I said the questions on this exam would be classical, but I still have to give you the set-up!! You are the newest members of the DEA's (Drug Enforcement Agency) special unit on cocaine analysis, but this is a probationary period and you really need to keep this job- your answers to the following questions will determine your job status. Express all numerical answers to the correct number of significant digits! Please use front and back of the pages for your answers - ask for additional pages if needed.

1. Your first task involves one of the largest busts in history. While the total amount of cocaine is large, the individual packages are numerous. 2000 packages containing ~1lb of cocaine each were recovered and you must devise a sampling scheme that can give an approximate purity of the cocaine within the hour to be able to hold the dealers. A single sample analysis takes 3 minutes from start to finish, and the mobile lab can only handle one sample at a time.

2. You found traces of THC in the cocaine at 50.0ppb. Express the concentration in terms of molarity, ppm, molality, and % mass

3. The balance that you used to weigh the cocaine needs to be corrected for buoyancy. Assume an average wt of each package of 2.23kg, d_a=0.0012g/mL, d_w=8.0g/mL, and d_cocaine=2.131g/mL.

Calculate the following for each method; avg., Std dev, 90% confidence interval, Q-test, and compare the two methods at the 95% confidence level.

5. Explain calibration curves, internal standards, and standard addition. Give an example of how each is prepared and why you might use each.

6. Why was equilibrium so important to the Potomac River, identify specific equilibrium conditions that had an impact.