The goal of this experiment is to determine the amount of vitamin C in a sample by a
redox titration.
Background
What is Vitamin C?
Vitamin C, known chemically as ascorbic acid and L-ascorbic acid, is a vitamin found in
various foods and sold as a dietary supplement. The body requires vitamin C to form
and maintain bones, blood vessels, and skin. This is a water- soluble vitamin, one that
cannot be stored by body except in insignificant amounts. It must be replenished daily.
The history of vitamin C revolves around the history of the human disease scurvy,
probably the first human illness to be recognized as a deficiency disease. Its symptoms
include exhaustion, massive hemorrhaging of flesh and gums, general weakness and
diarrhea. Resultant death was common. Scurvy is a disease unique to guinea pigs,
various primates, and humans. All other animal species have an enzyme which
catalyzes the oxidation of L-gluconactone to L-
ascorbic acid, allowing them to synthesize Vitamin
C amounts adequate for metabolic needs.
Vitamin C can be determined in food by use of an
oxidation-reduction reaction. The redox reaction is
preferable to an acid-base titration because a
number of other species in juice can act as acids,
but relatively few interfere with the oxidation of ascorbic acid by iodine.
What is a redox titration?
Titration is a laboratory method that is used to determine the concentration or mass of a
substance (called the analyte) by measuring it against a standardized titrant. A solution
of known concentration, called the titrant, is added to a solution of the analyte until just
enough has been added to react with all of the analyte (the equivalence point). If the
reaction between the titrant and the analyte is a reduction- oxidation reaction, the
procedure is called a redox titration. This type of titration involves a redox indicator or a
potentiometer.
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