Introduction
Vitamin C, also known as ascorbic acid, is an antioxidant that is essential for humans. The main source of vitamin C for most people is raw citrus fruits and their juices. There are several benefits of vitamin C including boosting your immunity, improving iron absorption, and reducing blood pressure. According to the FDA, the recommended daily allowance (RDA) for adults is 90 mg/day1 Dietary Supplement Label Database https://www.dsld.nlm.nih.gov/dsld/dailyvalue.jsp.
One way to determine the amount of vitamin C in juice is to use a redox titration. In a redox titration, one compound donates electrons to another compound. The compound losing electrons is oxidized and the compound gaining electrons is reduced. A redox titration is a better choice than an acid-base titration because the reaction is selective for vitamin C and the titrant doesn’t react with other acids in the juice.
In this redox reaction, vitamin C is oxidized to dehydroascorbic acid while iodine is reduced to iodide:
C6H8O6 + I2  → C6H6O6 + 2I– + 2H+
Iodine is relatively insoluble, but this can be improved by complexing the iodine with iodide to form triiodide. Triiodide also oxidizes vitamin C to form dehydroascorbic acid:
C6H8O6 + I3– → C6H6O6 + 3I– + 2H+
The triiodide ion is formed using iodate and iodide in an acidic solution according to the following equation:
IO3– + 8I– + 6H+ → 3I3– + 3H2O
In this experiment, you will use an Oxidation-Reduction Potential (ORP) Sensor to monitor the redox titration of vitamin C from a juice sample and determine its concentration.
Objectives
- Titrate a vitamin C solution.
- Determine the concentration of vitamin C in the solution.
Sensors and Equipment
This experiment features the following sensors and equipment. Additional equipment may be required.
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This experiment is #12 of Food Chemistry Experiments. The experiment in the book includes student instructions as well as instructor information for set up, helpful hints, and sample graphs and data.
