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Analysis of Commercial Vitamin C Tablets

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EXPERIMENT ( 1 ) Topic : Analysis of Commercial Vitamin C Tablets Introduction : In this experiment the vitamin C content of commercial tablets is determined titrimetrically and compared with the manufacturers' specifications. Vitamin C is ascorbic acid which is rapidly and quantitatively oxidized by iodine in acid solution according to the following equation : C6H8O6(aq) + I2(aq) --> C6H6O6(aq) + 2 H+(aq) + 2 I-(aq) The standard method for determination of ascorbic acid involves the direct titration of the acidified sample with a standard iodine solution. But the low solubility of iodine makes this procedure less than ideal. The proposed experiment avoids these difficulties by generating in situ a known excess quantity of iodine by the reaction between iodate(V) & iodide : IO3-(aq) + 5 I-(aq) + 6 H+(aq) --> 3 I2(aq) + 3 H2O(l) After reacting with ascorbic acid, the remaining iodine may then be titrated against standard sodium thiosulphate solution. Chemicals : Vitamin C tablets , 0.05 M Na2S2O3 , 0.5 M H2SO4 , 1 M KI , KIO3 , Starch solution (freshly prepared) ...read more.


tablet = ___________5.68____________ mole Mass of Vitamin C content of the tablet = __________0.659____________ g Table 1 Titration 1 2 3 4 Final Burette Reading (ml) 29.20 27.10 29.80 28.00 Initial Burette Reading (ml) 11.10 10.10 12.30 9.70 Volume of titrant (ml) 18.10 17.00 17.50 18.30 Mean volume of titrant (ml) = ________17.60_________ Table 2 Titration 1 2 3 4 Final Burette Reading (ml) 9.60 14.30 9.40 13.60 Initial Burette Reading (ml) 5.60 9.60 5.30 9.40 Volume of titrant (ml) 4.00 4.70 4.10 4.20 Mean volume of titrant (ml) = _________4.33_________ Questions : 1. What is the function of the starch solution? Why should it be added only when the reaction mixture becomes pale yellow? When the reaction mixture becomes pale yellow, it is more difficult to recognize whether the reaction mixture to reach to the end point, the starch solution can let the reaction mixture color more apparent. 2. Why is it preferable to carry out the titration immediately after the addition of sulphuric acid in step 3(b) ...read more.


It is due to the deterioration of vitamin C which is exposure in the air for the period of time. 4. What is the mass of the ascorbic acid per tablet? How does the result compare with the manufacturers' specification ? The mass of the ascorbic is 659mg. Compare with the manufactures' specification, it is only a little bit lighter. Hence I think the is manufactures' specification quite accurate. 5. Why is it preferable a tablet without flavouring & colouring ? Because the flavouring may affect the actual mass of the main constituent. And the colouring may affect the color change in the titrate experiments. 6. What is the term given to this kind of titration ? It is called back titration. The reagents haven't a suitable indicator for detecting the end point, so we need against the other reagents which it can be indicator for detecting the end point of titration. 7. Vitamin C is an anti-oxidant. State another vitamin that is also an anti-oxidant. Vitamin E. It can act as a natural antioxidant by scavenging free radicals and molecular oxygen. The vitamin E and C are interrelated in their antioxidant capabilities. ...read more.

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