of a Landolt-Type Reaction: The Later Phase of the Thiosulfate-Iodate . Am. ”Kinetics of the Persulfate-iodide clock reaction” c. Oxford University (2006). J. adjustment on the concentration of the persulfate is advised. Also it is recommended to make sure that the apparatus that you will be using are clean. If the mixture changed its color upon the addition of solutions (a) and (b) to solutions (c) and (d). Denes Varga et. "The chlorate-iodine clock reaction". (2010). André P. Chem. VII. Soc b.al.