II. Introduction:
Ascorbic acid or vitamin C is the analyte of this experiment.It is the most appropriate vitamin used to treat colds.It acts as a natural antihistamine that reduces the severity of cold symptoms and it is also used for allergy control.It is an antioxidant and makes headlines when it comes to cancer prevention.Besides,it helps to prevent cataracts,heart diseases and regulate blood sugar levels.
III. Purpose:
1-To practice redox titration.
2-To determine the amount of vitamin C present in vitamin C tablet. IV.Equippments,tools,chemical reagent: -starch solution 0.2% -potassium iodate KIO3 -potassium iodide KI -sulfuric acid H2SO4 0.6 M -sodium carbonate Na2 CO3 -vitamin C tablet -sodium thiosulfate Na2S203 -analytical balance -10 ml and 25 ml pipettes equipped with pipette bulb - burette -distilled water - dropper - 250 ml Erlenmeyer -500ml volumetric flask - graduated cylinder -beakers V.Experimental procedure: Reference experiment number 7,lab manual phar 205,2012 p.65 .
VI.Theory: Rather than titrating directly with iodine,an excess of iodine will be generated directly in the solution with ascorbic acid according to the following equation: IO3- + 5I- +6H+ → 3I2 + 3H2O Vitamin C is readily oxidized with I2 in acidic medium. Ascorbic acid + vitamin C → dehydroxyascorbic acid + 2H+ +2I- A back titration is performed since standard solution lacks stability.Excess I2 that did not react with ascorbic acid is then back titrated with standard sodium thiosulfate solution which is a strong reducing agent.