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Back titration problem - Analysis of OTC Vitamin C Twenty 350 mg tablet of ascorbic acid was dissolved in water and diluted to 250 mL in a volumetric flask. A 25.00 mL aliquot was added with 50.00 mL standardized 0.0925 M 12. The solution turned brown due to the excess 12. The excess 12 was back titrated with 19.25 mL standard 0.09890 M Na2S2O3 until lemon yellow. Starch was added to produce a violet complex and titration was continued until the solution becomes colorless by addition of 2.25 mL Na2S2O3 titrant. Calculate the %w/w ascorbic acid in one tablet. MW ascorbic acid = 176.12 I