Also the same person will have to look at the dot each time as each person can see a little differently, and someone might be able to see the dot at one point, while another cannot. So the person looking must be the same for consistency.
A simple precaution to make sure not to mix up would be, careful not to mix up the measuring cylinders for each of the liquids. An example would be, not using the same measuring for the hydrochloric acid and the Sodium Thiosulphate.
Method
I shall collect the required equipment and measure the acids out using different measuring cylinders. I shall set the equipment out, as shown in the diagram below.
To measure ot the quantities of liquids neede I shal use burets which are veryu accurate at measuring liquids. I shall place 28cm3 of sodium thiosulphate solution and 10 cm3 water into a flask with 10cm3 of hydrochloric acid. When both are placed into the test tube the stopwatch shall be started. I shall then watch the dot to see when it will disappear. The moment I cannot see the dot then I shall stop the stopwatch. The time taken for the dot to disappear shall be noted down in the table of results.
The experiment then shall be repeated with different concentrations of sodium thiosulphate, which will be achieved by dilution.
Accuracy and Precision
I shall to be accurate by measuring with burrets. To measure with accuracy I shall make sure that the burret is on a level surface and I shall get down onto eye level with the cylinder to check that the liquid does reach there and does not go above or below the required amount. To get accurate results I shall take repeat readings to get an average. Using the average I shall work out the rate of reaction. I shall repaet my experiment three timesTaking repeat readings shows up anomalous results that should not be used, and so getting a more accurate result.I shall record the time record the time taken for the reactino to take place in seconds because using the equiptment provided that is the maximum accuracy achieved.
Safety
As I will be handling acids I must ensure that I take safety precautions. I will be using safety goggles at all times, so if I do spill acid or it reacts violently, my eyes will be protected at all times. I shall keep bags and coats away from the area so I do not fall over them when carrying out the experiments. I shall check all equipment beforehand to make sure there are no hairline cracks or lingering acids inside. I will also take care when transporting the chemicals around the classroom and when pouring, and try to make sure that no mishaps occur.
Preliminary work
I am going to conduct an experiment to decide the scales I shall use for my final piece. I shall also do the test run because the experiment may not work and may have to use two different acids instead. I will not repeat the different variations because it would be impractical and I do not have the resources available, as this is only a pilot test.
During this experiment, I hope to find out whether the scale I have set is accurate enough to find out the question I am asking, and whether I need to modify anything for a more successful final experiment.
Results
These are my results.
Conclusion
I discovered that there was not enough variation in the concentrations. So I decided to change the concentrations I was going to use. I found out that doing seven concentrations was enough as it . I also did not make the tests accurate enough as I do not have a big enough range to draw many conclusions.
From these results, they look like they back up my prediction, as the time for the dot to disappear lengthens as the concentration of the Sodium Thiosulphate goes down.
I shall now vary the volumes of the water and Sodium Thiosulphate by 5cm3. An example of this would be having 45cm3 of Sodium Thiosulphate and having 5cm3 of water, then 40cm3 of Sodium Thiosulphate and 10cm3 of water. This then would carry on going up or down in either direction as needed, this will give me extra accuracy.
Final Experiment
I took three attempts for each variation and then made an average. They are shown below with the rate of reaction.
Conclusion
Using the graphs I have plotted, which show the rate of reaction and concentration graph as a straight line and the average time taken for dot to disappear and concentration graph as a smooth curved line, I can draw a conclusion from my experiments. I have found out that as the concentration of Sodium Thiosulphate decreased the time taken for the reaction to take place increased.
In my prediction I expected that as I added more water to the Sodium Thiosulphate solution the time it would take for the dot to disappear would lengthen.
In my results I took an average from the three attempts. This shall give me more accuracy and doing this lowers the chance of getting anomalous results.
The graph for rate of reaction and concentration of Sodium Thiosulphate shows that when the concentrations were relatively low the rate of reaction was also relatively low, and when the concentration increased the rate of reaction increased. This implies that they are linked, which would also support my prediction.
The graph for rate of reaction and concentration of Sodium Thiosulphate goes up at a uniform rate, which would suggest that the two axes are related.
The collision theory suggests that if the solutions of reacting particles are made more concentrated, and there are more particles in a given volume, collisions between the reacting particles are therefore more likely to occur, and rate of reaction would then go up. This statement does appear to be true as the graphs show this.
My predicted graphs and the graphs of actual observations are similar and do show related trends.
Overall, the prediction I made is supported by the results of my experiment because they show that as concentration goes down, the rate of reaction time also goes down and the time for the dot to disappear lengthened. This would also support the collision theory as it states that if the solutions of reacting particles are made more concentrated, collisions between the reacting particles are therefore more likely to occur.
Evaluation
My experiment relied on judgement when the dot disappeared and I may not have estimated the time accurately. The light may have been different or I may have been tired at the time.
Also I did not use the same equipment each time and the experiments were recorded on four different days. The light and temperature would most likely have been different, this would affect the particles, because they may have been moving faster or slower, so rate of reaction would have been different
There could have been an element of human error. I could have written down a result wrong or note noted the time down right.
This could mean that any conclusion I have come to may be slightly inaccurate.
When I carried out the experiments, I used a burret to measure out the different liquids, and used three different measuring test tubes for each liquid.
On the rate of reaction and concentration of sodium thiosulphate graph, there were three results that were noticeable on the graph to be away from the line of best fit. I think that these results is an anomalous result, as they are quite a way off the line of best fit.
The results were: ( , ) ( , ) ( , )
I think my investigation was fair as I made sure that the total volume stayed the same throughout the experiment .
I also tried to keep the temperature of the solution the same, but, I could not really control the temperature of the solution that easily.
I cleaned the test tube that was used for the experiment out, each time it was used, to make sure that no residue of the solution was left behind to contaminate the next variation I tried.
The same beaker with the same dot on the side was used the whole way through the experiment for consistency, and the same person judged each time whether i could see the dot still when the water went cloudy.
I think that I should have taken a few more repeats of certain concentrations, because if I had disocvered that some of my results were anomolous at the time I would have been able to modify the anomalous results that I found while analysing my results.
Therefore I think if I repeated this experiment I would repeat the variations at least 4 or 5 times rarther than three times, if I did then my results would be a lot more accurate.
Apart from that point I think that I did discover enough information to help me lead to a conclusion.
If I would do the experiment again I would use a light sensor to detect whether or not it could see the light through the cloudy reaction. This would mean that the experiment would be more accurate. Also using the same equipment may have a small effect on the results, or cleaning the flasks out after each experiment may help.
Another improvement could be to use a water bath to keep the temperature of the reaction the same throughout, as it would not then be affected by the heat from the classroom.
I would also do the whole experiment, including the repeats on the same day so no variations can occur because of different days.
To obtain more evidence to support my conclusion I would take more of a range of results. I might use more concentrated Sodium Thiosulphate or use less concentrated Sodium Thiosulphate.
More evidence would mean that there would be more verification that my prediction was correct, and would solidify the concept of the collision theory.
Overall I think I have done an interesting investigation, and have completed it to the extent of my abilities. I have tried to make it a fair test, and back everything up with solid evidence.
