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Name: ______________________ Glass Fragment Lab "There was a hit and run car accident in the school parking lot this morning. The police have requested that the students from this class compare the glass fragments found at the crime scene with those taken from two suspect vehicles. You will need to report your findings to the police department as soon as possible." Directions: In this lab, you will be required to note physical characteristics of individual glass fragments as well as determine their density and refractive index. For each glass fragment, try to use a descriptive physical property that will distinguish one fragment from the next (for example, color, thickness etc.,be detailed). Next determine the density (d = m/v) using the method below. Then do the refractive index for each glass fragment in each type of liquid. Then try to match the suspect with the crime scene. Procedure: 1. Obtain a balance, a beaker and a piece of wire 2. Obtain the Sample glass fragment 3. Mass the Sample fragment and record the value. 4. Place the beaker filled ¾ of the way with water on the balance and zero the balance 5. Wrap the wire around the glass fragment and suspend the wire and glass fragment from the glass rod. 6. Weigh the glass fragment suspended in water (adjust holding the rod so that the glass is not touching the walls of the beaker) 7. Record the weight of the glass fragment and convert to milliliters. (1g water =1ml) 8. Repeat this process for the other samples 9. Determine the density of each fragment in your data table Physical characteristics Mass Volume (ml) Density (g/ml) (thickness in mm, (grams) texture, clarity, color Window glass Bottle glass Tempered Glass Light bulb Laminated glass Physical characteristics Mass Volume (ml) Density (g/ml) (thickness in mm, (grams) texture, clarity, color Crime Scene Suspect #1 Suspect #2 Refractive Index test PROCEDURE: 1. With forceps, lower a sample piece of glass into a beaker with liquid of a known refractive index. Does it seem to disappear? 2. Test each type of glass in each type of liquid. LEAVE THE GLASS SAMPLES AT EACH LIQUID!! THIS WILL PREVENT CONTAMINATION BETWEEN LIQUIDS. 3. Record the liquid in which the sample tends to disappear. Using the following scale to rate: 1 = No change just looks larger 2= Blurs but can still see glass sample 3= slightly disappears but can still make out edges 4=disappears completely 4. Repeat with each liquid available. Sample Corn oil Castor Oil Mineral Oil Water Honey RI=1.473 RI = 1.482 RI = 1.476 RI = 1.330 RI = 1.484-1.494 Window Glass Laminated Glass Bottle Glass Tempered Glass Light bulbs Crime Scene Suspect #1 Suspect #2 Headlight glass has an IR of 1.47 - 1.49 Window glass and most bottles have an IR of 1.51 – 1.5 Write a conclusion for the Lab should be in paragraph format; be sure to include answers to the following questions in your conclusion: 1. List three methods used by forensic scientists to analyze glass fragments. 2. Describe the difference between physical and chemical properties. 3. What chemicals are used to make glass? 4. Where would a crime scene technician look for glass fragments? 5. Describe the glass making process. What changes in this process result in the difference between windows and tempered glass? 6. Why is laminated glass used for the windshields of vehicles? 7. Explain how refractive index is found. 8. Who committed the crime and what type of glass was found at the crime scene and in the two suspects vehicles?
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