“Ascorbic acid: a strong antioxidant” experiment

How vitamin C prevents oxidation

Did you think that ascor­bic acid was just a tasty vi­ta­min? It’s also a pow­er­ful an­tiox­i­dant and reagent which can be used for im­pres­sive ex­per­i­ments! In this ex­per­i­ment you will learn about the main prop­er­ties of ascor­bic acid, and find out why it is so im­por­tant for health.

Reagents and equip­ment:

  • 3% hy­dro­gen per­ox­ide so­lu­tion;
  • 10% iron(II) sul­fate so­lu­tion;
  • 10% am­mo­ni­um thio­cyanate so­lu­tion;
  • 1% ascor­bic acid so­lu­tion;
  • lemon juice;
  • pipette;
  • beaker.

Step-by-step in­struc­tions

Into three beakers, pour an iron(II) sul­fate so­lu­tion. Add lemon juice to the first beaker, leave the sec­ond un­changed, and to the third, add a so­lu­tion of ascor­bic acid. Now pour the so­lu­tions of am­mo­ni­um thio­cyanate and hy­dro­gen per­ox­ide into each beaker. Ob­serve the col­or change to red in the sec­ond beaker.

Pro­cess­es de­scrip­tion

An­tiox­i­dants are sub­stance which block ox­i­da­tion re­ac­tions in the body. One of these sub­stances is ascor­bic acid. It is con­tained in many fruit and veg­eta­bles, for ex­am­ple in cit­rus fruit and red bell pep­per.

In the first and third beaker, ascor­bic acid blocks the ox­i­da­tion of iron(II) to iron(III), i.e. it ab­sorbs the oxy­gen rad­i­cals which form in the break­down of hy­dro­gen per­ox­ide. There is no ascor­bic acid in the sec­ond beaker, and we ob­serve the red bond of iron (III) thy­ocyanate form

Fe²⁺ + 2H₂O₂ + 3CNS⁻ → Fe(CNS)₃ + 2H₂O + O₂