CHM130LL
Lab 2
Measurements: Accuracy and Precision
Name : _____________________________
A. Data Tables
Data Table 1 (12 points)
Measurement
Data
(1) Length of aluminum plastic packet
(2) Height of aluminum plastic packet
(3) Temperature of faucet water
(3) Temperature of ice water
(5) Volume of water in 10-mL graduated cylinder
(6) Volume of water in 50-mL graduated cylinder
Data Table 2 (10 points)
Measurement
Data
(1) Inside diameter of 50-mL graduated cylinder
(2) Height of 50-mL graduated cylinder
(3) Water temperature
(4) Initial volume of water in 50-mL graduated cylinder
10.0 mL
(5) Mass of water in the 50-mL graduated cylinder
10.0 g
(6) Volume of water and aluminum shot in 50-mL graduated cylinder
(7) Mass of aluminum shot (given on outside of packet)
B. Insert the picture of the plastic packet containing aluminum shots with student’s name and MEID (25 points)
C. Follow-Up Questions (Show all calculations for full credits)
Part I
1. Convert the length and height measurements for the packet that contains the aluminum shot from units of cm to units of mm using the unit-factor method. (10 points)
2. Convert the temperature measurements for the faucet water and the ice water from oC to oF, using the following equation: oF = 1.8(oC) + 32. (10 points)
3. Convert the volumes of the water in the 10-mL and 50-mL graduated cylinders from mL to L, using the unit-factor method. (10 points)
4. Looking at your measurements for the volumes of water in the 10-mL and 50-mL graduated cylinders, are your values identical? Discuss at least two reasons why the measurements were not identical. (5 points)
Part II
5. Calculate the volume of the 50mL graduated cylinder using your measurements of diameter and height, using the formula V = πr2h (r=½ diameter). This is your experimental value. (10 points)
6. Assuming the accepted value of the volume of the graduated cylinder is 50.00 mL, calculate the percent error of your volume calculation, using the following formula and the experimental value calculated in question 5: (10 points)
Percent Error
=
|
accepted value – experimental value accepted value
|
x
100
7. Calculate the mass of 10ml of water in the graduated cylinder using 1/5 the volume calculated in question 5, the density of water of 1.00 g/mL and this given the formula: (10 points)
Density
=
mass
volume
8. Using 10.0 g as the accepted value for the mass of the water, and the mass calculated in #7 above as the experimental value, calculate the percent error of your mass calculation, using the same formula as in #6 above. (10 points)
9. Calculate the volume of aluminum shot added to the graduated cylinder, using the information from Data Table 2 in the following formula: (10 points)
Volume of water and aluminum shot in 50-mL graduated cylinder(#6) – Initial volume of water in 50-mL graduated cylinder (#4) = volume of aluminum shot
10. Calculate the experimental value for density of the aluminum shot based on its mass (given on the outside of the packet) and its volume calculated in #9 above, using the following formula: (10 points)
Density of Al
=
mass of Al shot
volume of Al shot
11. If the accepted value for the density of aluminum is 2.70 g/mL, calculate the percent error of your density calculation, using the formula listed in #6 above. (10 points)
12. List at least 2 potential sources of error in this experiment? (6 points) Why is it necessary to know the error of one’s measurements? (4 points)
13. Suggest at least three ways to minimize error, if you were to repeat the experiment. (9 points)
Part III
14. Use the weight of an elephant (as given in Part III of the lab procedure) in scientific notation to complete two unit conversions, from lbs to kg and from kg to mg. Show all work for your conversions. (10 points)
15. Explain why the use of scientific notation in chemistry is very important. Give an example for justification your answer (10 points)
16. Give an example of a time when you have used unit conversions in everyday life, and explain why that knowledge is useful. (9 points)
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