Rinse your buret with a small volume of the iodine solution and then fill it.Add 25.00 ml of vitamin C standard solution to a 125 ml Erlenmeyer flask.Label the flask as your vitamin C standard solution. Dilute to 250 ml with distilled water in a volumetric flask.Dissolve 0.250 g vitamin C (ascorbic acid) in 100 ml distilled water.Label the beaker as your iodine solution. Transfer the solution to a 600 ml beaker.Pour this solution into a 500 ml graduated cylinder and dilute it to a final volume of 500 ml with distilled water.

Dissolve 5.00 g potassium iodide (KI) and 0.268 g potassium iodate (KIO 3) in 200 ml of distilled water.

Mix well and allow to cool before use.

Add 0.50 g soluble starch to 50 near-boiling distilled water.

What matters is that you know the concentration of the solutions and the volumes that you use. We've listed examples of quantities, but they aren't important. The first step is to prepare the solutions.

The goal of this laboratory exercise is to determine the amount of vitamin C in samples, such as fruit juice. The titration can be performed using just iodine solution and not iodate, but the iodate solution is more stable and gives a more accurate result. This titration procedure is appropriate for testing the amount of vitamin C in vitamin C tablets, juices, and fresh, frozen, or packaged fruits and vegetables. The blue-black color is the endpoint of the titration. However, when all the vitamin C is oxidized, iodine and triiodide will be present, which react with starch to form a blue-black complex. Triiodide oxidizes vitamin C to form dehydroascorbic acid:Д¬ 6H 8O 6 + I 3 - + H 2O в†’ C 6H 6O 6 + 3I - + 2H +ДЄs long as vitamin C is present in the solution, the triiodide is converted to the iodide ion very quickly. Iodine is relatively insoluble, but this can be improved by complexing the iodine with iodide to form triiodide: The redox reaction is better than an acid-base titration since there are additional acids in a juice, but few of them interfere with the oxidation of ascorbic acid by iodine. One way to determine the amount of vitamin C in food is to use a redox titration.

Juices with vitamin c