Using Properties to Identify Materials
Forensic chemists test the physical and chemical properties of materials found at a crime scene. They also do similar tests on the materials found on a suspect's skin or clothing. These materials are often complex mixtures, such as soil, which contain many substances. In this lab, yo will compare the properties of three known materials with two samples of “evidence.” These samples represent evidence from a crime scene and evidence from a suspect's shoe. Although your materials and equipment are less complex than those used by forensic chemists, your overall method will be similar to the methods they use.
Problem Can the properties of materials that appear similar be used to tell them apart?
Materials
2 spot plates
glass-marking pencil
5 laboratory spatulas
cornstarch
baking soda
baking powder
wash bottle of water
vinegar
iodine solution
sample from crime scene
sample from suspect's shoe
Skills Observing, Inferring, Predicting
Procedure
Part A: Properties of Known Substances
On a separate sheet of paper, copy the data table shown.
Use a glass-marking pencil to label 15 wells A through O on the spot plates. Make a mark next to each well, not in the well.
Use a spatula to place a small amount of cornstarch in wells A, B, and C. Record any physical properties of the cornstarch that yo observe.
Use a clean spatula to place a small amount of baking soda in wells D, E, and F. Record any physical properties of baking soda yo observe.
Using a clean spatula, place a small amount of baking powder in wells G, H, and I. Record any physical properties of baking powder yo observe.
Fill wells A, D, and G with water. Record any changes yo observe.