Analysis of Vitamin C content
Goal: Show how this exercise explores the interconnectedness of Biology, Chemistry, and Mathematics? The Biologist will explore the role of vitamin C in maintaining a healthy body and the disease that result when there is vitamin C deficiency. The Chemist will describe the chemistry of vitamin C and the determination the concentration in a sample. Mathematics is the tool that will bridge the two sciences.
To complete this module, data sets from completed exercises will be added. To make the exercise come alive especially for the visual learners, images of the laboratory set up can be added side by side with the description of the procedure.
Introduction:
Pills for the most part, come in various colors, forms, and sizes. The active ingredient is “incorporated” in a variety of fillers, most often starch or sugar. In this exercise, the student groups analyze the vitamin content of a Vitamin C tablet and calculate the percentage of ascorbic acid present, H2C6H6O6, in the tablet. Ascorbic acid has two ionizable hydrogens but the second one comes off only at a pH of 10 or 11. The reaction of ascorbic acid with sodium hydroxide will produce the acid salt, sodium hydrogen ascorbate, and not the normal salt when titrated using an indicator like phenolphthalein or bromothymol blue. This is a quantitative lab exercise so all measurements and calculations must be recorded to the proper number of significant digits.
Procedure:
Grind a tablet of Vitamin C with mortar and pestle. Dissolve the powder in 50 mL of warm distilled water in an Erlenmyer flask, stirring with a glass stirring rod. Add two or three drops of indicator to the flask to produce a colored solution. Using data acquisition devices such as Logger Pro (Vernier, titrate with sodium hydroxide solution until the endpoint is reached.
Expected Outcome:
- Write a balanced equation for the reaction of sodium hydroxide with ascorbic acid to form sodium hydrogen ascorbate.
- Calculate the number of moles of sodium hydroxide that reacted with the ascorbic acid at any time during the reaction.
- Calculate total the number of moles of ascorbic acid that was present in the tablet.
- Calculate the mass (in milligrams) of ascorbic acid present in the tablet. What percent of the whole tablet is the active ingredient?
- How will the percentage of ascorbic acid in the vitamin C tablet be affected if you forget to fill the tip of the buret with sodium hydroxide solution before you started the titration.
- If your lab partner "overshot" the endpoint in the second titration, would you be able to salvage the lab without compromising results? Explain.
References:
Vitamin C (Ascorbic Acid)
Analysis of Vitamin C