Chemistry Lab Measurement and Uncertainty
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I.PURPOSE OF EXPERIMENT
The purpose of this lab was to determine the magnitude of the uncertainties produced when making measurements using common lab equipment.
II.APPARATUS AND MATERIALS NEEDED
safety goggles
distilled water (at 20oC)
laboratory apron
dropper
laboratory balance
2 objects of unknown mass
standard masses
graduated cylinder, 10-mL
graduated cylinder, 100-mL
III.PROCEDURE
Part A: Estimating the Uncertainty of a Balance
1.We put on lab aprons and goggles. Then, we used the zeroing adjustment to adjust the scale so that it said zero with no mass on it. We then touched the pan, and checked that the balance returned to zero.
2.We determined the mass represented by the smallest increment. We recorded this value, and determined one half and one fifth of this value. We then recorded those values.
3.We found the mass of a standard mass on the balance pan. We recorded the mass as accurately as was allowed by the balance.
4.We moved the smallest counterweight over slightly until there was the slightest deviation from the zero point. We recorded that value. Then, we moved the counterweight in the opposite direction. We recorded that value.
5.We measured and recorded the mass of each of the two objects of unknown mass. We added those values to the class data bank.
Part B: Estimating the Uncertainty of Graduated Cylinders
6.We measured and recorded the mass of a dry 10-mL graduated cylinder and a dry 100-mL graduated cylinder.
7.We recorded the volume of the smallest volume increment on each of the cylinders. We also recorded the volume represented by one half and one fifth of the smallest volume increment.
8.We added 10.0-mL of distilled water to each cylinder using a dropper. We checked to make sure that the bottom curve of the meniscus was on the 10.0-mL mark.
9.We measured and recorded the mass of each cylinder containing 10.0-mL of distilled water. We subtracted the mass of the empty cylinder from the mass of the container containing 10-mL of water. We recorded those values and added them to the class data bank. We poured the water into the sink and returned all equipment to the supply area.
IV.DATA AND OBSERVATIONS
Part A: Laboratory Balance
Smallest mass scale increment
.10 gram
One half of smallest mass scale increment
.05 gram
One fifth of smallest mass scale increment .02 gram
Mass of standard weight
Highest Limit 5.10 grams Lowest Limit 4.90 grams
Mass of Unknown #1
8.09 grams
Mass of Unknown #2
112.85 grams
Part B: Graduated Cylinders
10-mL
100-mL
Smallest volume scale increment .10-mL
1-mL
One half of smallest scale increment .05-mL
.5-mL
Mass of empty cylinder 38.85 grams
118.85 grams
Mass of cylinder with 10.0-mL of water 48.85 grams 128.00 grams
Mass of 10.0-mL of water
10.00 grams
9.15 grams
V.DATA ANALYSIS
Part A: Uncertainty for Laboratory Balance
1.The mass of the standard weight followed by the uncertainty is 5.00g + 0.01g.
2.
Class Data Bank: Mass of Unknown #1
Group
Mass
Group
Mass
8.25 g
8.00 g
8.10 g
8.09 g
8.19 g
8.10 g
8.65 g
8.25 g
Average mass 8.20 g
V. DATA ANALYSIS CONTINUED
Class Data Bank: Mass of Unknown #2
Group
Mass
Group
Mass
111.60 g
112.80 g
106.35 g
112.85 g
113.04 g
111.25 g
111.05 g
110.80 g
111.60g+106.35+113.04g+111.05g+112.80g+112.85g+111.25g+110.80
Average