Publication No. 13963
“Bean Bag” Isotopes
Student Activity Kit
Materials Included In Kit
Kidney beans, 12 oz
Lima beans, 20 oz
Navy beans, 4 oz
Weighing dishes or small cups, 60
Zipper-lock bags, 15
Additional Materials Required
Balances, centigram (0.01-g precision), 3
“Bean bag” (Bg) isotopes: (See Preparation section)
Labeling pens or markers, 15
“Bean bag” isotopes may be mixed in any proportion to prepare samples for analysis. The mixtures analyzed in the Sample Data section were prepared by mixing navy beans, kidney beans and lima beans in the following proportion: 100 g navy beans, 280 g kidney beans and 500 g lima beans (Note: 1 oz = 28.35 g). The mixture (880 g total mass) was shaken in a large zipper- lock bag to mix the “isotopes” and divided into fifteen 50-g samples for student use. The samples are obviously not homogeneous— do not expect different student groups to obtain identical results for the percent abundance of each isotope. The percent abundance for the samples analyzed ranged from 22–28% for navy beans, 36–41% for kidney beans and 33–38% for lima beans.
Although the materials used in this activity are considered nonhazardous, please observe all normal laboratory safety guidelines. The food-grade items that have been brought into the lab are considered laboratory chemicals and are for lab use only. Do not taste or ingest any materials in the chemistry laboratory. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory.
None required. Save the “bean bag” samples for repeat use. The beans may begin to chip or break after repeated use. Discard any beans that are broken or otherwise very different from others.
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering PracticesDeveloping and using models
Planning and carrying out investigations
Analyzing and interpreting data
Using mathematics and computational thinking
Disciplinary Core IdeasMS-PS1.A: Structure and Properties of Matter
HS-PS1.A: Structure and Properties of Matter
Crosscutting ConceptsScale, proportion, and quantity
Systems and system models
MS-PS1-1: Develop models to describe the atomic composition of simple molecules and extended structures.
Answers to Prelab Questions
*The data for two trials are shown in order to demonstrate the range of results that might be obtained in a typical classroom setting.Results Table
Answers to Questions
This activity is from Flinn ChemTopic™ Labs, Volume 3, Atomic and Electron Structure; Cesa, I., Ed., Flinn Scientific: Batavia, IL.
“Bean Bag” Isotopes
At the beginning of the 19th century, John Dalton proposed his new atomic theory—all atoms of the same element are identical and equal in mass. It was a simple yet revolutionary theory. It was also not quite right. The discovery of radioactivity in the 20th century made it possible to study the actual structure and mass of atoms. Gradually, evidence was obtained that atoms of the same element could have different masses. These atoms were called isotopes. How are isotopes different from one another? What is the relationship between the atomic mass of an element and the mass of each isotope?
Two experiments in the early 20th century suggested the possible existence of isotopes. The first was work by J. J. Thomson with positively charged atoms in gas discharge tubes. When the positively charged atoms were bent by electric and magnetic fields and then allowed to strike a photographic film, they left curved “spots” on the film at an angle that depended on the mass and charge of the atoms. In 1912, Thomson found that when the gas in the tube was neon, he obtained two curves or spots. The major spot corresponded to neon atoms with a mass of about 20 atomic mass units (amu). There was also a much fainter spot, however, corresponding to atoms with a mass of about 22 amu.
The purpose of this experiment is to investigate the mass and relative abundance of isotopes for the “bean bag” element (symbol, Bg) and to calculate the atomic mass of this element.
Balance, centigram (0.01-g precision)
“Bean bag” element, symbol Bg, approximately 50 g
Labeling pen or marker
Weighing dishes or small cups, 4
Although the materials used in this activity are considered nonhazardous, please observe all normal laboratory safety guidelines. The food-grade items that have been brought into the lab are considered laboratory chemicals and are for lab use only. Do not taste or ingest any materials in the chemistry laboratory. Wash hands thoroughly with soap and water before leaving the laboratory.
Student Worksheet PDF