What percent of the naproxen in the original tablets was recovered? There is more to this than you might think, since you started with naproxen sodium and ended up with the free acid, and they have different molar masses. To answer this question, calculate the number of moles of free acid that you obtained and compare it to the number of moles of naproxen sodium that you started with.

Data of the experiment

mass of two naproxen tablets = 0.550 g, Mass of naproxen that was recovered= 0.383 g, melting point of product = 147-150oC, grams of naproxen used to make the methylene chloride solution = 0.18 g. Attach a copy of the IR spectrum (see the last page of the Naproxen report form that follows).

Experimental procedure

1. Obtain two naproxen sodium tablets (a 220 mg dose in each) and weigh them to the nearest 0.01 g. Place the tablets in a small beaker and add enough 95% ethanol to cover them. After a few minutes, the enteric coating will start to dissolve. Use a rubber policeman or spatula to remove the coating, being careful not to damage the tablet underneath. Once the coating is mostly gone, remove the tablets from the beaker and use a Kimwipe to wipe them clean.

2. Fold the two tablets up in a piece of weighing paper and then fold this packet up in another piece of weighing paper. Crush the tablets using mortar and pestle (the weighing paper makes it easier to transfer the resulting powder.)

3. Transfer the powder to a large 16x100 test tube. This is tube #1. Add 5 mL of ethyl acetate and 4 mL of 6M HCl. Repeatedly suck the liquid up into a pipet and squirt it back into the tube. The goal is to, by the end of the next few steps, have most of the naproxen either dissolved in water or in ethyl acetate. The undissolved white material in the tube is due to the inactive ingredients, which include cellulose.

4. Allow the organic (ethyl acetate) and aqueous (6M HCl) phases to separate. Use a pipet to transfer the top organic layer into a clean large 16x100 test tube (this is tube #2), leaving some of the organic layer behind to avoid transferring any of the aqueous layer. Do not transfer any undissolved white material or bottom layer. 5. Add 3 mL of ethyl acetate to tube #1 and repeat the mixing (squirting) process. Let the organic and aqueous phases to separate and use a pipet to add the top organic layer (leave some behind again) to the organic solution already present in tube #2.

6. Add another 3 mL of ethyl acetate to tube #1, repeat the mixing process, allow it to settle, and transfer the top organic layer (this time take as much as you can without also taking aqueous layer) into tube #2. You are now finished with tube #1.

7. Add 2 mL of saturated aqueous NaCl to tube #2, mix by squirting, allow it to settle, and remove the bottom aqueous layer (take just a bit of organic layer too, to make sure that all of the aqueous layer is gone.) Aqueous NaCl is very polar and will help extract any water-soluble compounds from the organic (ethyl acetate) layer. Add anhydrous sodium sulfate (Zubrick tells you how much to add) to tube #2 to dry the solvent, and then allow it to settle.

8. Tare (preweigh) a large watch glass and then, in a fume hood, carefully decant the organic layer from tube #2 into the watch glass. Leave the white sodium sulfate solid behind. The solvent will evaporate, leaving behind the naproxen product. Expect to get this far on day #1 of the experiment.

9. Reweigh the watch glass and determine the weight of naproxen.

Analysis of product.

10. Using a small bit of product, obtain an IR spectrum. A video containing IR information (some theory, how to obtain and interpret a spectrum) can be found in the Panopto folder of Canvas: Polarimetry and IR spectroscopy in the Naproxen folder. Another good video is VR-based, and lets you look around the lab as the experiment is being run: https://go.ncsu.edu/vrlab-ir-spectroscopy

11. Using a small bit of product, take the melting point.

12. Obtain a 10mL volumetric flask. Weigh out 0.20 g of your product (if you have less than 0.20 g, use it all and be sure to record how much you actually added) and transfer it to the flask.

13. Add methylene chloride (CH2Cl2) to the 10 mL flask (do this in the hood!), filling it about of the way to the fill line. Stopper the flask and let it sit (you may shake it if you want) until all of the product has dissolved. At that point, carefully fill the flask the rest of the way to the fill line with methylene chloride.

14. Find your instructor for help in setting up the polarimeter.

15. Measure the optical rotation of your methylene chloride solution. The polarimeter tube that you will use will be 2.0 dm long.