The input variable in my experiment is the temperature of the reactants. All the other variables must remain the same. From preliminary experiments, it can be seen that no catalyst was required, so none were used.
Prediction
I predict the higher the temperature of the reactants, the quicker the mixture will go translucent and the cross will not be able to be seen seen, up-to a point. My knowledge of chemistry tells me that this is because there will be more successful collisions between thiosulphate and hydrochloric acid molecules;,producing sodium chloride, sulphur oxide, sulphur and water. I said up-to a point because eventually the temperature of thiosulphate will stop varying the reaction, because the speed of the reaction will be too quick to find variations when using this method. This factor would be seen by the slowing down and eventual constant rate of results being produced; or a straight horizontal line on a graph just above 0 time.
I think that the graph showing time against temperature will have a strong negative curved shaped correlation. This is because, the greater the temperature, the less the rate of reaction. The effect of the temperature is more obvious at lower temperatures as can be seen in the preliminary experiment.
From the preliminary experiment, I can predict that that the rate gets faster the hotter the reactants get.
Apparatus Sodium thiosulphate solution, Hydrochloric acid, 100cm3 beaker, stopwatch, one 50cm3 measuring cylinder and one 5cm3 measuring cylinder, paper with a black cross marked on, bunsen burner, tripod, thermometer and a heat mat.
Reasons for choice
Stopwatch is accurate to 1/100 of a second. I will only record the times to a 1/10 of a second because all number of errors such as human reaction times can come into play at 1/100 of a second making it unnecessarily accurate; 2 measuring cylinders, to avoid contamination I will measure the two substances separately until I am ready to let the reaction happen. The cylinders are both accurate to 0.1 cm3; this is more than accurate enough to easily measure the volumes of the substances I will be using. It would be hard to use a cylinder with a larger scale because in using the small volumes of substances I am using it would be inaccurate. The bunsen is to heat the sodium thiosulphate, the tripod to hold the beaker containing the thiosulphate. The thermometer is for measuring the temperature at the start of the experiment.
My range will include at least 6 measurements in the final experiment; each will have three replicates for an average, for more reliable results.
The temperatures I will measure at will be: 30, 40, 50, 60, 70, 80 (in C) these should give me a wide range of accurate results.
Diagram
Method
1. Set up equipment as shown in the diagram above.
2. Heat the sodium thiosulphate solution to the required temperature.
The temperatures I will use are: 30, 40, 50, 60, 70, 80 (in C)
3. Put the sodium thiosulphate in to the beaker on the paper with the black cross marked on which has 5cm3 of hydrochloric acid in it allready.
then time how long it takes until the cross is no longer visible underneath the beaker.
4. Record the start temperature and time of reaction on a table.
5. Clean all equipment well.
6. Repeat experiment two times.
7. Then change the temperature from the list and repeat all again.
I will repeat each experiment two times. This will give three sets of results that I can find a average from this will also show if my results are reliable. I will process my average results for a graph.
Fair Test
I will make my experiment a fair test by only changing one variablethat is the temperature of sodium thiosulphate. I will keep constant the following variables: Total volume, Concentration of hydrochloric acid, catalysts, and Concentration of sodium thiosulphate. I will not use a catalyst. I will use 5cm3 of the same concentration of HCL each time. I will use 40cm3 of sodium thiosulphate .
Cleanliness of the beaker is an important matter of reliability because contamination could occur. If the beaker is not clean, then any acid left unreacted will react with the next concentration of thiosulphsate before I am ready. The beaker should not just be rinsed though. It needs to be scrubbed properley.
Safety goggles should be worn at all times, you should should take care when handling hot beakers and equipment.
Results Table
Graph
Conclusion: My variable (temperature of reactants) did have an effect on the time and rate for the cross to be obscured. This was that, as the reactant temp got higher, the time for the cross to be obscured got lower. This can be seen on my graph of average time against temperature, with a negative curve of strong correlation.
My results show that the hotter the reactants, the faster the mixture turns translucent and the cross can not be seen. My knowledge of science tells me that this is due to the fact there are more successful collisions between thiosulphate and hydrochloric acid molecules; producing sodium chloride, sulphur oxide, sulphur and water.
I agree with my prediction because as the temperature of the reactants increases so does the rate, but the graph did not level off as I had predicted. I think that if higher temperatures were used, then the graphs would level off. This is because the completion of the reaction would be so close to 0 that the difference between the reactions would be very small, so the graph would level off.
Evaluation
This investigation went very well, I proved my prediction and got very good results. If I was to do this experiment again I would take down more results, and go up to a higher temperature. I would also use a electric thermometer because I found the ones given to use harder to read and they may have been slightly inaccurate.
