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The equation for the redox reaction between iodine and Vitamin C

Foundations of Chemistry Laboratory Manual VITAMIN C DETERMINATION 3F


concentration was used to determine the concentration of a solution of sulphuric acid. Acids

and bases are found everywhere from food, to our bodies to cleaning products.

There are too many individual chemical reactions for chemists to be familiar with all of

them, so they are divided into categories of reaction that have specific features. For

example, all acid-base reactions like the one between sulphuric acid and sodium hydroxide,

involve an acid which donates a proton to a base. This means that if a chemist knows what

category a reaction falls into they can make predictions about it even if they are unfamiliar

with the specific reacting molecules.

Another category of chemical reaction is the “redox” category. Redox reactions involve one

reactant losing an electron (or electron density) to another reactant. You will learn about

this category of reaction in Semester 2. Just like with acid-base reactions, titrations can be

used with redox reactions. In this experiment you will perform a redox titration to

determine the concentration of Vitamin C and two solutions.

Vitamin C, or ascorbic acid (C6H8O6), is an essential nutrient. Its structure can be seen in

Diagram 2.1 below. Many animals can produce it within their bodies, but humans must

obtain it through their diet. Vitamin C deficiency can lead to skin, bone and teeth issues and

a serious deficiency can cause death. Some sources of Vitamin C are fruits and vegetables

(including citrus fruits, green chili peppers and broccoli), their juices and Vitamin C tablets.

Diagram 2.1 The chemical structure of essential nutrient Vitamin C, one natural source and

synthetically produced Vitamin C tablets.

In determining the amount of Vitamin C in samples, the redox titration is more useful than

an acid-base titration as natural sources are comprised of other acids and bases that may

affect the results.

In this experiment, the redox reaction is between iodine and Vitamin C – the Vitamin C loses

electron density and the iodine accepts it. The overall equation is shown below:

C6H8O6 + I2  C6H6O6 + 2I- + 2H + Equation 2.1