The elemental selenium dispersed in a dandruff control shampoo was determined by suspending a 10.0 mL sample in a warm ammonical solution that contained an excess of silver nitrate to give the following:
6 Ag? + 3Se(s) + 6NH3 + 3H2O → 2 Ag2Se(s) + AgSeO3(s) + 6NH4?
The mixed precipitate was filtered and washed free of excess Ag?. Treatment with excess nitric acid dissolved the AgSeO3 but not the Ag2Se. The Ag? produced from the dissolution of the AgSeO3 required 19.4 mL of 0.0166M KCl to reach the equivalence point in the titration of silver with chloride (Al? + Cl?→AgCl(s) ). How many milligrams of Se were there per milliliter of shampoo?