Vitamin C Titration

Chemicals:

Starch
Potassium iodide (KI)
Potassium iodate (KIO3)
Distilled water
Sulfuric acid (H2SO4)
Fruit juice (orange juice)

Apparatus:

250 ml volumetric flask
Beakers
Conical flask
Burette
Glass rod
Spatula
Electronic weighing scale
Bunsen burner or water bath (in our case, we heated the water beforehand)

Experiment date: 2/10/25

Written by: Jion Seong (Procedure + Calculation)

& Sophia Han (Explanation)

Edited by: Sophia Han

1) Preparing Solutions

1% Starch Indicator Solution
Iodine Solution

1% Starch Indicator Solution

Add 0.50 g soluble starch to 50 ml near-boiling distilled water.
Mix well and allow to cool before use.

Iodine Solution

Dissolve 3.00 g potassium iodide (KI) and 0.150 g potassium iodate (KIO3) in 200 ml of distilled water.
Add 10 ml of sulfuric acid.
Pour this solution into a 250 ml volumetric flask and dilute it to a final volume of 250 ml with distilled water.
Mix the solution.
Transfer the solution to the burette.

2) Titrating Juice Samples

Add 20 ml of juice sample to a 100 ml measuring cylinder.
Add 3 drops of starch indicator solution.
Titrate until the endpoint is reached (add iodine solution until you get a color that persists longer than 20 seconds).
Repeat the titration until you have at least two measurements that agree to within 0.1 ml.

Calculation

Calculate the average of volume of Iodine solutions used from your concordant titres.
Calculate the moles of iodine reacting (KIO3 + 5KI + 6H+ → 3I2 + 3H2O) n=m/M n : number of moles, m : mass, M : molar mass
Find the moles of ascorbic acid reacting (C6H8O6 + I2 → C6H6O6 + 2I-; same as the number of moles of iodine reacting).
Determine the concentration of vitamin C with the reaction n=c/v n : number of moles, c : concentration, v : volume

Explanation

Written by: Sophia Han

Technique used: Titration

Titration is the slow addition of a solution of known concentration (titrant) to determine the concentration of another solution (titrand).

What is Vitamin C?

Vitamin C, also known as ascorbic acid, is essentially a water-soluble antioxidant that assists the immune system by protecting the cells from infection and disease.

It plays a vital role in tissue growth and repair (help produce collagen), wound healing, and iron absorption.

Because it is not synthesized by the human body, they are acquired from dietary sources, primarily fruits and vegetables.

Science Behind the Experiment

Ascorbic acid acts as a reducing agent by donating electrons to other substances.

It reacts with iodine molecule at a mole ratio of 1:1, during which the ascorbic acid is oxidized and becomes dehydroascorbic acid (DHA).

When ascorbic acid is oxidized completely, the excess iodine and starch reacts, turning the solution into navy blue (endpoint of the reaction).