bEAN BAG ISOTOPES:ABUNDANCE AND ATOMIC MASS LAB
By: Catriona Whalley
Partner: Ming Siegel
A new atomic theory, in which all atoms of the same element are identical to one another and equal in mass, was proposed by the scientist Dalton. Although the theory had its flaws and was simple, it was revolutionary. Scientists became able to study the actual structure and mass of atoms after the discovery of radioactivity. Soon, isotopes were discovered, as atoms of the same element which have been built up to have different masses. Purpose
The purpose of this lab is to investigate the mass properties and relative abundance of isotopes for the “bean bag” element (symbol, Bg), and to calculate the atomic mass of this element. Equipment and Materials
Balance centigram (0.01-g precision)
“Bean Bag” element, Symbol Bg, approximately 50 g
4x Weighing dishes or small cups
Marker or pen for labeling
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 Prelab Questions
1. Neutrons were discovered in 1932, more than 10 years after the existence of isotopes was confirmed. What property of electrons and protons led to their discovery? Suggest a possible reason why neutrons were the last of the three classic subatomic particles to be discovered. The property that led to the discovery of electrons and protons was their charges. Neutrons were the last of the three subatomic particles to be discovered because they have no charge and therefore it was harder and took larger for scientists to discover them.
2. Silicon occurs in nature in the form of three isotopes, Si-28, Si-29, and Si-30. Determine the number of protons, neutrons, and electrons in each isotope of silicon. Si-28 has 14 protons, 14 neutrons, and 14 electrons. Si-29 has 14 protons, 15 neutrons, and 14 electrons. Si-30 has 14 protons, 16 neutrons, and 14 electrons. 3. “The atomic mass of chlorine represents the mass of the most common naturally occurring isotope of chlorine.” Decide whether this statement is true or false and explain why.
This statement is false, the atomic mass of chlorine represents the average mass of all the isotopes, and it takes into account the relative abundance of chlorine isotopes. Procedure
1. Sort the atoms in the “bean bag” element sample (Bg) into three isotope groups (1, 2, and 3) according to the type of bean. (Assume that each type of bean represents a different isotope and that each bean represents a separate atom.) 2. Place each isotope group into a separate weighing dish or small cup. 3. Count and record the number of Bg atoms in each isotope group. 4. Measure the total mass of Bg atoms belonging to each isotope group, and record each mass to the nearest 0.01 g in the data table. **Note: Zero the balance with an empty weighing dish on the balance pan, THEN add all of the Bg atoms of one type to the weighing dish and record the mass. (Do this for each isotope group.) Observations and Data
“Bean Bag” Isotope (Bg)
Number of Atoms
Total Mass of Atoms
“Bean Bag” Isotope (Bg)
1. Determine the average mass of each Bg isotope to three significant figures. Enter the results in the Results Table.
(See Data and Observations: Data Table)
2. What is the total number of “bean bag” (Bg) atoms in the original sample? Calculate the percent abundance of each isotope: Divide the number of atoms of each isotope by the total number of atoms and multiply the result by 100. Enter the results to one decimal place in the Results Table.
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