Forensics

Forensics is a Division C chemistry event that involves identification of powders, polymers, fibers, and hair samples, blood serum and fingerprint analysis, and interpretation of chromatography. Given a scenario and some possible suspects, students will perform a series of tests. These tests, along with other evidence or test results will be used to solve a crime. This event is closely associated with the Division B event, Crime Busters.

Topics Covered

 * Qualitative Analysis (powders)
 * Polymers
 * Chromatography/Spectroscopy
 * Fingerprint Analysis
 * DNA
 * Glass Analysis
 * Entomology
 * Spatters
 * Seeds and Pollen
 * Tracks and Soil
 * Blood
 * Bullet Striations

Qualitative Analysis
Qualitative Analysis is the section of the test that involves the identification of unknown powders. At the regional level, 3-8 powders will be given. 6-10 samples will be given at state, and 8-12 powders will be given at nationals. It is helpful to include a flowchart to aid with powders identification on your cheat sheet.

There are fifteen different substances that may be given on a test: sodium acetate, sodium chloride, sodium hydrogen carbonate (sodium bicarbonate), sodium carbonate, lithium chloride, potassium chloride, calcium nitrate, calcium sulfate, calcium carbonate, cornstarch, glucose, sucrose, magnesium sulfate, boric acid, and ammonium chloride. Utilizing all your availible means of identification will give the best results.

Methods of Identification

Flame test: The flame test uses a Bunsen burner and a nichrome wire. To perform this test, dip a clean nichrome wire in distilled water, and then dip the loop of the wire into a small sample of the dry chemical. Hold the loop of the wire in the cone of the flame, and observe the color of the burning chemical. If desired, a piece of cobalt blue glass may be used for viewing. Chemical cations determine the color of the flame, and their characteristics may indicate the chemical identity. Tests with liquids: Liquids used for identification are iodine, sodium hydroxide, hydrochloric acid, Benedict's solution, and water. Not all liquids are applicable to all samples.
 * Sodium: yellow flame, very distinct. Even a small amount of sodium will contaminate other compounds.
 * Lithium: carmine or red flame
 * Calcium: yellow-red flame
 * Boric Acid: bright green flame, very visable
 * Ammonium Chloride: faint green flame
 * Potassium: light purple, lavender flame
 * Iodine: When iodine is added to cornstarch, the sample will turn black. If cornstarch is not present, the iodine will remain brown.
 * Sodium Hydroxide: Sodium hydroxide is used simply to categorize your samples into two fields: NaOH reactive- and non-reactive. For this reason, it is extremely useful when using a flowchart.  To perform this test, a few drops of NaOH is added to a small sample of chemical dissolved in water.  If a milky-white precipitate forms, the sample is NaOH reactive.  If a precipitate does not form, the sample is NaOH non-reactive.
 * Hydrochloric Acid: Hydrochloric acid will react when added to samples contaning carbonates--therefore, it is useful in identifying calcium carbonate, sodium carbonate, and sodium hydrogen carbonate.
 * Benedict's solution: Benedict's solution is used to detect glucose. To perform this test, dissolve a small sample of chemical in water in a test tube.  Add two to three drops of Benedict's solution, then place the test tube in a hot water bath.  If the glucose is present, the sample will react and form an orange precipitate.  This test may take a few minutes; be patient.
 * Water: Water is used for determining the solubility of chemical samples, and is used for making solutions.

pH: The pH data for chemicals can be useful, especially for determining between two similar chemicals. Most samples have a pH of between 5 and 7, but two are distinct: sodium carbonate has a pH of 12, while sodium bicarbonate has a pH of around 10.

Conductivity: Certain chemical samples will dissociate and become conductive when dissolved in water. To perform this test, dissolve a small sample of dry chemical in water. Using a 9-volt conductivity tester will determine whether a sample is conductive or semi-conductive. This data is especially helpful when following a flowchart.

Solubility: All samples can be divided into two fields--soluble and non-soluble. Water is used to perform this test.
 * Soluble Samples: sodium acetate, sodium chloride, sodium hydrogen carbonate, sodium carbonate, lithium chloride, potassium chloride, calcium nitrate, glucose, sucrose, magnesium sulfate, boric acid, ammonium chloride
 * Non-soluble Samples: calcium sulfate, calcium carbonate, cornstarch

Blood Spatters
Blood Spatters are generally classified by velocity at which they form.

Polymers
Methods of Identification
 * Burn test (fibers and hair only)
 * Density in liquids--oil, water, alcohol, etc. (plastics)

Hints Burn tests for fibers, when permitted, will usually be done with a small candle (Bunsen burners are too hot). Burn tests on plastics will not be permitted at the event, but burn test results may be provided. If not, it is important to know densities and other identifying properties. Common liquids used to test plastic densities include water, vegetable oil, isopropyl alcohol, and NaCL solution.