Rate of Reaction - Sodium Thiosulphate and Hydrochloric Acid

Collecting and Interpreting Data

I have collected a my results, with three sets of results for each concentration, all initial results at 23 degrees centigrade although due to the outlier present at, along with unreliability, of results at a certain concentration tests had to be redone at this concentration although at a lower temperature of 21 degrees centigrade. The range of results does seem to be large enough, with three sets appearing to give me a reliable set of results and confirming that the results I do have are close enough.

Above is the graph showing initial results, with the questionable results being the 15ml Water to 35ml Sodium Thiosulphate results.

Bellow you will be able to the results with the new results on, the average is also marked on to this to show how close together the results are and the actual table containing these results (both original and re-dos) is also attached. Since on the lower graph all sets of data are within 5% of each other for time we can assume they are reliable as well as accurate.

These graphs both show, the second more so, show that as concentration decrease the reaction time increases slowing more and more as the concentration decreases. This can be explained by collision theory, and hence I will so. Increasing the concentration means there are more collisions and hence more successful collisions (though it useful to note the ratio of successful collisions to total collisions doesn’t increase). Consequently the rate of reaction increases as more reactant is being used up and more product is being created, for a reaction to take place two reactant particles must collide and the collision must have sufficient energy for the particles to actually react, and in a higher concentration there are more reactant particles, so there is a higher chance of a reaction with the necessary amount of energy occurring, hence no need for increase in ratio of successful collisions.

Evaluation

I think that the accuracy of my results was somewhat damaged by the primitive method of measuring the rate of reaction, that is to say having to measure by looking at a black cross through the liquid, and then stopping the stop clock when the cross was no longer visible, as well as the lack of reliability in mixing reactants, I think however the first problem is still the main, but this cannot be helped since there are not many other ways for a low budget school chemistry lab to measure reaction rate much more efficiently, I think using pipettes for all reactants and water (for dilution of sodium thiosulphate) could benefit accuracy as well and this would hence allow for greater accuracy with no cost effects and only a time difference.

As I have mentioned in my section on collection of data there was an outlier and two other anomalous results in my original testing, said results being all of the original results for 70% concentration (35ml Sodium Thiosulphate 15ml Water), but these have been replaced for my final results, which has enabled me to show better the evidence behind my conclusion, which is also in keeping with collision theory, so rest safe in the knowledge that collision theory still works.

Using my first graph I would say that the original Results were fairly accurate in their writing down, as we can see from the markings being exactly where they should be but that the testing could well have been a bit inaccurate, with the method making collection of accurate data rather tricky. The reliability of the First set of results is all good seemingly except from the 70% concentration tests which all appear to be unreliable, despite being done at separate times separated by other results, we can tell they are unreliable as they are all outside 5% of each other except for the upper two, which are just inside 5% of each other’s values, despite major discrepancies with the lower value and where they should be following the rest of the graph. The second Graph however shows an identical or nearly identical level of accuracy with a better level of reliability due to most results being where they should be and as closely grouped as they should be.

Due to the overall reliability and accuracy of my final results, which support the theory that rate of reaction increases as concentration increases I would say it entirely valid to say that my results are such as to allow me to confirm that Collision theory does work and concentration is a factor in rate of reaction.