Prediction
My predictions come from my preliminary results. Mainly as concentration is increased by a factor of 10, the reaction time decreases by 265 seconds therefore reaction rate approximately 10 times faster. Also, from the above results, when the concentration is doubled, time decreases by roughly a minute therefore for every 5ml of sodium thiosulphate added (and 5ml of H2O taken away) reaction approximately 1 minute faster. This is due to the Particle Theory. The higher the concentration of sodium thiosulphate, the more particles there are in the solution, which also means there are more particles for the Hydrochloric Acid particles to collide with, creating more energy thus a faster reaction.
With this experiment, I must take into account that temperature has an affect on reaction times so tests must be carried out at roughly the same time of day.
Range and Number of Results
I will carry out this investigation using five different volumes of sodium thiosulphate: 50ml, 35ml, 20ml, 15ml and 10ml. This will enable me to obtain a wide range of results, achieve a better picture of the nature of the reaction I am investigating and make the graph more accurate. I will not be using the 5ml of sodium thiosulphate due to the fact that, as seen in my preliminary results, it will take too long.
Equipment
- Measuring Cylinder (1x10ml and 1 x 50ml)
- 3 x 50ml Beakers
- Conical Flask (100ml)
- Timer
- Heat Mat
- Safety goggles
- Sodium thiosulphate
- Hydrochloric acid
- Distilled Water
- Black Cross on paper
Fair Testing
To ensure a fair test, I will make sure each piece of apparatus I will use is clean to minimise cross-contamination, enabling me to achieve a more accurate a reliable set of results. I will also make sure that the timer is started and stopped at the same point of the experiment and solutions will be made as accurate as possible to ensure that tests correlate with each other better.
Safety
Throughout this experiment, many risks may arise. I will make sure I wear safety glasses at all times to minimise the risk of chemicals entering my eyes and damaging them. I will also make sure that I know how and when to alert my teacher if a problem does occur, such as broken glassware or chemical if it spills. I will also use a heat mat so that the heat will not be damaged if there is a chemical spillage.
Method
- Measure 50mlof Sodium thiosulphate and 10ml Hydrochloric acid and pour them into separate beakers, making sure you take note of which chemical is which as both are colourless
- Place the conical flask onto the black cross so that you can see it through the base of the flask. Set up the timer and pour the two chemicals into the conical flask. Start the timer immediately.
- Keep an eye on the black cross through the top of the conical flask. When you can no longer see the cross through the solution, stop the timer.
- Record the results and repeat with other concentrations of Sodium thiosulphate. Make sure concentrations are accurate and always of an equal volume
- Between each test, make sure all apparatus is clean with distilled water to get better and more accurate results.
Diagram
Results
Analysis
This graph shows my results on a time against concentration graph. It shows that there is s definite curve in the results, as expected for this experiment. There may be a slight anomaly in the 20% concentration, though the result is not too far off. The rest of the results are quite close to the trend line. This therefore shows that as concentration decreases, the time taken for the reaction to take place increases. These results show that as concentration is increased by a factor of 5, reaction time decreases by roughly 4 minutes therefore reaction rate approximately 8 times faster, close to my prediction of 10 faster rate of reaction. Reaction rate can be seen clearer on the graph below:
As volume increases by 10, rate increases by about 5, therefore 2 times as fast thus for every 10ml, the reaction rate doubles.
This graph shows concentration plotted against reaction rate (x1000). The reaction rate is worked out like this: 1 unit of sulphur
Time take
This really means 1 over the time taken for each concentration. This should turn out to show a strong positive correlation and as seen in the graph, my results are quite close to the line of best fit therefore my results are quite reliable. My second prediction is not accurate. There seems to be no exact time gap between each concentration.
The science behind this is the particle theory. The higher the concentration of sodium thiosulphate, the more particles there are in the solution, which also means there are more particles for the Hydrochloric Acid particles to collide with, creating more energy thus a faster reaction.
Conclusion and Evaluation
Overall, I believe that the experiment was a success. The results were quite reliable, as seen in both graphs with my results being close to the line of best fit. There were a few outlier results, which could be a bit closer to the line of best fit, though they were not too bad (e.g. 35% concentration for the reaction rate graph.) My first sets of results for the 50% concentration were too high compared to my other results, so I had to them again. It later reminded to me that I had done the test at a different time of day to the other results, so I had a different temperature. This would have affected my results, so the new results were done at roughly the same time of day, and therefore same temperature. I also made a mistake in calculating the reaction rates of the sulphur the product which was made in the reaction as I mistyped the result into my calculator and got a completely outlier result. This was put right as soon as I noticed the error. The temperature may affect the results and make them faster or slower depending on the temperature the chemicals are stored at and the room temperature and finally, I believe that my investigation has proved that concentration has an affect on the results as well.
Using a measuring meant that my solutions were not as accurate as they could have been, e.g. when calculating 5ml volume in my preliminary results, the 10ml cylinder would have an error of 0.1ml one way or another, calculating as 20% difference, as seen in the formula below:
% Error = 0.1 x100
5.0
