Safety: A pair of goggles will be worn during the heating part of the experiment in order to protect the eyes. When handling hot beakers and measuring cylinders a pair of tongs will be used. A gauze and heatproof mat will be used while heating to avoid any damage to the equipment.
Fair test: In order for my findings to be valid the experiment must be a fair one. I will use the same standard each time for judging when the X has disappeared. I will make sure that the measuring cylinders for the Hydrochloric acid and the sodium thiosulphate will not be mixed up. The amount of Hydrochloric acid will be 5 cm3 each time and the amount of Sodium thiosulphate will be fixed at 25 cm3. During the heating stage of the experiment, a blue flame will be used throughout. Also the same Bunsen burner and gas tap will be used to maintain consistency. All of these precautions will make my final results more reliable and reduce the chances of anomalies, making the entire investigation more successful.
Diagram:
Measuring and Results: I am going to be measuring the amount of time taken for the hydrochloric acid and the sodium thiosulphate to react with each other. I will do this using a stopwatch, timing from the point the two are mixed until the time when the X below them can no longer be seen. I’m going to be varying the temperature by heating the sodium thiosulphate before adding it to the hydrochloric acid. I am going to write down the results in a results table, in the table there will be 3 sets of results for each temperature, plus an average e.g.
Plan:
- First set out all the equipment as shown in the diagram.
- Then pour 5 cm of hydrochloric acid and 25 cm of sodium thiosulphate out into the two measuring cylinders.
- Pour the sodium thiosulphate into the conical flask.
- Place the conical flask on top of the Bunsen burner on a blue flame.
- Heat the sodium thiosulphate to the necessary temperature (20ºC to 60ºC)
- Then take the conical flask off the Bunsen with the tongs
- Place the conical flask onto the paper with the X on it.
- Then get out the measuring cylinder with the hydrochloric acid in it.
- Then pour the hydrochloric acid into the conical flask
- Using the stopwatch, measure the time it takes for the X to disappear, then record you findings into a result table.
- The experiment is then repeated 3 times.
- The entire procedure is then repeated, but using a different temperature.
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Results:
(S)= Seconds
Graphs:
Analysis:
In this experiment I have found that as the temperature is increased the time taken for the reaction to take place decreases. I have also found out that the time taken for a reaction to take place decreased roughly by 15-20 seconds for each 10ºC increased. There was only one small anomaly and that was the 40ºC reading.
Conclusion:
From my results, my conclusion is that if the temperature is increased, the time for the reaction to occur is reduced. The cross disappeared much faster as the temperature was increased. I think this was because of the increase of energy between the particles and an increase in energy between collisions that successfully passed the energy barrier. This released the sulphur quicker, which turned the solution cloudy and made the cross invisible.
At the lower temperatures, the time for the cross to disappear was more because the particles did not have as much energy as they did at the higher temperatures
Evaluation:
I think that this experiment went well. My results were particularly accurate as I did each temperature the reaction was taking place three times and calculated an average from these times. There were no strange results (anomalies) in my results table and I think that this was because of the caution and care that I put into making sure that the experiment was set up correctly with careful measuring of chemicals and substances. I think that I could have repeated my results more for the reason that I feel although the experiment was repeated three times, the most accurate results in experiment can only come from a lot of results. I believe that I could have improved the method by making it more specific. I stated clearly all the various methods I took in setting the experiment up but I could have been more specific to how all the apparatus was used and perhaps why I used the apparatus I did as well. I think that I did get a suitable range of results for this experiment. I recorded results from temperatures that ranged from 20 C to 70 C and I think that this is a good range to see how temperature affects the rate of reaction. Another way I could have improved was on factors like controlling the stopwatch and measuring the amount of sodium thiosulphate and hydrochloric acid. There is lots of room for human error here. Overall, this investigation has been a very successful one. I feel my results and analysis have been as accurate. I could made it even more accurate bye trying other variables e.g. concentration or adding a catalyst.
