8th STEM Vitamin C Titration
Safety and setup:
Ø Safety googles must be worn for the duration of this experiment.
Ø Long hair must be secured in a bun prior to starting the experiment.
Ø Bulky jackets and sweatshirts are not permitted.
Ø Please store backpacks and materials away from benches and the floor surrounding them.
Ø Use caution when handling the iodine and wash hands thoroughly if contact occurs.
Ø Handle all glassware and instruments with care.
Ø Please thoroughly wash and dry all glassware when finished.
Ø Please thoroughly wash and dry the benches when finished.
Ø Please thoroughly wash hands before leaving the lab.
Ø Please arrive to lab on time and ready to work.
Background:
To further our study of atoms and ions, we are going to run a chemical reaction that changes an atom to an ion by reacting a neutral substance with an acid. We will do this by adding iodine solution to samples that contain Vitamin C, also known as ascorbic acid. In order to run this reaction, we will perform a simple titration reaction. A titration reaction is the slow addition of one solution of a known concentration (called a titrant) to a known volume of another solution of unknown concentration until the reaction reaches neutralization, which is often indicated by a color change. This color change is known as the endpoint. The solution called the titrant must satisfy the necessary requirements to be a primary or secondary standard. In a broad sense, titration is a technique to determine the concentration of an unknown solution.[1]
The chemical reaction that represents the titration we will perform is:
iodine + ascorbic acid dehydroascorbic acid + iodide ions + hydrogen ions
I2 + C6H8O6 C6H6O6 + 2I- + 2H+
Given the fact that iodine has a brown color when in solution, and iodide ions (the result of iodine reacting with ascorbic acid) are colorless in solution, we can make the iodide ions visible by adding starch – this makes a blue-black colored complex (something comprised by joining different types of molecules). In this titration, starch is the indicator - a chemical compound that changes color and structure when exposed to certain conditions and is therefore useful for chemical tests. We can use this reaction to compare the amounts of Vitamin C in different juices/supplements. To do this, we will add an iodine solution drop by drop to the juice to see how much iodine is needed to react with all the Vitamin C in the juice. The drops of iodine can be tallied so that a volume can be recorded. The concentration of the iodine we are using is 1g/100 mL. You will need to know this concentration to determine the concentration of Vitamin C in each of your samples.
Essential Question: Do you think juices/supplements with more Vitamin C will use more or less iodine to complete the titration reaction?
In order to gain a better understanding of the benefits of Vitamin C, please read the article on the article entitled, "Health Benefits of Vitamin C or Ascorbic Acid | Organic Facts" from this link: https://www.organicfacts.net/health-benefits/vitamins/health-benefits-of-vitamin-c-or-ascorbic-acid.html
In your notebook, please take notes on the procedure Mrs. Bork will demonstrate regarding how you will run your experiment. You need to come to lab prepared and ready to go as this experiment will take the entire class period.
[1] www.chemistrylibretexts.com; 12 July 2016