LAB 2

CHM138

Lab 2

Measurements: Accuracy and Precision

Name:

Data Tables

Place your completed data tables into your report here:

Data Table 1
Measuring Instrument
Decimal Known With Certainty
Decimal Estimated
Ruler
Tenths
Hundredths
Thermometer
Tenths
Hundredths
10mL graduated cylinder
Tenths
Hundredths
50mL graduated cylinder
Tenths
Hundredths
100mL graduated cylinder
Tenths
Hundredths

Data Table 2
Measurement
Data
Length of aluminum plastic packet
5.1cm
Height of aluminum plastic packet
6.5cm
Temperature of faucet water
21 degrees C
Temperature of ice water
9 degrees C
Volume of water in 10mL graduated cylinder
6.6mL
Volume of water in 50mL graduated cylinder
7.1mL

Data Table 3 (8 pts.)
Measurement
Data
Inside diameter of 50mL graduated cylinder
2.6cm
Height of 50mL graduated cylinder
9.9cm
Water temperature
23 degrees C
Initial volume of water in 50mL graduated cylinder
10.2mL
Mass of water in the 50mL graduated cylinder (remember, 1 g of water weights 1mL since its density is 1 g/mL)
10.2g
Volume of water and aluminum shot in 50mL graduated cylinder
18.3mL
Mass of aluminum shot (given on outside of packet)
20.07g

B. Follow-Up Questions (Show all calculations)

Part I (Each question is worth 8 pts.)

1. If two experimenters carried out the same measurements, would their measurements be identical? Why or why not?
If two experimenters carried out the same measurements, their measurements would not be identical. This is due to estimating the decimal in the hundredths. The experimenters may agree with the measurement to the tenths place but estimate on their own and may not agree on the hundredths digit.
2. Which graduated cylinder is capable of the greatest precision? Explain. Is the most precise graduated cylinder likely to be the most accurate as well? Why or why not?
The 10mL graduated cylinder is capable of the greatest precision. Using this cylinder allows the experimenter to estimate to the hundredths place. Accuracy refers to how closely a measurement agrees with the “true” value. The most precise graduated cylinder isn’t likely to be the most accurate as well because it could consistently give readings that are 0.4mL less than the actual volume, the measurements may be precise but not accurate.

Part II (Each question is worth 10 pts.)

3. 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.
10mm=1cm
Length of Aluminum Plastic Packet
5.1cm (10mm/1cm) = 51mm
Height of Aluminum Plastic Packet
6.5cm (10mm/1cm) = 65mm
4. 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.
Temperature of Faucet Water oF = 1.8(21oC) + 32 = 69.8oF
Temperature of Ice Water oF = 1.8(9oC) + 32 = 48.2oF
5. 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-mL Graduated Cylinder
6.6 mL * 1L/1000ml = 0.0066 L
50-mL Graduated Cyliner
7 mL * 1L/1000mL = 0.007 L
6. 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.
My measurements for the volumes of water in the 10mL and 50mL graduated cylinders are not identical. One of the reasons my values are not identical is because of my estimates – they were different for each graduated cylinder. Another reason is due to the fact that the 10mL graduated cylinder is much more precise than the 50mL graduated cylinder.

Part III (Questions 8-14 are worth 9 pts each.)

7. 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. 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:
V = 3.14(1.3) 2h
V = 3.14(1.69)(9.9)
V =52.54mL
|Percent Error = accepted value - experimental value| x 100 accepted value
Percent Error = |50.00 – 52.54/50.00| x 100
Percent Error = 5.08%
8. Calculate the mass of 10ml of water in the graduated cylinder using 1/5 the volume calculated in #7 above and the density of water of 1.00 g/mL. Calculate the mass of the water using the formula for density:
1g/mL = mass/10.51
Mass = 10.51g/mL
Density = mass volume

9. Using 10.0 g as the accepted value for the mass of the water, and the mass calculated using water's density in #8 above as the experimental value, calculate the percent error of your mass calculation, using the same formula as in #7 above.
Percent Error = |10.0g – 10.51 / 10| X 100
Percent Error = 5.1%
10. Calculate the volume of aluminum shot added to the graduated cylinder, using the following formula: (Volume of water + Al) - initial volume of water = volume of Al shot
Volume = 18-10=8mL
Volume = 8mL
11. Calculate the experimental value for density of the aluminum shot based on its mass (given on the outside of the packet) as well as its volume calculated in #7 above, using the following formula: Density of Al = mass of Al shot/ volume of Al shot
Density of Al = 20.07/8mL
= 2.51g/mL
12. 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 #7 above.
Percent Error = |2.70 – 2.51 / 2.70| X 100
Percent Error = 7.04%
13. What were the potential sources of error in this experiment? Why is it necessary to know the error of one's measurements? Suggest some ways of minimizing error, if you were to repeat the experiment.
The instrument I used to measure is a potential source of error in this experiment. Also, the measurement I recorded is another potential source of error. It is necessary to know the error of one’s measurements because it could affect the whole experiment. A way to minimize error is to measure your results twice. You could also compare the values you record from two different instruments of measure, such as a ruler, to see if they would be the same value.

Part IV

14. Provide your value for the weight of the Earth (in scientific notation) along with the citation. Then, show both conversions you chose to complete for this value. Show all work for your conversions. (15 pts.)
6.00 x 1024
Resource: http://science.howstuffworks.com/environmental/earth/geophysics/planet-earth-weigh.htm
Weight of the Earth 6,000,000, 000,000,000,000,000,000 kg
6.00 X 1024
15. Provide your value for the volume of the Atlantic Ocean (in scientific notation) along with the citation. Then, show both conversions you chose to complete for this value. Show all work for your conversions. (15 pts.)
3.10 X 108
Resource: http://www.ngdc.noaa.gov/mgg/global/etopo1_ocean_volumes.html
Volume of Atlantic Ocean is 310, 410, 900 km3
3.10 X 108
16. Provide your value for the weight of an African Elephant (in scientific notation) along with the citation. Then, show both conversions you chose to complete for this value. Show all work for your conversions. (15 pts.)
6.35 X 103
Resource: http://animals.nationalgeographic.com/animals/mammals/african-elephant/
2,268 to 6,350 kg
Using the maximum weight of the elephant:
6.35 X 103
17. Provide your value for the temperature of the Sun (in scientific notation) along with the citation. Then, show both conversions you chose to complete for this value. Show all work for your conversions. (12 pts.)
1.50 X 107
Resource: http://planetfacts.org/temperature-of-the-sun/
15,000,000° Celsius (center of the Sun)
18. Explain why the use of scientific notation in chemistry is very important. (12 pts.)
Chemistry uses numbers that are very small or large. In the case that a scientist is measuring something very small such as the width of a human hair, it is more convenient to write the number in scientific notation. The importance of the scientific notation is immeasurable as it saves time and makes very small or large numbers look a lot simpler.
19. Give an example of a time when you have used unit conversions in everyday life, and explain why that knowledge is useful. (12 pts.)
I like to experiment in the kitchen and cook new recipes often. One time one of the recipes I was using involved heating the stove to a certain degree in Celsius. I had to convert this to Fahrenheit so I knew what to heat my oven to so I could cook the food properly. To have the knowledge of making conversions in everyday life is so useful so we can understand different measurements used in other areas of the world. Since other parts of the world use different measurements than us in the U.S. we can easily convert it to what we’re familiar with. Also, it comes in handy like in my example in cooking.