Record this weight. Clean and dry the polarimeter tube. Add distilled water to the level of the solution used for the optical measurement. Weigh the combined tube plus water and record this weight. The concentration of naproxen in solution can now be calculated as the weight of naproxen divided by the volume of solution.
Units are grams per milliliter.
Dissolve the sodium salt from step 3 in water. Treat with aqueous HCl to precipitate the free acid. Dissolve the free acid in chloroform and extract the organic solution from the water. Rinse the MgSO 4 and flask with fresh chloroform and add the filtered rinsings to the original filtered solution. Evaporate excess chloroform until the volume of the solution fits into a polarimeter tube.