The Life and Times of Percy Julian

For Teachers

Activity 3B (Lab Activity)
Repeating Experiments

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Lesson Overview In this lab activity, students are required to write a procedure to be followed in a simple lab process and record the results they get from following that procedure. They then exchange procedures with another lab group, which will have written a procedure for a different process, and both groups try to follow their “new” procedure. Then they compare results.
Learning Objectives

Students will:

  1. Learn how to design a procedure for a simple lab process.
  2. Learn the importance of carefully recording procedures in the lab and the importance of recording data carefully.
  3. Understand that replicating the work of other scientists traditionally has been and continues to be important in chemistry and all the sciences.
Lesson Concepts

The primary concept in this activity is the idea that in science it is important that the work of any scientist can be replicated with the same results. New skills and techniques can also be learned through the duplication of another scientist’s work. In addition, science concepts may also be accrued. Your students should be familiar with the concepts of volume and density in this activity.

  1. You will need to divide your class in half so that an equal number of groups will carry out Process A (Finding the Volume of a Solid) as will carry out Process B (Finding the Density of a Solid). This is required so that when the groups swap procedures, each group will be following a procedure for a process different from the one for which they wrote a procedure.
  2. For the purposes of this lab, you could use any two processes (besides finding volume and density) that your students might be able to handle in the lab, as long as the two alternative processes will require about the same length of time to carry out. For example, the processes might focus on how to determine if a substance is soluble in water. In this case, half the class could be given a water-soluble substance and the other half an insoluble substance (or one half the class a solid and the other half a liquid). With this in mind, this lab could be incorporated into many areas of an existing curriculum.
  3. In the activity as written, Process B requires all of the steps in Process A, plus taking two additional measurements (weighing the sand and cylinder together and weighing the cylinder alone), as well as doing two additional calculations. This will take Process B groups longer to complete their activity than Process A groups. You might want to select more able lab groups to do Process B so that groups finish at almost the same time.
  4. The samples of sand (with air) should have the same dry volume (e.g., 50 mL). This makes the comparison of results easier at the end of the activity.
Materials Required

Per Lab Group:
The list of materials required for this activity is tentative, depending on the procedures created by the students. You should discuss with the class that their procedures should require only standard lab equipment or readily available materials.

Process A: Finding the Volume of a Solid

Process B: Finding the Density of a Solid

*Note: Whichever type of sample you choose, sand or small pebbles, be sure to use the same material for both processes. For example, do not use sand for process A and pebbles for process B.

Skills Required Lab measurement skills, ability to work with standard lab equipment, organizational skills, and writing skills.
Time Required Two class periods.
Safety Students should wear safety goggles.
Student Ability Level and Grouping Assign lab groups in a manner typical for your class.
  1. Use the background on Percy Julian’s duplicating the work of Ernst Späth to introduce the idea that one of the characteristics of a successful first-time science research experiment is that other scientists are able to reproduce the experiment’s results. You might also note that many experiments that are done in science classes are those in which the outcome is already known, but they are often done so that students can learn standard scientific methods and specific science concepts.
  2. Review, if necessary, the concepts of volume and density, but do not describe specifically the methods of measurement that students will be using in this lab.
  3. Be sure students understand the two phases of this activity—the first phase, in which their group writes a procedure for others to follow; and the second phase, in which they follow another group’s procedure for a different process.
Procedure Notes
  1. As the students work, monitor their procedures. Since the processes assigned and the actual procedures they come up with are not the main objective of this activity, assist groups as needed in finding a useful procedure. If volume and density have already been covered in the course, this activity will be a good review.
  2. As procedures are submitted to you at the end of the first phase, have pairs of groups exchange procedures (each pair should consist of one Process A group and one Process B group). Remind students that they may not talk to the group who wrote the procedure they have been given to follow.
  3. It is important that you discuss with the class the reason for this activity. Explain that one of the essential features of scientific activity is reproducibility. If a new discovery or process is formulated by a scientist, he or she publishes the new procedure. Other scientists should be able to follow that new procedure and get the original results. That is the setting for this activity. It might be equally important to stress to the class the importance of writing their procedures carefully and recording results accurately. Both of these are also traits of good scientists and good science.
Post-lab Discuss, as a class, generic problems encountered and how to avoid them in the future.
Assessment Collect from each student the results of step 10 in the student procedure, which they should record on the Post-lab Discussion Report Sheet.

This activity meets the following National Science Education Standards (Grades 5-8) and Curriculum Standards for Social Studies.

National Science Education Standards (Grades 5-8)

Science as Inquiry

  • Abilities necessary to do scientific inquiry
  • Understandings about scientific inquiry

Physical Science

  • Properties and changes of properties in matter

History and Nature of Science

  • Nature of science
  • History of science

Curriculum Standards for Social Studies

  • None

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