Vitamin C resembles a monosaccharide, but its structure has several unusual features. The compound has a five-membraned unsaturated lactone ring with two hydroxyl groups attached to the doubly bonded carbons. This enediol structure is relatively uncommon. As a consequence of this structure feature, ascorbic acid is easily oxidized to dehydroascorbic acid. Both forms are biologically effective as a vitamin. There is no carboxyl group in ascorbic acid, but it is nevertheless an acid with a pKa of 4.17. The proton of the hydroxyl group is acidic, because the anion that results from its loss is resonance stabilized and similar to a carboxylate anion.
Humans and a few other vertebrates lack an enzyme that is essential for the biosynthesis of ascorbic acid from D-glucose. Hence ascorbic acid must be included in the daily diet of humans and these other species. Ascorbic acid is abundant in citrus fruits and tomatoes. Its lack in the diet causes scurvy, a disease that results in weak blood vessels, hemorrhaging, loosening of teeth, lack of ability to heal wounds, and eventually death. Ascorbic acid is needed for collagen synthesis.
The aim of this experiment was to see how different juices of the same brand have varying vitamin C content even though on the container it states the same RDI%(Recommended Daily Intake Percnetage).
It is hypothesised that the juices containing the larger amount of citrus fruit concentrate will have the larger vitamin C content.
EQUIPMENT & MATERIALS
- Safety goggles/Lab coat
- Four Fruit juices (100 mL)
- Vitamin C standard solution (1.0 g/mL)
- Starch solution (1%)
- Iodine solution
- Hydrochloric acid (HCl) 1M
- Distilled water
- 50-mL burette
- Retort Stand and Burette Clamp
- 10ml Graduated pipette and pumpette
- 25-mL Graduated cylinder
- Two 125-mL conical flasks
- Two 100-mL beaker
- A 10-mL graduated pipette was used to obtain 10.0 mL of the vitamin C standard solution, and placed in a flask. In a 25-mL graduated cylinder, 20 mL of distilled water was obtained and added to the vitamin C solution in the flask. This helped with the ease in observing for the endpoint because the water added did not enter into either the reaction or the calculations.