01.07 Accuracy And Precision.docx

01.07 Accuracy and Precision: Balance Lab Worksheet Before You Begin: You may either copy and paste this document into a word processing program of your choice or print this page. Procedure Access the virtual lab and complete the experiments. Data 

Below is the table that you will complete for the virtual lab. Either type your results into this table or print the table from the virtual lab (it must be submitted to receive full credit for this assignment.)

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To print from the virtual lab:

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1. Be sure the data table is viewable. 2. Right-click (PC) or Command-Click (Mac) on the table and select print. Part I: Density of Unknown Liquid Trial 1

Trial 2

Trial 3

Mass of empty 10 mL graduated cylinder (grams)

25.31

25.39

26.03

Volume of liquid (milliliters)

8.12

8.26

8.52

Mass of graduated cylinder and liquid (grams)

35.46

36.01

36.41

Mass of solid (grams)

42.313

40.65

40.959

Volume of water (milliliters)

48.92

50.03

50.05

Volume of water and solid (milliliters)

53.91

55.04

55.05

25.95

27.62

25.67

Part II: Density of Irregular-Shaped Solid

Part III: Density of Regular-Shaped Solid Mass of solid (grams)

Length of solid (centimeters)

5.250

5.0

4.50

Width of solid (centimeters)

3.0

4.0

3.50

Height of solid (centimeters)

2.50

3.0

2.0

Calculations Show all of your work for each of the following calculations and be careful to follow significant figure rules in each calculation. Part I: Density of Unknown Liquid 1. Calculate the mass of the liquid for each trial. (Subtract the mass of the empty graduated cylinder from the mass of the graduated cylinder with liquid.) o

Trial 1 35.46 – 25.3 = 10.16

o

Trial 2 36.01 – 25.39 = 10.62

o

Trial 3 36.41 – 26.03 = 10.38

2. Calculate the density of the unknown liquid for each trial. (Divide the mass of the liquid calculated above by the volume of the liquid.) o

Trial 1: 53.91 – 48.92 = 4.991

o

Trial 2: 55.0 – 50.0 = 5.01

o

Trial 3: 55.05 – 50.05 = 5.001

Part II: Density of Irregular-Shaped Solid 1. Calculate the volume of the irregular-shaped solid for each trial. (Subtract the volume of the water from the total volume of the water and solid.) o

Trial 1: 53.91 – 48.92 = 4.991

o

Trial 2: 55.0 – 50.0 = 5.01

o

Trial 3: 55.05 – 50.05 = 5.001

2. Calculate the density of the irregular-shaped solid for each trial. (Divide the mass of the solid by the volume of the solid calculated above.) 3. o

Trial 1: 42.313 / 4.991 = 8.4626

o

Trial 2: 40.65 / 5.01 = 8.130

o

Trial 3: 40.959 / 5.00 = 8.2746

Part III: Density of Regular-Shaped Solid 1. Calculate the volume of the regular-shaped solid for each trial. (Multiply the length × width × height for each trial to get the volume in the unit cm3.) o

Trial 1: 5.250 x 3.0 x 2.50 = 39.40

o

Trial 2: 5.0 x 4.0 x 3.0 = 60

o

Trial 3: 4.50 x 3.50 x 2.0 = 32.0

2. Calculate the density of the regular-shaped solid for each trial. (Divide the mass of the solid by the volume calculated above.) 3. o

Trial 1: 25.95 / 39.40 = 0.659

o

Trial 2: 27.6 / 60 = 0.46

o

Trial 3: 25.6 / 32.0 = 0.80

Questions and Conclusions: 1. How would you determine the proper number of significant figures of a liquid using a graduated cylinder? (See practice interactive in "Activity" tab of lesson.) Ascertain as much from the nearest possible increment on the graduated cylinder the unknown variable.

2. Can just one measurement be considered precise? Can just one measurement be considered accurate? Explain your answers completely. Only one measurement cannot be precise, as it would be unable to compare it to other measurements, as there would be none. Accuracy is attainable for just one measurement, so long as it near enough to the accepted value. 3. In Parts II and III of the lab you used different sized objects in each trial. Compare the density values that you calculated for these items; how do the three trials compare? The trails have both accuracy and precision. The densities were constantly with less than one point of value difference.

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