Equipment needed:
- 1 pair of goggles
- 1 stopwatch
- 2 measuring cylinders
- 2 conical flasks
- 1 beaker
- 1 pipette
- 1 “X”
- 1 water bath
- 1 thermometer
I have planned to change one thing in my sodium thiosulphate and hydrochloric acid experiment and that is the temperature. Some of the important things that are going to be kept the same are the measurements of chemicals and the "X" because the pressure used to draw the “X” may be effected. I will observe the solution turning cloudy until the “X” disappears and the time taken for this to happen at varied temperatures.
Method:
5cm3 of hydrochloric acid, 10cm3 of sodium thiosulphate and 40cm3 of distilled water are poured into three measuring cylinders and the pipettes are used to get precise measurements. The distilled water and sodium thiosulphate is then poured into two conical flasks. These are then place into the water bath until they are the required heat. This can be achieved by using the thermometer. Whilst these are being heated up the hydrochloric acid is pour into the beaker at room temperature. This beaker should have a piece of paper with an “X” on the bottom of it. When the chemicals are all at the required heat they are poured into the same beaker as the hydrochloric acid. The stopwatch is then started and the measurements are taken. The entire procedure is then repeated three times for each temperature.
Because I will repeat the experiment three times this means I will find the mean average to improve the credibility of the findings. The repeat results will help to get rid of any unusual results to make the accurate summary. However if one set of results is entirely different to another, a fourth experiment will be performed.
Preliminary Experiment:
I decided which temperatures to use during my preliminary series of experiments:
- These are the measurements I used:
- 2.5cm3 hydrochloric acid
- 5cm3 sodium thiosulphate
- 20cm3 distilled water
- 20-70 degrees Celsius temperature (all these going up in steps of 10)
my preliminary work showed that any temperature under 20 degrees Celsius reacted too slowly and 80 to 90 degrees Celsius reacted too quickly to be worth including in my final results.
Results:
Accurate Calculations:
I have used a calculations to clearly obtain the averages needed to plot on my graph. I rounded each of my averages to 2dp to achieve a second and “mille” second recording. This makes my results more accurate and reliable. I may have been able to make my results more accurate by using a burette to measure out the sodium thiosulphate and hydrochloric acid in a very précis manner.
Conclusion:
From the experiment I carried out I have found that as the temperature is increased the time taken for the reaction to take place decreases. The time taken for the reaction to take place decreased by roughly 20-30 seconds for every 10 increase in temperature. This therefore proves my prediction to be correct. There is a clear trend in my results as stated above. This is also made clear in my graph as there is a curve that shows the declining time taken for each reaction. Using this graph I can draw a conclusion from my experiment. Firstly I can see that the graph has a negative correlation and a steep gradient meaning the reaction rate was very rapid. This is because when the temperature is increased the particles will have more energy and move faster. Therefore they will collide more often and with more energy. Particles with more energy are move likely to overcome the activation energy barrier to reaction and thus react successfully. My results support my prediction.
Evaluation:
I managed to achieve the results that I excepted to. I believe that my result was as accurate as I could make them using the equipment available. I made my averages using a scientific calculator and I used a pipette to measure the chemicals correctly. I tried to eliminate any odd results by repeating the experiment 3 times for each temperature. My method was very easy to follow. The only thing that I would possibly change would be my way in which to measure the cloudiness of the solution. This may have been achieved using a light metre to test how light was showing through the bottom of the glass beaker. I think that my data is very reliable. It is reliable enough to support my conclusion, as there are very few anomalies. I could have provided more evidence by expanding my experiments and testing a larger amount of variables. I have noticed that my result at 20 degrees is not as accurate as it could be because it is furthest away from that line of best fit. I studied my results table and realised that the was a big difference between the highest and lowest of the three recordings. The difference was 7.07 secs. This could have been improved by going back and retesting and taking down more results.