3.4: Procedure

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Part I: Exploring Colligative Properties

We are going to be looking at how boiling points change with solute changes for a variety of different solutes.

For each compound below, make 25 mL of 4 M aqueous solution in a 50 mL Erlenmeyer flask. Be sure to show your work for how much solute you added.

LiCl

NaCl

K₂CO₃

CH₃COOH (10 M solution)

Determine the boiling points of DI water and all of these solutions under the fume hood.

Describe what happened to the boiling points of the solutions compared to the boiling point of water. Remember we must use experimental data for all boiling points.

Rank the boiling points of the solutions from lowest to highest. Explain the chemical rationale behind your observations.

Part II: Unknown Substance Identification

The Raleigh police found an unknown powder at the scene of a local robbery and are hoping to identify it to get some leads on the suspect. Based on the powder’s physical appearance, the police have narrowed it down to this list of options. Next to each option is listed the use of each chemical.

NaCl (table salt)	Na₂SO₄ (laundry detergent)	CaSO₄(dentistry mold)	K₃PO₄ (cooking)	Na₃PO₄ (cleaner)
CaCl₂ (deicer)	K₂SO₄ (fertilizer)	MgSO₄ (laxative)	C₈H₁₀N₄O₂ (caffeine)	FeSO₄ (treats anemia)
C₆H₁₂O₆ (sugar)	CuCl₂ (dyes)	Mg(OH)₂ (flame retardent)	C₉H₈O₄ (aspirin)	NiSO₄ (battery production)
FeCl₂ (water treatment)	FeCl₃ (copper etching)	KCl (explosives)	NiCl₂ (glass coloring)	C₁₀H₁₃NO₂(phenacetin: cocaine cutting agent)

The police have given you the powder in a 4 M solution. Using tests that you have used in this course and general chemistry I lab, determine the identity of the powder. It might be helpful to think about ways to determine bond type, cation/anion identity, if applicable, and the number of cations and anions in the compound, if applicable.

Describe your proposed procedure here.

Write any observations or results from your procedure. If you deviated from your procedure, be sure to note that as well.

Determine the identity of the substance. Justify your answer using your experimental data.

Explain why knowing the identity of the substance be valuable for law enforcement.

Write a brief (~one paragraph) report to the law enforcement agency with the results of your tests and the identification of the powder. It is important for the agency to reference why each test was used and how it led to your conclusion.

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