Name: ___________________________________________
Attendance Number:_____________________
Lab 3: Uncertainty in Measurement
Introductory Information (we will cover more material on this topic in class)
Laboratory measurements are never exact. The uncertainty of a measured quantity
depends on the skill of the researcher and the limitations of the limitations of the
measuring instrument. These two factors determine the accuracy of a measurement.
Accuracy reflects the nearness of a measurement to the actual or accepted value. When
reporting g experimental data, researchers record all digits they are certain of plus one
digit they are uncertain of. These are known as significant figures. The uncertainty of
the measurement too is indicated. This depends on the size of the smallest increment on
the scale of the instrument.
When gathering data to solve a problem, skilled experimenters select instruments that
will produce the desired level of accuracy. Thus, they must know the level of accuracy
possible with calibrated instruments commonly found in laboratories. By studying some
simple laboratory equipment, a better understanding of uncertainty in measurements can
be achieved.
Purpose (no hypothesis is required for this lab)
Examine some calibrated measuring instruments, make some measurements, and record
data. Report data using the correct number of significant figures and scientific notation.
Indicate the uncertainty of the measurements.
Equipment
Laboratory balance
Centimeter ruler #1 (attached in this
packet, rip it out)
Graduated cylinder, 250 mL
Beaker, 100 mL
Centimeter ruler #2 (attached in this
packet, rip it out)
Safety goggles
Materials
Coin
Index card
Water
Safety
Handle glassware with care, especially thermometers and glassware. Always wear safety
goggles when working in the lab.
Removal of your safety goggles before the end of your experiment will result in a 10
point deduction from your lab report for each incident.
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Name: ___________________________________________
Attendance Number:_____________________
Procedure
1. On a new page in your lab notebook, write the title of this lab, today’s date, and the
due date of the lab.
2. Below the title, copy the following chart into your lab notebook:
Measurement
Instrument
Data
Comparison
(include unit)
Mass of Coin
Beam-balance
Bathroom scale
Length of Index
cm ruler #1
Card
cm ruler #2
Volume of 50 mL
100 mL
of water
graduated
Trial 1
cylinder
0g
250 mL beaker
Volume of 50 mL
100 mL
of water
graduated
Trial 2
cylinder
250 mL beaker
Volume of 50 mL
100 mL
of water
graduated
Trial 3
cylinder
250 mL beaker
You will record all measurements in the data table in your lab notebook.
3. Using the balance, measure and record the mass of the coin.
4. Using cm ruler #1, measure and record the length of the piece of the index card.
5. Using cm ruler #2, measure and record the length of the piece of the index card.
6. Using the 250 mL beaker, measure 50 mL of water. Record the volume.
Name: ___________________________________________
Attendance Number:_____________________
7. Carefully transfer this water to the 100 mL graduated cylinder. Record the actual
volume of the water that you measured.
8. Repeat steps 6 and 7 two more times, recording the data each time.
9. Complete the column title comparison in your lab notebook by writing which
instrument gave you a more accurate measurement.
Questions for your Results Section
1. For each measurement, which instrument gave you a more accurate measurement.
2. You did three trials of measuring 50 mL of water. Describe your precision in making
these measurements. You most likely had poor precision, why?
Conclusions Results Section
1. What is the difference between precision and accuracy? (we will go over this in class
before your lab write-up is due)
2. Is a precise measurement always accurate? Explain.
Include these things in your write-up
Introduction
Describe accuracy and precision (we will go over this in class)
Procedure
Describe how you took your measurements.
Results
Show your table and include the answers to the questions above.
Discussion and Conclusion
Provide answers to the questions listed in this handout. You can write the questions
followed by the answers rather than using a paragraph format.
References
You should always reference the lab handout. Give references for any source that you
used (textbook, website, etc.)
Use APA Format, which can be found at:
http://owl.english.purdue.edu/owl/resource/560/10/
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Name: ___________________________________________
Attendance Number:_____________________
Other Suggestions
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Lab reports must be typed using a word processing program.
Neatness counts
Text should use at least 1.5 spacing for paragraphs and single spacing for labels.
Always use spell-check.
Use proper grammar, complete sentences, correct punctuation and capitalization.
The metric system should be used for measurements.
Paragraphs should be divided correctly with headers for the separate sections.
Paragraphs should have starting and ending sentences that indicate the purpose of
the paragraph. A report or a section of the report should not be one long
paragraph.
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