Fun with Formula Stoichiometry: “Who poisoned Veronica Merriweather?”

text: "Who Poisoned Veronica Merriweather?" and crime scene tape

"Who Poisoned Veronica Merriweather?" is a fun application of formula stoichiometry for students who are placed in the role of a CSI lab sleuth helping to interpret chemical data to identify a murderer. When I taught a year-long, honors chemistry (SAT II preparatory) course to sophomores this was the culminating activity in our formula stoichiometry unit. More recently I've used the activity at the conclusion of our integrated science course (physics and chemistry for 9th-graders). It can be assigned to students working alone or in small groups.

Concepts: 
formulas
percent composition
stoichiometry
Background: 

As the director and senior analytical chemist with over 20 years of experience in LAPD’s crime lab, you thought you had seen it all—more murders committed in more wildly despicable ways than any one person should have to carry around in his head. But when LAPD homicide detective Joe Malone phoned you in the crime lab this evening, he had a story to share that both impressed and intrigued even you.

It seems that 68-year old Veronica Merriweather, former daytime television diva and fabulously wealthy widow of deceased Hollywood blockbuster movie producer Malcolm Merriweather, had met her untimely demise earlier this afternoon up in Malibu while having tea with her younger son on the veranda of her recently renovated, architecturally sophisticated, multi-million dollar beach house overlooking the Pacific. Although the precise details surrounding her death remain uncertain, investigators working the crime scene have already found several intriguing items in the house:

Exhibit A) Next to a vintage porcelain tea set on the veranda is: 1) a thumb-sized, golden colored, metallic nugget with isometric, striated crystals, and 2) a crumpled slip of paper with the handwritten words "gold heap leaching."

Exhibit B) Near a package of McVitie’s brand tea biscuits on the counter in the kitchen is what appears to be a very old box of d-Con rat poison.

Exhibit C) On a nightstand in Veronica’s bedroom is an open pack of cigarettes next to a round, glass terrarium containing some 1) tropical plants, 2) a bright yellow frog, and 3) several opalescent blue beetles.

Malone informed you that he suspects the chain-smoking cougar may have been the victim of poisoning. LAPD has fingerprinted and is holding 3 suspects for further questioning, each with sufficient motive, means, and opportunity:

Suspect 1) Miles Merriweather, age 38, elder son of Veronica and Malcolm and an anthropology professor at USC, had joined his mother for breakfast at her Malibu beach house this morning to once again implore her to supply him with additional research funding to support his field expeditions to western Colombia where he was studying the Chocó Indian tribes.

Suspect 2) Davis Merriweather, age 36, younger son of Veronica and Malcolm and a gold hunter recently returned to the United States from Papua, New Guinea, had joined his mother for her afternoon tea to beg her for additional funds to prop-up his failing overseas mining operations, and had been present in the house with his mother when she died.

Suspect 3) Joseph Graham, age 27, Veronica’s handyman and jilted former gigolo, had been phoned to take care of a rodent problem in the crawlspace beneath the beach house, and had been on the grounds with Veronica after her breakfast with Miles and before her tea with Davis.

Before he hung-up the phone, Detective Malone asked you to free-up crime lab personnel and analytical equipment due to the high profile nature of the case. “We’ve got to wrap this one up quickly,” he said. “We can’t have the Hollywood papparazzi buzzing all over Malibu asking about the old bird who went and got herself poisoned.” He mentioned that his men were continuing to work the crime scene, that he would deliver to you a sample of the victim’s blood once the coroner had begun examining the body, and that he would provide additional information and instructions as the investigation unfolded.

Procedure: 

Students are provided the background information above along with resources and directions for researching potential poisons. They are given 5 clues over the course of several nights of homework. I tend to parse the clues out one at a time as homework over 5 class days (which, on our new schedule, is two weeks). During class, we're working on the formula stoichiometry stuff, the molecular geometry connection with GCMS fragmentation, etc. Ultimately, they compile and submit a final report that summarizes their stoichiometric calculations and background research and explains who they think is the murderer and why.

A matrix of potential clues and villains is available in the TEACHER document (see Supporting Information) that makes it possible to provide slightly different scenarios for different sections of the same course or from one year to the next. Topics covered include formula stoichiometry (percentage composition, empirical and molecular formulas) and GCMS (gas chromatography–mass spectrometry) at the most basic level.

See the Questions section below for a summary of the homework portion of the activity.

Supporting Information: Both the STUDENT and TEACHER documents are available in the Supporting Information - (Log into your ChemEd X account to access. Don't have an account? ) 

Questions: 

Your assignment is to identify the poison used and help convict the killer.

Using whatever web-based resources are available to you, research each of the suspects and potential poison candidates suggested by the details above and any others that Detective Malone shares with you as the investigation unfolds, starting 1 first.  Then:

1. Complete the following table

 

2. For each of the poison candidates you identified in the table above, provide:

a) the poison’s name and structural formula (copy and paste electronically; 2 may be helpful);

b) a short summary of the poison’s history, background, and uses;

c) the means by which the poison attacks the body, and the symptoms it produces in the victim, etc. ( is a good place to start).

 

3. Calculate the molecular formula(s) of any foreign compound(s) you identify in Veronica Merriweather’s blood sample (and of any other samples Malone provides to you for chemical analysis) and identify them by name.

 

4. Compile and submit a typewritten summary that a) outlines the pertinent details of your calculations and web research, b) explains how all of the physical and chemical evidence indicates the poisons potentially or actually used and how they relate to the suspects and identify the killer.

Preparation: 

Print hard copies of student document if needed or upload to digital platform for their access. 

Attribution: 

1. Keith Veronese, 10 of the Most Dangerous Chemicals in the World, GIZMODO, 11/23/2011. https://gizmodo.com/10-of-the-most-dangerous-chemicals-in-the-world-5861680 (accessed 08/25/2022),

2. National Library of Medicine, PubChem. https://pubchem.ncbi.nlm.nih.gov (accessed 08/25/2022)
Wikipedia https://www.wikipedia.org
 

Collection: 

NGSS

Students who demonstrate understanding can use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.

*More information about all DCI for HS-PS1 can be found at  and further resources at .

Summary:

Students who demonstrate understanding can use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.

Assessment Boundary:

Assessment does not include complex chemical reactions.

Clarification:

Emphasis is on using mathematical ideas to communicate the proportional relationships between masses of atoms in the reactants and the products, and the translation of these relationships to the macroscopic scale using the mole as the conversion from the atomic to the macroscopic scale. Emphasis is on assessing students’ use of mathematical thinking and not on memorization and rote application of problem - solving techniques.