Presentation on theme: "Determination of Vitamin C Concentration by Titration"— Presentation transcript:
1 Determination of Vitamin C Concentration by Titration Ascorbic acid(Vitamin C)How much vitamin C is in fresh squeezed orange juice?Compared to orange juice, are vitamin C tablets a good source of vitamin C?
3 Vitamin C, more properly called ascorbic acid, is an essential antioxidant needed by the human body. oxidized vitamin CWe will determine the amount of vitamin C using a redox titration method. The chemical name for vitamin C is ascorbic acid.I2 + C6H8O6 → C6H6O H I–oxidized vitamin Cvitamin CWe need to have a standardize diodine solution
4 I2 + starch → Iodine-starch complex I2 + C6H8O6 → C6H6O H I–vitamin Coxidized vitamin CNone of these substances have a distinctive color. How will we know how much I2 to add?After all the vitamin C has reacted, excess I2 begins to react with starch indicator solution to form a colored complex with.I2 + starch → Iodine-starch complex
5 Acorbic acid + I2 → 2 I - + dehydroascorbic acid ExperimentThis method determines the vitamin C concentration in a solution by a redox titration using iodine.As the iodine is added during the titration, the ascorbic acid is oxidized to dehydroascorbic acid, while the iodine is reduced to iodide ions.Acorbic acid + I2 → 2 I - + dehydroascorbic acid
6 ExperimentDue to this reaction, the iodine formed is immediately reduced to iodide as long as there is any ascorbic acid present.Once all the ascorbic acid has been oxidized, the excess iodine is free to react with the starch indicator, forming the blue-black starch-iodine complex.This is the endpoint of the titration.The method is suitable for use with vitamin C tablets, fresh or packaged fruit juices and solid fruits and vegetables.
7 Solutions Needed Iodine solution: (0.005 mol L−1). Weigh 2 g of potassium iodide into a 100 mL beaker. Weigh 1.3 g of iodine and add it into the same beaker. Add a few mL of distilled water and swirl for a few minutes until iodine is dissolved. Transfer iodine solution to a 1 L volumetric flask, making sure to rinse all traces of solution into the volumetric flask using distilled water. Make the solution up to the 1 L mark with distilled water.Starch indicator solution: (0.5%).Weigh 0.5 g of soluble starch and add it to 50 mL of near boiling water in a conical flask. Stir to dissolve then complete to100 mL and cool before using.
8 Titration1.Pipette a 20 mL aliquot of the sample solution into a 250 mL conical flask and add about 1 mL of starch indicator solution.2. Titrate the sample with mol L−1 iodine solution. The endpoint of the titration is identified as the first permanent trace of a dark blue-black colour due to the starch-iodine complex.3. Repeat the titration with further aliquots of sample solution until you obtain concordant results (titres agreeing within 0.1 mL)
9 Burette containing iodine solution TitrationInitially you will see a deep blue color appear in the area that the drop is added. Once you begin to see a deep blue color that persists throughout the solution, add the titrant more slowly and swirl after every drop. Continue adding titrant until you obtain a blue color that lasts 60 seconds.Record the final number of ml Iodine added.Repeat the experiment once or twiceConical flaskAdd I2I2Vitamin C or sample solution +Starch indicatorSwirl
10 Calculations:Assume that the sample solution of vit.C was prepared by extraction of 10 g sample and completed to the total volume of 100mlCalculate the concentration of vit. C in mg/100mL or mg/100g of ascorbic acid, in the sample where:1ml of Iodine mol/L equivalent to 0.88 mg ascorbic acid or vitamin C
11 Explanation1ml of Iodine mol/L equivalent to 0.88 mg ascorbic acid or vitamin CAt the end point of titrationC1 V1 of iodine =C2V2 of ascorbic acidWeight of ascorbic acid (mg)= Volume(ml) X Concentration X Molecular weight of ascorbic acidWeight of ascorbic acid (mg )=1mlX0.005X176= 0.88 mg