Variables
For my actual experiment I am going to investigate what happens to the rate of reaction when different volumes of Sodium thiosulpahte is added .The key variables for this investigation could also be the temperature, (which I varied in my preliminary work), concentration of sulphuric acid and the preserve of catalyst (however there is no suitable catalyst for this experiment).
Fair testing
To ensure that the test is fair so reliable and accurate results are obtained I will make sure the following is done:
- I will make sure the measuring cylinders and conical flask is washed in between each test, so particles from the previous test are removed, as this could affect the reaction rate of the other tests.
- I will make sure I wipe the measuring cylinders after rinsing them so any excess water is removed.
- I will try to move the conical flask as least as possible in between the experiments so I do not speed up any reaction involuntary.
- I will try not to get the paper under the flask wet as this can result to a change in the letter ‘x’ or change in my visibility.
- I will work on a flat surface, so I make sure there is the right amount of volume and when transferring the water from the measuring cylinder to the conical flask, I will try not to spill any.
Safety
Safety is very important in a scientific experiment. To carry out this experiment I will always wear goggles, and try best to avoid physical contact with any chemicals as the chemicals can be dangerous and may well harm the body. Also any spillages I will wipe/ clean straight away to avoid further accidents. Any breakages I will report to the teacher immediately as glass can be very dangerous. Also I will keep the desktop that I am working as clean as possible, so that there is nothing on the desktop, except for the apparatus needed thus; an accident does not happen. Lastly I will not run around the laboratory as there could be an accident and one could get hurt.
Prediction
I predict that as I will increase the concentration of sodium thiosulphate in my investigation the rate of reaction will also increase, i.e. the reaction time will be less. This is because I know that the more concentrated the solution is the more sodium thiosulphate particles will collide with the other particles. If a solution is more concentrated it means there are more particles of reactant knocking about between the water molecules. This makes the collisions between important molecules more likely.
Low-pressure High pressure
Low concentration High concentration
Expected results
Time Rate
(s) 1000/time
Concentration Concentration
(Volume of Sodium thiosulphate) Volume of Sodium thiosulphate)
Scale
For this investigation I will make the total concentration volume add up to 30cm³ each time, and repeat every measurement twice to get more reliable and accurate results.
I think that this is a suitable range of measurements for me to experiment with and I think that they will enable me to recognise patterns in my graph clearly.
Apparatus
- Goggles
- Small conical flask
- Stop clock
- 5 cm³ measuring cylinder
- 10 cm³ measuring cylinder
- 25 cm³ measuring cylinder
Method
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Mark an ’x’ on apiece of paper
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Measure 5cm of sodium thiosulphate, 20cm³ of H O and 5cm³ of sulphuric acid, using different measuring cylinders for each one. (Make sure the cylinders are rinsed well before use).
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After measuring everything put the water in a conical flask, place the ‘x’ underneath it and add the sulphuric acid and sodium thiosulpahate. (Make sure the paper does not get wet).
-
Start clock immediately
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STOP CLOCK! Record the time it
takes for the ’x’ to be obscured
- Repeat each experiment twice according to the measurements in the table.
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Make sure the cylinders and conical flask is
rinsed out after each experiment.
OBTAINING EVIDENCE
Results
Conclusion.
I found out that as the concentration of sodium thiosulphate increased the rate of reaction got faster; hence it took more time for the ‘x’ to be obscured. From these set of results it shows that my prediction was correct.
From my results indicated in the graphs I can see that they agreed with my prediction. I predicted that the higher the concentration of sodium thiosulphate the faster the speed of the reaction, so the reaction time will decrease.
I expected that the graphs would look as follows:
Time Rate
(s) 1000/time
Concentration Concentration
(Volume of Sodium thiosulphate) (Volume of Sodium thiosulphate)
In graph one a curved line showed the concentration of sodium thiosulphate against the average time results. This shows a clear pattern, because it confirms that as the concentration of sodium thiosulphate increases the reaction time is slower.
The pattern shown in the graph shows my prediction was correct as I stated that that an increase in the concentration of sodium thiosulphate would mean an increase in the reaction rate, i.e. the reaction time will be less. This is because the more concentrated Sodium thiosulpahte is the more Sodium thiosulpahte particles will collide with the Sulphuric acid particles. These increase collisions between important particles, therefore the reaction time decreases.
The curved line produced on my graph is valid, as there is an obvious link between the concentration of Sodium thiosulpahte and the time taken for each reaction. Also my graph agrees with the collision theory as it shows that at a higher concentration of Sodium thiosulpahte there is a decrease in reaction time. Although I have one anomalous result it is not scattered very far as it is almost touching the curve so my graph is valid.
In graph two a line of best-fit shows that the concentration of sodium thiosulphate is directly proportional to the reaction rate i.e. a linear line. This shows a clear pattern, because it shows that the higher the concentration of sodium thiosulphate the faster the rate of reaction.
The pattern in the graph agrees with my prediction, because I stated that the more the concentration of Sodium thiosulphate the more collisions between Sodium thiosulpahte particles and Sulphuric acid particles will occur. From the results indicated in the graph I can clearly see a direct relation between the concentration of Sodium thiosulphate and the rate of reaction, as a consequence there should be a constant increase in the rate of reaction.
My linear graph is valid as all my results are close to the line of best fit. The one anomalous result I do have is not too far from the line to be actually classed as an anomaly.
I also know that my graphs are applicable as I compared my results with other students in the class and I saw that they had similar graph patterns.
EVALUATION
In graph one I had one anomalous result. (labelled on the graph). The anomaly was due to both pair of results. However it is very close to my curve so it is not very anomalous this shows my graph patterns are valid.
In graph two I also had one anomalous result. The anomaly (labelled on the graph) was once again due to both results of the pair. Although I had an anomalous result it was very close to my line of best fit and almost touched it, and it followed the trend of the other results, this confirms that my graphs patterns are applicable.
After studying my graph I know that they are good enough to support a valid conclusion because as I increased the concentration of Sodium thiosulphate the rate of reaction became faster and it took less time for the ‘x’ to be obscured. Also because my anomaly results are very close to my lines it shows that my results are reliable.
In general the procedure used was suitable for the experiment, however I think that to obtain more reliable and valid results, improvements could be made.
- From the curve I produced on graph one, I can see a clear distance between the results of 0-10cm³ of Sodium thiosulpahate. If more results are taken in that range it would be easier to plot a better curve.
- As a replacement for of using measuring cylinders and a conical flask to measure the volume a pipette could be used to obtain more accurate and reliable results.
- For working out the time it took for the reaction to happen instead of relying on the human eye which is not hundred percent accurate, an electronic device would be more suitable as it would be more precise. A computer setup device could be used such as a light and sensor combination. The lamp would be useful in detecting the disappearance of the ‘x’, which would result to the sensor giving off a noise. (A possible solution could also be that an automatic clock is also, which would give more definite results).
Overall I think my experiment went really well. I feel that I carried out my experiment reasonably, and I encountered no problems. As a result I ended up with a valid set of results.
Further work
Another experiment I could carry out which would agree with my conclusion would be placing a piece of magnesium in a common acid, such as sulphuric acid. I could time until it took the magnesium to disappear.
Solution
Magnesium
The key variables for this investigation could be the temperature, the use of a catalyst, different volumes of an acid, and the concentration of sodium thiosulpahte, which would be the most suitable for this experiment, as it would then agree with my conclusion. For this experiment all the measurements I used for my actual experiment would be suitable.
To ensure the test was fair to contain reliable results I would have to make sure that the equipments were washed and wiped between each experiment. Also I would have to try to move the conical flask with the magnesium in as least as possible as otherwise I could speed the experiment up involuntary. Also I would have to be very careful in measuring the right volumes as this could affect the time. Safety would also be very important in this experiment I would have to handle all the equipment with utmost care, to ensure accidents did not happen.
I could use the same apparatus and idea of the method, which I used in my experiment, and repeat each concentration twice to more reliable results. One difference, which I could make to this experiment, is to add the improvements, which I mentioned for my actual experiment.
The results which I would expect would be that as I increased the concentration of Sodium thiosulpahte the rate of reaction would also increase, i.e. the reaction time would be less. This is because the more concentrated the solution is the more sodium thiosulphate particles collide with the other particles. This would make the collisions between important molecules more likely.
All my research I have carried out from Edexel modular science- revision guide: book one.
