B. %SO3 determination 1. Dry the soluble sulfate sample at 100°C for 1-2 hours, and cool in desiccator. Weigh out 0.5 – 0.7 g (± 0.3 mg) duplicate samples. Transfer to 400-mL beakers. Dissolve each in 200 mL of dist. H2O + 4 mL of 6M HCI. 2. Precipitant is prepared by dissolving 1.3 g BaCl2 · H2O in 100 mL water. Filter if solution is not perfectly clear. 3. Heat the BaCl2 solution and sulfate sample solution nearly to boiling, and then add the entire amount to the HOT sulfate sample solution while stirring vigorously. Wash stirring rod with distilled water and include washings in your final mixture. 4. Digest by letting stand for 1-2 hours. Overnight standing is acceptable. Filter through an ashless filter paper of fine porosity (Whatman no. 42). Slowly pour the supernatant liquid through the filter paper. 5. Transfer all precipitate to the filter paper avoiding any loses during the filtration procedure. One may use a rubber policeman to scrape remaining precipitate in the beaker. Wash the precipitate in the beaker 3X with hot water before transferring to the filter paper. Test the washings with 0.1 M AgNO3 solution. Cloudiness indicates presence of chloride ions, therefore there is a need to wash more the precipitate. Carefully lift the paper out of the funnel, fold it as demonstrated by your instructor and transfer it onto the constant weighed crucible. 6. Dry the crucible cautiously with a small flame, as instructed by your instructor. The flame should be directed at the top of the container, and the lid should be off. Avoid spattering. After drying, char the filter paper by increasing the flame temperature. The crucible should have free access to air. The lid should be kept handy to smother the filter paper in case it catches fire. Any soot left in the crucible and the lid should be removed by directing these to the flame. Use tongs to manipulate crucible. Finally, ignite the product for 15 minutes with the full heat of the burner. 7. Cool the crucible, briefly in air and then in a desiccator for 30 min. weigh the crucible, re-ignite, and bring to constant weight (±0.3 mg) with repeated heatings. 8. Calculate the %SO3 in the sample, the average, SD, and % RSD.