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Rate of Reaction - Formation of Sulfur

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Aim: To investigate the effect of changes in concentration of sodium thiosulfate on the rate of formation of sulphur. Independent Variable: Different concentration of sodium thiosulfate (Na2S2O3) Dependent Variable: Rate of formation of sulfur Controlled Variable: Equipment: The same equipment such as the conical flask would be used throughout the experiment as this would lessen the possibility of errors. Swirling: The chemical, sodium thiosulfate reacting with hydrochloric acid, in the conical flask would be swirled only twice. Volume of chemical: The same amount of hydrochloric acid, 5mL, and a total volume of 50mL of sodium thiosulfate and distilled water is to be used throughout the experiment and trials. Same Cross: The same paper with the cross in the centre will be used throughout the trials as an indication to when the reaction is complete. Hypothesis: As the concentration of sodium thiosulfate decreases, the rate of formation of sulfur decreases. Materials: 1. Dilute hydrochloric acid 2. 0.25molL-1 sodium thiosulfate 3. Stopwatch 1. Measuring cylinder 50mL and 10mL 2. 250mL conical flask Methods: 1. Measure out 50mL of prepared sodium thiosulfate in a 50mL cylinder then place into a 250mL conical flask. The different volumes of thiosulfate used throughout the practical constitute the independent variable. 2. Add 5mL of dilute hydrochloric acid to the flask at the same time as starting a stop watch. Keeping the same timer for each trial is a controlled variable. ...read more.


The trend shows that the graph is inverse proportionally as to when the concentration of sodium thiosulfate decreases the time taken for the reaction to complete also decreases. In relation to the ?collision theory? the investigation showed that the frequency of collision between the reactants decreases as the concentration decreases. It can be seen that in a more concentrated solution, there are more particles in the same volume of solution as to the dilute solution, and therefore this increases the chance of collision between the reactants. Thus the concentrated solution would have a much quicker reaction rate as there are more particles to collide. Concentrated Sodium Thiosulfate Dilute Sodium Thiosulfate Furthermore, the graph?s trend is also a curved line and this is because the gradient of the line which shows the rate of reaction is changing. In the second graph, graph 2, it shows the relationship between the inverse of time (rate) and the concentration, hence showing the rate of reaction. The trend indicates that the rate and concentration is proportional to each other, consequently when the concentration increases the time for the reaction to complete also increases. By doing the investigation, it was founded that by decreasing the concentration of sodium thiosulfate for each sample, the time it took for the reaction to complete or for the cross to disappear decreases as well, thus the rate of reaction also decreases. ...read more.


Another strength was that the experiment was done at a constant temperature and that was the room temperature. The collision theory indicates that temperature is a factor of the rate of reaction, an increase in temperature will increase the rate and a decrease in temperature will decrease the rate. In this case the experiment was kept at the same temperature, thus all of the trials had the same temperature affecting on the rate. This increases the consistence of the experiment. However there were some weaknesses. One of the weaknesses was that when looking directly vertical at the marked cross, it is still visible even after the reaction had fully completed. The method is said to be that the reaction is fully completed once the cross disappears but as experimented, the cross is still visible. This weakness reduces the chance of observing the correct time after the reaction had completed. Another weakness uncovered is? The data is shown to be acceptable as to when it was graphed; the graph proves the hypothesis and the collision theory. In relation to this the confidence in the data observed is high. The data and trend in the data showed that the concentration is a significant factor of the rate of reaction, in which the trend showed a decrease in concentration means a decrease in the time it takes for the reaction to complete. The evaluation of data and trend of the graph stated the collision theory and hypothesis, thus the confidence in the overall conclusion of the experiment is considered high. ...read more.

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