Significant What?

Prep for Teachers

Prior to teaching this unit, bookmark all sites mentioned above. Take the time to cue your videotape to the first viewing segment. Photocopy all student handouts for distribution as they are needed during the lesson. Cut the rope into the three to four foot segments needed for the Introductory Activity.

Please go through the instructions, as a student would, on the student materials handouts to make certain you are familiar with the format of the lesson prior to class use.

When using media, always provide students with a FOCUS FOR MEDIA INTERACTION, a specific task to complete and/or information to identify during or after the viewing of video segments, Web sites, and/or other multimedia.

The following activities are used to provide your students with a personal link to the subject matter of this unit.

Step 1

Distribute the student handout "It's HOW Big?" along with the lengths of rope and a set of markers to each pair of students.

Step 2

Discuss the historical background of the measurement of one cubit. (Cubits were used in ancient time as the length from the fingertip to elbow of a grown man. References to this measurement are made in many historical documents and in the Bible. For example, Noah's ark was to be 300 X 30 cubits in measure.)

Step 3

Ask the students to mark off the length of 1 to 2 cubits on their ropes. They are to measure the various objects listed on the handouts as accurately as possible using their rope measuring instruments.

Complete the chart on the "It's HOW Big?" handout and the analysis questions. Discuss the answers to the questions with the class and try to determine any problems they encountered with this procedure. Have them record their concerns for future reference.

Step 4

Distribute one Velcro dart game to each group of 4 to 6 students, along with a copy of the handout "Bombs Away" for each student. Have the groups complete the activity as outlined on the handout, and record their results. Discuss the results and ask, "How accurate and precise were your bombing runs? What do we mean by accuracy and precision?" We are now ready to look at a video to see what scientists consider accuracy and precision to be.

Step 1:

Distribute the Focus for Media Interaction Answer Sheet given in the student materials section of this lesson. Insert World of Chemistry, Episode #3: Measurement into your VCR. START the tape immediately after the opening credits for the program. The audio track will be stating, "Measurements are made everywhere..." Provide your students with a FOCUS FOR MEDIA INTERACTION, by asking them to watch the following segment and write down as many different kinds of measurement shown as possible. They must also record the units used.

STOP the tape at the word "MEASUREMENT" written on the screen. The audio track will be stating, "They are all determined by measurement." CHECK your class to see how many they were able to find in the tape. Ask if it was all too fast and would they like another chance to get the information. REWIND the tape to the start of the segment and REPLAY. CHECK again and compare lists among the class with your master list shown here.

Measurement Units Used
Gasoline Liters and gallons
Octane Octane
Air Pressure Pounds per square inch
Electricity Amperes
Wheel alignment Angles in degrees
Ignition voltage Volts
Engine speed Revolutions per minute (RPM)
Specific gravity No units
Spark plug gap Inches or mm
Exhaust particulates Parts per million (PPM)

Provide your students with a FOCUS FOR MEDIA INTERACTION, by asking them to listen for the definition of the term "measurement" and for what all measurements have in common. PLAY the tape through Paula Herron saying, "...a volume to a known volume." The visual will be a green liquid reaching the 70 mL level in a graduated cylinder. PAUSE the tape to CHECK for student comprehension. Discuss the class concept of measurement and how all measurements are alike or different. (A measurement is a comparison of a known to an unknown. All measurements are composed of numbers and units in most cases. The number of digits used for the measurements is different.)

Provide your students with a FOCUS FOR MEDIA INTERACTION, by asking them to find out what the International Standards actually are, and where they are found in the United States. PLAY the tape through the picture of the platinum kilogram mass standard put down on the counter. The audio portion of the tape will be stating that, "All measurements of mass in the United States start with this as a reference point." STOP the tape and discuss what standards the students think would be found in the United States. (The International Standards are found in a sub-basement of the National Institute for Standards and Technology outside Washington, D.C. The United States actually has both English and metric system standards in the reference set.)

Step 2:

Provide your students with a FOCUS FOR MEDIA INTERACTION, by asking them to determine "What is a significant figure and how does it relate to the true measurement?" START the tape and play through the visual of a tablet swaying on the analytical balance. The narrator will be stating, "The more sensitive the balance; the closer we can get to the true value." PAUSE the tape and CHECK for student comprehension. You might wish to TURN THE AUDIO OFF during this segment and let the students infer the answer to the focus prompt from the visuals shown. You can then REWIND and REPLAY the segment through to CHECK for comprehension. (Significant figures are defined as the number of places found on the instrument and one more place value that the student must estimate for themselves. This answer is not specifically given in the tape, but may be inferred from the visuals and commentary. The number of significant figures then relates how close to the students will be able to come to the actual/true measurement of the item.)

Provide your students with a FOCUS FOR MEDIA INTERACTION, by asking them "What must we do when we measure?" PLAY the tape until you see a picture of a boat at sunset and hear the audio, "How do chemists apply their measurement techniques to the world outside?" STOP the tape. (Check to make sure that your students realize that they should calibrate their instruments. This means they are checking the accuracy of the instrument.)

Step 3:

Provide your students with a FOCUS FOR MEDIA INTERACTION, by asking them to determine, "What are the results of mercury poisoning?" FAST FORWARD the tape to the visual of the underwater scene directly following the picture of the U.S. Environmental Protection boat. The audio cue will be, "Other substances are present in only very minute quantities." PLAY the tape through to the visual of a snow-covered cemetery. The audio will be the answer to the focus question, which is given at the end of this paragraph. STOP the tape and CHECK for student comprehension. You might wish to refer your students to the historic case of the fishing community of Minamata and the widespread mercury poisoning that took place there for further research. (The results of mercury poisoning are brain damage, blindness, weakened muscles, and death.)

Provide your students with a FOCUS FOR MEDIA INTERACTION, by asking them to determine, "How does metallic mercury get into the food chain?" PLAY the tape through the visual of water coming out of a chute after the extrusion of paper pulp. The audio cue is, "Some industrial plants had been dumping as much as 100 kilograms of mercury every day." STOP the tape, and discuss the information shown with your class to make sure they understand how the metallic mercury gets into our food chain without actually being eaten in that form. (Bacteria change metallic mercury into methyl mercury, which is water soluble. Since the mercury is now dissolved in the water, water organisms -- fish, shellfish, plants -- all absorb and store varying amounts of the methyl mercury over time. This causes a larger problem.)

Provide your students with a FOCUS FOR MEDIA INTERACTION, by asking them to determine, "What is the USDA safe level for mercury and why is it necessary to keep the level so low?" PLAY the tape through to the visual of the scientist drawing up a sample with a syringe. The audio will be stating, "...in fish tissue." PAUSE the program and discuss the students' answers to CHECK their comprehension. (The USDA safe level for mercury is 0.000001 or 1 ppm, one part per million. Biological concentration in fish tissue causes an increase in overall level as you move up the food chain.)

Provide your students with a FOCUS FOR MEDIA INTERACTION, by asking them to determine, "Why do scientists do at least three measurements and take an average?" START the tape and play through the audio cue, "...there is always a certain amount of error in the measuring procedure and the measuring instrument." STOP the tape at the audio cue given as the picture of the spectrometer is shown alone on the screen. Discuss the students' answers found from the program and compare to the answers shown here. (Scientists do at least three measurements because repeated measurements of the same sample are never the same; there is always a certain amount of error in the measuring procedure and the measuring instrument.)

Provide your students with a FOCUS FOR MEDIA INTERACTION, by asking them to determine, "What is a true value?" (You might want to caution them that hardware store answers will not be accepted.) What does precise mean? What is accuracy? They will need to be able to compare precision and accuracy. PLAY the tape through the audio cue, "A scientist's goal is to find measurements that are both precise and accurate." The video will be of the graph they have been referring to in the segment. STOP the tape and CHECK for comprehension. (The same value found by using different measuring instruments and procedures is accepted as the "true value." Accuracy is the measure of how close the average of your set of measurements comes to the "true value." The precision of your measurements is determined by how closely the measurements are clustered together.)

Allow your students fifteen to twenty minutes to complete the analysis questions for the Introductory Activities they have performed. Discuss their answer to CHECK for comprehension of the terms accuracy and precision.

Step 1:

Have the students break into computer pairs and go on line to the Antoine site for significant figures. They will be completing the site as a pair after you work through the first page together. Provide your students with a FOCUS FOR MEDIA INTERACTION by having the class look at the illustration of the beetle and trying to select the most appropriate measurement value given the ruler scale shown beside it.

Allow the students to select the appropriate radio button but DO NOT CLICK NEXT UNTIL DIRECTED. Check to make sure everyone has made a selection before allowing them to check their answers. Take a few minutes to discuss what they based their answers on, and how they could predict the number of significant figures they should be using with each measuring instrument. (They need to select the answer that contains one more place than the units actually shown on the scale itself. The final digit is the uncertain or estimated portion of their answer.)

Distribute supplies for this activity to each pair of students (chromatography paper strips, four test tubes, water-soluble markers and solvents). Say to students, "We will be using several of the ideas discussed in this lesson to separate the components of various colors, using a technique called chromatography. The word chromatography comes from two ancient roots: 'chroma,' which means color, and 'graph,' which means writing."

Inform students that chromatography is a technique used by scientists to separate the components of mixtures using principles of polarity, surface tension, and capillary rise. The liquid travels up the surface of the paper as it is absorbed. This is why water travels up into a straw even when it is not siphoned or sucked. Different colors have different polarities and will travel along with the water if its polarity is close to that of water. This means that the more polar a dye molecule is, the further it will travel up the surface of the paper.

Provide a FOCUS FOR MEDIA INTERACTION by asking students to revisit the Chromatography of Mr. Sketch Markers Web site (http://science.csustan.edu/tutorial/color) to better understand this technique. Scroll down the page to the heading "Chromatographic Separation of Black Ink." Duplicate the start point of the experiment by placing a pencil dot on the paper strips about 1-2 cm above the bottom of the strip. Use one of the hypothesized mixture markers to place an ink dot sample directly on the starting point indicated by the pencil dot. Get a small amount of each of the polar solvents as demonstrated by the "wax paper" experiment. (Those substances that have properties similar to water should have been identified.) Add the first solvent (water) to the test tube so that the level of the liquid in the test tube will be beneath the level of the sample spot to be tested. Gently stand the paper strip in the test tube. Allow the liquid to travel up the surface of the strip until the colors travel with the liquid. (The liquid in the test tube is called the solvent because it dissolves the sample and is available in a relatively large amount. The solvent is part of what is known as the mobile phase in chromatographic terms, because it is actually moving.)

Once the liquid continues to travel above the level of the separated colors, the experiment is complete. Repeat the activity using a different solvent (vinegar, alcohol, and dilute alcohol). Sketch diagrams of experiment results on the Color Analysis Sheet similar to those included on the Chromatography Web site. Compare chromatograms to expected hypothesis. Write an explanation of the results on the Color Analysis Sheet.

Step 2:

Allow the students to work through the significant figures site at their own rate. Upon completion, they are to go to the Significant Figures Quiz site and take the quiz individually. They will receive an assessment of their quiz scores that they must print out to be used as an assessment/quiz on the material covered.

CHEMISTRY
Set up several stations in your room with lab procedure handouts that do not specify size or calibration of measuring instruments. Have the students read the procedures and select the appropriate glassware and measuring instruments to be used for each station. They should record their selections on the answer sheet provided. This serves as a pre-lab test of the student knowledge of lab procedures and usage.

ART
Have your students investigate the effect of different degrees of precision in the measurement of pigments to create a blended paint color. Give them a swatch of paint to match and the specific measurements of pigments to be used. Have them mix a small sample of the paint and then evaluate how close they came to the original color to be created. They must address what factors may have influenced their results in their final report.

Have the students visit this Web site to investigate the same type of pigment problem shown above:

http://mc2.cchem.berkeley.edu/Java/RGB/example1.html

• Have your students find the various utility meters for their household. They are to record the units and the number of places found on each meter. Have the class get a copy of their last utility bill for each meter they checked. What units and number of significant digits are shown on the bill? Are they the same? Why or why not? Do you pay for the actual "true value" of the utility used or an estimate? Why are periodic adjustments made to your bill?

• Have the students go to the local supermarket and select one item from the produce department that is paid for by weight. Have them calculate the cost of the object using the hanging pan scale present in the department. Record their data. At the checkout counter, have the students record the weight given on the electronic balance used by the checker. What is the cost of the item? How do the two measurements and costs compare? What is the significance of the number of digits (precision) of the scales?