NATIONAL CENTER FOR CASE STUDY TEACHING IN SCIENCE
Is It a Meteorite?
Applying Problem-Solving Strategy to Mass Spectra and Atomic Mass
by
Maryuri Roca
Chemistry Department
Skidmore College, Saratoga Springs, NY
Part I – Introduction
Some years ago, a Missouri farmer found a rare meteorite. The news media went crazy announcing the discovery when
the meteorite was appraised for more than three million dollars. Since then, Dan was obsessed with finding a rock
from space to change his life.
“I’ll help you with that once I get rich,” was Dan’s declaration to anyone in need, no matter if they were friend or
strange to him. Dan was a selfless old man who had encountered many adversities during his life; he had gone down
many times, but he had never lost his faith. Yes, Dan was a dreamer, but somehow he was certain that a shooting star
was going to change his luck.
Tracy, who had known Dan for many years, was keenly aware of his friend’s naïveté, and it was Tracy’s quantitative and
inquisitive nature that protected Dan from heartless scammers. Tracy was an amateur meteorite collector; intrigued
by their rarity, he looked at meteorites for their historical and scientific value. Regardless of the reason, both friends
wanted to find a meteor; and together they bought an old farm only because it had once been hit by a meteor shower.
But when they arrived at the farm, they thought the meteorites fell days and not decades ago. Holes had been dug all
around the land, and heaps of soil were too many to count. Tracy was not encouraged by what he saw; if there was
ever a meteorite here, the person who made all those holes would have found it. On the contrary, Dan was happy
because half the work was already done.
Although Dan was eager to get into the dirt, Tracy forced him to get in the rundown farmhouse in order to make a
plan. Tracy’s intention was to make a map of the area, but while looking for a piece of paper to draw the map, Dan
found many disintegrating pieces of paper that looked like invoices. One handwritten fragment caught Tracy’s interest.
It described the chemical treatment of a green rock.
1.000 g of green rock boiled with acid then decanted → black sediment + green liquid
Black sediment dried and weighed → 0.832 g
Green liquid separated (chromatography) → two liquid fractions
Fractions reduced (heated H2)→ solids formed → Solid #1 = 0.144 g + Solid #2 = 0.015 g
Solids analyzed (Mass Spectrometry) → MS spectrum #1 + MS spectrum #2
It appeared that a long time ago someone found a green rock and tried to analyze it. At the end, two elements were
isolated and analyzed via mass spectrometry. Tracy had in his hands the mass spectra of the elements from the green
rock. Was the rock a meteorite? Could there be more in the yard? Where they going to be rich? ... only if Tracy knew
how to read the mass spectra.
Case copyright held by the National Center for Case Study Teaching in Science, University at Buffalo, State University of New York.
Originally published March 1, 2018. Please see our usage guidelines, which outline our policy concerning permissible reproduction of this
work. Licensed image in title block © Victor Zastol`skiy | Dreamstime.com, id 29365097.
NATIONAL CENTER FOR CASE STUDY TEACHING IN SCIENCE
Task
Before next class watch the following brief video that explains how a mass spectrometer works and then answer the
questions below.
Video
• The Mass Spectrometer, 2:43 min, uploaded 2012 by Evagating, at: <https://youtu.be/EzvQzImBuq8>
Questions
1. In a mass spectrum, where all particles have the same charge, the X axis indicates
a. Mass of the particles
b. Abundance of the particles
c. Geometry of the particles
d. Geological source of the particles
2. In a mass spectrum, where all particles have the same charge, the Y axis indicates
a. Mass of the particles
b. Abundance of the particles
c. Geometry of the particles
d. Geological source of the particles
3. All atoms of an element have the same number of protons but can have different masses; why?
“Is It a Meteorite?” by Maryuri Roca
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NATIONAL CENTER FOR CASE STUDY TEACHING IN SCIENCE
Part II – Problem-Solving
Each solid formed in the chemical treatment of the green rock is a pure element. The following (Figure 1) is a clean
reproduction of the mass spectra found by Tracy.
Figure 1. Mass spectra for solid #1 (Element 1) and solid #2 (Element 2).
Use the problem-solving approach described below. Each of the five stages will require you to write something down.
At the end of the process, you will identify the elements from their mass spectra in Figure 1.
Stage I: Think About the Answer
Think about what your answer should look like, then think about a strategy to obtain it. Describe your strategy.
Our answer should be in the form of two seperate atomic masses that have two varying proton counts
that are respective towards their element. First anaylze the data provided by Mass Spectra to obtain the
mass and the particle count for each element to find the isotopic abundance. Through that we can evaluate
the average atomic mass.
Stage II: Examine the Data
Examine the data provided and think about the relations that may be needed to apply your strategy. Hint: Summarize
the information from the graphs into tables.
Element 1
X- axis
Has mass values
at 53.93 amu,
55.92 amu, 56.92
amu, 57.91 amu
Y- axis
Max value at 36700
particles, 2340
particles, 848
particles and min 112
particles
(53.93, 2340), (55.92, 36700),
(56.92, 848), (57.91,121)
The element likly has a mass
around 56 amu because that
is where the most particals
are
“Is It a Meteorite?” by Maryuri Roca
Element 2
X- axis
has mass values
57.97 amu, 59.95
amu, 60.91 amu,
61.92 amu, 63.92
amu.
Y- axis
Has max value at
6808 particles,
2622, 363, 114,
and min at 93
(57.97, 6808), (59.95,2622), (60.91,114),
(61.92,363), (63.92, 93)
The element likely has an amu of around
58 because that is where the most
particles are
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NATIONAL CENTER FOR CASE STUDY TEACHING IN SCIENCE
Stage III: Make a Detailed Plan
Write detailed steps (Step 1, Step 2, etc.) to take in order to solve the problem. If necessary, gather information that is
needed but not provided in the problem (e.g., conversion factors, equations, periodic table).
Step 1:
step 1) Record the data provided by the Mass Spectra to gain information about the mass of both elements
step 2) use the masses provided and the amount of particles of each element's graph to determine the
isotopic abundance of each element
Abundance= (particle count / total particle) * 100
step 3) use the percentages gained from the isotopic abundance of each isotope and the mass of each
isotope to find the average atomic mass of each element
step 4) once the masses are found for the individual elements, check the periodic table for each element
Stage IV: Crunch the Numbers
Solve the problem following your steps. Keep record of significant figures and units.
Step 1: Element 2
Element 2
The isotopes of element 1 are most abundant at 55.92 amu
which is closest to iron on the periodic table
Stage V: Check the Answer
Explain why your answer makes sense:
The isotopes of element 2 are most abundent at 57.97
amu which is closes to 58 amu which is closes to nickel
The answer make sense because in meteorites iron and nickel are abundant as they're dense elements that easily
gravitate towards each other.
“Is It a Meteorite?” by Maryuri Roca
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NATIONAL CENTER FOR CASE STUDY TEACHING IN SCIENCE
Part III – Assessment
Questions
Iron & nickle
1. What is the identity of Elements 1 and 2 in the green rock? ______________________________
2. In the graphs below, sketch the mass spectrum for each element; write the symbol of the isotope above each
spectral line.
Ni
Fe
Abundance (%)
Abundance (%)
91.75%
68.08%
5.85%
26.22%
2.12%
.3%
3.63%
1.14%
.93%
Mass (a.m.u.)
Mass (a.m.u.)
3. Although nickel has a higher atomic number than cobalt, nickel’s atomic mass is less than that of cobalt. Why?
4. (Optional) Is this rock a meteorite or a meteorwrong? (Hint: look at the metal composition of FeNi meteorites;
http://meteorites.wustl.edu/id/metal.htm.)
“Is It a Meteorite?” by Maryuri Roca
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