Lecture Notes:

Chapter One, Introduction to Forensic Chemistry

• Case Study: Whose Side Are They On? The story of the death of Enrique "Kiki" Camarena, US DEA agent
  • Why would Camarena have been killed? He had had too much success in disrupting drug trafficking.
  • Why did the US Gov't bring strong pressure to bear with regard to this disappearance? Camarena really was an important DEA agent and knowing the circumstances of his death would help in the fight against drug traffickers.
  • Why do you think FBI forensic geologist Ron Rawalt suspected as cover-up by the Mexican gov't? Pictures of the ranch and the bodies must have shown different types of soil.
  • Why did agent Rawalt request two soil samples, one from the body and one from the ranch? He strongly suspected they would not match, which would indicate the bodies had actually not been dug up at the Bravo ranch.
• Section 1.1 Welcome
  • “Forensic” comes from the Latin, forensis: “of the forum”, a place of public debates and trials.
  • Forensic science is highly interdisciplinary drawing from geology, physics, psychology, and especially chemistry.
• Section 1.3 Physical Evidence: Matter and its Forms
  • What is matter? The physical material of the universe.
  • How is matter relevant to investigations of crime? You need to understand the properties of matter to analyze evidence.
  • See the States of Matter applet at PhET.
  • In answering the following keep the molecular level in mind:
    • What is a solid? …
    • What is a liquid …
    • What is a gas? …
  • How does matter change between forms? Heat added or removed brings about phase changes.
  • Why does heat make phases changes occur? (Have students write down this question and try to answer it on their paper before discussing it. This question should follow discussion of the mechanism of phase changes with adding and removing heat.) Adding heat increases the random motion of the particles that make up matter, removing heat reduces this motion. Increased motion (increased speed) leads to the ability of particles to overcome the attraction between molecules that hold them in place in a solid or in contact in a liquid.
  • To extend the prior discussion see the activity Modeling the Molecular Level. It should help students to develop mental modeling skills for relating macroscopic events to molecular scale reality.
  • For the following discussion points a demonstration of a chemical reaction between two solutions that produces a precipitate is useful. Solutions of sodium carbonate and calcium chloride are homogenous mixtures. They react to make insoluble calcium carbonate--a heterogeneous mixture. Finally, the precipitate can be filtered out to show physical separation (possible for mixtures but not for compounds).
  • According to a chemist what is a pure substance? It is a substance made of only one component which cannot be separated into parts by physical means such as sorting, distillation, filtration, or chromatography.
  • What is an element? The only kind of pure substance whose smallest whole unit is an atom—compounds all require atoms of two or more different elements bound together.
  • What is a compound? A substance made of atoms of two or more elements bound together and in a particular ratio. The elements in a compound cannot be separated by physical means but only by chemical reaction.
  • What is a mixture? Two or more pure substances physically combined but not chemically bound.
  • What is a homogeneous mixture? A mixture so well mixed that an arbitrarily small sample taken from any part of the mixture will have the same composition as any other part. Examples: salt or sugar solution, the air we breathe, an alloy.
  • What is a heterogeneous mixture? A mixture in which different parts of have different compositions. Care must be taken in analyzing the contents of a heterogeneous mixture so that a representative amount is collected.
  • See Worked Example 1 on pg. 9 and justify the correct choices.
• Section 1.4 The Periodic Table
  • What is the periodic table? A systematic way to display information about the elements.
  • How was the periodic table developed? By 1869 there were 63 known elements. Dmitri Mendeleev was interested in organizing information about them because teaching chemistry had become so complicated. There was not yet a theory for understanding chemistry in a general way and there were a lot of seemingly unrelated facts to learn. Mendeleev was able to organize the known elements by atomic mass in a pattern of repeating (i.e., periodic) chemical and physical properties. His predictions of elements not yet discovered made his system famous (even though others had come up with similar systems before).
• Evidence Analysis, Thin-Layer Chromatography Optional: Demonstration of chromatography using colored markers and filter paper. Wash-able markers and water may work.
• Section 1.5 Learning the Language of Chemistry
  • Some elements have obvious symbols, some do not. Learn to recognize elements by either name or symbol.

  • Element	Symbol	Latin Name
    Antimony	Sb	Stibium
    Copper	Cu	Cuprum
    Gold	Au	Aurum
    Iron	Fe	Ferrum
    Lead	Pb	Plumbum
    Mercury	Hg	Hydragyrum
    Potassium	K	Kalium
    Silver	Ag	Argentum
    Sodium	Na	Natrium
    Tin	Sn	Stannum
    Tungsten	W	Wolfram (actually from German)

  • See Worked Example 2 and 3 on pp. 13 and 14 and justify the correct choices.
  • What are metals and where can they be found on the periodic table? Metals make up most of the table and are found on the left and in the middle. They are generally solids with high to very high melting points. They are good conductors of heat and electricity. Metallic bonds between atoms of metals have the characteristic that electrons can move easily from atom to atom in a ‘sea of electrons’.
  • What are nonmetals and where can they be found on the periodic table? Nonmetals are found on the right side of the table and are poor conductors of heat and electricity and have (generally) lower melting points. Some are a liquid and many are gases. Interesting exception: carbon is a conductor of electricity, especially in the form of graphite.
  • What are metalloids and where can they be found on the periodic table? Elements with properties intermediate between metals and nonmetals. B, Si, Ge, As, Sb, Te, Po, and At.
  • What are chemical formulas and why are they used? They are a shortened means of communicating about compounds using atomic symbols and subscripts that indicate the ratio of the elements found in the compound. They simplify the writing process.
  • See Worked Examples 4, 5 and 6 on pp. 15 and 16 and justify the correct choices.
  • Allow students to color periodic tables to match the table found here.
  • Also show the videos about periodicity found on YouTube by the Open University. Carbon and Silicon. Halogens. Alkali Metals.
• Section 1.6 The Most Important Skill of a Forensic Scientist: Observation
  • Read the quote by Paul L. Kirk from Crime Investigation very carefully aloud in class. To what is he contrasting physical evidence in this quote? Eyewitness testimony. What are the advantages of pursuing physical evidence in the investigation of a crime? What are the limitations of physical evidence in crime investigation?
• Section 1.7 Critical Thinking and the Crime Scene: The Scientific Method
  • What is the scientific method? A system of methodical problem solving. Construct a model on the board during class through discussion, perhaps in small groups who report to the class their conclusions. Another round might be had using problems similar to that outlined in Worked Example 7 on pg. 18.
• Case Study Finale: Whose Side Are They On? The story of the death of Enrique "Kiki" Camarena, US DEA agent
  • What did Rawalt find when he compared the soil sample from Camarena’s body to the soil from the Bravo Ranch? It was clearly not the same (details on pg. 19).
  • What did Rawalt have to do to prove that the soil on Camarena’s body came from Jalisco State Park, as indicated by his research into the scientific literature? He had to travel there to take a sample and show that it matches the soil from the body.
  • What were the consequences of this investigation into soil types? Conviction of Mexican officials for conspiracy, identification and conviction of the drug family members responsible for Camarena’s death.
• Other notes:
  • Practice, practice, practice!
  • Use the resources in the chapter, your peers, and your teacher to fully understand the material.

Based on the book Investigating Chemistry: A Forensic Science Perspective, second edition by Matthew E. Johll, W.H. Freeman, © 2009