General considerations of sensation Basic features of sensory structures One way to classify sensory structures is by the stimuli to which they normally respond; thus, there are photoreceptors for lightmechanoreceptors for distortion or bendingthermoreceptors for heatchemoreceptors e. This classification is useful because it makes clear that various sense organs can share common features in the way they convert transduce stimulus energy into nerve impulses.
Label two boiling tubes A and B. Mark a dark spot on the side of a cm3 beaker, then? Using a measuring cylinder, transfer 10cm3 of sodium thiosulfate solution to tube A.
Using a clean measuring cylinder, transfer 10cm3 of hydrochloric acid to tube B and place the tube in the beaker of water. Allow both solutions to reach thermal equilibrium with the water in the beaker for a few minutes.
Add the solution from tube B to that in tube A, starting a timer as you do so. Mix the solution in A by gently stirring using the thermometer. Read and record the temperature.
Observe the spot on the side of the beaker by looking at it through the solution in A. Record the time at which the spot can no longer be seen due to it becoming obscured by the sulphur precipitate formed in A.
Dispose of the mixture in tube A as directed. Rinse out tube and wash and dry the thermometer. The first will be at room temperature and the other four evenly spaced between zero degrees celcius and about 50oC try not to exceed this temperature.
Record your results in a suitable manner. Processing Data To work out Average Time: Add all trail results for one specific temperature together and divide by the number of trials done for this drop height in this case 3 for every temperature eg.
Find the highest and lowest values of the time taken for each temperature. Add the uncertainty on the time taken to the highest value and minus the uncertainty on the time taken from the lowest value. Minus the new smallest value from the highest value to find the range, divide this range by two to find the uncertainty eg.
This then becomes 23cm and 19cm when you add and minus the uncertainty on the time taken from the maximum and minimum values respectively. Then largest value minus smallest value: To round the average time taken: The averaged time taken must be rounded to the same number of decimal places as the uncertainty eg.
As this percentage is bigger than the random uncertainty percentage on the activation energy I calculated. This indicates that there is significant systematic errors in the experiments that I ran.
This has a strong impact on the time taken for the experiment. As the result I got was less than the expected value it indicates that not only did I not identify the same point when the cross was obscured for each experiment, but I also in order from the set of experiments at the hottest temperature to the set of experiments at the coldest temperature I first observed the obscuring of the cross as much later then the actual obscuring of the cross.
From there with each set of experiments I conducted I observed the obscuring of the cross a little less later than I did in the previous set of experiments. Another major systematic error in this experiment would have been my inability to keep the temperature of the experiments constant with each set of experiments.
This could also be included as a random error as the temperature of the experiment at the time of the reaction does not stay at the same temperature as the water bath. Yet another systematic error would have been the uncertainty on the exact time the reaction started and the starting of the stop watch.
This would impact on the time taken of the reaction, as the activation energy I calculated was less than the book value this indicates that for each set of experiments I altered the difference between the starting of the reaction and the time I started the stop watch. Chemistry behind Reaction and Experiments At higher temperatures the experiment speeds up and reaches an endpoint quicker because an increase of temperature means an increase in average kinetic energy of the particles involved in the reaction.
This in turns increases the chance of particles colliding with enough speed and force to set off the reaction and more collisions means a quicker reaction. Improvements on the Experiment One major issue in this experiment is how to determine when the cross is obscured.
To combat this in the next time doing this experiment I would suggest the use of a calorimeter, to calculate the exact moment the cross is obscured. To improve the temperature issue I would measure the temperature of the reactants of the experiment rather than the temperature of the water bath around it, this would make the temperature of the experiment more accurate.
To help with the random uncertainty of the accuracy of the equipment, I would use a burette to measure the volumes of the reactants as a burette has less of an uncertainty on it than a measuring cylinder. To increase the over all accuracy of the Arrhenius plot of the reaction I would repeat the experiment for a greater range of temperatures-though as this would lead to safety issues I would use a fume cupboard for any experiments above a temperature of 55 degrees Celsius.
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