Chapter 21 — Self-Check Quiz

24 questions: multiple choice and short answer. Try them closed-book. The answer key is in the collapsed block at the bottom.

Multiple choice

1. The core question the forensic-chemistry section exists to answer is: - A. Who owned the substance - B. What the substance is, and how confidently - C. Whether possessing the substance was a crime - D. What the substance means for the suspect's motive

2. A presumptive color test on a suspected drug establishes: - A. The exact compound, to the exclusion of all others - B. Consistency with a class of substance — a lead, not an identification - C. The quantity of the drug present - D. Who handled the substance

3. Compared with a color test, a microcrystalline test is generally: - A. Less specific and never used - B. More discriminating (crystal shape narrows the identification) but still presumptive and partly subjective - C. A confirmatory, instrumental method - D. Useful only for explosives

4. "Orthogonality," as the chapter uses it, means a sound identification combines: - A. Two runs of the same color test - B. Techniques based on different physical principles, so their failure modes don't overlap - C. A presumptive test repeated by two analysts - D. Any two tests done quickly

5. A confirmatory identification of a controlled substance is best supported by: - A. A second, differently colored presumptive test - B. A trained analyst's confidence - C. An instrumental method such as GC-MS that interrogates the molecule itself - D. The packaging and logos on the item

6. In Melendez-Diaz v. Massachusetts, the Supreme Court held that a lab's drug-identification certificate is: - A. Inadmissible in all cases - B. Testimonial — the analyst can be required to appear and be cross-examined - C. Sufficient on its own without any analyst - D. Required to be based on a color test

7. The forensic value of post-blast explosives residue is high, but its great difficulty is that: - A. Explosives leave no residue ever - B. The event consumes most of the explosive, leaving only trace material, and contamination/background are pervasive - C. Residue can only be analyzed by color tests - D. Residue always identifies the person who placed the device

8. Finding no explosives residue at a scene means: - A. No explosive was used, definitively - B. The analysis was done wrong - C. Nothing conclusive — absence of detected residue is not proof no explosive was used - D. The device was a high explosive

9. Low explosives (e.g., black/smokeless powder) leave residues that are largely: - A. Organic molecules like TNT and RDX - B. Inorganic ions (nitrate, nitrite, chlorate, perchlorate) and metal cations - C. Pollen - D. DNA

10. Fire-debris samples should be collected into: - A. Ordinary plastic grocery bags - B. Clean, unused metal cans or special nylon bags (plastics can off-gas/leak hydrocarbons) - C. Paper envelopes only - D. Any available container

11. A control sample of unburned material in a fire case is collected to: - A. Increase the sample weight - B. Distinguish a genuine accelerant from background hydrocarbons that ordinary materials release when they burn - C. Replace the instrumental analysis - D. Identify the victim

12. A trained accelerant-detection canine's alert is best described as: - A. A confirmatory identification of gasoline - B. A sensitive field indication (a screen) that must be confirmed by laboratory instruments - C. Proof the fire was arson - D. Irrelevant to the investigation

13. The "Willingham error," in chemistry terms, is: - A. Running too many instruments - B. Treating a visual burn pattern as if it were a chemical confirmation of an accelerant - C. Using a control sample - D. Confirming an accelerant by GC-MS

14. The honest verb for a confirmed instrumental result is "identified as"; the honest verb for a presumptive result is: - A. "proves" - B. "individualizes" - C. "is consistent with / indicated" - D. "establishes beyond doubt"

15. On the validity spectrum, confirmed instrumental forensic chemistry ("this substance is X") sits: - A. At the discredited end, like bite marks - B. Near the strong end, alongside DNA, because its core claim is validated, testable, and instrument-checked - C. In the contested middle with firearms - D. Off the spectrum entirely

16. A roadside drug field test is most accurately described as: - A. A confirmatory test - B. A valid screen but an invalid identification - C. Junk chemistry with no legitimate use - D. Equivalent to GC-MS

17. Why are novel psychoactive substances and fentanyl analogs a particular problem for presumptive screens? - A. They are always brightly colored - B. They may give no/unexpected color reactions and appear in adulterated mixtures the screen cannot resolve, exactly when potency makes the stakes highest - C. They cannot be detected by any method - D. They make color tests more reliable

18. In the cold case, the fire-debris finding after this chapter is most defensibly stated as: - A. "Gasoline confirmed by GC-MS" - B. "Arson established" - C. "Accelerant indicated — consistent with gasoline (confirmation pending)" - D. "No accelerant present"

Short answer

19. In two sentences, explain why a presumptive color test cannot, by itself, identify a specific drug — and why running a second chemical screen does not fully fix this.

20. Name three things that make post-blast explosives-residue analysis treacherous, and for each, state in one phrase how it threatens an honest conclusion.

21. Explain the "chain of harm" in the roadside field-test problem in two or three sentences, ending with the single structural fix.

22. A bombing analyst is told, before analysis, which explosive is "expected." State the bias risk and the safeguard (preview of Chapter 31).

23. In the cold case, why can the chemistry call the accelerant "indicated" but not the fire "arson"? Name which chapter earns the arson finding and on what basis.

24. Write one sentence an honest expert could say on the stand about the Mill Creek fire-debris evidence at this stage, and one sentence that would overstate it.

Answer key (click to expand) **Multiple choice:** 1-B · 2-B · 3-B · 4-B · 5-C · 6-B · 7-B · 8-C · 9-B · 10-B · 11-B · 12-B · 13-B · 14-C · 15-B · 16-B · 17-B · 18-C **Short answer (model points):** **19.** A color test reacts with a *functional group common to a whole class*, so the same color can come from different members of the class or from unrelated compounds — it indicates a class, not a compound. Running a second chemical screen helps a little but does not fully fix it, because both screens are *chemical reactions* and a substance that fools one chemistry can fool a related one; only an *orthogonal* instrument (different physical principle) closes the gap. **20.** Any three, e.g.: (a) **trace/near-absent sample** — the event consumes most of the explosive, so a clean scene proves nothing; (b) **contamination/background** — some explosive-associated compounds (nitrates) are environmentally common and sensitive methods detect background, risking a false association; (c) **investigator-carried contamination** — equipment and personnel can move residue between scenes, defeated only by controls; (d) **conservative interpretation needed** — "residue consistent with type X" is not "the defendant handled the device." **21.** A field test "turns positive," the person is arrested, and — facing a felony charge with unaffordable bail and a distant trial — many plead guilty *before any laboratory confirmation*, so the conviction rests on the screen alone; later lab testing has sometimes shown the "drug" was no drug at all. The structural fix: **confirmatory instrumental analysis before conviction, every time.** **22.** **Risk:** the "expected" explosive *anchors* the interpretation — an ambiguous, contamination-prone trace gets read toward the expectation (contextual/confirmation bias, Chapter 31). **Safeguard:** keep domain-irrelevant information away from the bench, insist on controls, and have an independent analyst verify the critical identification blind; the high stakes make this more important, not less. **23.** Detecting (indicating) an accelerant is a *chemistry* finding; calling a fire **arson/incendiary** requires fire-science analysis of *origin and cause* (Chapter 22), not a single accelerant indication — and certainly not the discredited burn-pattern folklore that killed Willingham. **Chapter 22** earns the arson finding, on valid fire-dynamics grounds; **Chapter 23** supplies the GC-MS confirmation that turns "indicated" into "identified." **24.** **Honest:** "At the scene, a hydrocarbon odor and a handheld detector indicated volatiles consistent with gasoline in the front-room debris; this is a presumptive indication, and instrumental confirmation is pending." **Overstated:** "Gasoline was confirmed in the debris and the fire was therefore arson." (The first respects "indicated, not confirmed"; the second claims an instrumental result and an arson conclusion the chemistry has not earned.)