Iodine clock reaction experiment using potassium iodide and hydrogen peroxide

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Iodine clock reaction experiment using potassium iodide and hydrogen peroxide. Please give proper reference to my IB student, Azam if you use his material.

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Iodine clock reaction experiment using potassium iodide and hydrogen peroxide

  1. 1. Candidate Name: Muhammad Azam bin IsmailCandidate Number: 02206 – 007Date of experiment: 22/04/09PRACTICAL 15 – Kinetics: Investigating the relationship between concentration of reactants and rate of reaction using iodine clock reaction.AimTo study the effect of manipulating the concentration of hydrogen peroxide on rate of oxidation ofiodide, I- ions by hydrogen peroxide, H2O2 using the iodine clock reaction.IntroductionThe iodine clock reaction was discovered by Hans Heinrich Landolt1 and is mainly used todemonstrate kinetics in Chemistry. The basis of its mechanism is that two clear solutions of knownconcentrations are mixed together and after a delay, the solution will suddenly turn yellow (or darkblue with addition of starch).In this experiment, the solutions used are hydrogen peroxide, H2O2 and potassium iodide, KI withthiosulphate ions, S2O32- as a delaying agent. Starch is added to the system for a clear indication ofthe end-point of reaction by a change in colour to blue-black. The time taken for the colour to changewill be measured and the rate of reaction can be determined by taking the reciprocals of themeasured times.Several factors influence the rate of reaction of a substance. According to the collision theory thesefactors include concentration of reactants. As such, the effect of concentration of hydrogenperoxide on the oxidation of iodide ions will be tested in this experiment. The reaction which willtake place is as below: H2O2(aq) + 2H+(aq) + 2I-(aq) 2H2O(l) + I2(aq)However, the reaction would take place too quickly if a delaying mechanism is not introduced intothe system. As such, sodium thiosulphate solution is added to introduce thiosulphate ions in thesystem. These ions act as a reducing agent which will reduce the iodine, I2 formed in the first reactionto back to iodide ions, I- according to the equation below: 2S2O32-(aq) + I2(aq) S4O62-(aq) + 2I-(aq)Once all the thiosulphate ions have been exhausted, there will be free iodine in the system which willform the blue-black starch complex.1 “Iodine Clock Reaction” Wikipedia: The Free Encyclopedia, Wikipedia 2009 th<http://en.wikipedia.org/wiki/Iodine_clock_reaction#cite_note-0> 19 April 2009 Page | 1
  2. 2. Candidate Name: Muhammad Azam bin IsmailCandidate Number: 02206 – 007Date of experiment: 22/04/09HypothesisAccording to the Collision Theory2, a reaction will occur only when reactant particles fulfil theserequirements:  The reactant particles collide with one another  The collision must be energetic enough to overcome the activation energy of the reaction  The collision must occur in the correct geometrical alignmentIn addition, the Collision Theory states that several factors will affect the rate of reaction. The factorbeing studied in this experiment is the concentration of reactant particles, i.e. hydrogen peroxide.According to this theory, the higher the concentration of hydrogen peroxide, the higher the rate ofreaction. This is because as the concentration of hydrogen peroxide increases, the number ofhydrogen peroxide particles per unit volume will increase. Thus, the number of effective collisionswill thus increase.This however only holds true when the volume of iodide ions and all other variables are keptconstant. As the volume of the entire system is kept constant, increasing the concentration ofhydrogen peroxide would decrease the relative concentration of iodide ions. At high concentrationsof hydrogen peroxide, the chances of an effective collision to happen will be higher.The addition of a delaying mechanism should not interfere with the rate of reaction as theconcentration and volume added throughout the experiment is kept constant.As such, the hypothesis for this experiment is the higher the concentration of hydrogen peroxide,the higher the rate of oxidation of iodide ions.2 John Green & Sadru Damji, Chemistry for the International Baccalaureate, p. 234 Page | 2
  3. 3. Candidate Name: Muhammad Azam bin IsmailCandidate Number: 02206 – 007Date of experiment: 22/04/09Variables Variable Measured Method of measuring variableDependent Time taken for blue-black starch complex The time taken will be measuredVariable to form using a digital stopwatch (±0.1s). To reduce random errors, three readings will be taken and an average will be calculated. Rate of reaction The rate of reaction will be calculated by taking the reciprocal of the average time taken for the complex to form.Independent Concentration of hydrogen peroxide Using a stock solution of 6%Variable solution hydrogen peroxide, a serial dilution will be performed to achieve solutions of 3%, 1.5%, 0.75% and 0.375% concentrations using a micropipette (±0.003cm3) Method of controlling variablesControlled Concentration and volume of sodium The solution of knownVariables thiosulphate solution added concentration will be prepared. The volume used will be accurately measured using a micropipette (1.000±0.003)cm3 Concentration and volume of potassium The solution of known iodide used concentration will be prepared. The volume used will be accurately measured using a micropipette (1.000±0.003)cm3 Volume of starch solution used 5 drops of starch will be added for each sample. Temperature of reactants Temperature of the reactants was kept at a constant by conducting the experiment at room temperature. Table 1: List of variables Page | 3
  4. 4. Candidate Name: Muhammad Azam bin IsmailCandidate Number: 02206 – 007Date of experiment: 22/04/09Apparatus and Materials o Electronic balance (±0.001g) o 6% Hydrogen peroxide solution o Micropipette (±0.003cm3) o Potassium iodide powder o Pipette (10 ± 0.02cm3) o Sodium thiosulphate powder o 6 beakers (50cm3) o Distilled water o 2 Volumetric flasks (100cm3) o Starch solution o 3 conical flasks o Droppers o Spatulas o Filter funnel o Wash bottleMethod DesignA preliminary experiment was conducted to obtain the optimal volumes of reactants to be used inorder to yield results. A trial and error approach was utilised. The volume of sodium thiosulphatesolution had to be altered several times for the experiment to finally work. Other possibleweaknesses and shortcomings were also identified.Procedure A) Preparation of 0.01M potassium iodide solution: 1. 1.66g of potassium iodide powder is weighed in a small beaker. 2. Some distilled water is added to the powder until it dissolves and the solution is transferred into a 100cm3 volumetric flask via a filter funnel. 3. The beaker and filter funnel are washed down with distilled water to make sure all the potassium iodide is transferred into the volumetric flask. 4. Distilled water is added into the volumetric flask up to the calibration mark. 5. The volumetric flask is capped and inverted several times until a homogenous solution is formed. B) Preparation of 0.03M sodium thiosulphate solution: 1. 0.745g of sodium thiosulphate powder is weighed in a small beaker. 2. Some distilled water is added to the powder until it dissolves and the solution is transferred into a 100cm3 volumetric flask via a filter funnel. 3. The beaker and filter funnel are washed down with distilled water to make sure all the sodium thiosulphate is transferred into the volumetric flask. 4. Distilled water is added into the volumetric flask up to the calibration mark. 5. The volumetric flask is capped and inverted several times until a homogenous solution is formed. Page | 4
  5. 5. Candidate Name: Muhammad Azam bin IsmailCandidate Number: 02206 – 007Date of experiment: 22/04/09 C) Preparation of hydrogen peroxide solution of different concentrations: 10cm3 distilled water 10cm3 10cm3 10cm3 10cm3 6% H2O2 3% H2O2 1.5% H2O2 0.75% H2O2 0.375% H2O2 Diagram 1: Serial dilution of 6% hydrogen peroxide solution. 1. 20cm3 of 6% hydrogen peroxide was transferred into a beaker using a pipette. 2. 10cm3 of the 6% hydrogen peroxide in the beaker is transferred into another beaker using a pipette as seen in Diagram 1. 10cm3 of distilled water is added into the beaker to form a hydrogen peroxide solution of 3%. 3. Step 2 is repeated consecutively until a hydrogen peroxide concentration of 0.375% is achieved. D) Iodine Clock Reaction: 1. 3 test tubes are labelled A, B and C respectively. 2. Using a micropipette, 2.00cm3 of 0.01M potassium iodide solution is transferred into test tube A. 3. Using a micropipette, 2.00cm3 of 6% hydrogen peroxide solution is transferred into test tube B. 4. 5 drops of 1M hydrochloric acid is added into test tube B to acidify the hydrogen peroxide. 5. Using a micropipette, 0.25cm3 of 0.03M sodium thiosulphate solution is transferred into test tube C. 6. Solutions from test tubes A and C are added together in a conical flask. 7. 5 drops of starch solution is added into the conical flask and the conical flask is lightly swirled. 8. The contents of test tube B are inserted into the conical flask and the stopwatch is immediately started. The conical flask is swirled to ensure a homogenous mixture. 9. When the blue-black starch complex is formed, the stopwatch is stopped. 10. The time taken for the formation of the blue-black starch complex is recorded in a table. 11. Steps 1 to 10 are repeated for two more replicates. 12. Steps 1 to 11 are repeated using hydrogen peroxide concentrations of 3%, 1.5%, 0.75% and 0.375% Page | 5
  6. 6. Candidate Name: Muhammad Azam bin IsmailCandidate Number: 02206 – 007Date of experiment: 22/04/09 E) Calculations: 1. The average time, tAVE for the blue-black starch complex to form is calculated using the formula: 1 + 2 + 3 = 3 2. The rate of reaction for each concentration is calculated using the formula: 1 Rate of reaction = Data Collection and ProcessingQuantitative Data:Concentration of hydrogen peroxide solution / % Time taken for blue-black starch complex to form, t/s (±0.01s) t1 t2 t3 tAVE 6.0 57.75 81.09 85.00 74.6 3.0 143.37 197.50 205.50 182.2 1.5 220.71 271.34 207.09 233.1 0.75 302.34 322.22 251.28 292.0 0.38 - - - - Table 2: Time taken for the blue-black starch complex to form and the average times for all concentrations tested. Concentration of hydrogen tAVE /s 1 Rate of reaction, / s-1 peroxide solution / % 6.0 74.60 0.0134 3.0 182.2 0.0055 1.5 233.1 0.0043 0.75 292.0 0.0034 0.38 - - Table 3: Rates of reaction for different concentrations of hydrogen peroxide solution.Qualitative Data:  When hydrogen peroxide (from test tube A) was added to sodium thiosulphate solution (from test tube C), the solution remained colourless and no reaction was evidently occurring. When starch was added, the solution still remained colourless. It is ready to be reacted with the potassium iodide (from test tube B). Page | 6
  7. 7. Candidate Name: Muhammad Azam bin IsmailCandidate Number: 02206 – 007Date of experiment: 22/04/09  After addition of potassium iodide, the solution did not change colour immediately and took some time for the blue-black starch complex to form.  For hydrogen peroxide concentration of 0.38%, the solution did not change colour even after a very long time and so the experiment was stopped.UncertaintiesUncertainty due to dilution of hydrogen peroxide solution (shown on the x-bar of graph):Uncertainty due to 10cm3 pipette = ±0.02cm3 Concentration of Uncertainties hydrogen peroxide Volume of Volume of Total percentage Absolute solution / % hydrogen peroxide distilled water error for uncertainty for solution added/ added / cm3 concentration of concentration of 3 cm hydrogen hydrogen peroxide/ % peroxide/ % 6.0 - - - - 3.0 10.00 ±0.02cm3 10.00 ±0.02cm3 ±0.4 0.012 = 10.00 ± 0.2% = 10.00 ± 0.2% 3 1.5 10.00 ±0.02cm 10.00 ±0.02cm3 ±0.4 0.006 = 10.00 ± 0.2% = 10.00 ± 0.2% 0.75 10.00 ±0.02cm3 10.00 ±0.02cm3 ±0.4 0.003 = 10.00 ± 0.2% = 10.00 ± 0.2% 0.38 10.00 ±0.02cm3 10.00 ±0.02cm3 ±0.4 0.002 = 10.00 ± 0.2% = 10.00 ± 0.2% Table 4: Uncertainty table for concentration of hydrogen peroxide solutionUncertainty due to time taken for blue-black starch complex to appear (shown on the y-bar ofgraph):Uncertainty due to digital stopwatch = ±0.01sConcentration of hydrogen peroxide Uncertainties solution / % tAVE /s 1 1 / s-1(%) / s-1( x 10-4) 6.0 74.60 ± 0.01 0.013 0.017 = 74.60 ± 0.013% 3.0 182.2 ± 0.01 0.0055 0.003 = 182.2 ± 0.0055% 1.5 233.1 ± 0.01 0.0043 0.002 = 233.1 ±0.0043% 0.75 292.0 ± 0.01 0.0034 0.001 = 292.0 ±0.0034% 0.38 - Table 4: Uncertainty table for time taken for blue-black starch complex to form. Page | 7
  8. 8. Candidate Name: Muhammad Azam bin IsmailCandidate Number: 02206 – 007Date of experiment: 22/04/09Data Presentation:The graph of average time of reaction was plotted against the concentration of hydrogen peroxide solution to ascertain the relationship between the two. Aline of best fit is drawn with the equation and R-squared value of the line shown. Error bars on both the x-values and the y-values are also included. Graph of average time of reaction, t against concentration of hydrogen peroxide solution/% 350 300 250 Average time, t/s 200 150 y = -101.4ln(x) - 195.3 R² = 0.9686 100 50 0 0.00% 1.00% 2.00% 3.00% 4.00% 5.00% 6.00% 7.00% 8.00% Concentration of hydrogen peroxide solution/% Page | 8
  9. 9. Candidate Name: Muhammad Azam bin IsmailCandidate Number: 02206 – 007Date of experiment: 22/04/09A graph of rate of reaction against concentration is drawn to show the relationship between these two variables. A line of best fit is drawn with the equationand R-squared value of the line shown. Error bars on both the x-values and the y-values are also included. Graph of rate of reaction/s-1 against concentration of hydrogen peroxide solution/% 0.014 0.012 y = 0.1843x + 0.0014 R² = 0.9527 0.01 Rate of reaction,/s-1 0.008 0.006 0.004 0.002 0 0.00% 1.00% 2.00% 3.00% 4.00% 5.00% 6.00% 7.00% 8.00% Concentration of hydrogen peroxide solution/% Page | 9
  10. 10. Candidate Name: Muhammad Azam bin IsmailCandidate Number: 02206 – 007Date of experiment: 22/04/09ConclusionBased on the data acquired from this experiment, we can see a trend in the rate of reaction whenconcentration of its reactants are manipulated. The relationship between concentration of hydrogenperoxide and rate of reaction fits a linear regression line as seen in the graphs above. The higher theconcentration of hydrogen peroxide solution, the higher the rate of reaction. As such thehypothesis is accepted.EvaluationBased on the calculations of uncertainties, the percentage error in this experiment is not very big andthe results are quite reliable. It is relatively safe to say that there is a linear correlation betweenconcentration of hydrogen peroxide and rate of reaction.However, there are several limitations to this experiment. Firstly is in the time taken for the blue-black starch complex to form. This colouration should appear suddenly and the digital stopwatchshould be stopped when this happens. However in this experiment, the colour did not appearsuddenly but gradually formed in the conical flask. As a result, there was some confusion as to whento stop the digital stopwatch. To remedy this, a white tile with a mark may be placed under theconical flask and the time taken for the mark to disappear can be taken instead.Also, as seen in both graphs there is a large uncertainty when it comes to concentration of hydrogenperoxide prepared. This is due to the limitation of the instrument used. Conversely, a micropipettewith a smaller uncertainty can be used to prepare the solutions of desired concentrations in minuteamounts. This will also prevent wastage but the experiment must be done on a smaller scale. Also, at0.38% concentration of hydrogen peroxide, the time could not be taken. The limitation could be dueto the concentration of potassium iodide being too low. Thus, an increase in the concentration ofpotassium iodide would be more effective as more data points can be plotted and a better line ofbest fit can be drawn. Page | 10

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