Sulfur clock reaction between sodium thiosulphate and hydrochloric acid

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Sulfur clock reaction between sodium thiosulphate and hydrochloric acid. Kinetics experiment done by my IB student, Tony. Please give proper reference to him if you use this material.

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Sulfur clock reaction between sodium thiosulphate and hydrochloric acid

  1. 1. Candidate Name: Tony Hong (Seung Mo Hong) IB Chemistry HLCandidate Number: 00213-021Date: August 28, 2010How will changing the temperature affect the rate of sulfur formationmeasured using a stopwatch.AimTo investigate the relationship between temperature and the rate of sulfur formation or therate of disappearance.IntroductionThe sulfur formation equation is the following: Na2S2O3 + 2HCl  2NaCl + H20 + S + SO2The rate of sulfur formation is affected by the following: a) Concentration – As the concentration increases, the particles within a given space will also increase, hence leading to more particles colliding with each other, which allows the rate of formation to increase.1 b) Temperature – As it can be seen on figure 1, the temperature increases, the average kinetic energy of the particles increases, which allows more particles to have a greater energy than the activation energy. Therefore, by increasing temperature, the rate of formation also increases. In addition, by increasing the temperature, the collision per time unit increases, which makes the rate of reaction faster. But, it is important to note that this is a minor factor as the increase in kinetic energy is the main reason why the rate of reaction increases. Figure 1: Maxwell –Boltzmann Distribution21 Clark, Jim. "The effect of concentration on reaction rates." Chemguide. 2002. Chemguide. 28 Aug 2010<http://www.chemguide.co.uk/physical/basicrates/concentration.html>.2 "Maxwell Boltzmann Distribution." Webchem. 01 Feb 2005. WebChem. 28 Aug 2010<http://www.webchem.net/notes/how_far/kinetics/maxwell_boltzmann.htm>.
  2. 2. Candidate Name: Tony Hong (Seung Mo Hong) IB Chemistry HLCandidate Number: 00213-021Date: August 28, 2010Variables Variable Measured Method of measuring / controlling the variable Amount of sodium thiosulphate 10cm3 of sodium thiosulphate is used in solution each trial. It is accurately measured through a 10cm3 pipette. Concentration of sodium thiosulphate 1M of sodium thiosulphate is used in each solution trial. Amount of hydrochloric acid solution 10cm3 of hydrochloric acid is used in each trial. It is accurately measured through a 10cm3 pipette.Controlled Room temperature All trials are experimented in roomVariables temperature which is approximately 28℃ Concentration of hydrochloric acid 1M of hydrochloric acid is used in each solution trial. Temperature of hydrochloric acid The temperature of hydrochloric acid is solution kept constant by conducting the experiment at room temperature (approximately 24.5℃) for each trial. Size of conical flask 125cm3 conical flask is used for each trial as the size of conical flask can affect the rate of formation if not constant. A small conical flask is preferred as it can take a long time for a large conical flask to change colour.Independent Temperature of sodium thiosulphate The temperature of the sodium thiosulphate Variables solution solution is 14.5℃, 24.5℃ (room temperature), 34.5℃, 44.5℃, 54.5℃. the 24.5℃ sodium thiosulphate solution is created by putting the room temperature sodium thiosulphate solution into a refrigerator and the solutions above the room temperature is processed by using a water bath. All temperature is measuring using a temperature probe Time taken for sulfur formation The time is taken for the sodium (change of color over period of time) thiosulphate solution to change its color from transparent to a pale yellow color using a stop-watch. To make the experiment more accurate, an X is drawn and the timeDependent for the X to disappear (due to the colorVariables change) is measured. Rate of sulfur formation The rate of sulfur formation would be calculated by taking the reciprocal of the time taken for sulfur formation. Table 1: List of Variables
  3. 3. Candidate Name: Tony Hong (Seung Mo Hong) IB Chemistry HLCandidate Number: 00213-021Date: August 28, 2010HypothesisThe sulfur formation equation is the following: Na2S2O3 + 2HCl  2NaCl + H20 + S + SO2The rate of sulfur formation is determined by the different variables of concentration andtemperature. However, as it can be seen on table 1, the concentration of sodium thiosulphateand the concentration and the temperature of hydrochloric acid solution are listed ascontrolled variables. Hence by changing the temperature of the sodium thiosulphate solution,the rate of sulfur formation would change.As explained in the introduction, the rate of sulfur formation would increase if thetemperature of the sodium thiosulphate increases. This is because of the fact that when thetemperature increases, the average kinetic energy of the particles of the sodium thiosulphateis also increased. Hence it would allow more particles to collide with greater energy then theactivation energy, which leads to the increase of rate of sulfur formation. Furthermore, byincreasing the temperature, the collision of particles per time unit would also increase, whichmakes the rate of reaction faster. However, it is important to note that this accounts for as aminor factor as the increase in average kinetic energy is the main reason for the increase inthe sulfur formation reaction.Also, when observing the Arrhenius Equation, it is possible to predict the trend of the rate ofsulfur formation against temperature. The following equation displays the ArrheniusEquation3: k=Ae(-Ea/R*T)Where:k = the rate coefficientA = a constantEa = the activation energyR = the universal gas constantT = temperature (in Kelvin)When observing this equation and relating it to the experiment; the only variable that changesis the T or the temperature in Kelvin. Hence, as the temperature of the sodium thiosulphatesolution increases, the rate of formation of sulfur should also increase, allowing the graph tohave a positive correlation. And when looking at the Arrhenius Equation, as the temperatureincrease, the constant rate should increase exponentially allowing the rate of sulfur formationto also increase exponentially.*It is important to note that the Arrhenius Equation is a calculation for the rate constant, notthe actual rate of the reaction itself. However, since the concentration of the solutions in theexperiment is kept constant, when looking at the rate equation below, the rate constant woulddirectly affect the reaction rate3 "Arrhenius equation." Wikipedia. 20 Dec 2010. Chemguide. 29 Aug 2010<http://en.wikipedia.org/wiki/Arrhenius_equation>
  4. 4. Candidate Name: Tony Hong (Seung Mo Hong) IB Chemistry HLCandidate Number: 00213-021Date: August 28, 2010 Rate = k [A]x[B]yWhere:k = rate constantA = concentration of solution Ax = order of solution AB = concentration of solution By = order of solution BAs such, the hypothesis for this experiment is that as the temperature of the sodium thiosulphatesolution increases, the rate of sulfur formation should increase exponentially. Rate of sulfur formation, r/s-1 against Temperature, t/℃ of Na2S2O3 solution Rate of sulfur formation, s-1 Temperature, ℃ Figure 2: graph showing the hypothesized relation of reaction rate against temperature
  5. 5. Candidate Name: Tony Hong (Seung Mo Hong) IB Chemistry HLCandidate Number: 00213-021Date: August 28, 2010Apparatus - Logger Pro - Temperature probe - Sodium thiosulphate solution (Na2S2O3) - Hydrochloric solution (HCl) - 10.0cm3 pipette (±0.05)cm3 - 125.00 cm3 conical flask (±6.25)cm3 - Stopwatch - Paper - Pen - Water bath - Electronic weighing machine (± 0.001g) -ProcedurePreparation of making 1M of Na2S2O3 solution 1. Measure 79.05g of sodium thiosulphate (Na2S2O3) using an electric weighing machine. 2. Measure 500cm3 of distilled water using a conical flask and put the 79.05g of Na2S2O3 inside it 3. Stir well until all the Na2S2O3 is completely dissolved.Preparation of making 1M of HCl solution 1. Measure 18.23g of hydrochloric acid (HCl) using an electric weighing machine. 2. Measure 500cm3 of distilled water using a conical flask and put the 18.23g of HCl inside it 3. Stir well until all the HCl is completely dissolved.Preparation of 14.5℃ and 24.5℃ Na2S2O3 solution 1. Put 10cm3 of 1.0M Na2S2O3 solution into a 125cm3 conical flask using a 10cm3 pipette 2. Place the conical flask into the refrigerator and wait for approximately 10 minutes 3. Take the conical flask out and measure the temperature of the Na2S2O3 solution using a temperature probe (should be lower than 14.5℃, if not put it back into the refrigerator and wait until it is lower than 14.5℃) 4. Put a temperature probe inside the Na2S2O3 solution (make sure the temperature probe does not touch the conical flask) and wait until the temperature goes up to 14.5℃ 5. Measure the rate of sulfur formation straight away (as the temperature of the solution would increase because it is lower than the room temperature) 6. Repeat step 1 in order to make the 24.5℃ Na2S2O3 solutionPreparation of 34.5℃, 44.5℃, 54.5℃of Na2S2O3 solution 1. Put 10cm3 of 1.0M Na2S2O3 solution into a 125cm3 conical flask using a 10cm3 pipette 2. Place the conical flask in a water bath with a temperature probe in the solution (make sure the temperature probe doesn’t touch the conical flask 3. Measure the temperature of the 1.0M Na2S2O3 solution using the temperature probe 4. When the temperature reaches 34.5℃ remove the conical flask from the water bath and measure the rate of sulfur formation straight away (as the temperature of the solution would decrease because it is higher than the room temperature) 5. Repeat steps 1-4 in order to prepare 44.5℃ and 54.5℃ Na2S2O3 solution
  6. 6. Candidate Name: Tony Hong (Seung Mo Hong) IB Chemistry HLCandidate Number: 00213-021Date: August 28, 2010 Figure 3: for preparation of 34.5℃, 44.5℃, 54.5℃of Na2S2O3 solutionMeasurement of the rate of sulfur formation 1. Draw a X mark with a pen on a white piece of paper 2. Put the conical flask with 24.5℃ Na2S2O3 solution on top of the X mark. 3. Put 10cm3 of 1.0M of HCl using a 10cm3 pipette 4. Measure the time starting from the beginning of the input of the 1.0 HCl solution until the X mark is not visible due to sulfur formation (colour change from transparent to a cloudy yellowish colour) 5. Repeat steps 2-4 three times for triplicate data 6. Repeat steps 2-5 with 14.5℃, 34.5℃, 44.5℃and 54.5℃ Na2S2O3 solution Figure 4: Side view of the diagram of the process of measuring the rate of sulfur formation Figure 5: Top view of the diagram of the process of measuring the rate of sulfur formation
  7. 7. Candidate Name: Tony Hong (Seung Mo Hong) IB Chemistry HLCandidate Number: 00213-021Date: August 28, 2010Data CollectionQuantitative Data Temperature of Time taken for sulfur formation, t/s Na2S2O3 solution, (±0.01s) temp/℃ Trial 1 Trial 2 Trial 3 (±0.1℃) 14.5 23.68 22.80 23.35 24.5 16.65 15.41 15.78 34.5 12.98 13.30 12.06 44.5 10.60 9.02 9.52 54.5 6.40 6.01 6.27 Table 2: Time taken for sulfur formation for different temperaturesQualitative Data Temperature of ObservationsNa2S2O3 solution, temp/℃ Before the input of HCl solution After the input of HCl solution (±0.1℃) 14.5 - Solution is colourless - Solution became a pale yellow - No reaction occurred colour - Reaction occurred as sulfur formation was visible 24.5 - Solution is colourless - Solution became a pale yellow - No reaction occurred colour - Reaction occurred as sulfur formation was visible 34.5 - Solution is colourless - Solution became a pale yellow - No reaction occurred colour - Reaction occurred as sulfur formation was visible 44.5 - Solution is colourless - Solution became a pale yellow - No reaction occurred colour - Reaction occurred as sulfur formation was visible 54.5 - Solution is colourless - Solution became a pale yellow - No reaction occurred colour - Reaction occurred as sulfur formation was visible Table 3: Observations of the change of solution after the input of HCl solution
  8. 8. Candidate Name: Tony Hong (Seung Mo Hong) IB Chemistry HLCandidate Number: 00213-021Date: August 28, 2010Data ProcessingThe average time taken for sulfur formation of the three trials was calculated by the followingequation: Temperature of Average time taken Na2S2O3 solution, Calculation for sulfur formation, temp/℃ t/s (±0.1℃) (s ± s.d4) 14.5 23.28 ± 0.36 ≈ 23.28 24.5 15.95 ± 0.52 ≈ 15.95 34.5 12.78 ± 0.53 ≈ 12.78 44.5 9.71 ± 0.66 ≈ 9.71 54.5 6.23 ± 0.16 ≈ 6.23 Table 4: Calculation of average time taken for sulfur formation Temperature of Na2S2O3 Average time taken for sulfur Rate of sulfur formation, solution, temp/℃ formation, t/s -1 (±0.1℃) (s ± s.d) 14.5 23.28 ± 0.36 0.04296 24.5 15.95 ± 0.52 0.06270 34.5 12.78 ± 0.53 0.07825 44.5 9.71 ± 0.66 0.1030 54.5 6.23 ± 0.16 0.1605 Table 5: Rate of sulfur formation for different temperatures of Na2S2O3 solution4 s.d - Abbreviated form of Standard Deviation
  9. 9. Candidate Name: Tony Hong (Seung Mo Hong) IB Chemistry HLCandidate Number: 00213-021Date: August 28, 2010 Time taken for sulfur formation, t/s against Temperature, temp/℃ of Na2S2O3 solution 25 Time taken for sulfur formation, s 20 y = 36.39e-0.031x R² = 0.9868 15 10 5 0 0 10 20 30 40 50 60 Temperature, ℃ Figure 6: Graph showing the average time taken for sulfur formation for five different temperatures
  10. 10. Candidate Name: Tony Hong (Seung Mo Hong) IB Chemistry HLCandidate Number: 00213-021Date: August 28, 2010 Rate of sulfur formation, r/s-1 against Temperature, temp/℃ of Na2S2O3 solution 0.18 0.16 0.14 Rate of sulfur formation, s-1 0.12 y = 0.0275e0.0313x 0.1 R² = 0.9868 0.08 0.06 0.04 0.02 0 0 10 20 30 40 50 60 Temperature, ℃ Figure 7: Graph showing the average rate of sulfur formation against different temperature variables
  11. 11. Candidate Name: Tony Hong (Seung Mo Hong) IB Chemistry HLCandidate Number: 00213-021Date: August 28, 2010ConclusionThe relationship between the average time taken for sulfur formation for five different temperaturecan be seen in figure 6. It may seem as if it decreases linearly. However, the reason why I chose toshow a exponential decrease is because when looking on table 5 (which shows the exact relationshipbetween the average time taken for sulfur formation and the five different temperature of sodiumthiosulphate solution), although the difference of the values for the average time taken for sulfurformation of 24.5℃ – 34.5℃, 34.5℃ – 44.5℃, 44.5℃ – 55.5℃ are approximately 3℃, thedifference between 14.5℃ – 24.5℃, is 7.33℃. Hence, the difference value of 7.33℃ compared to3℃ is too big of a gap to take a linear relationship into consideration. Furthermore, although onfigure 6, the data points do not perfectly fit the exponential decrease, when taking the error bars intoconsideration, I believe that the exponential decrease does relatively fit the data well. In addition,when looking at figure 7, although it may fit a linear regression, since the data are the inverse values -1of the data on figure 6 as the equation of rate of sulfur formation is (exactrelationship can be viewed on table 5); an exponential increase would definitely fit bitter. As suchthe hypothesis is accepted.EvaluationThe overall random error of the experiment is relatively low as there are only the small uncertaintiesof the temperature probe and the 10cm3 pipette. However, I believe that there are a lot of systematicerrors involving human error and hence leading to a high uncertainty. Thus, I believe that the datacollected from the experiment is not as reliable because of the uncertainties caused by human errorsand systematic errors. Here are some of the weaknesses of the human/systematic errors in thisexperiment and the ways to improve them:Weaknesses ImprovementsThe temperature would have changed from its Could have run each experiments in differentinitial temperature as all experiments were run in atmosphere (with different temperatures) so thatroom temperature. Hence the sodium the change of initial temperature is altered in athiosulphate solution would have either great amount.cooled down or heated up while running theexperiment leading to a high uncertainty.Human error of the stop watch – Since the time Use a reliable mechanic method where the time isof the sulfur formation was recorded by a measured by a machine rather than humans, sostopwatch where a human stops the stopwatch that it would reduce the human error and allowrelying on his sight; it would lead to a big more accurate data.uncertainty.The drawing of the X. Each drawing of the X had Should have used a printed X Mark where all thedifferent thickness and darkness. Hence when darkness would have been the same as thestopping the time for the complete sulfur computer would have drawn it. It would haveformation (when the X mark was no longer reduced the human error.visible) it would have ass been different as thedissimilar darkness would have caused me tohave different standard of darkness of thesodium thiosulphate solution and hence leadto great uncertainty.

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