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LAB in Dimensional Analysis, Significant Figures. Last updated May 30, 2017.

Summary

In this lab, students determine both the diameter of one single BB and the length of an oleic acid molecule using simple measurements and volume/surface area relationships.

Grade Level

High school

Objectives

By the end of this lesson, students should be able to

  • use effective measuring techniques.
  • perform calculations using length, area, and volume.
  • use metric conversions.

Chemistry Topics

This lesson supports students’ understanding of

  • Quantitative chemistry
  • Dimensional analysis
  • Significant figures

Time

Teacher Preparation: 1 hour

Lesson: 1 hour

Materials

For each group:

  • Large round tray
  • 3 graduated cylinders (10 cm3, 25 cm3, 50 cm3)
  • 91% isopropyl alcohol
  • small cup oleic acid
  • beakers
  • dropper pipet
  • water
  • baby powder (or lycopodium powder)
  • centimeter ruler
  • BBs
  • petri dish

Safety

  • Always wear safety goggles when working with chemicals in a laboratory setting.
  • Keep isopropyl alcohol away from open flames as it is highly flammable.
  • Students should wash their hands thoroughly before leaving the lab.
  • When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.

Teacher Notes

  • The following links provide resources with information on how to effectively complete this lab:
    From Rob Snyder
    From Tony Zayle
  • This lab can extend to a discussion of environmental oil spills and how they are contained and cleaned up.
  • A 5% solution of oleic acid/ethanol is often used for this lab.

For the Student

Lesson

Purpose

To determine both the diameter of one single BB and the length of an oleic acid molecule using simple measurements and volume/surface area relationships.

Safety

Always wear safety goggles when working with chemicals in a laboratory setting.

Materials

  • Large round tray
  • 3 graduated cylinders (10 cm3, 25 cm3, 50 cm3)
  • 91% isopropyl alcohol
  • small cup oleic acid
  • beakers
  • dropper pipette
  • water
  • baby powder (or lycopodium powder)
  • centimeter ruler
  • BBs
  • petri dish

Procedure

Part I: Determining the diameter of a BB

In this part of the lab, you will calculate an experimental value for the diameter of a BB using surface area and volume relationships.

  1. Pour a layer of BBs into your petri dish. There should be just enough that the BBs are tightly packed without stacking, forming a monolayer.
  2. Measure the surface area of your dish (cylinder) of BBs.
  3. Now pour these BBs into a graduated cylinder, and measure the volume of your BBs.
  4. Use the relationship between volume and area of a cylinder to calculate the diameter of one BB. Express this answer in nanometers.
  5. Now check your results by lining 17 BBs in a row, measuring the length with a ruler, and determining the diameter of one single BB. How does this value compare to the value calculated in question four?

Part II: Determining the length of a molecule of oleic acid

In this part of the lab, you will use the same techniques used in part I to determine the length of one molecule of oleic acid.

  1. Produce a dilute solution of oleic acid by mixing oleic acid with alcohol. (This should be very dilute!) Record the ratio of oleic acid volume to the total volume of the solution.
  2. One drop at a time, drop the solution into a graduated cylinder. Count the number of drops required to reach the one mL mark. Calculate the amount of oleic acid in one mL of the solution and use that value to calculate the amount of oleic acid in one drop of the solution.
  3. Pour water into your petri dish until it is about half full. Sprinkle baby powder or lycopodium powder onto the surface of the water.
  4. Dispense one drop of the dilute oleic acid solution. The alcohol will be absorbed by the powder and the oleic acid will form a monolayer over the top of the powder.
  5. Measure the diameter of the patch of oleic acid. Use this to calculate the surface area of the patch.
  6. Using the known volume of oleic acid (found in step two), determine the thickness of this monolayer. Express your answer in nanometers.
  7. The accepted length of an oleic acid molecule is 1.97 nanometers. How does this compare to your experimental value?