Untitled Flashcard Set

For Science Olympiad Crime Busters (Division B), the event centers on identifying unknown substances and analyzing physical evidence using standard qualitative lab tests. Common powders include sodium chloride (salty, soluble, neutral pH, no reaction with iodine), cornstarch (insoluble in cold water, blue-black with iodine), glucose (soluble, positive Benedict’s after heating to green/yellow/orange), baking soda (NaHCO₃, reacts with acid to produce CO₂ bubbles, slightly basic), calcium carbonate (CaCO₃, reacts with acid but does not dissolve well in water), sand (insoluble, gritty, no chemical reactions), and flour (off-white, iodine may turn dark due to starch). Liquids may include water (neutral pH), vinegar (acidic, reacts with carbonates), ammonia (basic, strong odor), and sometimes hydrogen peroxide (bubbles with catalyst like yeast).

Fibers are identified by appearance and burn tests: cotton smells like burning paper and leaves soft gray ash; wool smells like burning hair and forms brittle black beads; polyester melts and forms hard beads; nylon melts and may smell celery-like. Plastics are often identified by density (float/sink in water or salt solutions) and burn characteristics. Glass comparison may involve density or refractive index (match if densities are very close). Hair analysis looks at medulla pattern—human hair typically has a thin or fragmented medulla, while animal hair often has a thick continuous medulla.

Fingerprint patterns include loops (most common), whorls (circular), and arches (least common). Soil can be compared by color, particle size, texture, magnetism, and pH. Chromatography separates ink into component dyes based on solvent movement (Rf = distance traveled by dye ÷ distance traveled by solvent front). Shoeprints and tire tracks are compared by tread pattern and size.

pH paper indicates acidity/basicity (0–6 acidic, 7 neutral, 8–14 basic). Conductivity testers show whether a solution contains ions (salt solutions conduct; sugar solutions do not). Flame tests can show characteristic colors (sodium = bright yellow, potassium = lilac). Density = mass ÷ volume and is useful for solids and liquids comparison. Evidence must be matched by consistent physical and chemical properties, and conclusions are based on eliminating substances that do not fit all observed test results.

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