· Conical flask
· Beaker
· Stopwatch
· Paper with a cross marked on it
· 300cm3 Sodium Thiosulphate solution
· 100cm3 Hydrochloric Acid
· 200cm3 Water.
· Pipette
Diagram:
Safety:
To conduct my experiment safely I will follow normal laboratory rules, which include:
· Wearing of safety goggles to protect my eyes from chemical splashes.
· Standing up to conduct the experiment, therefore reducing the risk of tripping and spilling chemicals etc.
· Taking care whilst handling chemicals, particularly Hydrochloric acid and Sodium Thiosulphate because they are both irritant. I will not touch my eyes or mouth until I have thoroughly washed my hands.
· Taking care when using glassware to prevent injury.
Meathod:
I am going to measure how changing the concentration of sodium thiosulphate affects the reaction time between it and hydrochloric acid. At each stage of the experiment I will add 20 ml of hydrochloric acid, to that I will add 20 ml of a sodium thiosulphate and water solution. By varying the amount of water in the 20 ml of sodium thiosulphate solution I will vary the concentration. I will first put the hydrochloric acid in a test tube. Then I will add the sodium thiosulphate and will start the stopwatch immediately. As soon as the cross disappears I will stop the timer.
Obtaining Evidence:
Evaluation and Conclusion
Evaluation:
The results I have gathered from this experiment are quite as I expected and this shows clearly in my prediction. The higher the concentration of reactive substance in the experiment the faster the reaction will take place. This is because if there is a high concentration of reactive substances it increases the likely-hood of the two different sets of particles colliding.
So therefore in relevance to this particular experiment I have found that the more sodium thiosulphate that is added to the solution speeds up the reaction, for example: where there is a high concentration; 10cm3 of hydrochloric acid and 50cm3 of sodium thiosulphate, it takes on average 53.665 seconds for the reaction to be complete. And where there is a low concentration; 10cm3 of hydrochloric acid and 10cm3 of sodium thiosulphate it takes on average 353.02 seconds for the reaction to complete, this is because there is a lower probability of the particles colliding. Though other things have to be taken in to account such as the amount of particles in the solution, for example when the water is equal to the amount of sodium thiosphate particles it creates an even lower chance of the particles colliding as many of the sodium thiosphate particles can collide with the water, using up their energy and producing no reaction. When described like this the water that was added altered the time of the reaction a bit like a catalyst would and slowed the reaction down.
Conclusion
I think the results that were gathered are reliable, though I did not use any complex measuring devices; I used an ordinary stop watch to time how long the reaction took to complete, I used manual measuring devices for the liquids which cannot be exact. Also the judge for when the reaction was complete was simply when I could not see the cross on the piece of paper, this also cannot be exact. I think the results could have been made more accurate but the ones I have provide an idea about how concentration can affect the speed of a reaction.
As with most experiments there were a few anomalous results within the results I acquired. During the experiment at the second stage, the second reading was 45.01 seconds, the first reading was 54.63 seconds, and this was quicker than the first reading of stage two by almost ten seconds. And, on the fourth set of results the first result was 96.63 seconds and the second result was 82.80 seconds, this is nearly a fifteen second range, a much larger range than with any of my other results. These anomalous results may have been caused for a different reasons; one may be because the measurement of the thiosulphate, hydrochloric acid and water was measured wrong. There could have been more of the thiosulphate than there should have been, this would have speeded up the reaction when it should have taken longer.
I do believe that my experiment was a success and the results accurate, as there is a distinctive pattern to be seen. When studied the graphs clearly back up my prediction.
Though my results did prove my prediction well enough, as always there is stillroom for improvements until there are no anomalous results. Ways in which I could improve the experiment could be that I measure the chemicals more accurately or in order to eliminate human error I use a light sensor to decide when the experiment is complete. Just using the eye is not accurate way of judging the end of the experiment, as it is not unremitting.
If I had the chance to do the experiment again I would find a way of measuring the chemicals more accurately in order to produce more accurate results. Not only that I would try to extend the experiment so I could try different combinations of sodium thiosulphate and hydrochloric acid, this would show me if it changed the rate of reaction any further. I would keep the room temperature stable so that a change of heat would not effect the movement of the particles, which would make the move faster into each other and react faster. And finally I would use a light sensor to judge when the experiment was complete.
