Like any experiment, there were a number of potential errors during the procedure of the experiment. Errors could have arisen as a result of the uncertainties associated with the instruments I used to take measurements, and also as a result of errors associated with the actual method. Of course, due to the limitations of the procedure, they could not be eliminated completely, so I will explain what I did to reduce them to an acceptable level and how I could have improved my method to reduce them even further.
The following table shows the reasons for my choice of equipment in carrying out my method.
100 cm3 burette| I needed to accurately measure out large quantities of hydrogen peroxide (90 cm3 and 150 cm3). The 100 cm3 burette is a precise instrument and would allow me to measure out the hydrogen peroxide by filling it fewer times than I would need to with 50 cm3 burette.| 50 cm3 burette| I needed to repeatedly measure out small volumes of solutions A–I. The burette made the task convenient, and it is a precise instrument. | 250 cm3 volumetric flask| I needed to make up a specific volume of a standard solution. The volumetric flask has a low error.| 100 cm3 volumetric flask| I needed to make up a specific volume of a standard solution. The volumetric flask has a low error.| Top pan balance| I needed to accurately weigh out small amounts of solid when making up my solutions.| 25 cm3 Mohr pipette| I used the pipette to accurately transfer sulfuric acid when making up solutions. I could not do this with a volumetric pipette, as the volume I transferred was 20 cm3.| Distilled water| I used the distilled water to wash out any glassware and storage jars before using them to avoid contamination.| Crushed ice| I used the ice to cool my reactants down to 10 °C.| Water bath| I used the water bath to heat my reactants up to 30 °C, 40 °C and 50 °C. It kept the temperature constant—it does not cool down like hot water in a beaker.| Thermometer| I needed to measure the temperature of the reactants before pouring them into the beaker and stirring them.| Magnetic stirrer| I used the stirrer to ensure the reaction mixture was uniformly mixed. This was necessary to produce sharp colour changes.| Stopwatch| I used the stopwatch to record the times of the colour changes. These are the values I needed to investigate the effect of temperature and concentration on rate.|
These are the errors associated with the equipment I used when weighing out solids, measuring volumes of liquid, recording the temperature of my reactants, and recording the times of the colour changes.
100 cm3 burette| ±0.2 cm3|
50 cm3 burette| ±0.1 cm3|
250 cm3 volumetric flask| ±0.3 cm3|
100 cm3 volumetric flask| ±0.2 cm3|
25 cm3 Mohr pipette| ±0.1 cm3|
Top pan balance| ±0.005 g|
Thermometer| ±0.5 °C|
Stopwatch| ±0.005 s (for instrument), ±0.5 s (for measurements), ±0.05 s (for measurements at 50 °C)|
The stopwatch could record to 2 d.p. but the times I recorded were affected by my reaction time. Recording to 2 d.p. would be pointless, as I could not record that precisely. I decided to record the times to the nearest second, except for my results at 50 °C, where I recorded them to 1 d.p. because of the short duration of time between the colour changes.
Using the measurement errors, I can work out the percentage uncertainties for my measurements. I can do this using the formula:
percentage uncertainty = error / value of measurement x 100%
I made multiple measurements with many of the instruments I used. For these measurements, I will find the uncertainties for three of the values (the highest, the lowest and one close to the average) to give an indication of how the uncertainty changed across the range of measurements I made.