The experimentally obtained data collected for the reaction between 103- and HSO3- at various temperatures is clearly supported by the Arrhenius equation. Referring to Graph 1. 7, the line of best fits clearly passes through most of the data points displaying a linear relationship between temperature and the rate of the reaction. The R-squared of the graph which is a statistical measure of how close the data are to the fitted regression line is 0. 9818. This number is extremely low which indicates that the data points are very close to the theoretically derived calculations.
Looking at Graph 1. , it can be said with confidence that the rate of the reaction is directly proportional to the approximate temperature. For e. g. At 15 °C, the rate is approximately 0. 03733 S-1 and at approximately 25°C, it reaches 0. 05659 S-1. This shows that as temperature increase, so does the time taken till the reaction is complete due to the collision theory explained earlier in the Introduction. Although it is evident that temperature plays a key role in the rate of a reaction, the experimental data is not confidently supported by thumb rule of Arrhenius which states that rate doubles every 10°C.
Referring back to Graph 1. 6, the rate at 5°C is approximately 0. 02573. Theoretically, this should have increased to approximately 0. 05146 S-1 in the next 10°C. However, it only increases to about 0. 03733 S-1. This shows that the experimental rate was slower than the theoretical rate which can be justified by the sources of error. EVALUATION The data collected from this experiment indicates a medium level of inaccuracy and inconsistency. Due to the lack of literature value for the effects of temperature on the rate of the lodine Clock Reaction, there was no final percentage error.
However, Looking at Graph 1. , the line of best fits clearly shows the low precision throughout this experiment resulting in an increase of Random error. This could be due to the many assumptions being made in this experiment. We are assuming that there was no cross contamination between Solution A, B and water. Though it is highly likely that someone used the same pipette or measuring cylinder to measure chemicals as all utions were clear and colourless as notes in the overall observations.
This could affect the content of each of the beakers as it would change the concentrations and/or volume of the solutions which was to be kept constant (refer to Table 1. ) greatly affecting the data obtained. It was also assumed that both Sol. A and Sol. B beakers were exactly at the same temperature when the reaction occurred. Even though the temperatures of both beakers were recorded, it was highly likely that the temperature increased or decreased between the time when they were taken out of the water baths and the time they were mixed together. Though this would not be a primary source if error, nonetheless, it can account for a very small part of the experimental error.
Referring to Table 1. 4, the maximum apparatus uncertainty was calculated to be 2. 38% contributing significantly to the source of error in this experiment. Out of this 2. 138%, 1. 724% can be accounted for due to the use of a Thermometer when measuring the temperature of Solution A and Solution B. For every temperature variable, three trials were held at the same time for convenience. This meant that three different people were stirring the mixture of Solution A and Solution B. There was only one stirring rod used at a time which meant that two of the trials were not properly mixed. This affected the inhomogeneity of the solution and would have taken the trial a longer time for a precipitate to form.
This is evident in the general observations for 5 °C and 10 °C in Table 1. 2 which notes that one of the reaction (most likely the one which was stirred using a stirring rod) changed faster than the other two reactions. Since it was clearly evident to the naked eye, the lack of use of the stirring rod can be accounted for a large percent of experimental error. Another major factor adding to the experimental error was Measurement estimation. A vital part of the overall experiment was to record the time taken till a blue-black precipitate formed which indicated the end of the reaction.
This was crucial as it directly influenced the data collected and the overall calculations. There wasn’t an objective way to determine the end of the reaction as visual judgement, which differs person to person was used to note the end of the reaction. IMPROVEMENTS There are multiple ways to improve this experiment to achieve accurate results and minimise the error. An Improvements to the methodology is that instead of using a black “X” on a white sheet, an objective way of measuring the end of the reaction can be used.
In an ideal situation, a spectrophotometer which measures the transmittance and reflectance of a solution would help achieve accurate results, however, it is expensive equipment. Therefore, a spectrometer software can be downloaded on the school computers which requires minimum equipment. Looking at Table 1. 4, it can be determined that the greatest contribution to the total apparatus uncertainty was by the thermometers. Measuring the temperature of the solution A and Solution B was a vital part of the overall experiment as it directly influenced the time taken for the reaction to occur.
Due to this, the use of Digital thermometers would be an improved choice in future clock reaction experiments as it would accurately monitor temperature and reduce the thermometer apparatus uncertainty from 1. 724%. The use of a magnetic stirrer instead of a stirring rod would have decreased the experimental error. As noted previously in the evaluation, only one of the three trial at each temperature used a stirring rod, and the effects of this was clearly visible to the naked eye as noted in the general observation.
The use of a magnetic stirrer at a constant speed could have significantly increased the consistency between the trial runs, reducing the random error as average times would be within closer proximity. The accuracy of the data could have been improved if more trials were held at cooler temperatures. Since the rate of the reaction was noted to be much slower at cooler temperatures compared to warmer temperatures, there was a larger error margin between the three trial runs at 5°C and 10°C clearly evident in Graph 1. . An increase in the data collected at the cooler temperatures would minimise the experimental error in regards to the time taken till precipitate formed. Extending the range of the temperature variables would benefit this experiment in the future. This would create a greater gap between the temperatures at which the reaction takes place and would allow the experimenter to determine the highest and lowest temperature at which this reaction does not take place.