The experiment will end when I take the third reading of 30cmi??sodium thiosulphate solution, 20cmi?? water. The safety goggles are the most important aspect of the experiment, as it is crucial to maintain a high standard of safety when working with corrosive chemicals. Diagram: Graph to show predicted appearance of results Method and Results I carried the experimental investigation as stated in the Plan section, under Experimental Procedure. Having gained satisfactory results, I have arranged them in a table. Table of Results cmi?? of Na2S3O2 Time taken (seconds) Mean results solution 1 2 3 (average).
To draw my graph, I used the reciprocal function on my calculator on each of the averages, to gain a number that can be used to draw up a graph to show direct proportionality between 1/Average Time taken and concentration of sodium thiosulphate. Conclusion In terms of drawing a conclusion from my results, I can say that they compliment my prediction, as shown by the similarity in my prediction graph (a straight declining line), and also generally in the description of inverse proportionality.
As anticipated, inverse proportionality is shown between the concentration of sodium thiosulphate and the time taken for the solution to turn opaque. Na2S2O3 + 2HCl —> 2NaCl + S + H20 + S02 Scientific Explanation As the hydrochloric acid particles and the sodium thiosulphate particles collide into each other solid sulphur is given off and gives the solution a yellowish tinge. After a while this sulphur builds up and clouds the solution to the point when the cross beneath becomes cloaked.
The particle collision theory states that the more of a particular chemical there is present in a solution (in my case sodium thiosulphate) then the more it will collide with the other particles (the particles that concern my experiment are the hydrochloric acids). Therefore, if a 100% concentrated solution of sodium thiosulphate is added to a solution of hydrochloric acid, all the particles will collide more often, and the reaction will occur quicker than a 60% sodium thiosulphate 40% water solution, because the 40% water has replaced what used to be sodium thiosulphate, thus reducing the speed of the reaction.
Another point to make is the time of the reaction increased rapidly towards the end of my results. Evaluation The results I have obtained were of quite a high general standard, however there were a few minor anomalies. One anomaly was the second result for 30cmi?? of sodium thiosulphate solution. Here is the extract from my table of results, with the anomaly shown in italics. 30 47’2 50’6 49’3 49’0 It stood out as being an abnormally long time taken, in comparison with the other two results, and also seen in the effect on the graph of results it has.
This could be for a number of reasons. Firstly, going back to the planning section, there is the issue of temperature control, which was left aside despite being recognised as an influencing variable. If left uncontrolled then chances are that anomalies like the above will occur. I have decided not to ignore this result because the unconformity is only slight Also, the slight inconsistencies between each group of three results are also down to the fluctuating room temperature.
These errors however, are only slight and therefore are not to be worried about in terms of being insufficient for drawing solid conclusions. I still believe my results to be reliable, as they average out quite impressively. There are minor differences in each of the sets of three readings that were bound to occur due to uncontrolled temperature. The differences are merely fractional, and the averages worked out give a very clear picture of ideal results. There were bound to be the odd fluctuation in the length of time for the solution to turn opaque because of human error.
Every time it is myself that judges when the solution has turned sufficiently opaque and I stop the watch systematically. Because my reflexes are not perfect it may seem like one measurement was longer than another, when it was only my slow reactions that distorted the result slightly. The particle collisions theory may also be to blame because if the region of the solution directly above the cross X had a larger amount of collisions, just by chance, then the reaction time would be quicker than average.
I would suggest that in further experiments, the variable of heat be included, and the pair who carries out the investigation work as a team and play different roles in the experiment. One of them should time the reaction as I did, and the other should keep the temperature as constant as possible. That way anomalous results will be almost entirely eradicated. The other two issues of human reflexes and of chance of areas of collision are unfortunately uncontrollable. Some kind of computer will surely be able to judge when a solution has turned opaque better than a human being.
To test my conclusion, I would suggest doing a similar investigation, but with magnesium strips instead of sodium thiosulphate. It will be easier to judge reaction time because one would only have to stop the watch upon seeing the magnesium completely dissolve. Also using magnesium in an experiment is a lot simpler and cheaper than using sodium thiosulphate. Show preview only The above preview is unformatted text This student written piece of work is one of many that can be found in our GCSE Patterns of Behaviour section. Download this essay Print Save Not the one?
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