Summary

In this lesson, students will use their knowledge of the properties of ionic and covalent compounds to examine the evidence from a crime scene. Students will conduct several tests, and compare their data with known data in a collection of SDS documents. Using the evidence from their investigation, students will write a claim, evidence and reasoning statement detailing whether the victim was murdered or died accidentally.

Grade Level

High School

NGSS Alignment

This lesson will help prepare your students to meet the performance expectations in the following standards:

• HS-PS1-1: Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms. 
• HS-PS1-2: Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.
• HS-PS1-3: Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.
• Scientific and Engineering Practices:
  • Asking Questions and Defining Problems
  • Analyzing and Interpreting Data
  • Planning and Carrying Out Investigations
  • Engaging in Argument from Evidence
  • Obtaining, Evaluating, and Communicating Information

Objectives

By the end of this lesson, students should be able to:

• Differentiate between an ionic and covalent compound and their properties using lab data.
• Use a SDS to collect information about a given substance.
• Write a complete and correct claim, evidence and reasoning statement.

Chemistry Topics

This lesson supports students’ understanding of:

• Physical Properties
• Chemical Properties
• Density
• Ionic Bonding
• Covalent Bonding
• Inferences

Time

Teacher Preparation:

• Day 1: 10 minutes make copies
• Day 2: 30 minutes to make lab copies and prep chemicals
• Day 3: 30 minutes to make lab copies and prep chemicals

Lesson:

• Day 1: 40 minutes to examine evidence folder
• Day 2: 60 minutes to complete melting point, solubility and conductivity labs
• Day 3: 60 minutes to complete density lab
• Note: It’s recommended that the Claim, Evidence and Reasoning Lab is assigned as homework

Materials

Day 1:

• Copies of the Crime Scene Photos document
• Copies of the Witnesses and Suspects Case File document
• Copies of the Evidence Folder document

Day 2:

• Melting Point Analysis Lab (each class, 6 lab groups)
  • 10 gram sample of alum, calcium carbonate, calcium chloride, corn starch, salt, sodium acetate, sodium bicarbonate for each lab group
  • Contaminated sample of sucrose and sodium acetate (1/4 sucrose and 3/4 sodium acetate—label as sucrose)
  • Full size metal pie pan for each group
  • Tea light candle for each group
  • Timing device
• Solubility and Conductivity Evidence Lab (each class, 6 lab groups)
  • The same samples from the Melting Point Lab
  • Well plate (1 per group)
    
  • 90% isopropyl alcohol in dropper bottles (1 per group)
  • Water in dropper bottles or wash bottles (1 per group)
  • Conductivity meters (probes can be used, but the lab wording would need to be changed)

Day 3:

• Density Blunt Force Trauma Lab (each class, 6 lab groups)
  • Samples containing 10-20 grams mossy zinc, copper (wire or shot), glass beads, iron nail, aluminum shot, wood
    • *My samples come from a density set our school purchased
    • **Aluminum foil does not work due to buoyancy
  • Balance (1 per group)
  • 25 ml graduated cylinder (1 per group)
  • 2 weigh boats (1 per group)

Safety

• See SDS in evidence folder for alum, calcium carbonate, calcium chloride, corn starch, salt, sodium acetate and sodium bicarbonate.
• SDS for Zinc, copper, iron, and aluminum
• Always wear safety goggles when handling chemicals in the lab.
  
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
• Always use caution around open flames. Keep flames away from flammable substances.
• Always be aware of an open flame. Do not reach over it, tie back hair, and secure loose clothing.
• Open flames can cause burns. Liquid wax is hot and can burn the skin.
• Exercise caution when using a heat source. Hot plates should be turned off and unplugged as soon as they are no longer needed.
• When lighting the match and wooden splint, be cautious with the flame.
• An operational fire extinguisher should be in the classroom.
• Do not consume lab solutions, even if they’re otherwise edible products.
• Food in the lab should be considered a chemical not for consumption.

Teacher Notes

• This is an abbreviated version of a longer unit that focuses on ionic and covalent compounds. If you wish to make this a larger unit please see the extensions below.
• Students are first presented with a crime scene (see Crime Scene Photo document). Ideally you would want to create the crime scene for the students to examine, however if that is not possible then using the photos should be sufficient to peak student interest.
• If you wish to set up the crime scene see the supplemental document, Crime Scene Set-up 101.
• After presenting students with the crime scene, students are able to examine the other physical evidence at the crime scene (see Evidence Folder document). Students are also able to view the document, Witness and Suspect Folder.
• After viewing all of the evidence, I have students complete the handout, Knows, Need to Knows and Next Steps. Essentially this helps them summarize what have they learned viewing this evidence and what is still missing that they need to figure out to solve this crime. From this students should be able to figure out that they need to test the chemicals at the crime scene to determine their identities.
• Important information students should gather from the evidence folder and pictures:
  • The victim was hit on the head (could be from falling or it could be someone hit him).
  • The victim was testing the cooking ingredients for contaminants.
  • The chemicals he was testing were for Martin’s Food and Beverage.
  • The results of some of his lab tests.
  • General information about the suspects and witnesses.
• Students will complete 2 different labs to analyze the chemicals found at the crime scene:
  • First, they will determine melting point data for evidence samples; refer to the Melting Point Analysis Lab handout. 
  • Then they will investigate solubility and conductivity of the evidence samples; refer to the Solubility and Conductivity Evidence lab handout. 
  • To determine if the data collected for each evidence sample is correct (the results are consistent with the known properties of the substance), students should compare the data that they have collected to the SDS for the sample provided in the evidence folder.
• After analyzing the evidence students should determine that one of the samples is contaminated and has properties that are not as they should be, according to the SDS. Knowing this, students then need to determine why Mr. Avery has died. The autopsy report shows blunt force trauma to the head. Students determine who hit him by investigating density data and matching it to what the suspects have available to them. Refer to the Density Blunt Force Trauma lab handout. 
  • For the density investigation, I usually make one set of the density samples and set-up a station for each sample. Students will rotate through to each station.
• At this point students should have all the information they need to determine who murdered Mr. Avery. Students should be directed to complete the Claim, Evidence and Reasoning handout. 
• Students should include a variety of evidence, but it will vary between students. It could be information from the interviews and their labs. 
• The correct killer is Austin Bowling. If students did not determine their density measurements carefully they may have incorrectly chosen Ray Wilson. If this is the case then it is an excellent opportunity to discuss with students the importance of careful measurements and how incorrect measuring can cause severe consequences (i.e. they arrested the wrong person!)
  

Extensions:

• Other ideas for additional activities to combine with this unit/lesson:
  • The crime scene pictures show 3 liquid samples that are present. Students can do a flame test to determine if they are contaminated.
  • Set-up a physical crime scene, and students can create a crime scene sketch.
  • If you have a theater class students can ask questions to the witnesses and suspects. If I do this I usually give the witnesses and suspects a small paragraph of their role and then provide them with student questions ahead of time so that they can prepare.
  • These labs could also be done with an inquiry based approach, if your students are familiar with determining these properties.