Question

an alternative titration method for determining the concentration of vitamin C in a sample is through the use of iodine. In this reaction, iodine oxidizes the ascorbic acid to C6H6O6. A 20.00 mL sample of a 1.00 mg/mL vitamin C solution is placed in a flask along with 1 ml of a 1% starch solution to serve as an indicator. A dilute solution of idoine is placed in a buret. A titration is performed using the intense blue color produced by the reaction of excess I2 with the starch as an indicator that the end point has been achieved. The titration is repreated using a 20.00 mL sample of juice.

Answer 1

The determination of vitamin C concentration in a sample is achieved through a redox titration using iodine, with a starch indicator marking the end point by forming a blue complex with excess iodine.

Step-by-step explanation:

The concentration of vitamin C in a sample such as orange juice can be determined by a redox titration using iodine. In this method, iodine (I2) acts as the titrant and oxidizes the ascorbic acid to dehydroascorbic acid. The presence of excess iodine can be detected with a starch indicator, which forms a deep blue complex with iodine. The end point of the titration is characterized by the appearance of this blue color, indicating that all of the ascorbic acid has been oxidized.

To report the concentration of ascorbic acid in the sample, one would perform the titration and calculate the amount of iodine reacting with the sample. A back titration, such as the reaction with sodium thiosulfate (Na2S2O3), can be used to measure any excess iodine. Together, these measurements allow for the calculation of the ascorbic acid concentration in the juice sample.