2. Fingerprint Project

3. Objective Students will demonstrate the ability to explain, design, and calculate stoichiometric problems with the investigation of a chemical reaction used to retrieve latent finger prints from crime scenes.

4. Background Silently read over the Chemistry of Latent Fingerprints handout while I read the background aloud. Chemical Reaction Silver nitrate (AgNO3) can react with the salt (NaCl) left from the perspiration on the friction ridge skin to form solid silver chloride (AgCl) and sodium nitrate. The silver chloride can then be converted to silver oxide (Ag2O), which is dark in color and can be more easily seen.

5. Problem Suppose the fingerprint processing technique that uses silver nitrate to react with the salt from perspiration produced 5.8 x 10 -2 grams of silver chloride. How many grams of salt was left by the initial latent fingerprint?

6. Instructions On a poster illustrate the steps to solving this problem. Be sure to include each step of the process – Write the chemical equation – Balance the chemical equation – Follow the steps to dimensional analysis Start with what is given Set up a series of equivalent measures End with your goal Solve the problem by cancelling units Record the appropriate answer with units. Create a small scenario where the fingerprints were collected.

7. Rubric and Deadline This is a SUMMATIVE assessment. Your poster should include: – A written or typed unique scenario where the fingerprints were collected- (2-3 complete sentences!) (10 points) – The problem and answer (20 points) – The balanced equation (20 points) – Steps for calculating the problem along with a visual showing the steps (40 points) – Illustrations or visuals relating to the theme of the project (10 points) The poster is due at the end of class on Monday Feb 9 th

8. Extra Credit (+5) On a separate sheet of paper Using the same chemical reaction determine the number of grams of silver nitrate needed to produce 110 grams of silver chloride. Turn this in with your poster at the end of class on Monday.

9. Example Poster Follows…However A picture of the example poster is online now. A copy of this ppt is on my website along with the latent fingerprint background information. This assignment must be completed on a poster NOT computer paper! (-20 points) Be creative with your poster layout! Make it unique…like a finger print!

10. Name: John Doe Period 6 Scenario : Fingerprints found on Lego building blocks helps police crack a 23-year-old cold case murder mystery in Utah. The fingerprints were found in the entryway of the victims living room. Problem: Suppose the fingerprint processing technique that uses silver nitrate to react with the salt from perspiration produced 5.8 x 10 -2 grams of silver chloride. How many grams of salt was left by the initial latent fingerprint? Balanced Equation: AgNO 3 + NaCl  AgCl + NaNO 3 Steps for Stoichiometric Calculations: Start with what is given Set up a series of equivalent measures End with your goal Solve the problem by cancelling units Record the appropriate answer with units. ANSWER: g NaCl 5.8 x 10 -2 g AgClg NaCl