Chemistry coursework iodine clock reaction

The stopclock was then stopped when the reaction was completed, the end point could be observed with a sudden change in colour from an initial colourless solution, to a deep purple solution. The time taken for the reaction to finish was then recorded. This method was then repeated in exactly the same way, except that the concentration of H2O2 used was diluted down to 2.

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The results of this second experiment were also recorded. Results Concentration of H2O2 Vol. Time taken for reaction to reach End point.

An actual concentration may be deduced through further trial experiments as this may also be effected by the other reactants. Experiment 2 Aim: The aim of the following trial experiments is to investigate as in the first trial, which of the remaining substances affect the rate of reaction i. KI, and H2SO4. Through carrying out these experiments, I must also determine which concentrations must be used in the main experiment, bearing in mind the following points: 1.

Whichever substance is being investigated, the other reactants must be in excess 2. When the strongest concentrations are being investigated, the time for the reaction to reach its end point must be long enough to start and stop the timer with accuracy. On the other hand, when the weakest concentrations are being used, the time taken must not be so long that valuable laboratory time is wasted. Method The method used was the same as in the first set of trials. Results a Varying the concentration of KI. Concentrations used: H2O2 - 2.

The rate at which this reaction takes place, is dependant on the concentrations of: -H2O2 -KI 2. Varying the concentration of H2SO4 had no effect on the rate of reaction, as can be seen from the results. The presence of H2SO4 is required however for the reaction to proceed, it can therefore be deduced that it is acting as a catalyst, and is not a factor that should be investigated.

Problem 2 Before the effects of temperature on reaction rate can be investigated in the main investigation, it is important that the procedure used is accurate, and uses the laboratory time most efficiently. Therefore, I must conduct trial experiments to decide the best method to use, and become acquainted with that method. Experiment 3 Aim: To determine the best method of conducting experiments investigating how temperature affects the rate of reaction.


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Once the contents of both tubes had reached this temperature, the were mixed and left in the water bath. Results The were no valid results gained from these trials, however they illustrated that there were large inaccuracies in the method Analysis of Results Although there were no valid results gained from these trials it proved that the method was flawed. Gaining the correct temperature of both solutions using the water bath heated by a bunsen, was almost impossible, the temperature fluctuated constantly.

The Iodine Clock Investigation - GCSE Science - Marked by ecchiadenchai.tk

By the nature of the water bath, it also meant that only very few experiments could be heated and prepared at any one time. Bearing in mind that there is limited lab time, this is also not ideal. Therefore, in the main experiment, a thermostatic water bath will be used that will accurately maintain the temperature of the water, and also be capable of holding a large volume of test tubes at any given time. Modifications to Key Variables Now that it has been made clear exactly which substances affect the rate of the reaction, it can be stated exactly which variables are to remain constant, and which to vary.

Therefore a 1. However, part of this investigation is to investigate how the temperature affects the rate of reaction, therefore this will be varied when investigating the effects of temperature. Risk Assessment Before I can start conducting the main experiment, the issue of laboratory safety must be considered so that any possible exposure to risk is avoided. The chemicals, quantities and techniques that are to be used will all be looked at, and assessments will be made. Procedures Chemicals: - H2SO4 1. It should not be swallowed or allowed to penetrate the skin as it may have toxic properties at these concentrations.

Contact with the skin or eyes must also be avoided as it may be slightly corrosive, but more likely it would cause irritation to the skin. It should be treated as having the same hazardous properties as above, but also containing iodine which although in this form is not particularly hazardous, has the ability to stain skin and clothing.

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Therefore when conducting these procedures, extra care and vigilance must be taken; acknowledging these possible risks should result in safe laboratory work. In the case of H2O2 however, the concentration will not be measured in mol dm-3, but in 'Vol. Hydrogen peroxide is sold commercially in '20 Vol. A 20 Vol. Therefore: A 2Vol. Therefore, if it was required to calculate the concentration of H2O2 in mol dm-3 for the use in an equation for example, this could now be done. For 2 Vol. Each burette was then labelled accordingly.

The first concentration that was investigated, was that of H2O2. Once the two flasks had been prepared, the contents were mixed together, and the stopclock was turned on simultaneously. Once the reaction was completed and the instantaneous colour change was seen, the stopclock was stopped immediately. The time was then recorded, and the experiment was repeated three more times. This procedure was again repeated another four times, except in the second conical flask was placed a different concentration of H2O2, it contained: - 18ml H2O2 - 2ml distilled water This gave an overall concentration 1.

This method was repeated another eight times, and each time the volume of H2O2 in the second conical flask was reduced by 2ml, and the volume of distilled water was increased by two. For each concentration, the experiment was repeated four times; this enabled means and errors to be calculated.


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Once all of these experiments had been completed, the concentration of KI was then varied. This was conducted in exactly the same way as the H2O2, However, the total volume of KI used was only ever 10ml; the same number of different concentrations were still tested though. All of the results were recorded, and tabulated.

Eight test tubes were taken; in each of the first four test tubes was placed: - 5ml H2SO4 - 5ml Na2S2O3 - 5ml KI In each of the remaining test tubes was measured out 20ml of H2O2, and all of the eight tubes were placed into the water bath. Two tubes were taken each containing one of the different solutions; the tube containing the peroxide was then added to the second tube containing the mixture as described above. As soon as the two solutions had been added, the tube containing all of the reactants was placed back into the water bath, and the stopclock was started.

Once the reaction had finished as seen with an instantaneous colour change from colourless to a deep purple the stopclock was stopped, and the time was recorded. The method was then repeated using each of the remaining prepared test tubes; all of the results were recorded. Results All of the results gained from all of the experiments conducted will now be presented in a series of tables and graphs. In each case, through conducting a large number of experiments it has been possible to gain Maximum, Minimum, and Average results, displaying the occurrence of any anomalies, or inaccuracies in the results.

Time taken for reaction to reach End point. An actual concentration may be deduced through further trial experiments as this may also be effected by the other reactants. Experiment 2 Aim: The aim of the following trial experiments is to investigate as in the first trial, which of the remaining substances affect the rate of reaction i. KI, and H2SO4. Through carrying out these experiments, I must also determine which concentrations must be used in the main experiment, bearing in mind the following points: 1.

Whichever substance is being investigated, the other reactants must be in excess 2. When the strongest concentrations are being investigated, the time for the reaction to reach its end point must be long enough to start and stop the timer with accuracy. On the other hand, when the weakest concentrations are being used, the time taken must not be so long that valuable laboratory time is wasted. Method The method used was the same as in the first set of trials.

Results a Varying the concentration of KI. Concentrations used: H2O2 - 2.

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The rate at which this reaction takes place, is dependant on the concentrations of: -H2O2 -KI 2. Varying the concentration of H2SO4 had no effect on the rate of reaction, as can be seen from the results. The presence of H2SO4 is required however for the reaction to proceed, it can therefore be deduced that it is acting as a catalyst, and is not a factor that should be investigated.

Problem 2 Before the effects of temperature on reaction rate can be investigated in the main investigation, it is important that the procedure used is accurate, and uses the laboratory time most efficiently. Therefore, I must conduct trial experiments to decide the best method to use, and become acquainted with that method. Experiment 3 Aim: To determine the best method of conducting experiments investigating how temperature affects the rate of reaction. Once the contents of both tubes had reached this temperature, the were mixed and left in the water bath.

Results The were no valid results gained from these trials, however they illustrated that there were large inaccuracies in the method Analysis of Results Although there were no valid results gained from these trials it proved that the method was flawed. Gaining the correct temperature of both solutions using the water bath heated by a bunsen, was almost impossible, the temperature fluctuated constantly. By the nature of the water bath, it also meant that only very few experiments could be heated and prepared at any one time.

Bearing in mind that there is limited lab time, this is also not ideal. Therefore, in the main experiment, a thermostatic water bath will be used that will accurately maintain the temperature of the water, and also be capable of holding a large volume of test tubes at any given time.

Initial rates and the iodine clock

Modifications to Key Variables Now that it has been made clear exactly which substances affect the rate of the reaction, it can be stated exactly which variables are to remain constant, and which to vary. Therefore a 1. However, part of this investigation is to investigate how the temperature affects the rate of reaction, therefore this will be varied when investigating the effects of temperature. Risk Assessment Before I can start conducting the main experiment, the issue of laboratory safety must be considered so that any possible exposure to risk is avoided.

The chemicals, quantities and techniques that are to be used will all be looked at, and assessments will be made. Procedures Chemicals: - H2SO4 1. It should not be swallowed or allowed to penetrate the skin as it may have toxic properties at these concentrations. Contact with the skin or eyes must also be avoided as it may be slightly corrosive, but more likely it would cause irritation to the skin.

It should be treated as having the same hazardous properties as above, but also containing iodine which although in this form is not particularly hazardous, has the ability to stain skin and clothing. Therefore when conducting these procedures, extra care and vigilance must be taken; acknowledging these possible risks should result in safe laboratory work.