Saftey Precautions:
Effect of the different concentration of metal solutions to the amount of time taken
Resolution: Stopwatch 0.01 Measuring Cylinder 1mL
Different concentration of Sodium Thiosulfate Affecting on the Time Taken
for the Reaction to be Complete
Different Concentration of Sodium Thiosulfate Affecting
on the Rate of Formation of Sulfur
Discussion:
By collecting results from the investigation, graphs were able to be created to show the relationship between the affects on the concentration of sodium thiosulfate (Na2S2O3) on the rate of reaction. Two graphs were created to show the relationship with one being the rate of reaction graph. The inverse of time (
) is graph against concentration to show the rate of reaction. The rate formula is given as Rate=
where the concentration is a constant, and due to this rate is inversely proportional to t, but proportional to
, thus it is an indication of the rate of reaction. Therefor the inverse of time is graphed against the concentration to show the rate of reaction.
During the experiment, hydrochloric acid was added to different concentrations of sodium thiosulfate in which after certain time an opaque precipitate occurred. This shows that a reaction had occurred between the sodium thiosulfate and hydrochloric acid forming a formation of sulfur. This is when the reactant’s particles meet and collide, thus this is also known as the, ‘collision theory’. This theory is based on an idea that for a reaction to occur, particles have to collide in the correct orientation and with enough energy to break the bond. The minimum energy required for a reaction to happen between the reactants is called the activation energy, Ea. However, by increasing the concentration of reactants, the frequency of collision is also increased, thus increasing the rate of reaction.
The graph of the concentration against time, graph 1, shows the time taken for the cross to disappear, thus for the reaction to complete. 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. This also means that by increasing the concentration of sodium thiosulfate, the rate of reaction would also increase, as it was founded that the rate is proportional to the concentration of sodium thiosulfate. This proves the predicted hypothesis, ‘as the concentration of sodium thiosulfate decreases, the rate of formation of sulfur decreases’.
Although the experiment did prove the hypothesis, it was identified that there were errors in which affected the precision of the data. One of the errors, a random error, was not being able to record exactly the time it took for the reaction to complete. This was due to the subjectivity of determining when the reaction was actually completed. The reaction is assumed to be completed once the cross disappears. This is an error as it is difficult to determine if the reaction had actually completed once the cross disappears. It could be that in some trials the reaction was nearly completed but the cross is thought to have already disappeared and the time was recorded. Therefore the time recorded is not precise to when the reaction is completed, thus the result would differ from the true value and affect the precision of the data.
An improvement to this conjuncture is instead of determining when the cross disappears in which it does not completely disappear but well enough to be considered as vanished, is to use a laser light to shine through the solution. The laser light is much thinner and will disappear completely once the solution precipitates to an opaque form, thus a more accurate time to when to when the reaction completes can be recorded. This increase the possibility of obtaining true values.
Another random error is not being able to fully rinse and clean out the conical flask before committing the next trial. When the solution reacted together, a cloudy opaque precipitates of sulfur is formed. Once the solution is emptied out in preparation for the next testing, some of the solution remains within the conical flask, which was identified from the cloudiness of the solution at the bottom of the flask. Due to this, small volumes of previous solution are left over and when the next trial is conducted, that trial would have more volume of solution than the previous trial, and by increasing the volume of solution, the time it takes for the reactant’s particle to collide and react decreases. This can be seen on the table such as when 0.15mol L-1 of sodium thiosulfate was tested to determine its reaction time, the reaction time increase after each trials, ‘trial 1 at 23.78, trial 2 at 24.69, trial 3 at 25.07’. This affects the precision of the data and reduces the possibility of obtaining true values.
An improvement to this is to use a new cleaned beaker for each trial. This improvement would lessen the chance of increasing volume to the reacting solution, thus this would also reduce the possibility of cross contamination. By doing this, the data would be closer to the true value and reduce the possibility of precision and scatter in the data.
Although errors affected the experiment, there were strengths that were presented during the investigation. One of the strength was that all controlled variable was taken into consideration. The same equipment, such as the stopwatch was used throughout the trial and this lessens the chance of anomalies. Also the solution was swirled twice for every trial and by doing this; all trials are kept constant and consistence throughout. 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.