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 gogglesdistilled water (at 20°C)
laboratory aprondropper
laboratory balance2 objects of unknown mass
standard massesgraduated 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 #18.09 grams

Mass of Unknown #2112.85 grams

Part B: Graduated Cylinders10-mL100-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 water10.00 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
1
8.25 g
5
8.00 g
2
8.10 g
6
8.09 g
3
8.19 g
7
8.10 g
4
8.65 g
8
8.25 g
8.25g+8.10g+8.19g+8.65g+8.00g+8.09g+8.10g+8.25g =
8

Average mass 8.20 g
V. DATA ANALYSIS CONTINUED

Class Data Bank: Mass of Unknown #2
Group
Mass
Group
Mass
1
111.60 g
5
112.80 g
2
106.35 g
6
112.85 g
3
113.04 g
7
111.25 g
4
111.05 g
8
110.80 g
111.60g+106.35+113.04g+111.05g+112.80g+112.85g+111.25g+110.80 8

Average mass 111.22 g

3a Found the deviation in the mass measurements by computing the absolute value of the difference between average mass value and each of the mass measurements in the data list for Question 2.

Deviation from Average Mass of...
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