How does temperature affect the rate of reaction between Hydrochloric acid and sodium thiosulphate solution.

David Macmillan Science 1 Investigation Chemistry 11Q7 SSW

Centre number: 49051

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How does temperature affect the rate of reaction between

Hydrochloric acid and sodium thiosulphate solution

Prediction

The prediction for this experiment is that when the temperature increases the time taken for the reaction to complete will decrease. I believe this will happen because of the collision theory. This states that when particles have more energy they collide more often and much harder and the reaction occurs at a faster rate. This can be done by increasing the temperature, concentration or surface area and also by adding a catalyst. In this experiment the temperature is the variable factor each time and as it increases the particles gain more energy to collide more often therefore increasing the rate of reaction.

Results

Analysis

These results show that as the temperature increases the rate at which the reaction occurs also increases. This is shown by the time taken for the reaction to complete getting shorter as the starting temperature increases. The table above showing a higher rate of reaction as the temperature increases also proves this. And this comes from the collision theory suggesting that when particles have a higher temperature, larger surface area or stronger concentration they will react at an increased rate thus having an increased rate of reaction. This therefore supports the prediction made before the experiment began that with decreasing temperature there is an increase in time for the reaction to complete. What is also seen by these results is that with lower temperatures the difference in time between 5oC is greater. For instance between 45 oC and 50 oC the difference is 2seconds whilst between 15 oC and 20 oC the difference is 32seconds, 30seconds longer. This happens because at lower temperatures the particles collide a lot less and not as hard because of having less energy and 5 oC is a big difference when the temperature is lower and this is why there is a bigger difference in time between 15 oC and 20 oC than 45 oC and 50 oC. The graph made also supports this reasoning with a line of best fit showing strong negative correlation and the pattern that with a higher temperature the rate of reaction is faster. There is also a definite pattern demonstrated on the graph that as the temperature gets lower the points become more spread out because of a much slower rate of reaction. There is also a definite relationship between the starting and end temperature. The temperature at the end of each reaction is about 2 oC higher after each of the reactions. This shows that there is a definite pattern and that the reaction produces the same amount of heat no matter what the starting temperature is because the collisions and reaction create the same amount of friction and heat each time.

Conclusion

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Conclusion

From the results and analysis I can therefore conclude that the rate of reaction is affected by temperature and that the collision theory plays a part in this experiment. This is shown by the fact that as the starting temperature increases the time taken decreases, which is explained using the collision theory that with more energy comes more collisions that are harder and therefore an increasing rate of reaction. I can also conclude that the same amount of heat is produced from each test as it is demonstrated after all 8 results. The other point I can also conclude is that between higher temperatures the time difference is much smaller than with lower temperatures as shown on the graph and results table. This happens because of the collision theory and that at lower temperatures there is a greater amount of time taken because of the lack of energy meaning softer and less often collisions and this is even more effective when the temperature is lower and it takes a great deal longer for reactions to complete than at higher temperatures.

Evaluation

Reliability

The results aren’t completely reliable because as the experiment went on the boiling tubes had to be cleaned and that means that some of the residue from the previous experiment may still be left in and this would affect the reaction rate if there was more sodium thiosulphate solution or hydraulic acid still left in the boiling tube. The sodium thiosulphate solution also had to be heated to a certain temperature but this was very difficult to keep constant so therefore the starting temperature may not be completely reliable. The temperature was at some points slightly too high then too cold by a few degrees and so the time taken for the reaction to complete may have a measure of inaccuracy.

Accuracy

Due to human error and different opinions the results may be less accurate. Some people would judge that the boiling tube was cloudy earlier than other people. It was also quite difficult to get the exact amounts of each substance and so the results would be more inaccurate without the exact same volume of thiosulphate solution or hydraulic acid used each time. The timing may also have a degree of inaccuracy because it was not easy to start the timer at precisely the same time as the hydraulic acid was added in whilst checking the temperature and putting the boiling tube into the rack and stirring the reactants. The time in which there was to do the experiment was one lesson so only about 8 or 9 different recordings could be made. This limits the accuracy because there wasn’t enough time to make lots of readings for more accuracy.

Anomalous Results

From the results that I obtained none of the results that I collected were anomalous and they all fitted to a certain extent of accuracy into a pattern. Any anomalous results from my experiment may have been obtained by a misreading in the temperature on the thermometer. Another reason for any unusual results may have been obtained from the boiling tube not been cleaned thoroughly leaving extra reactants or maybe an accidental over or under adding of hydraulic acid meaning the reaction was too quick or too slow than if the proper amount of 2cm3 was added to the sodium thiosulphate. If the stopwatch was timed wrongly this would also affect the results and be a reason for anomalous results.

Improvements

The ways in which the experiment could be improved are if there was a greater length of time to do the experiment so a larger range of results could be collected to make the experiment more accurate and reliable. This would lead to more detailed graphs and would help prove that certain patterns exist. Another way would be to have a better method of keeping the temperature constant. This provided a problem during the experiment because it was very difficult to not let the temperature get slightly high or low. If new boiling tubes were used after each experiment this would reduce greatly the chance of mixing thiosulphate with the precipitate of sulphur from the last experiment and a reaction occurring too early.