Precision in Measurement - Finding When an Object Changes Color

Dan Larson, Anoka High School, Anoka, Minnesota
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Summary

This activity is an introduction to measurement. The main idea that students will be asked to learn is precision in measurement. Specifically, the concept that the number of significant figures to use in measuring devices is one more than the markings on the measuring instrument. This means that since the thermometers used in most high school classes are marked to the nearest degree, the measurements should be made to the nearest tenth of a degree. The student's task is to determine at what temperature a temperature dependent, duel-colored object changes color. The students will report the precision, accuracy (margin or error) and confidence level of their results.


Learning Goals

One goal is to have students learn about measurement, especially measuring with correct precision. A second goal is to have the students note their uncertainty in measurement. A third goal is to have them compare their results to other groups so they can gain some understanding of accuracy in measurement. A fourth goal is to have them practice experimental design.

Vocabulary:

-Precision = the number of significant figures in a measurement; Precision is also how close one trial result is to other trial results.
-Accuracy = how close is the result to the correct answer; In this activity the correct answer will be the class average.

The key concepts involve measuring equipment correctly and scientific lab design (an inquiry activity). Noting the difference between precision and accuracy in measurement is one of the main ideas.
The main higher order thinking skills will involve data analysis.
Skills need with include activity design, observations, reading equipment correctly (precisely), and writing a lab report. Students will also need to analyze data.

Context for Use

This activity is an attempt to have students become familiar with issues in measurement (precision and accuracy) and problem solving (they will design the lab activity.).
This activity is for a high school chemistry class of any size, and both the lab and activity will likely last 1 hour.

Materials:
-Mood objects that will change color with temperature change - pencils (American Chemical Society at chemistry.org/earthday) or straws
-Thermometers
-Ice
-Heat source (Bunsen burners or candles)
-Beakers and/or test tubes


No special skills ahead of time although previous lab experience or inquiry activity would be helpful.
This will be used as an introduction to measuring.
This activity could be used as a problem solving or short inquiry activity.

Description and Teaching Materials

This activity is designed to be an introduction to measurement. Many students have difficulty understanding the need to be precise or even what is precision - the number of significant figures/ the degree of uncertainty in the measurement. This activity will also give them experience in problem solving and using inquiry. Students will be given the problem to solve and the materials. They will need to report back to their classmates their results.
The problem to solve: At what temperature does the mood object change color? Also, does it make any difference if it is warming up or cooling down?

Materials:

-Mood object(s) (pencil, straw, etc.) - this object changes color
-Water
-Ice (for cooling)
-Bunsen burner or candle (for heating the water - NOT the mood object)
-Water holders (beakers, test tubes)
-Thermometers

The students will be given the problem and have the materials available. They will need to develop their own experimental design. They will need to record their procedures and data. After finding their conclusions, they will report their results to rest of the class. This should include not only the temperature, or temperature range at which each object changes color, but also their uncertainty.

Teaching Notes and Tips

This activity has not been attempted before. One thing that the author thinks could be an issue is students heating or cooling too quickly to make good measurements. When they report their results, it will be noteworthy if various student groups get similar answers for the same colored temperature changes.
Another issue is students reading the thermometers to an incorrect number of significant figures. One goal of the activity in the end is to have them learn that an instrument should be read to one more decimal point than the markings on the instrument. Since most high school thermometers are marked to the nearest degree, they should be read to the nearest tenth of degree.
The only activity used before with reading thermometers has been each student take one temperature reading of ice water and recording their results on the board. Discussion then followed of their precision (the correct number of significant figures) and accuracy (how close were they to the correct answer of 4 degrees Celsius if the thermometers were on the bottom of unstirred ice water).
The students should NOT heat the mood objects directly. They should be placed in water with the water being heated.

Assessment

The students will write a lab report to be handed in and will also make a brief oral presentation that will show their results that could include precision, accuracy, margin of error, degree of uncertainty, and level of confidence. They will also have to relate their results to other groups' results.

Standards

Grades 9-12; History and Nature of Science; Sub-Strand B - Scientific Inquiry; Standard - The student will design and conduct a scientific investigation.

References and Resources