# Analysis of Commercial Vitamin C Tablets

Topics: Vitamin C, Iodine, Ascorbic acid Pages: 6 (1957 words) Published: October 23, 2008
Analysis of commercial vitamin C tablets
Objective
To determine the vitamin C content in commercial vitamin C tablets by titration between vitamin C (ascorbic acid) & iodine solution. Hence, compare this data with the manufacturer's specification. Principle

In this analysis, certain amount of iodine solution, which is known in excess, is added to acidified ascorbic acid solution. Brown iodine can be easily reduced by acidified ascorbic acid to form colourless iodide ion: ← Equation I

The excess iodine is then back titrated by standard sodium thiosulphate solution, by using a burette and starch solution (used as end point indicator) Similarly, iodine can also be decolourized by thiosulphate ion: 2S2O32- + I2 → S4O62- + 2I- ← Equation II Any iodine present will react with starch to form a blue-black complex. However, when all available iodine has been reacted, the blue-black complex becomes colourless which signals the end-point. Hence, the mass of ascorbic acid reacted by iodine can be calculated. Chemicals

vitamin C tablet(s), NaIO3, 1M NaI solution, 0.5M H2SO4, approximately 0.06M Na2S2O3, freshly prepared starch solution Apparatus
electronic balance, beaker, volumetric apparatus, pipette, glass rod, white tile, dropper, measuring cylinder Procedure

Mass of NaIO3 : 0.63 g ∴ Molarity of 250cm3 standard NaIO3 solution : (0.63 ÷197.89 ÷ 0.25)M = 0.012734 M By equation III, no. of moles of I2 formed = no. of moles of NaIO3 x 3 ÷10 = (0.63 ÷197.89 x 0.3)mol = 9.550761x10-4 mol By equation II, no. of moles of S2O32- needed to react all I2 = no. of moles of I2 formed x 2...