Before the experiment I will carry out a preliminary trail to see what volume of each substance, that I would need and what variations of volume to use. So the experiment should not be too time consuming or to be so fast that I have a chance to record the results.
Here is a diagram of what the experiment would look like
For the experiment I will be using 60cm3 total volume in the conical flask before the reaction takes place, this is crucial because there needs to be the same amount of volume in each experiment, for it to be a fair test.
The volumes in the different variables are going to be:
60cm3 of Sodium Thiosulphate
50cm3 of Sodium Thiosulphate and 10cm3 of water
40cm3 of Sodium Thiosulphate and 20cm3 of water
30cm3 of Sodium Thiosulphate and 30cm3 of water
20cm3 of Sodium Thiosulphate and 40cm3 of water
10cm3 of Sodium Thiosulphate and 50cm3 of water
The accurateness of the experiment is dependent on using accurate measuring equipment. The measuring equipment that I am going to use is a burette and a pipette, because the measuring capacity of each is within 0.05 of a cm3. I would like to use light sensors to detect when the reaction has finished than relying on my judgement to finish the experiment, but there are no light sensors available school.
The variable that I am going to change is the concentration of Sodium Thiosulphate reacting with Hydrochloric acid. The remaining variables pH, temperature, surface area and the use of a catalyst are going to stay the same.
Each varied experiment will be repeated 3 times and the average between those results would be calculated to give a more accurate prospective than just doing one reaction for each variable.
I am going to keep each variable the same by:
-
pH – I will make sure that I use the same reactants for each experiment so that the pH can’t be changed. The pH needs to be maintained because if one experiment has a higher acidity or alkalinity them the experiment won’t be fair.
-
Surface area – There are no solids in the reaction so there is no need for maintenance of surface area.
-
Catalyst – There is no catalyst being used.
-
Temperature – The most critical variable is temperature; this is because it can change the energy of the particles in a short time. I will keep the temperature the same by carrying out all the experiments at room temperature.
Safety
The main safety point here is that goggles must be worn at all times because i will be working will acids.
Hypothesis
As the concentration gets higher the rate of reaction will get faster. This is because if there are more particles in a volume then it is more likely to be collisions between particles, thus creating a faster rate of reaction.
As you can see a high concentration is more likely to collide more and react because firstly there are more particles in a volume meaning that there would be more collisions between the particles. The increased activity creates more collisions between the particles, creating a faster rate of reaction.
I predict that the graphs for the reaction will look like this.
I predict that the graph for the rate of reaction will look like this.
PRELIMINARY WORK
The following results are from the preliminary work, which was carried out.
Below: We use our work to determine what volume of hydrochloric acid to use. We did not want to use too much as the experiment could be too quick to time, and we did not want the experiment to be too time consuming because we would not have enough time to carry out other experiments.
From this preliminary work we decided to use 20cm3, as this seemed suitable.
Below: We used 20cm3 of water to get an idea of how long the experiments were going to take.
RESULTS
The results of the investigation are below.
From these results I worked out the average time it took for each concentration, these are shown below.
From the average results I have drawn a graph to show the relationship between concentration and the time taken for the reaction (see graph 1).
Another graph was drawn to show the rate of reaction of the experiments (see graph 2).
ANALYSIS AND CONCLUSION
I have noticed a pattern, this is, the higher the concentration of Sodium Thiosulphate, the faster rate of reaction.
Both Graphs 1 and 2 show this. Graph 1 shows the effect of concentration on the time taken for the reaction; at 10cm3 the time is 200 seconds whereas doubling the concentration to 20cm3 cause the time to half to 100 seconds. Doubling concentration again to 40cm3 causes the time to half again to 45 seconds. The time will continue halving until a certain point of full colliding capacity. This is because a certain number of particles can collide with the other reactant at any one time. This means that if the volume of Sodium Thiosulphate exceeds the collision capacity, the reaction will not speed up. Graph 2 shows the effect of concentration on the rate of reaction. The graph shows a straight line, the line shows that as the concentration increases the rate of reaction increases.
I have found out that as the concentration gets higher the rate of reaction will get faster. This is because if there are more particles in a volume then it is more likely to be collisions between particles, thus creating a faster rate of reaction. A high concentration will collide more and react than a low concentration because there are more particles in the volume meaning that there would be more collisions between the particles. The increased activity creates more collisions between the particles, creating a faster rate of reaction.
From Graph 1, I have no anomalous results, however there is the result for 50cm3, which was over best-fit line by 5 seconds. This does not drastically affect my results or the judgment of my conclusion. This result could have missed the best-fit line, as it was an average of the three experiments taken of this volume.
My conclusion “as the concentration gets higher the rate of reaction will get faster” matches my hypothesis, because the results of my investigation supports what I had hypothesized.
As I have previously identified that as concentration doubles the time taken halves, this shows that time taken is inversely proportional to concentration. I have plotted Graph 2 to show this.
EVALUATION
I believe that the investigation has gone well, this is because my results prove what I has hypothesized “as the concentration gets higher the rate of reaction will get faster”, this is shown in Graph 1 and 2.
The results I have obtained through my investigation on the face of it look accurate. I have no anomalous results, however there is the result for 50cm3, which was over best-fit line by 5 seconds. This does not drastically affect my results or the judgment of my conclusion. I believe that the number of repeat test were enough, however a wider range of concentration levels would have given a sureness of results.
Some problems occurred with the investigation, which affected the judgment and accuracy of each experiment. After experiments were cleared contents of the conical flask were poured out and then it was washed out. If the conical flask was not washed out properly then it could contaminate and affect the next experiment that it was used for. We were not able to keep the temperature the same for all the experiments; there may have been subtle differences in temperature. Light intensity was not kept the same, but steps were taken to keep the intensity roughly the same. Strenuous efforts were made to ensure the minimal effect of the table being jogged whilst experiments were taking place. Judging when the X had disappeared proved to be the major problem; at least two observers were used to accurately determine when the X had disappeared. If the X was judged to have disappeared before it had then it would affect the overall time, the same applies for judging after it had disappeared.
Improvement to the current method and plan can be made to make the investigation more accurate. More concentration levels would make the investigation more accurate and give sureness of results than a limited range of concentrations. The experiment could be carried out in water baths; this would ensure that temperature is kept constant. Light sensors could be used to accurately judge when the X disappears from sight. The sensors would also automatically time the experiment, which would make the investigation very accurate. However the school does not have a light sensor for use. Clean conical flasks could be used to avoid contamination as used ones are washed out and then reused. The investigation should be carried out on one day; this would decrease the risk of human error in the obtaining of reactants because the reactants can have different molar values.
