a. Calculate the standard deviation in the measured mass of the empty stopperred flask (see Appendix: Mistakes, Errors, Accuracy, and Precision). b. Determine the number of significant figures in the mean measured mass of the flask that is allowed by the precision of the mass measurement (see Appendix: Mistakes, Errors, Accuracy, and Precision). Give the mean mass with the correct number of significant figures. c. How does this result compare with the claimed precision of your balance? d. What, if anything, can you claim about the accuracy of the mean mass?
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2. Make buoyancy corrections for the weights in part 1 to determine the real mass of each sample of water. Use the buoyancy correction equation, assuming the balance weights have a density of 8.0 g/mL. Use the density of water determined from the appendix (the temperature is 22°C). The Density of Water at 22 degrees Celsius is 0.9977735 (g/mL).
1. Using a 25-mL volumetric transfer pipet, pipet 25 mL of DI water into a dry, pre-weighed, conical flask or a beaker and weigh the sample. Use an analytical balance (± 0.0001 g) to make these weighings. Read and carefully follow the "Analytical Balance" instructions. Repeat 3 times. Calculate the average value of your measurements and the standard deviation.
Wvac = Wair + Wair [(0.0012/Do)-(0.0012/Dw)]
Wvac = weight in vacuum, g; Wair = weight in air, g
Do = density of object; Dw = density of weights
0.0012 = density of air
This table shows the results of the 25 mL transfer:
25-mL Trial # | Mass of flask (without water) | Mass of flask (with water) | Mass of the water (Difference in masses) |
1 | 48.0485 g | 72.6685 g | 24.6200 g |
2 | 51.5100 g | 76.2950 g | 24.7850 g |
3 | 55.2756 g | 80.1296 g | 24.8540 g |
Average value: 24.5730 g
Standard Deviation: 0.0981733 g
This table shows the results of the 10 mL transfer:
10-mL Trial # | Mass of flask (without water) | Mass of flask (with water) | Mass of the water (Difference in masses) |
1 | 48.0167 g | 57.9463 g | 9.9295 g |
2 | 52.0842 g | 62.0142 g | 9.9300 g |
3 | 55.2745 g | 65.2300 g | 9.9555 g |
Average Value: 9.9383 g
Standard Deviation: 0.12140 g (five significant figures within the mass of water).