Vitamin C Titration with Iodine

Measuring ascorbic acid content in fruit juice

Titrations Intermediate (High School) 40 min ~$10.00

Objective

Determine the vitamin C (ascorbic acid) content of fresh fruit juice using an iodine titration with starch indicator.

Background

Ascorbic acid reduces iodine to iodide ions in a 1:1 molar ratio. Starch indicator turns dark blue-black in the presence of excess iodine. When all the vitamin C is consumed, the next drop of iodine produces the blue-black color, marking the endpoint.

Safety Warnings

  • Iodine stains skin and clothing
  • Wear safety goggles
  • Handle iodine solution with care

Required PPE

goggles lab_coat

Materials

  • Fresh orange juice (200 mL)
    Freshly squeezed preferred
  • Iodine solution (100 mL)
    0.005M
  • Starch indicator solution (10 mL)
    1% solution
  • Distilled water (200 mL)

Equipment

50 mL burette Burette stand and clamp 250 mL Erlenmeyer flask 25 mL pipette Pipette filler White tile

Procedure

1

Rinse and fill the burette with the standardized iodine solution. Record the initial volume.

3 min Iodine stains
2

Pipette 25.0 mL of orange juice into the Erlenmeyer flask.

2 min
3

Add 5 drops of starch indicator to the flask.

1 min
4

Titrate by adding iodine solution slowly while swirling. The brown iodine color will disappear as it reacts with vitamin C.

8 min
5

Near the endpoint, add drop by drop until a persistent dark blue-black color appears for 20 seconds.

3 min
6

Record the final volume and repeat for concordant results.

15 min
7

Calculate the mass of vitamin C per volume of juice. Compare with the labeled value.

5 min

Expected Results

Fresh orange juice typically contains 40-80 mg of vitamin C per 100 mL. The starch-iodine endpoint should be a sharp transition to blue-black. Older or heat-treated juice will show lower vitamin C content.

Cleanup

Dispose of iodine waste in designated containers. Rinse all glassware with water. Clean any iodine stains with sodium thiosulfate solution.

Details

Category
Titrations
Difficulty
Intermediate (High School)
Duration
40 min
Est. Cost
$10.00
Steps
7
Materials
4

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Frequently Asked Questions

What is the objective of Vitamin C Titration with Iodine?
Determine the vitamin C (ascorbic acid) content of fresh fruit juice using an iodine titration with starch indicator.
How difficult is Vitamin C Titration with Iodine?
This experiment is rated as Intermediate (High School). It takes approximately 40 minutes to complete.
What safety precautions are needed for Vitamin C Titration with Iodine?
Key safety precautions include: Iodine stains skin and clothing; Wear safety goggles; Handle iodine solution with care.
What materials are needed for Vitamin C Titration with Iodine?
The main materials required are: Fresh orange juice, Iodine solution, Starch indicator solution, Distilled water.
What results should I expect from Vitamin C Titration with Iodine?
Fresh orange juice typically contains 40-80 mg of vitamin C per 100 mL. The starch-iodine endpoint should be a sharp transition to blue-black. Older or heat-treated juice will show lower vitamin C content.