1) 50ml Na S O (aq) : 0ml H O
2) 40ml Na S O (aq) : 10ml H O
3) 30 ml Na S O (aq) : 20 ml H O
4) 20 ml Na S O (aq) : 30 ml H O
5) 10 ml Na S O (aq) : 40 ml H O
I will repeat this three times for each concentration so I can get an average and a more accurate result.
To try this out I will conduct a series of trial runs using the first, third and fifth solution.
Trial run results
To make this experiment a fair test I will only vary one thing – the concentration of the Sodium Thiosulphate solution. I will conduct all the tests at room temperature because temperature has an effect on the rate of the reaction. The measures of Hydrochloric acid will all be the same (5ml). The person timing the experiment will look for the disappearance of the cross, otherwise there would be a time lapse between seeing the cross disappear and telling the other person to stop the clock and then eventually stopping the clock.
To conduct my experiment safely I will follow normal laboratory rules, which include:
· I will wear safety goggles to protect my eyes from chemical splashes.
· I will stand up to conduct the experiment, therefore reducing the risk of tripping and spilling chemicals.
· I will take care when handling chemicals, particularly Hydrochloric acid and Sodium Thiosulphate because they are irritants. I will not touch my eyes or mouth until I have thoroughly washed my hands.
· I will take care when using glassware to prevent injury.
Results
Graph
Analysis & Conclusion
I have come to this conclusion because of several reasons. Firstly, my results give pretty conclusive evidence that as the amount of Sodium Thiosulphate decreases, and the amount of water in the solution increases there are less atoms to collide and therefore less successful collisions causing chemical change so the reaction rate is slower. In a more concentrated solution, there are more atoms to collide so the reaction time is quicker.
My results support the prediction I made because I said the greater the concentration of Sodium Thiosulphate the faster the rate of reaction time. This is because the reaction time will be faster with a more concentrated solution as the more molecules there are, the frequency of successful collisions is greater and therefore the reaction rate is speeded up.
Evaluation
My experiment went according to plan but there were flaws in it. I think there is a human error factor involved when you are measuring liquids and looking for an end point in the reaction. Although the reaction I chose had a fairly definite end point it was still hard to tell whether the whole cross had disappeared or not. Instead of using a cross a light beam could be used and when the beam goes out that is the end point. A better standard of measuring cylinders and pipettes could be used aswell.
My results are good in their accuracy and the points on the graph were plotted as accurately as possible. Although, I did get one anomalous result (highlighted in green) but that is to be expected and I didn’t include it in my average. All my ‘good’ results fitted my prediction and made a strong trend in the graphs. I tested my results 3 times to ensure that I had not made any mistakes, and I also did preliminary work in order to familiarise myself with the project, set-up and equipment and to see if there was a better way of doing the experiment.
