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Iodine Clock Reaction: Concentration Effect

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EFFECT OF CONCENTRATION ON REACTION RATE The aim of this experiment is to find the effect of varying the concentration of iodide ions on the rate of reaction between hydrogen peroxide and an acidified solution of potassium iodide: H2O2(aq) + 2H+(aq) + 2I? > 2H2O(l) + I2(aq) The course of this reaction can be followed by carrying it out in the presence of small quantities of starch and sodium thiosulfate solutions. As the iodine molecules are produced they immediately react with the thiosulfate ions and are converted back to iodide ions: I2(aq) + 2S2O32? (aq) > 2I? (aq) + S4O62? (aq) During this period the reaction mixture remains colourless.

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But once the thiosulfate ions have been used up, a blue/black colour suddenly appears because the iodine molecules now get the chance to react with the starch. A series of experiments will be carried out in which only the concentration of the iodide ions will be varied.

the concentration and volumes of the other chemicals involved will be kept constant as well as the temperature at which the experiments are performed. Since the amount of thiosulfate ions initially present will be the same in each experiment, the appearance of the blue/black colour will always represent the same extent of the reaction.

So it t is the time taken for the blue/black colour to appear then we can take 1/t as a measure of the reaction rate*. Apparatus and Chemicals selection of syringes 100 cm3 glass beakers white tile timer distilled water 1 mol dm? 3 sulfuric acid 0. 1mol dm? 3 potassium iodide 0. 1mol dm? 3 hydrogen peroxide 0. 005 mol dm? 3 sodium thiosulfate 1% starch Hazards: Both the sulfuric acid and hydrogen peroxide solutions irritate the eyes. Care: Wear eye protection. If any chemical splashes on your skin, wash it off immediately. When using the syringes always keep them pointing downwards.

Procedure 1. Using syringes make up the following mixtures in five dry 100 cm3 beakers. Mixture Volume of sulfuric acid/cm3 Volume of sodium thiosulfate/cm3 Volume of starch/cm3 Volume of potassium iodide/cm3 Volume of water/cm3 1 10 10 1 25 0 2 10 10 1 20 5 3 10 10 1 15 10 4 10 10 1 10 15 5 10 10 1 5 20 2. Place the beaker containing the mixture 1 on the white tile. 3. Measure 5 cm3 of hydrogen peroxide into a syringe. Add it to mixture 1 as quickly as possible and at the same time start the timer. 4. Carefully swirl the reaction mixture in the beaker from time to time.

When the blue/black colour just appears stop the timer and record the time (in seconds). 5. Repeat steps 2 to 4 with each of the remaining solutions Note: Since the total volume of the reaction mixture was the same in each experiment we can assume that the volume of the potassium iodide solution is a measure of its concentration**. DATA COLLECTION Record your results in the most appropriate way. DATA PROCESSING AND PRESENTATION 1. For each set of results, calculate the value of 1/time. (This is a measure of the rate of reaction*). 2. Plot a graph of rate against volume of potassium iodide. Remember that volume is a measure of concentration here**). CONCLUSION AND EVALUATION 1. Give a valid conclusion to this experiment with an explanation. 2. Describe any sources of error in your experiment. 3. Describe ways of improving your experiment in order to reduce the errors you mentioned above. Data Collection: Data Table 1:The Time Taken for the Mixture to Turn Blue/Black Once Potassium Iodide is Added Volume of Potassium Iodide: (± 0. 05 cm3) Mixture 1 ­ (25cm3) Mixture 2 ­ (20cm3) Mixture 3 ­ (15cm3) Mixture 4 ­ (10cm3) Mixture 5 ­ (5cm3) 18. 82 22. 78 30. 10 45. 90 87. 94 17. 59 22. 9 29. 03 43. 09 85. 93 16. 63 23. 13 28. 97 43. 59 49. 97 17. 68 22. 70 29. 37 44. 19 74. 61 Trial 1 Time (± 0. 01 sec) Trial 2 Time (± 0. 01 sec) Trial 3 Time (± 0. 01 sec) Average Time (± 0. 01 sec) Rate of Reaction   (s? 1) 0. 05656 0. 04405 0. 03405 0. 02263 0. 01340 Sample Calculation: Average Time: eg. Rate of eg. Trial 1 + Trial 2 + Trial 3 number of trial 22. 78 + 22. 19 + 23. 13 = 22. 70   3 1 Reaction : Average Time   1 22. 70 =  0. 0441 Data Processing: Data Table 2:The Rate of reaction of each Mixture Rate of Reaction ( s? 1) 0. 05656 0. 04405 0. 03405 Volume of Potassium Iodide: (± 0. 5 cm3) Mixture 1 ­ (25cm3) Mixture 2 ­ (20cm3) Mixture 3 ­ (15cm3) 0. 02263 0. 01340 Mixture 4 ­ (10cm3) Mixture 5 ­ (5cm3) Graph 1: The Relationship Between the Rate of Reaction and the Amount of Potassium Iodide Used Please view the hand drawn graph. Conclusion: The aim of this experiment is to find the effect of varying the concentration of iodide ions on the rate of reaction between hydrogen peroxide and an acidified solution of potassium iodide. As seen in the graph there is a positive correlation between the volume( Concentration) of the potassium iodide and the rate or reaction.

The graph on the trend line shows a linear correlation showing that the increase amount of volume of potassium iodide added to the mixture will increase the rate of reaction. Based on the graph   when 5cm3 is added the rate of reaction is 0. 01340  and when the volume of potassium iodide increased to 10cm3 the rate of reaction also increased to 0. 02263. This result is backs up the collision theory1 that states in order to show a positive increase in the rate of reaction, the amount of collision must also increase.

In order to to increase to amount of collision, having more volume of potassium iodide(increasing the concentration) there is more chance of collision resulting in a faster rate of reaction. As seen in the graph, the line of best fit does not successful go through the first point (5,0. 01340). This could be due to systematic errors such as the reaction time of the student. As human reaction time is slower than the actual time the reaction takes place, it would have affected the results as the mixture would have turn blue/black earlier than the time the students stopped the time. There are also random errors such as the change of temperature.

During the lab, the temperature of the room increased resulting in a faster reaction changing the correlation between the rate of reaction and the volume usage. Evaluation: Error Change in Temperature Problem The room temperature increased as the lab was conducted affecting the lab speeding up the reaction when the temperature increased. Solutions Keep the temperature of the room constant by turning of the aircon before the lab starts, and checking the room temperature as the lab is being done 1 BBC GCSE Bitesize: Collision Theory http://www. bbc. co. uk/schools/gcsebitesize/science/ocr_gateway_pre_2011/rocks_metals/7_faster_slower1. html Reaction time When the student takes the time it takes for the reaction to take place, there is a slower reaction to take the time for the reaction to take place, causing the rate of reaction to be longer than what it should have been. The stirring motion was not kept constant and affects the time it takes for the potassium iodide to react with sodium thiosulphate as the rate of reaction would increase when the swirling motion is quick. If there is too much of the concentration added to the mixture, the rate of reaction will be faster and if too little of the potassium iodide is added, it reacts at a slower place.

There is no possible way to change the speed of reaction as it is a human flaw, therefore using a more precise instrument will be more appropriate for the lab. Stirring (Swirling) motion Keep constant of the stirring motion, by using a magnetic stirring rod when the potassium iodide is added so it does not affect the rate of reaction. Measurement Since it is not possible to eliminate the error margins of an instrument, it would be wiser to increase the precision of the instrument instead. A way to make the measurements more precise is to use the same error margins on all instruments thus allowing a constant error margin.

Between every test, the starch used should be a fresh batch or to make sure to preserve the starch used for the experiment. Starch- Indicator When starch is left in mixture for a long period of time, it starts to degrade and will take longer for the reaction to be seen affect the time taken. Overall, these systematics and random errors do not influence the majority of the lab result as it continues to back up the collision theory and highlights the relationship between the rate of reaction and the concentration of the potassium iodide.

Cite this Iodine Clock Reaction: Concentration Effect

Iodine Clock Reaction: Concentration Effect. (2016, Nov 21). Retrieved from https://graduateway.com/iodine-clock-reaction-concentration-effect/

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