In this lesson, students are introduced to the world of Forensic Chemistry using the prologue of Deborah Blum’s The Poisoner’s Handbook. Discussion revolves around why murder by poison was so prevalent during the nineteenth and early twentieth centuries, and why it is so rare today. Students create their own Safety Data Sheet on a poison of choice, and learn about how mass spectroscopy has helped revolutionize the modern analysis of toxins.
This lesson will help prepare your students to meet the performance expectations in the following standards:
- HS-ETS1-3: Evaluate a solution to a complex real-world problem based on prioritized criteria and trade-offs that account for a range of constraints, including cost, safety, reliability, and aesthetics as well as possible social, cultural, and environmental impacts.
- HS-ETS1-2: Design a solution to a complex real-world problem by breaking it down into smaller, more manageable problems that can be solved through engineering.
- Scientific and Engineering Practices:
- Analyzing and Interpreting Data
- Engaging in Argument from Evidence
- Obtaining, Evaluating, and Communicating Information
By the end of this lesson, students should be able to:
- Describe the factors that made nineteenth and twentieth century New York such a hot spot for murder by poison.
- Read and interpret a Safety Data Sheet.
- Design a Safety Data Sheet for a poison of choice.
- Read and interpret a mass spectrum.
- Discuss how instruments such as the mass spectrometer make murder by poison so rare today.
This lesson supports students’ understanding of:
- Safety Data Sheet (SDS)
- Mass Spectroscopy
- Identifying an Unknown
- Molecular Structure
Teacher Preparation: 30 minutes
Lesson: 230 minutes total (over the course of 3-4 class periods)
- Introductory Lessons:
- Read prologue to The Poisoner’s Handbook and answer questions: 20 minutes
- Discuss prologue and student answers: 10 minutes
- Introduction to Toxicology slides: 25 minutes
- Reading and SDS Discussion: 15 minutes
- SDS Project:
- SDS Poster Project: 1 hour and 15 minutes
- Note: I give students a single period to work on the presentation in class, and then make them finish it at home if they need more time
- Modern-Day Applications Lesson:
- Reading a Mass Spectrum PowerPoint Presentation: 25 minutes
- Mass Spec Activity: 50 minutes
- Deborah Blum’s The Poisoner’s Handbook (you can find it on Amazon, or download the Sora app for free on your phone using either the Apple or Google app store)
- If unable to obtain a copy of Deborah Blum’s The Poisoner’s Handbook, consider using the free online interactive version sponsored by PBS.
- Introduction to Forensic Chemistry Slides (adapted from Bertino & Bertino: Forensic Science: Fundamentals and Investigations, second edition)
- Material Safety Data Sheets
- SDS Poison Poster Project Handout
- SDS Poster Project Template
- Mass Spectroscopy Notes
- No specific safety precautions need to be observed for this activity.
- *Blum, D. (2010). The poisoner's handbook: Murder and the birth of forensic medicine in Jazz Age New York.
- Background information on the content can be found in the set of introduction slides, which are also available in the ‘Flow of Lesson’ section below. I use the information in the textbook Bertino & Bertino: Forensic Science: Fundamentals & Investigations, second edition to create my own slides. Note that these slides are very bare bones, as they are more just meant to lay out the information for you. I suggest adding in videos and images as well, and making this presentation your own!
- Reference: Bertino, A.J. & Bertino, P.N. (2016). Forensic Science: Fundamentals & Investigations. Cengage Learning.
- Before assigning the SDS project, I recommend taking some time to review the components of an SDS with your students. For my students, this is most likely the first time they are seeing one of these documents. I myself did not realize they existed until college! I suggest using the standards published by OSHA. I also like to show students the SDS of water from Flinn Scientific. I think it really drives home the understanding that any substance can be a toxin, it’s all about quantity and lethal dosage.
- For the SDS project, I let students choose from any of the following poisons: Chloroform, Methanol, Cyanides (HCN, KCN, or NaCN), Arsenic, Mercury, Carbon Monoxide, Radium, Ethanol, and Thallium. All of these toxins have their own chapter in The Poisoner’s Handbook, which I have students use as their primary reference. At this point, I also make my students conduct a web search for the official SDS of their chosen poison. I make my students choose from one of the poisons listed above so that they can use The Poisoner’s Handbook. If a group of students really wants to focus on a different toxin, I make them check in with me first, and show me some good primary sources they intend to use.
- My classes are typically composed of 24 students. I generally aim for 8 groups of 3 for the SDS project. I wouldn’t go any larger.
Flow of Lesson:
- I introduce students to the unit on Forensic Chemistry by having them read the prologue of Deborah Blum’s The Poisoner’s Handbook. This helps students start to formulate an idea of why murder by poisoning was very prevalent in earlier centuries, but is much rarer today. (Less than half of one percent of murders are by poison in our modern world). It is also just a great hook that builds interest in this topic. This book is available for free in the Sora virtual library if your school has a subscription. If not, you can purchase a copy of the text online. NOTE: If you cannot purchase the book, this lesson can still be completed using PBS’s free online interactive version of the text!
- Also, consider showing the Arsenic video from Sam Kean’s Disappearing Spoon Video series in the AACT library when introducing this lesson.
- While reading the prologue, give students a chance to answer The Poisoner’s Handbook Discussion Questions (available to download from the sidebar). These questions help students begin to formulate their own hypotheses as to why murder by poison is so rare today. An answer key has been provided.
- Once students have been hooked on the subject using The Poisoner’s Handbook, use a set of slides, “Introduction to Forensic Chemistry PowerPoint” (available to download from the sidebar) to introduce them to the world of Forensic Chemistry. This is a good way to provide some basic information that will be useful while completing the SDS project later in this lesson plan.
- Optional: I usually show one or two Forensics Files episodes while reviewing these slides. Some of my favorite episodes for this content include: Season 7, Episode 18: “A Bitter Pill to Swallow” and Season 10, Episode 33: “Penchant for Poison”.
- Next, I use OSHA’s safety standards to introduce students to the layout of a SDS before diving into the project portion of this lesson plan.
- The SDS Poison Poster Project student handout is available to download from the sidebar. One of the biggest goals of this project is for students to learn how to read and interpret the data found on the SDS. Students should be able to look up the answers to all the questions posed using the SDS for their substance. The goal is that they learn exactly where to look for this information.
- Once students have researched the answers to all the questions, they must organize their information into a one-page PowerPoint slide that will double as a poster. A sample template is included.
- NOTE: I require students to use only one PowerPoint slide because it helps to resemble an informational research poster. If you think this may be an issue for any of your classes, feel free to allow more space. I do not force the use of the provided template, as long as students abide by the single slide limit, but a lot of students who would otherwise struggle find it very helpful.
- The last portion of this lesson involves a discussion about how mass spectroscopy (MS) has revolutionized the field of forensic chemistry. MS is typically used for trace and toxic metal analysis in toxicology laboratories. For many students, this is the first time they’ve even heard of mass spectroscopy, so before talking about the applications of this instrument, I suggest first teaching them about how it works. A slide presentation called, Mass Spectrometer, is available to download to use for this purpose.
- NOTE: I created these slides using information from Brown & LeMay’s Chemistry: The Central Science. (Brown, T.L. & LeMay, E. H. (2018). Chemistry: The Central Science, 14th Edition. Pearson.)
- After the slide presentation, teach students how to read a spectrum using Zirconium (included in the presentation). Then then move into a discussion where students theorize how mass spectroscopy is helpful to the field of forensics.
- The final activity in this lesson is used to give students practice reading the mass spectra of pure elements and simple compounds. Use the Mass Spectrum Activity student handout (available to download from the sidebar).
- I do not teach my students how to read the mass spectra of complex compounds. Due to this, I do not require students to interpret the spectra of the metabolities, but instead the original substances.
- When it comes to the mass spectra of pure elements, my goal is for students to recognize that the peaks correspond to different common isotopes of the substance in question.
- When it comes to the mass spectra of compounds, the objective is for students to identify the M+ peak, and to match it up with the molar mass of the compound of interest.
- At the end of this activity, I will present students with the mass spectra of the metabolites so they can see how different they are, and we will have an open discussion about how this might have made the detection of certain poisons difficult.
- Implementation of the Mass Spectrum Activity:
- I suggest dividing students into small groups. I split my class into six groups of four for this assignment.
- Set up six lab stations. Each station will be dedicated to the mass spectrum of a different poison. Each spectrum is linked to its respective substance below. Spectra are taken from the NIST Chemistry WebBook, as well as WebElements.
- When printing the spectra, I make sure to white out the element names before passing them out. I like each student to have a mass spectrum to mark up, so I print off as many copies as there are students for each spectrum.
- Suggested set-up:
(Mass Spectrum linked)
|1||Arsenic||Arsenic has a molar mass of 74.92 amu. The mass spectrum attached shows a single peak at 75 amu, because in this case the most intense ion is set to 100%.|
|2||Hydrogen Cyanide||Hydrogen cyanide, formula HCN, has a molar mass of 27.03 g/mol. The spectrum shows a peak with greatest intensity at m/z 27.|
|3||Lead||Lead has four naturally occurring isotopes, which I have listed in order of increasing abundance: Pb-204, Pb-206, Pb-207, and Pb-208. On the spectrum, the most abundant peak can be seen at 208, and then there are peaks of lesser intensity at 207, 206, and 204.|
|4||Mercury||There are seven stable isotopes of Mercury, with Hg-202 being the most abundant. This corresponds to the intensity of the peak shown on the mass spectrum.|
|5||Methanol||Methanol has an average atomic mass of 32.04 g/mol. A peak of high intensity is seen at this m/z ratio.|
|6||Carbon monoxide||Carbon monoxide has a molar mass of 28.01 g/mol. The most intense peak on the spectrum is at m/z ratio of 28.|
- Next, along with the printout of the spectra for each poison (remember to remove its name), place a single copy of the corresponding background story for each poison at the station. (The student handout has copies of each story for reference).
- Direct one student at each station to read the background story out loud to his or her peers. Based on the story, students should form a hypothesis of which poison they are working with.
- Students will work together to analyze the mass spectrum. They should mark it up completely, and come to a conclusion of which poison it represents. Students can be given a list of possibilities if needed. The background stories are all about the same level of difficulty. They should also discuss whether their hypotheses were correct. I generally give students 8 minutes per bench, so the overall activity takes about 50 minutes if you factor in time for directions.