AACT MemberOnly Content
You have to be an AACT member to access this content, but good news: anyone can join!
Chemical Analysis of Martian Rocks Mark as Favorite (101 Favorites)
LESSON PLAN in Identifying an Unknown, Percent Composition, Mole Concept, Percent Composition, Emission Spectrum, Empirical Formula. Last updated March 21, 2023.
Summary
In this lesson, students are challenged to analyze the spectral graphs obtained by the Curiosity Mars Rover. Based on their examination students will determine the component elements of each sample, as well as the relative abundance of each element. With this information the student will complete calculations to find the empirical formula and identify the composition of the unknown rock. Finally students will complete research to see if these rocks are actually like those on Earth.
Grade Level
High School
NGSS Alignment
This classroom resource will help prepare your students to meet the performance expectations in the following standards:
 HSESS12: Construct an explanation of the Big Bang theory based on astronomical evidence of light spectra, motion of distant galaxies, and composition of matter in the universe.
 Disciplinary Core Ideas
 PS4.B: Electromagnetic Radiation: Atoms of each element emit and absorb characteristic frequencies of light. These characteristics allow identification of the presence of an element, even in microscopic quantities.

Crosscutting Concepts:
 Connections of Nature of Science: Scientific Knowledge Assumes an Order and Consistency in Natural Systems
 Science assumes the universe is a vast single system in which basic laws are consistent.
 Scientific knowledge is based on the assumption that natural laws operate today as they did in the past and they will continue to do so in the future.
 Science and Engineering Practices
 Analyzing and interpreting data
 Using mathematics and computational thinking
 Constructing explanations (for science) and designing solutions (for engineering)
 Engaging in argument from evidence
 Obtaining, evaluating, and communicating information
Objectives
By the end of this lesson, students should be able to:
 Determine an empirical formula from percent composition data of a substance.
 Analyze and interpret a spectral analysis graph.
 Use evidence to draw conclusions.
 Present their reasoning logically using facts and system thinking.
Chemistry Topics
This lesson supports students’ understanding of:
 Quantitative Chemistry
 Spectral Analysis
 Percent Composition
 Empirical Formulas
 Significant Digits
Time
Teacher Preparation: 15 minutes
Lesson: 40 minutes
Materials
 Teacher PowerPoint Presentation with examples
 Student Handout
 Spectral Graphs
 Periodic Table
 Calculator
 Device with Internet access for research
Safety
No specific safety precautions need to be observed for this activity.
Teacher Notes
 The key to this lesson is excitement. Show enthusiasm for the amazement that is the landing of Curiosity on Mars. Be enthralled by the ability to record information from rocks on the Martian surface!
 The lesson should begin with review of key concepts such as percent composition and empirical formulas (use slides 14 from the provided PPT). Note that this should be a review – if it is being introduced for the first time, consider doing another activity on these concepts before completing this lesson.
 Next use the short video clips to engage and motivate students:
 7minutes of Terror: The Challenges of Getting to Mars (approximately 5 minutes)
 Curiosity Mars Rover CheMin Data (approximately 2 minutes)
 Following the videos use the teacher led example of how to solve reverse percent composition questions with students (use slides 59).
 Depending on the level of your students, additional practice questions may need to be reviewed before giving the students the “rock data” included in the student activity to analyze. However there is a practice question at the start of the student handout to either be worked through individually or collectively that will serve as good preparation.
 I would suggest creating groups of student with similar ability levels. Plan to provide each group with an empirical formula based on difficulty level. A variety of examples are available for use with this activity, progressing in difficulty level by number. For example Asteroid 1 data is the least difficult to analyze, while Asteroid 5 is the most difficult.
 Each group should be given one graph to analyze and will report their findings to the class.
 Although partners could work together to submit a result, I would suggest having groups of 23 students and using a whiteboard to organize their thinking and calculations. This will allow for presentations of their results at the conclusion of the period.
 Each presentation should be 12 minutes with a brief explanation of any difficulties they had in analysis.
 Note that there is background noise in the graphs. I don’t address this prior to the activity and allow for students to discover it on their own. Some students may try to include the smaller percentages in their calculations, but quickly realize that there are no corresponding elements for these peaks, but also that the total percentage will exceed 100. This often leads to a discussion during the presentations.
 I have attached hypothetical graphs of spectral analysis for Asteroids 15, “Martian Rocks”. Based on their analysis, students should determine the following empirical formula for each asteroid. (Note that a complete answer key, showing all calculations is available for download):
 Asteroid 1: SiO_{2}
 Asteroid 2: FeO_{2}
 Asteroid 3: CaCO_{3}
 Asteroid 4: Mg_{2}SiO_{4}
 Asteroid 5: Fe_{2}SiO_{4}
 Provide each group with a different graph and have them work through the reverse percent composition to arrive at the chemical formula. For large classes, groups may analyze identical graphs. For accelerated students, give them multiple graphs to analyze.
 If time allows (or alternatively as a bellringer in the following class) have students give presentations of their findings as described in the student lab handout. This should not be graded, but should serve as discussion and review.
 Bonus Extension: students use IUPAC nomenclature to name their rock and research common names to see if they can be found on earth. (List of rocks on Mars)
 Teachers can find the data used to create the graphs in the downloadable Excel spreadsheet. If more samples are desired, create copies of one of the sheets and edit the values for the peaks in the data table to reflect the desired compounds and create more graphs for analysis.
For the Student
Lesson
Background
Reverse Percent Composition is a method used in spectral analysis of stars and meteors. This method can also be used to analyze rocks. Using data collected from spectrographs, the percentage of each element present in a sample is determined. By knowing the gram formula mass of each element (from a periodic table), the empirical formula of a specimen may be determined.
Example A rock sample is determined to contain 58.8% Barium, 13.74% Sulfur, and 27.45% Oxygen by mass. What is the empirical formula of the compound? Step 1: Assume there is a 100g sample: Our 100g sample would contain 58.8g of Barium, 13.74g of Sulfur, and 27.45g of Oxygen. Step 2: Using the gram formula mass of each element, calculate the number of moles of each element in the sample Barium: 58.8 grams x (1mole/137.3grams) = 0.43 mole Barium Sulfur: 13.74 grams x (1mole/32.1grams) = 0.43 mole Sulfur Oxygen: 27.45 grams x (1mole/16.0grams) = 1.72 mole Oxygen Step 3: Empirical formulas contain whole numbers as subscripts. Find the common denominator between the molar quantities to arrive at subscripts for the empirical formula for the compound. Ba_{(0.43/0.43) }S_{(0.43/0.43) }O_{(1.72/0.43)} Empirical Formula = BaSO_{4} 
Practice Question
A compound has 14.6% Carbon and 85.4% Chlorine by mass. What is the empirical formula for the compound?
Objective
Analyze the spectral graph to determine the empirical formula for the Martian Rock (asteroid) discovered by Curiosity Rover. Be prepared to defend your answer to your classmates.
Procedure
 Use the graph provided to determine what elements are in your sample:
 Locate the Emission Energies that exhibit peaks.
 By comparison to the Chart of Emission Energies, determine the element that most likely caused that peak.
 Record the element names in the data table provided.
 Use the graph provided to determine the percentage of each element that is present in your sample.
 Record the Percent Composition for each element that an obvious peaks occur in the data table.
 Read the graphs to the nearest TENTHS.
 Use the percent composition of each element to complete calculations and determine the empirical formula for your sample.
 Once you have the empirical formula, you can find molecular formulas that naturally exist on earth. Use your research materials (textbook, Google, etc.) to find the name of your compound and locate, if possible, where a similar sample could be found on earth.
 As a group, prepare a brief presentation of your findings on your whiteboard. Include your estimated percent compositions (from the graph), all calculations, and any difficulties you had arriving at results.
Data (you may not need all of the rows)
Asteroid #:  
Elements Present

Percent Composition

Calculations
Record all necessary calculation used to determine empirical formula below:
Conclusion
Is this compound unique to Mars or can it be found on Earth? Explain.