Preliminary experiment:
Before I completed my main investigation, I preformed a preliminary experiment. I completed this experiment to test my method and gather an initial set of set of results. After I successfully completed my preliminary experiment I set out to collect my official set of results. I planned to make this series of tests more accurate so I could therefore collect a more reliable set of data.
Method
- Set up the conical beaker on a laminated cross, and two sets of burettes, one to measure out distilled water, and the other for measuring sodium thiosulphate. The reason I used burettes for my experiment was because they can accurately measure out the right amount needed for the concentration.
- Empty the right amount of sodium thiosulphate (and water if needed) into the conical beaker, using the burettes.
-
Measure out 5ML of hydrochloric acid, using a pipette.
- Start the timer at the same time as you squeeze the Acid into the sodium thiosulphate (and distilled water), then swirl it once, and place the beaker back onto the laminated cross.
- The solution should start to turn cloudy, and stop the timer as soon as you can no longer see the cross underneath the bottom of the beaker.
- Wash the equipment and dry as much as possible, re-measure the sodium thiosulphate and water, and start the experiment again, either repeating the same concentration, or doing another.
Conclusion
When the concentration of the Sodium Thiosulphate decreases by adding water, the time it takes for the Hydrocloric Acid to react increases. The graph shows the time for the concentration 0.02M is considerable above the times for the other higher concentrations.
I collected three sets of results for each concentration, which contained no outliers which needed re-testing. This makes the average times more reliable.
Most of my results were accurate because all of the results seem to show a relatively sensible time, and show to be reasonably the same, apart from the average with the longest error bar, concentration 0.02M. The times ranged from 535.93seconds – 608.70seconds, which gives us a difference of 72.77seconds.
The 0.02M concentration was a lot more inaccurate because a slight error in measurements or equipment would have a greater effect on the results, because the Sodium Thiosulphate has been diluted to a greater extent, reducing the amount of molecules.
Evaluation
We collected three sets of data, enough for a relatively approximate average, with enough time and equipment for a fourth experiment for any outliers. As you can see in the results they were fairly accurate because the fourth column wasn’t needed for any extra data. Most of our results fit a similar pattern, with small error bars, apart from the third experiment on 0.02M, which was based on an unknown error, and it should have probably been repeated. The error could have been caused by a varied surface area or temperature. It could also be based on inaccurate measurements, affecting the concentration levels.
